Final steps in making BP motors - seeking advice

[hcb]

Be careful with your volumetric measurements of nitrate when making fuel--it's super hygroscopic and you will have difficulty in standardizing your fuel if one batch contains extra water in the initial mix versus the next. Especially if you're blowing endcaps (not tubes/nozzles???) on an endburner, which is weird. I dry out my KNO₃ religiously in the oven (safe and quick insurance) before making large batches, or if it has sat around awhile (even with dessicant) because it will absorb atmospheric water. Then at least you will know if your oxidizer ratio is truly the same from batch to batch; a few % makes a difference. Especially when you're starting at CATO and dialing back to ideal.

 

But really amigo, a reasonable scale that measures 0.01 grams costs perhaps $10, and, for small batches, is much more helpful in repairing/optimizing fuels than relying on cooking spoon volumes!

 

Maybe press an extra gram or two of clay on your bulkhead and see if it makes your tubes blow instead. You're having coreburner issues with an endburner... Why change your nozzle (except for diameter) if it's not blowing out or undergoing crippling deformation? If cat litter alone works, and nozzles are not (yet) blowing out, eroding, or filling with slag, why change yet another variable? Maybe leave it (for now)!

 

Dextrin? Do I recall you were considering using dextrin? NO! Get your BP consistent. You're lifting a rocket not a shell. No dextrin needed. Adjust your BP ratios to adjust your BP burn rate, but solve your end cap blowouts first.

 

Weight bedamned, your aluminum rod tails scare the hell outta me, no matter how desolate your testing grounds are (i.e., worried that YOU might get speared, not a bystander). Glad they bent on impact because they have no role in 1/2" rocket guidance.

 

Keep at it, good luck, and please stay safe!

 

I'm sorry if I miss communicated somewhere (or I didn't read my own post carefully), but when I portion out the chemicals, it's all by weight. I'm only using volumetric measurements for addition of the finished comp and nozzle mix to the tube.

 

I will dry out the next batch of KNO3...this stuff is old, some of it 6 or 7 years old, and is in "not-air-tight packaging".

 

I have a 0.1 gram scale now.

 

I'm over the dextrin stuff for the moment. I had started with that when my granules for cannons were crap (soft). But I've started pucking and cracking and I'm getting tough BP granules now. I may go to 1% on the rocket motors at some point, but after I've got this solved.

 

With the one recovered nozzle being damaged, I think I need to reduce the starter core length. I've not had time to do that as I don't live where my shop is so I get "business hours" to tinker on this stuff. Maybe tomorrow....

 

Thanks for the input.

 

--HC

[Boophoenix]

As I’ve stated I’m not a rocket guy and don’t have much experience with them, but the few I’ve done I just use plain old bentonite for the nozzle. My simple mind has to wonder what purpose wax is serving in a nozzle? Seems like it would get hot and break down compromising the bonding of the sand and bentonite. I guess the sand is they to kind of lock things together, but still seems weird to me too.

With that said if I was having nozzle problems I’d consider removing things to see what happens maybe once.

I can’t really tell from the photos, but the one nozzle looks pretty thick. How thick are they? Can you share a picture of the tooling? All of the tooling I’ve ever used makes a nozzle that is formed like the middle section of an hour glass and those angles have names that I don’t recall.

[Bigmark]

Are you using the 75 15 10 BP formula in that nozzled rocket. If so your fuel is to hot. Leave the nozzle out and press straight BP 2% water. If you going to keep the nozzle in try a slower fuel.

Are you useing a clay bulkhead are the blowing out ?

[hcb]

 

Text can be so emotionless. Amazing that we could write love poems before we had emojis I just wanted to check, sometimes obvious things are easy to overlook. Glad you didn't take offense. My next question: Have you tried pressing at higher pressures? 3k on the comp is pretty low, especially for dry propellant. That might explain why your nozzles are performing better when using finely ground clay and also why you're getting CATOs. If the fuel grain has gaps from not being fully compacted you will get massive spikes in pressure as the flame front spreads through those gaps. Notice that Just Visiting reduced pressure down to 3500 when using damp propellant, which is still higher than the pressure you are using.

 

There's lots of variables but I'd start by upping the pressure a bit. End burners tend to be pretty forgiving so if you're getting consistent CATOs using a quality tube I have to suspect an issue with the fuel grain.

 

Oh, and I wouldn't mess with the water putty. I mean, feel free to experiment, but that works best if you're doing cast grains or the like and, IMO is expensive and hard to work with when cheap litter will get the job done fine. I use Kitty Diggins brand litter from WalMart. It was less than $2 for a 7lb bag and it works for all my bentonite needs. It works as is but I did run some through a grain mill for my nozzles.

 

Um, I don't know where to stick the fuse or igniter in a love poem so I'm just gonna stick to rocket stuff. I have hit over 4k PSI on the comp dry-pressing them. The two failures were both with the longer core, but the three or four successes I've had were split up between damp and dry comp with 3k to 4k+ PSI. I don't keep notes for crap and I'm regretting that now. I'll try to be better about that for more useful forensic analysis. I do not feel it was grain fracture that caused the problems with the CATOs. I am convinced (but not necessarily right/correct) that it was the longer core. I've not shortened the core yet. I have just a few hours each day to work on stuff and I've been devoting my little bit of free time to making igniters. Tomorrow I should have all day to play and I may shorten that core and press some more motors. I also, just because I don't have enough variables in my project, just charred and milled some red cedar bed shavings. The company claims it's "Easter Red Cedar" (like I'd know how to tell the diff between that and Western Red Cedar), and ERC is supposed to be good stuff (I read that on the Internet, so I know it's TRUE). It did reduce to liquid-like powder in about 30 minutes in the mill.

 

Back to the fractures...when I was a kid doing (trying) this stuff, I was re-using Estes motor tubes because I had no resource to get or make tubes. Between poor powder, poor tools, poor knowledge, and poor tubes, I had hell. I, now, totally understand about flame propagation through a fractured grain (or at least I understand it enough to know it's gonna blow something). Further testing, and shortening the core, will reveal if this is fracturing or just over-pressure from too much core.

