Questions on Rockets

[billofca]

You guys are the experts on rocket building, and I am happy to be able to ask some questions. For the last 30 years I've been an expert on commercial shell building and now I want to up my experience and round out my knowledge with rockets. About 6 months ago I bought David Sleeter's book on Amateur Rocket Motor Construction. I have read it a few times now. It's pretty good and thorough.

 

I recently purchased a 10 ton hydraulic shop press with an H frame. I also purchased a 6# ball mill from Pyro Creations, and a set of 3# rocket tools from Rich Wolter. I have all the chemicals, clay, grog, and tubes needed to start building rocket motors but I won't start until I am completely comfortable with the knowledge necessary.

 

The 3# rocket tools are for a core burning motor, and has a 1/2 inch throat at the nozzle. Motor casing length is supposed to be 10 inch long. In Sleeeter' book, he gives a formula for an engine with 1/2 inch nozzle throat and names it KG3-78-F55, and rates it at 30 pounds of peak thrust and total impulse at 78.9 NT.-Secs. Here is his formula:

 

KNO3 - 72.1%

Charcoal - 7.3%

Carbon Black - 4%

Red Gum - 7.0%

Sulfur - 9.6%

Bicarbonate of Soda - 5% additional as a burn rate modifier

Ball mill for 12 hours

Binding is done with 2 cc of acetone per 20 grams of propellant. Press pressure is 5200 psi.

 

My question for you guys is: Have any of you ever tried this formula or similar using Wolter's 3# rocket tools? I don't want my first rocket motor test to explode and wake up the dead (or my neighbors).

 

I like the data on this rocket motor. Sleeter shows graphs and data claiming this motor will lift a 1.41 pound finned rocket 36 inches long to an altitude of 1,402 feet. Delay time to apogee is 7.9 seconds with motor burn out at 200 Ft. Motor propellant burn time is 1.42 seconds.

 

Also, could you guys share a good reliable delay comp formula with me that will give me 8 seconds of delay with this motor? Any help is much appreciated.

[dagabu]

Bill,

 

If I may, I would like to suggest that you start on something a little easier and work your way up to the Sleeter motors. What tubes are you using? Are you using NEPT or another convolute wound tube? If not, a nozzled 3# rocket may be out of your reach.

 

I suggest that you start with a nozzleless rocket motor, use a standard 75:15:10 BP formula and an additional 10% (yes, I know, thats a lot) coarse charcoal after the milling is done. Take the mix, whet it and rice it, let dry and press a motor WITHOUT a nozzle and see how that flies. You will find that one type of charcoal will CATO your motors while another that seems to be the same will work just fine. Stay with a single charcoal while dialing it in.

 

Frankly, there is just no need to make a BP rocket so complicated as some of Sleeters are. I also suggest that you start with kitty litter for a nozzle with the throat being 1/2 ID deep when you try the nozzled type.

 

I know you dont want CATOs but that is unlikely to happen, even good ole' LaDuke pops one every once in a while

[ausgoty]

I agree with Dag, get something a bit less powerfull going first then step up to the bigger and better.

 

Keep detailed notes and go for consistancey otherwise you just chase your tail between CATOS, feeble weakness and the dreadful "choofers" that blow big parts of the nozzle out with each choof.

 

I am rather partial to willow diadem as a delay comp in all things. Burns slow and looks great!

 

 

[dagabu]

Saweet, Ausgoty, do you have a recipe for the willow diadem? I would like to try that.

[TSO]

I got tired of all the dust while ramming so I riced my mill dust (again, the basic 75/15/10) and tried that in my 1/2" core burners. First one took off and CATO'd. Ricing made a BIG difference in my BP speed...so I too added 10% of 80 mesh hardwood charcoal and ran it through a 20 mesh a couple of times to break up the riced ganules. The second rocket went up just fine, and with no boom. Next millling I'll take the shorter route and add the 10% and then rice, will save me some time as compared to breaking up the rice to homonogize the mix.

Now that I have the motors dialed in, on to the headers!

 

 

Bill,

If you don't mind sharing. Which 10 ton press did you decide upon?

Edited November 1, 2010 by TSO

[billofca]

I got tired of all the dust while ramming so I riced my mill dust (again, the basic 75/15/10) and tried that in my 1/2" core burners. First one took off and CATO'd. Ricing made a BIG difference in my BP speed...so I too added 10% of 80 mesh hardwood charcoal and ran it through a 20 mesh a couple of times to break up the riced ganules. The second rocket went up just fine, and with no boom. Next millling I'll take the shorter route and add the 10% and then rice, will save me some time as compared to breaking up the rice to homonogize the mix.

Now that I have the motors dialed in, on to the headers!

 

 

Bill,

If you don't mind sharing. Which 10 ton press did you decide upon?

 

OK guys, keep in mind I am new to the rocket lingo here. I presume CATO means the motor explodes. My tubes are 1" ID x 1-3/8" OD convolute wound from Hobby House (very nice quality), recommended by Rich Wolter. I also have the 1" ID x 1-1/2" OD convolute from Skylighter. I bought a 10 ton benchtop shop press with gauge from Northern Tool (Torin Jacks Model 51003). I also have Wolter's direct read in psi pad and gauge you place under the motor while pressing.

 

It's my understanding from reading Sleeter's book that chuffing comes from a fuel-rich motor. He talks about slowing down a black powder motor burn rate using baking soda starting at 10% additional to the formula. The motor will chuff. Remix a new batch with 1% less baking soda and keep doing this until the motor stops chuffing. The motor is now dialed in to a smooth burn rate with no chuffing, and not so hot that it will CATO.

 

Wolter sent a milled formula with his tool set that is basically 60-30-10, requiring a press of 5200 PSI using his special pad with gauge that gives a direct reading in psi.

 

The Wolter 3# tooling has a 1/2 throat and requires a 1" ID tube, and Sleeter's formula I described in my last post also requires a 1/2" throat in a 1" ID tube. The difference is that Sleeter's motor drawing shows a 7 Inch tube, while Wolter's tools require a 10" tube. I'm going to dial in Sleeter's formula exactly how he describes to do it. I want to cut to the chase and will accurately follow the directions to a "T". I will be using hardwood air float charcoal so it doesn't burn so hot. The carbon black in the formula helps to smooth out the combustion and adds to the length of the orange exhaust tail. So the amount of carbon in the fuel is the sum of the charcoal + carbon black.

 

Sleeter's book gives an excellent method of making clay nozzles that don't erode. Its a mixture of bentonite clay, grog (a fine grain crushed ceramic) and a small percentage of wax. He gives a detailed description of how to bake and mix the clay-wax mixture that forms a glassy finished hard nozzle when pressed but feels like powder before you put it in the tube. The grog prevents erosion from the exhaust flame. He says to only use plain bentonite for the top end plug.

 

I have a willow tree on my property, with lots of dead wood fallen branches on the ground around it. Eventually I plan to make some willow charcoal, but not for rocket fuel.

[dagabu]

Bill,

 

You may be one of only a few that have ever taken such steps to put up a BP rocket. KISS is the term best used when designing or trying something new, (Keep It Simple Stupid) you are talking about a fuel that takes several ingredients, and a burn modifier. To each his own I say but I think the extra is unnecessary to be successful in making a great BP rocket IMHO.

 

Jim's NEPT tubes are great but the Skylighter tubes are chipboard and will work fine but they would not be my first choice.

 

Considering that you have tooling for a rocket that will have a core 3" longer then the comp you are using calls for, you may overpressure the rocket. The rule of thumb is to add more charcoal if the rocket CATOs (Catastrophe At Take Off) to weaken it or add more KNO3 until it CATOs to get it to the red line then back off 1-2% until they dont CATO any more.

 

If you read the posts here and at Passfire, you will see that a glassy nozzle can be made with un-milled kitty litter just as easy as grog, wax and bentonite, plus, you will scratch your tooling with grog. I suggest you dont sacrifice your new tooling to the rocket gods.

[ausgoty]

Saweet, Ausgoty, do you have a recipe for the willow diadem? I would like to try that.

 

No worries, just taken from Pyroguide - http://www.pyroguide...e=Willow_Diadem. Very nice, my favourite star by a long shot. They look dim on vids but very different when you see it in the sky. The powder makes an excellent roman candle or rocket delay and can be tuned with charcol or Kno3 to get the timing right.

 

Thats one hell of a rocket you are planning to make Bill. The fuel seems to be very hot for a rocket of that size but if Sleeter says it will fly, then it most likely will.