 

I'm listening to you on the water putty. I was wrong about the kitty litter brand, it's supposed to be Fresh Step. I had an image in my head of the package, having seen it before, when I read the post somewhere. I'll try some of that, it's the best stuff ever (I read that on the Internet, too).

 

Thanks for the reply and info.

 

--HC

[hcb]

As I’ve stated I’m not a rocket guy and don’t have much experience with them, but the few I’ve done I just use plain old bentonite for the nozzle. My simple mind has to wonder what purpose wax is serving in a nozzle? Seems like it would get hot and break down compromising the bonding of the sand and bentonite. I guess the sand is they to kind of lock things together, but still seems weird to me too.

 

With that said if I was having nozzle problems I’d consider removing things to see what happens maybe once.

 

I can’t really tell from the photos, but the one nozzle looks pretty thick. How thick are they? Can you share a picture of the tooling? All of the tooling I’ve ever used makes a nozzle that is formed like the middle section of an hour glass and those angles have names that I don’t recall.

 

I got the "recipe" for the nozzle mix from an article on Skylighter's website. I agree that the wax sounds counterproductive but, the theme for the day is, "I read it on the Internet". The only theory (hypothesis) I've read to back up using the wax is to reduce the amount of shrinking/swelling the clay may endure due to atmospheric humidity. The idea behind the sand is that it gives the mix a little grit to help hold it into the smooth wall of the tube. In the article I read, they used "grog" which, depending on whose info you're reading means different things. In that article, "grog" meant broken, fired pottery that was ground/sorted. I've read somewhere else, and there's an article on Passfire (but I'm not a member so I haven't read it), about waxing the inside of the rocket motor tubes to improve this or that, reduce erosion of the inside of the tube, and increase your tax refund. Waxing the inside of the tube would seemingly guarantee a blowout and grit in the nozzle and bulkhead mix would seem a requirement.

 

I'll get a picture of the tooling, maybe tomorrow but no promises, and post it. I just kind of thought how a nozzle should look and made the first one. Once I'd read about the de Leval (I think I got the name right) nozzles, when I re-made the tooling, I modified the design to use the recommended nozzle angles which are 15 degree half angle on the divergent (exhaust/exit) section and 30 degree half angle on the convergent (input) section. For those who are wondering what the heck a "half angle" is: if you have an angle of, say, 60 degrees, half of it is 30 degrees. If you have an angle of 30 degrees half angle, you have a 60 degree angle. Yes, I know, it seems needlessly confusing, but I think the magic is this: if you spec an angle of 60 degrees and no other data, then you don't know where the arc begins, centers up, or ends. If you spec it as 30 degrees half angle then you know that it's centered on some line, 30 degrees on one side and 30 degrees on the other side. That way, when you are told to use a 30 degree half angle, there's no ambiguity causing you to build a nozzle which has a 60 degree angle which is not centered (concentric) with the major axis of the motor. This is super helpful because I thought it didn't matter if the nozzle was perpendicular to the motor tube as long as it was a 60 degree cone. (rolls eyes)

 

All that said, my nozzles do look kind of like an hourglass.

 

--HC

[hcb]

Are you using the 75 15 10 BP formula in that nozzled rocket. If so your fuel is to hot. Leave the nozzle out and press straight BP 2% water. If you going to keep the nozzle in try a slower fuel.

Are you useing a clay bulkhead are the blowing out ?

 

Yes, 75-15-10. I sized the nozzle opening to the diameter based on an end-burner. I'm using 2% H2O now, but I've fired some with no water added during the pressing, and they worked fine. This is happening after I lengthened the starter core (very short core, about 3/8" at this time). Yes, this had the remaining fuel which became a star and a clay bulkhead.

 

--HC

[Bigmark]

 

 

Yes, 75-15-10. I sized the nozzle opening to the diameter based on an end-burner. I'm using 2% H2O now, but I've fired some with no water added during the pressing, and they worked fine. This is happening after I lengthened the starter core (very short core, about 3/8" at this time). Yes, this had the remaining fuel which became a star and a clay bulkhead.

 

I'm betting if you switch to a slower fuel our leave your clay nozzle out you will see an improvement. Back when I first started making rocket's I did the 75 15 10. And could not get one to fly with a clay nozzle in it. I didn't start seeing success till i left the clay out on that fuel mixture.

When I switched to a slower fuel I was able to put the clay nozzle back in. I both hand ram and press with the same results. Changing your fuel and our leaving the clay out of your nozzle would be the easiest way to start troubleshooting.

[Boophoenix]

HCB, one saying that hasn’t been mentioned here yet is rockets are tricky to inquire about. You can ask 10 rocket guys a question and you might get 11 answers. It ends up that you have to settle a little on what you want to accomplish and filter threw enough information to accomplish that goal. Unless you meet a rocket guy that does exactly what you want and follow his process exactly. Almost every rocket guy has his own way of doing things. Strangely enough some times other accomplished rocket builders actually have troubles trying someone else’s methods.

One of the most interesting rocket things I’ve seen and it wasn’t the goal they were aiming for was at my one and only PGI to date. Multiple rockets someone built would lift from the rack to just a few feet above it hover blow the plug out and fall to the ground. I found it interesting that had the great of consistency even if it wasn’t the goal.

I noticed you mentioned waxing the tube. That was some of Justvising’s work that got that fired up. When you get into settled in on the processes you like you may find some value in it.

On your nozzle mix I can’t say that I’ve ever had any erosion of the nozzle to look like from anything I have built. To me the erosion looks mostly to be surface erosion implying the mixture isn’t holding up for what ever reason. I do see some erosion at times, but not like that in the spent tubes I’ve been able to recover. My bentonite’s have been just dr else cat litter or pottery bentonite to date. I don’t think I’ve ever blown a plug either but I don’t normally and may not have ever made a 75/15/10 rocket in the limited number I’ve made to be fair to the conversation. I have tooling and materials for various types and sizes of rockets they’ve just not excited me yet. Even though I hang out at club events with guys making much large rockets than I have tooling for.

Keep plugging away at it if it entertains you. You’ll get them dialed in and start having a lot of fun with them.

[BetICouldMake1]

Are you using the 75 15 10 BP formula in that nozzled rocket. If so your fuel is to hot. Leave the nozzle out and press straight BP 2% water. If you going to keep the nozzle in try a slower fuel.

Are you useing a clay bulkhead are the blowing out ?

 

Mark, I think you might have missed that he is building endburner rockets. If he leaves out the nozzle that thing is going nowhere. You're right that full power bp is probably too hot for a coreburner, but it can be done. For endburners hot powder is basically mandatory. You could use toned down powder, but you shouldn't have to.

 

 

Um, I don't know where to stick the fuse or igniter in a love poem so I'm just gonna stick to rocket stuff. I have hit over 4k PSI on the comp dry-pressing them. The two failures were both with the longer core, but the three or four successes I've had were split up between damp and dry comp with 3k to 4k+ PSI. I don't keep notes for crap and I'm regretting that now. I'll try to be better about that for more useful forensic analysis. I do not feel it was grain fracture that caused the problems with the CATOs. I am convinced (but not necessarily right/correct) that it was the longer core. I've not shortened the core yet. I have just a few hours each day to work on stuff and I've been devoting my little bit of free time to making igniters. Tomorrow I should have all day to play and I may shorten that core and press some more motors. I also, just because I don't have enough variables in my project, just charred and milled some red cedar bed shavings. The company claims it's "Easter Red Cedar" (like I'd know how to tell the diff between that and Western Red Cedar), and ERC is supposed to be good stuff (I read that on the Internet, so I know it's TRUE). It did reduce to liquid-like powder in about 30 minutes in the mill.

 

Back to the fractures...when I was a kid doing (trying) this stuff, I was re-using Estes motor tubes because I had no resource to get or make tubes. Between poor powder, poor tools, poor knowledge, and poor tubes, I had hell. I, now, totally understand about flame propagation through a fractured grain (or at least I understand it enough to know it's gonna blow something). Further testing, and shortening the core, will reveal if this is fracturing or just over-pressure from too much core.

 

I'm listening to you on the water putty. I was wrong about the kitty litter brand, it's supposed to be Fresh Step. I had an image in my head of the package, having seen it before, when I read the post somewhere. I'll try some of that, it's the best stuff ever (I read that on the Internet, too).

 

Thanks for the reply and info.

 

--HC

 

Plenty to be learned from reading online, though this is a wealth of terrible information out there. You are correct that Eastern Red Cedar (which is actually juniper) make great charcoal for black powder.

 

When it comes to nozzle/bulkhead mix there are some guys that tout fancy mixes using grog or crushed pots or special clay harvested under a full moon and lightly dampened with the sweat of a virgin. Maybe if you're building crazy redline rockets that would make a difference. IMO clay is clay, and clay works. Like Boo said, rockets can be tricky and when someone finds something that works they will often treat that as the holy grail of methods.

 

A couple other thoughts. Are you using a support when pressing? If you are damaging the tube that could also cause issues. Also, if the failures are consistently the bulkhead blowing out you might just try pressing a slightly larger bulkhead. Or upping the pressure a bit when pressing just the bulkhead.

 

Waxing the inside of the tube IS the holy grail of methods. Really though. It prevents so many common issues when pressing rockets. It minimizes tube compression when pressing and it (the theory goes) inhibits the outside of the fuel grain reducing the possibility of flame creeping up the sides and causing a CATO.

[Bigmark]

 

Mark, I think you might have missed that he is building endburner rockets. If he leaves out the nozzle that thing is going nowhere. You're right that full power bp is probably too hot for a coreburner, but it can be done. For endburners hot powder is basically mandatory. You could use toned down powder, but you shouldn't have to.

 

 

Plenty to be learned from reading online, though this is a wealth of terrible information out there. You are correct that Eastern Red Cedar (which is actually juniper) make great charcoal for black powder.

 

When it comes to nozzle/bulkhead mix there are some guys that tout fancy mixes using grog or crushed pots or special clay harvested under a full moon and lightly dampened with the sweat of a virgin. Maybe if you're building crazy redline rockets that would make a difference. IMO clay is clay, and clay works. Like Boo said, rockets can be tricky and when someone finds something that works they will often treat that as the holy grail of methods.

 

A couple other thoughts. Are you using a support when pressing? If you are damaging the tube that could also cause issues. Also, if the failures are consistently the bulkhead blowing out you might just try pressing a slightly larger bulkhead. Or upping the pressure a bit when pressing just the bulkhead.

 

Waxing the inside of the tube IS the holy grail of methods. Really though. It prevents so many common issues when pressing rockets. It minimizes tube compression when pressing and it (the theory goes) inhibits the outside of the fuel grain reducing the possibility of flame creeping up the sides and causing a CATO.

 

You correct I miss red something somewhere. When I saw the pictures of the nozzles they looked to me as they had a longer core in them. So I figured he was building core burning rockets. I had forgotten what he had said earlier in the post.

[hcb]

 

 

Yes, 75-15-10. I sized the nozzle opening to the diameter based on an end-burner. I'm using 2% H2O now, but I've fired some with no water added during the pressing, and they worked fine. This is happening after I lengthened the starter core (very short core, about 3/8" at this time). Yes, this had the remaining fuel which became a star and a clay bulkhead.

 

I'm betting if you switch to a slower fuel our leave your clay nozzle out you will see an improvement. Back when I first started making rocket's I did the 75 15 10. And could not get one to fly with a clay nozzle in it. I didn't start seeing success till i left the clay out on that fuel mixture.

When I switched to a slower fuel I was able to put the clay nozzle back in. I both hand ram and press with the same results. Changing your fuel and our leaving the clay out of your nozzle would be the easiest way to start troubleshooting.