 

You could lift a small cat on that! (not that I think its a good idea)

Edited November 1, 2010 by ausgoty

[TSO]

I was looking at that press too, but the working distance between the deck and the ram looked pretty limiting. So I think I'm going to go with http://www.grizzly.com/products/10-Ton-Floor-Shop-Press/H6232 instead as it gives alot more working space. I think 3# is the absolute max you can press with the Torin table top press...and it looks like even that will be pretty tight working quarters. Have you worked with the tooling and press yet? How's the space issue between the ram and deck for you?

[dagabu]

TSO,

 

The Firesmith tooling is a little too long for the table top presses as is but both Wolter and Bens tooling should be ordered with a certain max in mind, Rich and Ben will do the trimming at no charge.

 

Yes, 3# is the max you can press in the bench top presses.

 

The Grizzly press looks good and the single actuating ram can be hooked up to a power pack in the future if you want. Nice press.

[WSM]

Yes, 3# is the max you can press in the bench top presses.

 

Oh, I'm not so sure about that. Less than a decade ago, I aquired a "benchtop" log splitter from Harbor Freight Tools (with a 4 ton bottle jack), turned the wedge section upside down and pressed 6 lb rockets with it and flew them (I can prove it; someone video'd the whole thing). For that matter, given a decent size mallet (I like the 3 Lb iron clamshell with rawhide inserts) and ramming block for BP rockets, I've done 1 lb, 3 lb, 4 lb and 6 lb by hand and they flew just fine w/o CATO's.

 

My preferred composition is 6:3:1 and only vary the charcoal granulations (if using commercial components). If you ball-mill fertilizer nitrate to talc consistancy, back off on the nitrate percentage and make it up with more charcoal. The larger the rocket, the lower the fine charcoal percentage and the larger the course charcoal percentage, is a good rule of thumb.

 

When experimenting; test, test, test! Everyone has had good input here, but you need to get your hands dirty and make a few to gain confidence. Have fun doing so and share the experience with us. We'd love to hear about it.

 

WSM

[billofca]

Bill,

 

You may be one of only a few that have ever taken such steps to put up a BP rocket. KISS is the term best used when designing or trying something new, (Keep It Simple Stupid) you are talking about a fuel that takes several ingredients, and a burn modifier. To each his own I say but I think the extra is unnecessary to be successful in making a great BP rocket IMHO.

 

Jim's NEPT tubes are great but the Skylighter tubes are chipboard and will work fine but they would not be my first choice.

 

Considering that you have tooling for a rocket that will have a core 3" longer then the comp you are using calls for, you may overpressure the rocket. The rule of thumb is to add more charcoal if the rocket CATOs (Catastrophe At Take Off) to weaken it or add more KNO3 until it CATOs to get it to the red line then back off 1-2% until they dont CATO any more.

 

If you read the posts here and at Passfire, you will see that a glassy nozzle can be made with un-milled kitty litter just as easy as grog, wax and bentonite, plus, you will scratch your tooling with grog. I suggest you dont sacrifice your new tooling to the rocket gods.

 

What does NEPT stand for? The Hobby Horse tubes are excellent and have a glossy shine to the exterior. BTW, thank you for your input on this. It's exactly the kind of tips and information I am looking for. Wolter's spindle is coated with an anodizing and looks dark gray or black, to harden the outside surface. I would think it will help protect it from the abrasions of the grog mix that uses wax as a lubricant. If you say it won't, I will reconsider.

 

You should know that I have been involved in fireworks for now over 30 years, both as a professional manufacturer and as a hobbyist. I am now qualified as an expert witness and have successfully worked on 17 law cases over the past 7 years; working as a friend of the court to educate lawyers, judges and juries about fireworks. I have to fly to Florida in 2 days for a deposition in another case. My point is that I am totally familiar with the chemistry of pyro, and have literally mixed tons of star comp, flash, pulverone, etc. over the years, and have made many thousands of shells of all sizes. I worked for 23 years as the supervisor of electrical engineering at Dyno Nobel, the worlds largest explosives manufacturer with plants all over the world. Their products are used mainly in commercial blasting operations such as mining. I have 3 patents for explosive devices. I don't want you to think I am a boring brag, and would rather stay humble and modest. I mention these things now because I want you folks to understand that I am not new to pyrotechnic chemistry or explosives. I have had probably the best safety training one could ever obtain having worked in both worlds (Pyrotechnics and HE). I am not trying to say that I know it all, or I wouldn't be asking questions here. At 63 years old, the more I learn the more I realize what I don't know. So you folks can teach me a lot when it comes to tips and techniques you use in making rockets. I am also happy to share any of my knowledge with you guys if I think it would help. The comradeship and friendly exchange of information is a great part of this hobby.

 

When I read Dave Sleeter's book on rocket motors, I find it refreshing from an engineer's point of view. He is thorough with his explanations and warnings as well. He provides the math and the data that anyone who has an understanding of can duplicate the chemistry and physics (on paper as well as in practice) thus testing his work and theories. He too has a method of dialing in performance to prevent CATOs, grain cracking, and burn rates. He has a pellet test for dialing in the amount of solvent to give the absolute best pressing confinement and solid propellant grain without spring back and cracking to form a very hard solid grain. He writes about using red gum as a binder, and softening it with a small amount of acetone and then pressing immediately, or consolidating by tamping. He states the pellet test is mandatory for every formula in his book and must be done before pressing any comp to prevent air pockets and grain cracking. He has a method of swabbing the inside of tubes with contact adhesive and allowing it to dry, explaining the acetone for the binder (red gum) will soften the dried adhesive and provide a solid connection & seal of the grain to tube ID, thus preventing fire from sneaking along the OD of the grain (one cause of CATOs). He writes that bentonite clay alone (kitty litter) will erode from the exaust and reduce performance, but the grog method of making clay for nozzles will never erode. His recipe for nozzel clay is 60% bentonite clay, 32% fine sand-like grog, and 8% wax. The grog mix is heated in an oven to 300 F for one hour and the wax is melted in a pot separately. Once the grog mix is oven-heated, the melted wax is combined and all is mixed together with a fork until there is no dark spots from the wax. The oven heated grog mix keeps the wax from hardening while mixing. The wax is used as a lubricant during pressing, but cannot be felt with your fingers. Bentonite clay alone presses in small platelet layers, and exhaust gas can rip off the layered platelets, while grog mixed in will lock the platelets together and prevent erosion. If you are looking for quality and performance, I think this is the way to go. I think the wax as a lubricant will prevent spindle sticking and scratches.

 

I am not one to take short cuts or make substitutions. I am very careful about following directions, but I am also the kind of guy who needs complete understanding of all principles involved with any pyro project. I want to work up to Sleeter's motors, but I will follow the good advice here and work my way up. Yes, I too believe in the KISS principle during the learning process. I also know that if you are careful, precise, and make no substitutions, and take no short cuts, one can find success. The extra effort to do things correctly is cheap insurance.

 

When I get to experimenting with Sleeter's motors, I will start with 10% baking soda (as he recommends) and make several motors reducing the baking soda in 1% increments until I find a CATO, and then move back up by 1 or 2% to dial in the performance.

 

Thanks for the advice (keep it coming). - Bill

[dagabu]

Oh, I'm not so sure about that.

 

I was really referring to the ones that Harbor Freight and Grizzly were selling with a max opening just shy of a 3# BP set with the long rammer at full extension.

 

I have my press sitting on my desk too and it has 24" of working space between the ram and the bottom.

[WSM]

I was really referring to the ones that Harbor Freight and Grizzly were selling with a max opening just shy of a 3# BP set with the long rammer at full extension.

 

I have my press sitting on my desk too and it has 24" of working space between the ram and the bottom.

 

Hi dagabu,

 

I meant no disrespect, just that my milage varied from that comment. How've you been? I've been too busy to play, but hope to get some things done now that the weather is cooling down . My press is in storage in a container over 100 miles away, safe and sound. I need to get out there and play sometime.

 

WSM

[Algenco]

Bill.

 

NEPT

New England Paper Tubes

[nater]

Bill.

 

NEPT

New England Paper Tubes

 

Which is what he sells from Hobby Horse.

[WSM]

What does NEPT stand for? The Hobby Horse tubes are excellent and have a glossy shine to the exterior. BTW, thank you for your input on this. It's exactly the kind of tips and information I am looking for. Wolter's spindle is coated with an anodizing and looks dark gray or black, to harden the outside surface. I would think it will help protect it from the abrasions of the grog mix that uses wax as a lubricant. If you say it won't, I will reconsider.