 

I shortened the core on the former by 1/8" and they don't blow up anymore. Being end burners, they don't produce gas at near the rate a core-burner would, and, as I've personally witnessed, when the nozzle opening is enlarged, the lift is gone. E.g.: I shortened the core (as mentioned), pressed a motor, and ignited it. It took off fantastically, went up maybe 70-90 feet, then began to fall while still burning. I had pressed 20 grams of 75-15-10 and had a beautiful nozzle (NASA doesn't do nozzles this well <grin>) and it worked...until it didn't. It fell all the way to Earth, burning the whole way. When I recovered the motor, the nozzle was eroded away heavily (no pic). The opening which started at 1/8" was about 3/16" in diameter. So, the rate of burn from this mix, apparently needs a nozzle when configured as an end-burner. More to come in following posts as I try to reply to all and then I will post a pic in reply to my OP with a pic.

 

--HC

[hcb]

HCB, one saying that hasn’t been mentioned here yet is rockets are tricky to inquire about. You can ask 10 rocket guys a question and you might get 11 answers. It ends up that you have to settle a little on what you want to accomplish and filter threw enough information to accomplish that goal. Unless you meet a rocket guy that does exactly what you want and follow his process exactly. Almost every rocket guy has his own way of doing things. Strangely enough some times other accomplished rocket builders actually have troubles trying someone else’s methods.

 

One of the most interesting rocket things I’ve seen and it wasn’t the goal they were aiming for was at my one and only PGI to date. Multiple rockets someone built would lift from the rack to just a few feet above it hover blow the plug out and fall to the ground. I found it interesting that had the great of consistency even if it wasn’t the goal.

 

I noticed you mentioned waxing the tube. That was some of Justvising’s work that got that fired up. When you get into settled in on the processes you like you may find some value in it.

 

On your nozzle mix I can’t say that I’ve ever had any erosion of the nozzle to look like from anything I have built. To me the erosion looks mostly to be surface erosion implying the mixture isn’t holding up for what ever reason. I do see some erosion at times, but not like that in the spent tubes I’ve been able to recover. My bentonite’s have been just dr else cat litter or pottery bentonite to date. I don’t think I’ve ever blown a plug either but I don’t normally and may not have ever made a 75/15/10 rocket in the limited number I’ve made to be fair to the conversation. I have tooling and materials for various types and sizes of rockets they’ve just not excited me yet. Even though I hang out at club events with guys making much large rockets than I have tooling for.

 

Keep plugging away at it if it entertains you. You’ll get them dialed in and start having a lot of fun with them.

 

There's another saying: "You can't scare me, I'm married." I do a lot (nightly) thermal hunting of hogs/coyotes/bobcats. I talk hunting with some folks and made the mistake of reading some gun publications when I first started. Differing opinions, lies, and general misinformation are easy to come by in the truck-load. I understand your point. Thank you. (None of that meant rudely or ugly). I'm try to be open-minded about trying new stuff. Sometimes it takes some convincing.

 

I've changed the nozzle mix and tested a couple and I'll cover that with a pic when I'm done replying to everyone.

 

I enjoy this, I'm succeeding at something that I failed at when I was young. I don't like to fail and making some progress makes me happy.

 

--HC

[hcb]

 

Mark, I think you might have missed that he is building endburner rockets. If he leaves out the nozzle that thing is going nowhere. You're right that full power bp is probably too hot for a coreburner, but it can be done. For endburners hot powder is basically mandatory. You could use toned down powder, but you shouldn't have to.

 

 

Plenty to be learned from reading online, though this is a wealth of terrible information out there. You are correct that Eastern Red Cedar (which is actually juniper) make great charcoal for black powder.

 

When it comes to nozzle/bulkhead mix there are some guys that tout fancy mixes using grog or crushed pots or special clay harvested under a full moon and lightly dampened with the sweat of a virgin. Maybe if you're building crazy redline rockets that would make a difference. IMO clay is clay, and clay works. Like Boo said, rockets can be tricky and when someone finds something that works they will often treat that as the holy grail of methods.

 

A couple other thoughts. Are you using a support when pressing? If you are damaging the tube that could also cause issues. Also, if the failures are consistently the bulkhead blowing out you might just try pressing a slightly larger bulkhead. Or upping the pressure a bit when pressing just the bulkhead.

 

Waxing the inside of the tube IS the holy grail of methods. Really though. It prevents so many common issues when pressing rockets. It minimizes tube compression when pressing and it (the theory goes) inhibits the outside of the fuel grain reducing the possibility of flame creeping up the sides and causing a CATO.

 

I'm aware of the mis-information available online. I usually run things through a filter in my brain and try to identify the truth (or something akin to it). Testing and common sense help, too.

 

I didn't know juniper was known as ERC. I have no way of knowing if what I have is really ERC or WRC. Looks like cedar to me (we have plenty in North Central Texas). I'm cooking my second batch of it now, and I've made a 200g batch of BP with it but I've not even pulled that out of the ball mill yet. I can tell you that the cedar bedding chips turned to molecular dust in 30 minutes in my big ball mill (0.690" WW (wheel weights) cast round ball projectiles). I let it run another 1.5 hours just because I could but I thought it was too loud (too little charcoal) at 30 minutes and opened it to add more....I think that cloud is still hanging in the shop 4 days later). I hope it's awesome because it got supah fine, wicked fast.

 

I reload ammo for my hunting...I'm very familiar with "it worked well once...that's *the only way ever to do it*" mentality. Talk reloading centerfire rifle with folks who seek accuracy (read: consistency, read: tight groups). I get a tummy ache just thinking about it. But, this is true, you need the sweat of a *fair-haired* virgin...brunette virgin sweat *WILL NOT WORK*!

 

I am supporting the tubes when pressing. Particularly, for those who haven't done it yet, I found that support was *required* for damp composition. It was entirely too easy to distend the tubes with damp powder, even with moderate pressing force. Today I added more support for the nozzle pressing (details in a post later), but I've been doing well with basic support. Shortening the former intrusion into the fuel grain by 1/8" has ended my blowouts...for now.

 

I'm onboard with the waxing for....what's the term? "Inhibiting a surface"? I'll visit that, it seems from your post, when it becomes necessary but I take it that it's not necessary at this point.

 

--HC

[hcb]

Okay, an update. I made a mistake, crossed some wires, and blah blah blah. I got a new nozzle mix to try and I got Tidy Cats (instead of Fresh Step) clumping cat litter which comes in small spheres. I pressed a nozzle @ 4k PSI. Wow, amazing! Musk is burning up Twitter asking me to build stuff for him. Okay, not that good, but, WOW! I launched it and it worked well. I've shortened the core on the former by 1/8" so it's not going as far into the fuel grain now and it flew and didn't purge the fuel grain/bulkhead. But it eroded the snot out of the nozzle.

 

Today I pressed another nozzle after I put another reinforcing ring on the tube (double wrapped in PVC and clamped) and pressed another nozzle but this time at 8k PSI. Another work of art cum rocket nozzle. I fired this one, too, and it, too, eroded badly. This was a static test so I got to watch it closely during the whole burn. The ignition almost immediately brought forth a flame which ran to one side and the nozzle eroded to one side (not surprising). *$%. I thought the "hard part" of this project was going to be the ball mill (which I made myself).

 

The 4k PSI nozzle has the white residue (unknown source and it didn't look like that after it was fired, this appearance came about since I fired it day before yesterday). The dark nozzle was the 8k PSI nozzle done and fired today.

 

I think I need the Fresh Step everyone talks about but they make a billion variations. Could someone please narrow this down for me and tell me specifically which variant has worked for them?

 

Thank you.

 

--HC

Edited March 9, 2020 by hcb

[BetICouldMake1]

 

I'm aware of the mis-information available online. I usually run things through a filter in my brain and try to identify the truth (or something akin to it). Testing and common sense help, too.

 

I didn't know juniper was known as ERC. I have no way of knowing if what I have is really ERC or WRC. Looks like cedar to me (we have plenty in North Central Texas). I'm cooking my second batch of it now, and I've made a 200g batch of BP with it but I've not even pulled that out of the ball mill yet. I can tell you that the cedar bedding chips turned to molecular dust in 30 minutes in my big ball mill (0.690" WW (wheel weights) cast round ball projectiles). I let it run another 1.5 hours just because I could but I thought it was too loud (too little charcoal) at 30 minutes and opened it to add more....I think that cloud is still hanging in the shop 4 days later). I hope it's awesome because it got supah fine, wicked fast.

 

I reload ammo for my hunting...I'm very familiar with "it worked well once...that's *the only way ever to do it*" mentality. Talk reloading centerfire rifle with folks who seek accuracy (read: consistency, read: tight groups). I get a tummy ache just thinking about it. But, this is true, you need the sweat of a *fair-haired* virgin...brunette virgin sweat *WILL NOT WORK*!

 

I am supporting the tubes when pressing. Particularly, for those who haven't done it yet, I found that support was *required* for damp composition. It was entirely too easy to distend the tubes with damp powder, even with moderate pressing force. Today I added more support for the nozzle pressing (details in a post later), but I've been doing well with basic support. Shortening the former intrusion into the fuel grain by 1/8" has ended my blowouts...for now.

 

I'm onboard with the waxing for....what's the term? "Inhibiting a surface"? I'll visit that, it seems from your post, when it becomes necessary but I take it that it's not necessary at this point.

 

--HC

 

Haha, I hear you man. I'm also a reloader and if you took all the advice you read online you'd spend all your time buying new tools for prepping your brass and no time actually shooting.

 

Glad to hear you're finally getting them to fly. I wax all my rocket tubes. I'm making core burners and whistle rockets and though I never had a cato before I started waxing, I do it as cheap insurance and because it helps prevent the comp from grabbing the walls of the tube when pressing and creating wrinkles. But hey, if what you're doing works you can't argue with success.

 

As for your clay question, from what I've read the "litter of choice" is Dr. Elsey's. I'm too cheap and never tried it since the kitty diggins has been working for me.

[justvisiting]

I've tried quite a few different nozzle mixes, and I have to say that the Dr. Elsey's Precious Cat is the best one I've tried. This makes sense, since it was the retired manager of Estes that suggested it Like any nozzle mix, there is a tendency for it to grab the spindle. I wipe the spindle with wax at the nozzle area to minimize that. The Dr. Elsey's is a waxy-feeling dense bentonite mixture that slides on itself smoothly, and makes a perfect-looking nozzle. I bought mine at a pet food store. Another helpful addition is to shake a cupful of the nozzle clay with a teaspoon of graphite- (no more!) before using it.

 

It makes a big difference what nozzle mix you use if you are hand ramming, especially without a support. Some clay is too hard to consolidate properly without splitting the tube. Ramming the nozzle in 2 increments can be helpful, if you don't bottom out your first rammer. I've never previously read of anybody moistening nozzle mix, and never found a need to do it. I found that mixing hard clay with softer bentonite works too. I don't like most bentonite because I find it to be too fluffy (voluminous). There is less tendency to pull the tube down if there is less rammer travel when consolidating an increment. I've used waxed nozzle mix before, and it worked fine. I don't see the need for it when using Dr. Elsey's. I've used the mixes with ground up flower pots (Laduke), and ground up floor tiles (Passfire). That's a good way to scratch your tooling.

 

One thing that can be helpful to prevent uneven erosion of the nozzle is to use a 'leveller' on the nozzle increment before pressing/ramming. For me, that's as simple as a piece of PVC pipe, with notches in the end, twirled in the tube after loading the nozzle mix, before consolidating it. EZPZ. A nozzle with a longer throat is less likely to erode unevenly too. Nozzles are not necessarily as simple as they seem at first glance, especially in end burners.

[hcb]

 

Haha, I hear you man. I'm also a reloader and if you took all the advice you read online you'd spend all your time buying new tools for prepping your brass and no time actually shooting.

 

Glad to hear you're finally getting them to fly. I wax all my rocket tubes. I'm making core burners and whistle rockets and though I never had a cato before I started waxing, I do it as cheap insurance and because it helps prevent the comp from grabbing the walls of the tube when pressing and creating wrinkles. But hey, if what you're doing works you can't argue with success.

 

As for your clay question, from what I've read the "litter of choice" is Dr. Elsey's. I'm too cheap and never tried it since the kitty diggins has been working for me.

 

My favorite (sarcasm) is: "There's an accuracy node at xx.xgr." Maybe the bullet's been spec'd, maybe not. Same, too, with the powder. Nevermind the fact that barrels, like tuning forks, have harmonics and, even from one manufacturer, they may not be the same from barrel to barrel, so what worked like magic in their barrel may be a shotgun pattern in mine.