 

 

Hi Bill,

 

NEPT is New England Paper Tube Companies products. Our preferred tubes are their Hi-burst type sized to our needs (comparable to Estes engine casings in strength and quality). The Wolter tools are aluminum with a Nituff coating (hard anodizing with a "teflon" fill, if memory serves) and are the only tools out there able to handle hard components (metals and abrasives) with little wear or effect. As long as the aluminum under the hard coating holds up, the tools will serve you well for a long time (Rich makes good stuff, rest assured; plus he backs it up!).

 

Mr. Sleeter has his way of approaching rockets. It works well for him and is one way of doing things. It all depends on what your goals are. There are as many approaches to rocketry as there are enthusiasts, I think. Try several and see what works for you. When you get some more experience and get comfortable with it, try some variations (within reasonable bounds) and note the differences. We are all constantly learning as we go and that's part of the joy in it. Have fun, be safe and share your experiences with us.

 

WSM

[dagabu]

Hi dagabu,

 

I meant no disrespect, just that my milage varied from that comment. How've you been? I've been too busy to play, but hope to get some things done now that the weather is cooling down . My press is in storage in a container over 100 miles away, safe and sound. I need to get out there and play sometime.

 

WSM

 

Very good, thank you! Been working on headers but after seeing TRs headers at 4F, I think I should go back to lighting sparklers.

 

Nope, no disrespect taken, my posts just come off rather harsh though there is no anger at all behind them. We seem to go around and around with presses and when the guys get the bench top kind and put a 10" tube and a 14" rammer in the press and discover that they don't fit, they get kind of pissed that someone didn't say something till afterwords.

 

With six kids, I do a lot of the warning stuff and it leaks out here and there on postings, sorry.

[dagabu]

You should know that I have been involved in fireworks for now over 30 years, both as a professional manufacturer and as a hobbyist.

 

Oh, I think its fair to say that everyone that has dabbled in the black arts knows who you are Bill. I have all but your last publishing on my book shelf.

 

Down to the nitty-gritty, APC is all about amateur pyrotechnics so when someone asks about a particular item and they have not made one of them before, we try to throw our own two cents in to try to eliminate the problems we found.

 

I can't think of a single person here that has measured their rocket thrust in Newtons or Impulse Seconds but rather, will it lift a weight of X to the height of Y and will the tail look really cool?

 

I am thinking you are more looking for the Model Rocketry section and if that is what you are thinking about, a much more efficient fuel such as APCP (ammonium perchlorate composite propellant) would be my choice for fuels.

 

I am afraid that we may not be of much assistance in regards to fuels that we have not used before.

 

Enjoy the cookies

[billofca]

Oh, I think its fair to say that everyone that has dabbled in the black arts knows who you are Bill. I have all but your last publishing on my book shelf.

 

Down to the nitty-gritty, APC is all about amateur pyrotechnics so when someone asks about a particular item and they have not made one of them before, we try to throw our own two cents in to try to eliminate the problems we found.

 

I can't think of a single person here that has measured their rocket thrust in Newtons or Impulse Seconds but rather, will it lift a weight of X to the height of Y and will the tail look really cool?

 

I am thinking you are more looking for the Model Rocketry section and if that is what you are thinking about, a much more efficient fuel such as APCP (ammonium perchlorate composite propellant) would be my choice for fuels.

 

I am afraid that we may not be of much assistance in regards to fuels that we have not used before.

 

Enjoy the cookies

 

Thanks for your reassurance and I really am open for advice. I keep thinking about everything you guys have said, and it all makes perfect sense to go slow and to build up my rocket knowledge and experience. I'm kind of torn between going the amateur rocketry route and the stick rocket FW route. I probably want to do both and will eventually do both. In the early 1960's as a youngster, model rocketry was my hobby. I was also dabbling in homemade fireworks at that time. Smelling the smoke for the first time. I now watch the kids on you tube post their trials and tribulations and it reminds me of myself when I was a kid. I never did some of the insane crazy and dangerous stuff I now see on you tube. Like making rocket candy on an open flame burner on the floor of the garage between two cars and next to their gas tanks. Talk about potential Darwin awards. Wow.

 

I haven't assembled the press yet, but I'll post here when I do and let you all know how it works with the 3# tooling. I think that by tamping the fuel in increments, and then pressing, I should not have any problem with the work distance under the press. We'll see.

 

I would like to eventually build a test stand for motors and incorporate some instrumentation and electronics to measure and record thrust and burn time. It's a bit out of my budget range right now. But having that would make experimentation a hole lot more interesting. How do you guys know when you have dialed in a motor to its best performance? Is it mostly by trial and watching it perform?

[dagabu]

Sorry everyone on Bogarting this post:

 

Bill, If you are serious about making a test stand, you will want to use a scale of some kind and a video camera to start with. The Pelouze Y50G is a nice scale that can be had for around $50.00 if you look hard. Put your video camera on a tripod and zoom in so you can see the motor and the scale clearly, make/find a suitable holder for the rocket motor, I prefer to use some epoxy in a dog dish, the kind with the extended skirt at Wall Mart for $2.00 (more details if you want them). Start the camera and light the motor... uh, facing the wrong way with the nozzle up.

 

The camera will take either 30 or 60 frames per second, you can advance the film frame by frame to see the correlation of thrust to burn time if you wish or plot dots on a graph for the thrust curve.

 

Moving on to bigger and better, you will want top build a load cell for PC hook up and let it do all of the work for you. My upcoming test stand uses a load cell from eBay for $7.00 (2kg) and the DI-194RS from Dataq and a custom amplifier board from a buddy over at Passfire.

 

Performance for me is measured by the beauty of the tail, its viewability (the ability for the audience to watch it) and lift, in that order. For example, I have a 1# motor that will carry a 2 pound (1000g) heading to 500 feet. The tail isn't real pretty so I use a dense delay full of Ti to get some color but it is fast! On the other hand, I also have a 3# motor that will only lift a 300 gram shell but it will lift it to 1000 feet gracefully, slowly and with a huge charcoal tail.

 

One word of advice, dont pound the rocket and then press it, the fuel will resist compaction by the static load after a dynamic load is applied. You can consolidate the fuel by hand, that gets you about 50% of the way there.

 

On the subject of model rockets or pyro rockets, try both. See which speaks to you and work with it for a while.

[billofca]

Sorry everyone on Bogarting this post:

 

Bill, If you are serious about making a test stand, you will want to use a scale of some kind and a video camera to start with. The Pelouze Y50G is a nice scale that can be had for around $50.00 if you look hard. Put your video camera on a tripod and zoom in so you can see the motor and the scale clearly, make/find a suitable holder for the rocket motor, I prefer to use some epoxy in a dog dish, the kind with the extended skirt at Wall Mart for $2.00 (more details if you want them). Start the camera and light the motor... uh, facing the wrong way with the nozzle up.

 

The camera will take either 30 or 60 frames per second, you can advance the film frame by frame to see the correlation of thrust to burn time if you wish or plot dots on a graph for the thrust curve.

 

Moving on to bigger and better, you will want top build a load cell for PC hook up and let it do all of the work for you. My upcoming test stand uses a load cell from eBay for $7.00 (2kg) and the DI-194RS from Dataq and a custom amplifier board from a buddy over at Passfire.

 

Performance for me is measured by the beauty of the tail, its viewability (the ability for the audience to watch it) and lift, in that order. For example, I have a 1# motor that will carry a 2 pound (1000g) heading to 500 feet. The tail isn't real pretty so I use a dense delay full of Ti to get some color but it is fast! On the other hand, I also have a 3# motor that will only lift a 300 gram shell but it will lift it to 1000 feet gracefully, slowly and with a huge charcoal tail.

 

One word of advice, dont pound the rocket and then press it, the fuel will resist compaction by the static load after a dynamic load is applied. You can consolidate the fuel by hand, that gets you about 50% of the way there.

 

On the subject of model rockets or pyro rockets, try both. See which speaks to you and work with it for a while.

 

Good advice, than you for taking the time to post.

 

I assembled my bench top press last night. It came with a 3/4" thick plate that sits on the bottom cross bar. The bottom cross bar is one that can be raised and lowered with pins that fit into the vertical side supports to support the position of the cross bar. All the way down, and with the 3/4" base plate sitting on the cross bar, there is 15-1/4" clearance to the ram. If I remove the adjustable cross bar, and set the base plate on the welded cross bar (base of stand) I can get 3 more inches, or 18-1/4" clearance to the ram. Wolter's press pad gage takes up another 2-1/2 inches. I won't have any problems with 3# motors, but that is about the limit of this press as posted by others. It will also come in handy pressing comets and other nice things like home made ball milled BP pressed into hockey pucks (clinkers) to make good lift powder.