 

They've all flown (since I've started this mess again as adult), but with varying degrees of success. I'd like to know how to wax the tubes but I figure that'll wait until I get this sorted. If I was getting cato's in the form of ruptured tubes or consistent blown nozzles/plugs, I'd think I had a void/fracture in my grain and be sorting that out. One problem/step at a time. I want the end-burner to work for the model stuff. I am coming to realize, though, that core-burners may be necessary for fireworks to afford the lift power necessary to get a heading into the air. But I'm gonna get me some end-burners to work. Maybe.

 

I suspect that Dr. Elsey's and Kitty Diggins are regional or by country (I'm not sure where you're from, no offense intended). We little people in north central Texas don't have those brands that I'm aware of (and we have cats so buying litter is a common thing). I tried a couple more things today which I'll post about as a general follow up to my OP.

 

--HC

[hcb]

I've tried quite a few different nozzle mixes, and I have to say that the Dr. Elsey's Precious Cat is the best one I've tried. This makes sense, since it was the retired manager of Estes that suggested it Like any nozzle mix, there is a tendency for it to grab the spindle. I wipe the spindle with wax at the nozzle area to minimize that. The Dr. Elsey's is a waxy-feeling dense bentonite mixture that slides on itself smoothly, and makes a perfect-looking nozzle. I bought mine at a pet food store. Another helpful addition is to shake a cupful of the nozzle clay with a teaspoon of graphite- (no more!) before using it.

 

It makes a big difference what nozzle mix you use if you are hand ramming, especially without a support. Some clay is too hard to consolidate properly without splitting the tube. Ramming the nozzle in 2 increments can be helpful, if you don't bottom out your first rammer. I've never previously read of anybody moistening nozzle mix, and never found a need to do it. I found that mixing hard clay with softer bentonite works too. I don't like most bentonite because I find it to be too fluffy (voluminous). There is less tendency to pull the tube down if there is less rammer travel when consolidating an increment. I've used waxed nozzle mix before, and it worked fine. I don't see the need for it when using Dr. Elsey's. I've used the mixes with ground up flower pots (Laduke), and ground up floor tiles (Passfire). That's a good way to scratch your tooling.

 

One thing that can be helpful to prevent uneven erosion of the nozzle is to use a 'leveller' on the nozzle increment before pressing/ramming. For me, that's as simple as a piece of PVC pipe, with notches in the end, twirled in the tube after loading the nozzle mix, before consolidating it. EZPZ. A nozzle with a longer throat is less likely to erode unevenly too. Nozzles are not necessarily as simple as they seem at first glance, especially in end burners.

 

Okay, so, after I replied to one post I read this and took the time to search...Dr. Elsey's is made in (well, available in, anyway) Los Estados Unidos, in CO, amazingly enough. IIRC, Estes is in CO...there may be a good-ol'-boy network here. The problem I'm having is that erosion is causing me 1) lost thrust and 2) misdirected force (uneven erosion throwing the jet/flame/gasses off to one side). I get some darned fine lookin' nozzles but they're performing poorly in burn tests. I had read elsewhere about using graphite in the nozzle mix and I have a # which should be here tomorrow meaning it'll be Wednesday when I'm next at the shop after receiving that. I'm going to first try it with straight supah plain kitty litter.

 

I'm pressing and with a support, FWIW. I ram in two increments but, because of the way my tooling is formed, the increments are 1/2 tsp then 1/8 tsp, so not much "increment" there. Since I'm not blowing nozzles out, I'm reluctant to add "grit" to the mix and your suggestion that it may scratch the tooling doesn't make me any more excited about adding grit to it.

 

If I'm reading/understanding the "leveller" thing right: you have a piece of PVC tubing which has been notched (crenelated) which fits inside the paper tube and then is twisted by hand to basically center up the loose stuff prior to pressing it? My nozzle design gives about 1/8" (maybe 3/32") throat. No, they are not simple at all, at least not the material selection. This has been the worst/hardest part. I tested a couple more things today which I'll write up about now as a general reply to my OP.

 

--HC

[hcb]

So, I decided to try a couple more things today. First, I tried just pressing plain, cheap, unscented, non-clumping kitty litter (PKL) I bought the small bag with the idea of milling it to dust and using it as bentonite clay dust. This time I just dumped the stuff in the tube and pressed it to about 7,600PSI. Made a BEAUTIFUL nozzle. Didn't work worth a crap.

 

Second, despite what I'd posted earlier, I was desperate so I bought some Durham's Water Putty (DWP) locally and made a nozzle with it. For those in future-land who follow this someday: read my lips: Don't Do It. With the data (right or wrong) that it does set up (like a plaster or cement product) with water added, I misted some of the powder and then rammed it. Getting the stuff damp but not wet and also not clumpy as heck, *sucked*. It made a beautiful nozzle, too. It, too, didn't work worth a darn. I "cooked" the motor in the dehydrator for over an hour (maybe not long enough, but I have no idea).

 

Static testing of both of the nozzles was sad. The PKL started well but then appeared to lose strength/thrust a little. Almost immediately the thrust flame (discharge, whatever it's called) appeared to be off axis to the motor body, but not too much...but still. The DWP did the same, strong but not true-to-bore jet of gas, but then turned into a fountain. :-| The PKL nozzle eroded some in throat diameter but stayed mostly concentrically formed along the major axis of the motor body. The DWP was a joke (yes, maybe not fully cured). The throat is eroded to about 1/4".

 

I'm questioning the need to use a de Leval nozzle on the BP rockets after some reading about the exhaust gas velocities. Looking at the Estes motors I have, they have almost no divergent area (very little conical exit from the nozzle). They also seem to be using a smaller orifice than my tooling makes (I did 1/4 ID giving 1/8" nozzle orifice. I read about Texas Pottery in some thread somewhere today and they're about 45 minutes from me. I have found another nozzle recipe (this is *the ONE*!, sorry, a little BS leaked out there) and I'm considering making the drive in the morning to get real fire clay and grog. Maybe I can sign up for a pottery class in case this rocket nonsense doesn't pan out.

 

I do notice, now that I'm looking closely, that the Estes nozzle has quite a bit more throat to it than mine do. I think I'm gonna burn one in a static test tomorrow and then do a forensic analysis of it. Maybe I need to start over fresh. The Estes nozzle sure doesn't appear to have fire clay or red pot shards or virgin's sweat in it.

 

--HC

[justvisiting]

Ya know, it's funny how some guys say it doesn't matter what the mix is, it all works. Then there are others (like us) that say maybe it's not so simple May I suggest that you could be off on your pressing force? If you are pressing lighter than you think, your nozzles would all be weak. Just a thought.

 

I've actually gotten clay from the bank of Lake Erie, broken it down, and used 12-20 mesh as my nozzle mix. It worked, but not as well as the Dr. Elsey's. I've pressed most of my nozzles, often to 9000psi. Your erosion seems excessive, which is why I suggested a possible miscalculation on your pressing force.

 

I'm guessing you could get a bag of the Dr, Elseys Precious Cat delivered pretty cheaply in your country. This is the stuff I use. I bought a huge bag, on Ed Brown's recommendation. He knows (EDIT: knew. He's passed on.) end burners

 

https://www.petsmart.ca/cat/litter-and-waste-disposal/litter/dr.-elseys-precious-cat-ultra-cat-litter---unscented-clumping-multi-cat-strength-2621253.html

 

One cool thing I found when testing end burners: immediately after testing, the residue around the nozzle hole was red. But then it changed to gray/white. I'm told it's from potassium sulfide, which degrades and changes color.

Edited March 10, 2020 by justvisiting

[markx]

The most successful trick that I've used for nozzles was to bind the bentonite granules with "waterglass".....sodium silicate solution that is. Upon pressing it forms a rockhard composite that really can not be dislodged without a major cato.

I would pour a premeasured amount of bentonite granules into the case, then add a suitable squirt of the silicate solution on top of the granules (a syringe is of help to keep the amounts constant) and press. One has to figure out the right volume of solution to add to the granules, so that it would be enough to soak through the entire nozzle when pressed and no more. Otherwise it shall force itself out and make a mess. Works like a treat! I also used the same mixture for end plugs.

 

Also a note about the waterglass being available in different concentrations. The most concentrated solutions are thick and resemble a syrup. These can be diluted with water at will to make a more liquid binder that seeps into the granules way better than the thick stuff. Trial and error type work

Edited March 10, 2020 by markx

[hcb]

Success!!!

 

I went to the pottery shop where I think I paid too much for stuff but...I got 50# each of: bentonite clay, 40 mesh grog (mullinite or something), and 48 mesh Hawthorne fire clay. Following a recipe (sort of) from AmateurPyro.com (61% Hawthorne FC, 31% grog (I fudged this part, it was 16% grog and 15% kyanite but they didn't have kyanite), and 8% wax. I mixed the stuff, heated it, blah blah blah. I pressed the "standard" (for my tooling and goals) 1/2 tsp and compressed to almost 8k PSI (7,961 PSI or so) then added another 1/8 tsp (as usual for me) and hit the same pressure. I pressed a fuel grain and bulkhead and dried the motor in the dehydrator for 1:15 (per usual). It lost 0.64g, all the water weight I'd added (3% to 15g powder) and then some (maybe moisture from the KNO3). I did a static burn test and it worked very well with very little throat erosion.

 

Seeing that I added another 1/8 tsp (I added/pressed 1/2 tsp then 1/4 tsp) to the next one and pressed another 15g fuel grain (15g plus H2O @ 3%). I didn't have time to dry it so I let it sit in the bed of the truck while I drove the 30+ minutes to get my son from school and it stayed there until about 5:30 after I'd pressed it. It got to dry out some. I taped a 3/16...maybe 1/4"...dowel rod to it, balanced it, and shot it with a fuse (I'm not using ematches for testing motors). WOW!! Just GONE! Took off sharply and kept going and going. It went straight up, it went up hard and fast. I lost sight of it and, with the light breeze, it landed on the neighbor's place...or the next neighbor's place. These are 5 acre chunks of ground and not where I normally test my stuff in the air. Had I known it would work so well, I would have taken it to another place.

 

I figured adding the extra 1/8 tsp would give me a longer throat (which it did) which wouldn't erode so badly. I can't tell now, because I can't find the darned thing. I'll do a similar, but static, build/burn tomorrow.

 

I'm using ERC in a 75/15/10 mix now, having exhausted all my processed BP with willow charcoal. This stuff is working very well. Tomorrow I'll probably get gutsy and try a delay (delay fuel already mixed and ready) and a passfire in the bulkhead and some ejection charge for grins. I'm using Tidy Cats unscented scoopable kitty litter for the bulkheads and I've had no failures other than the 2 motors with too much core in the fuel grain.

 

I started making a new tooling set to make a nozzle like the Estes motors but I got too aggressive on the lathe work and broke the former for the bottom of the motor casing (exhaust side/end). Ooops! Didn't have time to start over today. I'll try it again tomorrow. Maybe I can get similar performance out of a stumpier nozzle and save the weight (still being unsure if a de Laval design is necessary for BP motors).

 

--HC

[hcb]

Ya know, it's funny how some guys say it doesn't matter what the mix is, it all works. Then there are others (like us) that say maybe it's not so simple May I suggest that you could be off on your pressing force? If you are pressing lighter than you think, your nozzles would all be weak. Just a thought.

 

I've actually gotten clay from the bank of Lake Erie, broken it down, and used 12-20 mesh as my nozzle mix. It worked, but not as well as the Dr. Elsey's. I've pressed most of my nozzles, often to 9000psi. Your erosion seems excessive, which is why I suggested a possible miscalculation on your pressing force.