 

I played with pressing clay nozzles (only bentonite) on a few motor tubes. Question for you: If you press a clay nozzle instead of ramming it, what is a good pressure to use? I think that 3 raised and rounded teaspoons (not heaping) of clay is about right. Do you weigh the clay for your rocket motors? That would be more accurate and consistent. What is the correct weight of clay for a 3# motor if you know?

[dagabu]

Bill,

 

Because tooling varies so greatly, there is no hard and fast rule on nozzle weight, just pay close attention to the go/no-go marks on your rammers and don't pass the bottom one or you will be spending a lot of time getting it un-stuck! I.e., I have a BP set that takes 20 grams of clay to make a nozzle while my Universal Hybrid tooling takes a full 30 grams.

 

Here is my way of determining the nozzle mass. I take a 1-1/4" copper pipe cap, solder it to a section of 1/8" brass rod to make a scoop out of it and then fill it to the top with clay, strike it even to the top and press the nozzle. I then measure the nozzle throat, it should be 1/2 ID minimum in order to hold the pressure.

 

If the throat is more then 1/2 ID, I take off some of the scoop by running it through the bandsaw and run a file over it to smooth it and press another nozzle and repeat until I have a scoop that holds the perfect amount of nozzle mix for that tooling set. I then mark the scoop with the tooling name and reserve it for that set.

 

As far as pressure goes, 9000 loading pounds per square inch is rather universal. Passfire has a calculator for rocket loading pressures that is worth the price of admission by itself. I have a 12V hydraulic box frame press that has a 3" x 16" ram so on a 1" (3#) rocket, I press to 1000 psi on the fluid pressure side of my press for 9000 LPI on the 1" rammers. Wolter should have sent you the ram specs, (if it's 2.7") 1250 PSI should yield 9000 LPI on the rammers.

 

-D

[WSM]

I played with pressing clay nozzles (only bentonite) on a few motor tubes. Question for you: If you press a clay nozzle instead of ramming it, what is a good pressure to use? I think that 3 raised and rounded teaspoons (not heaping) of clay is about right. Do you weigh the clay for your rocket motors? That would be more accurate and consistent. What is the correct weight of clay for a 3# motor if you know?

 

The ideal amount of clay for the nozzle is enough to make a pressed nozzle that is no less than 1 tube ID in height. I use a scoop sized to approximate that amount in one press. You may measure the exact mass of your nozzle by pressing a good one and weigh the tube before and after. Then weigh that same amount of nozzle mixture each time. The same mass and pressure should give the consistant results you seek.

 

It's important to do the nozzle all in one shot. Multiple scoops and pressing makes a nozzle prone to coming apart during the thrust phase of the rocket's performance. During pressing or ramming the point of highest density is at the face of the rammer (whether clay or composition) and those points are the place where a nozzle will come apart if not pressed all at once.

 

For higher performance of a rocket, one technique is to press shorter increments of composition, thereby yielding a higher overall loading density (more propellant in the same space).

 

Have fun, Bill.

 

WSM

[dagabu]

The ideal amount of clay for the nozzle is enough to make a pressed nozzle that is no less than 1 tube ID in height.

WSM

 

W,

 

How shall we interpret the 1 ID in height? Throat, overall distance between the convergence and divergence, any clay in the tube? The reason I ask is that I have a tooling set made for porcelain nozzles (kaolin) that uses a standard bell shaped nozzle with a long convergence of 1 ID. These nozzles are pressed wet, air dried and fired at 2700° F and are used for APCP rockets instead of using milled graphite nozzles. The overall length in a 3# rocket motor is 2.5" so one ID would be way to short and a full ID for the throat would be too long.

 

Consider if you will the spindle. At which point does the spindle start to become aggressively tapered compared to the base width? The Universal hybrid tooling has a consistent taper of 1-1/2° from divergence end to spindle tip, a full ID of throat length decreases the nozzle a full 1/32" on my set and I would lose a full increment of fuel on the spindle.

 

-D