 

I'm guessing you could get a bag of the Dr, Elseys Precious Cat delivered pretty cheaply in your country. This is the stuff I use. I bought a huge bag, on Ed Brown's recommendation. He knows (EDIT: knew. He's passed on.) end burners

 

https://www.petsmart.ca/cat/litter-and-waste-disposal/litter/dr.-elseys-precious-cat-ultra-cat-litter---unscented-clumping-multi-cat-strength-2621253.html

 

One cool thing I found when testing end burners: immediately after testing, the residue around the nozzle hole was red. But then it changed to gray/white. I'm told it's from potassium sulfide, which degrades and changes color.

 

There are too many variables to make a blanket statement that nozzle mixture "does not matter". Not saying that you're saying that, just saying that in response to some claiming it doesn't matter. Method of consolidation, consolidation force, consolidation increments, and nozzle form all spring to mind as variables which could impact whether or not a mixture would work or not work.

 

Oh, boy, MATH! I love math. Oh, father, you're so wrong...allow me to explain. (Zorg, The Fifth Element). 1/2" rammer = (0.25^2) * pi = 0.0625 * pi = 0.196 sq in. The ram on my hydraulic short-stroke cylinder (which has a gauge to read pressure on the ram face) is 3 sq in ((1.971/2)^2 * pi = 0.9855^2 * pi = 0.971 * pi = 3.05 sq in. The gauge reads, for an example, 500 PSI. That's 1,500# applied force (500# per square inch * 3 square inches putting pressure on the fluid). 1,500# / 0.196 sq. in. of rammer face = 7,653 PSI on the composition/nozzle mix. I was wrong/inaccurate when I reported it as 7,9xx PSI. Close, but wrong nonetheless. Reversing that: 7,653 PSI to applied force on a 1/2" diameter face = PSI * sq in = 7,653 * 0.196 = 1,500# applied force. Applied force / sq in spread over the fluid = 1,500 / 3 = 500PSI on the gauge. I love this stuff. I think I am right about all this. Please correct me if I'm wrong.

 

I can probably get it in Texas. It's a different country for sure...'specially compared to Colorado...or the other "C" state. :-|

 

I think I made a sort of "discovery" in the nozzle stuff and I'll post that to the general replies to my OP.

 

--HC

[hcb]

The most successful trick that I've used for nozzles was to bind the bentonite granules with "waterglass".....sodium silicate solution that is. Upon pressing it forms a rockhard composite that really can not be dislodged without a major cato.

I would pour a premeasured amount of bentonite granules into the case, then add a suitable squirt of the silicate solution on top of the granules (a syringe is of help to keep the amounts constant) and press. One has to figure out the right volume of solution to add to the granules, so that it would be enough to soak through the entire nozzle when pressed and no more. Otherwise it shall force itself out and make a mess. Works like a treat! I also used the same mixture for end plugs.

 

Also a note about the waterglass being available in different concentrations. The most concentrated solutions are thick and resemble a syrup. These can be diluted with water at will to make a more liquid binder that seeps into the granules way better than the thick stuff. Trial and error type work

 

I was wondering what the heck "waterglass" was. I've seen it mentioned in other threads regarding something to do with rocket motors. I hadn't taken the time yet to look it up. Thank you. IIRC, sodium silicate is the stuff that is used as a threadlocker for muzzle devices for attaching suppressors on threaded barrels. It, reportedly, has a high heat tolerance, which regular "locktite" doesn't have. Thanks for the tip. I will keep this in mind. It sounds a bit sketchy doling it out so that there's enough to do the job rightly, but not so much that it leaks all over the tooling. Sounds like something that should be removed from the mandrel thoroughly, and that the motor/nozzle assembly should be removed from the mandrel promptly.

 

Good tip on being able to thin it with water, too. I had a really solid success today with my nozzle puzzle and I hope I have found the answer that will work for me. But I'll keep this as an idea to try if my "solution" today doesn't solve things.

 

Thank you.

 

--HC

[hcb]

Further info/thoughts on the nozzles and materials: So, I had pressed some nozzles using different materials, including straight-from-the-bag cheap litter from Wal-Mart (not the red-bag Special Kitty, some small, green bag stuff). It isn't "scoopable" or scented or anything. I hit the 7,653 PSI range on it. I didn't have graphite to add to the stuff. It looked amazing. I shot it and it eroded quite a bit. I took time today (very late in the process) to study more closely the Estes nozzles on a their motors and I noticed that it's very flat on the exhaust end with a very short and minor cone shape before going to the fuel grain in a straight-walled cylinder.

 

I found that the Estes nozzle had a 0.125" bore through the throat and then appeared to taper out to a maximum opening of 0.200". The taper distance appears to be 0.125" or so. The whole nozzle measures about 0.300", top to bottom. This gives: 0.300" - 0.125" = 0.175" of throat, assuming my measurement of the depth of the nozzle (0.300") and guess at the taper length (0.125") are accurate. That's 0.050" longer than my target throat of 0.125" maximum on my de Laval design. I have marks on my tooling to indicate the throat length but they're just informational, I don't add material until it's perfectly at 0.125" of throat, so I often get less than 0.125" of throat. I think that my general understanding of the nozzle and how it will be impacted by the exhaust gasses was wrong. I thought of the nozzle as being kind of permanent and bulletproof. It's not, that's for sure, as I've seen tons of erosion occur across quite a few different mixtures. Today, my last test (as documented in my previous "general" reply to the OP) had a longer throat and worked really well (no forensic analysis because the test subject is simply gone). My thoughts, though, are that the longer throat was necessary to allow the erosion to occur further up in the nozzle without breaking out into the divergent section. That and using a mixture which seemed to not erode nearly as much as earlier mixtures.

 

I'm now questioning if the de Laval design is necessary in (relatively) low pressure BP rocket motors. If I employ a nozzle formed like the Estes nozzles then I can shave a bit of material off the nozzle by making it a more compact design, eliminating the 30 degree divergent section.

 

And the final point upon which I'm ruminating is this: maybe some nozzle materials are better at holding more complex shapes than others. That is: maybe plain kitty litter alone would work fine if I didn't have a detailed, hourglass form I was making it to. Maybe a simple, "cinder block simple" nozzle like the ones Estes uses (at least in their B and C motors) would work fine with plain kitty litter.

 

I'll attempt to make the plain nozzle forming tools again tomorrow and test a few.

 

--HC