Rocket Tooling - Spindle Material?

[btdk34]

I am just beginning to scratch the surface of making my own rocket tooling. I am currently working on a 2 ounce (3/8" ID) tooling set, and have finished the base which is made out of 6061 aluminum. I am working on the spindle next, but am unsure of what material to use. I have heard that aluminum is pretty flexible when using such small diameters (3/16") and from my experience, it isn't very scratch resistant. I have also heard that 303 stainless would be a good spindle choice. However, I don't have any experience turning 303 stainless steel on a lathe, and I have heard it is difficult. I've also heard brass is a good spindle choice! Is it less flexible than aluminum, and how scratch resistant is it? Keep in mind that I will be making very small spindles (~3/16" diameter, 2" length).

 

Looking forward to learning some new information

Edited July 23, 2012 by btdk34

[mikeee]

If you want to save some time on making the spindles, you could use a taper pin.

They are available in stainless steel, plain base or threaded base style.

WWGrainger and McMaster Carr sells them for very little money.

They make them in different lengths and different diameters.

You can use a taper reamer to drill the hole in the base to accept the taper of the plain base pin.

You can buy the taper reamers on Ebay for about $10.00 ea.

WWGrainger also has stainless steel spacers that can be used to center the rocket tube onto.

For the tool base I am using a stainless steel blind piping flange.

If you use a threaded base taper pin you would need to drill and tap threads in the base for the pin.

 

#4 Stainless Steel Taper Pin = $10.00

1/2" Diameter SS Spacer = $5.00

3/4" SS Blind Flange = $8.00 (clearance sale)

 

You would still need to make your ramming rods.

 

Mikeee

[btdk34]

Thanks for the info! I've never considered taper pins before, mostly because I'm trying to create a specific nozzle geometry. I think for now I'll stick with turning materials on a lathe.

 

I've also looked into anodizing my 6061 aluminum, and it sounds like although this is an excellent scratch protector, it does nothing to add to the physical strength of the spindle...

[dagabu]

If you have access to a lathe, there is nothing to gain from using taper pins, spacers, etc for rocket tooling. Stainless steel is a 'dry' metal, which means that it will grab the clay nozzle material and comp more aluminum would.

 

If you have brass, us it instead of aluminum, it is harder, not as plastic and is by far the easiest spindle material to pull out of a finished rocket. navel brass is the best of the brasses you can buy but it is very expensive. 6061-T6 aluminum is a very good material and will turn and polish well. It is also cheap so should you destroy a spindle, you can make another up for a buck or less.

 

Remember to use a convergence and divergence when forming the spindle and first rammer, you will decrease CATOs and increase usable thrust.

 

-dag

[btdk34]

It's good to know that stainless steel grabs on to comps more than aluminum or brass. In that case, I will stay away from it, at least for now.

 

As far as brass goes, it is super expensive! OnlineMetals.com sells naval brass rod (0.4375" OD) for ~$17, whereas 6061 aluminum (0.5" OD) for ~$3. What a difference! Although I must say, the brass spindles I've seen, such as Ben Smith's tooling, looks awesome. Is the brass noticeably stronger than the 6061? If so, I may have to splurge and get some. Plus, it has the addition of easier rocket release like dag mentioned...

 

The nozzle I am planning closely follows the De Laval nozzle geometry, using a 45^o convergence and a 15^o divergence relative to the spindle axis. I'm hoping to maximize thrust efficiency.

[mikeee]

Spend the money and buy the brass if you are going to machine it yourself.

The reason I use the spacers is to be able to make different nozzle designs.

I also have easy/cheap access to the parts I use to make the tooling.

The machined spacer is then pressed onto the taper pin

Since you have a lathe you can turn the nozzle and spindle assembly as one piece.

What kind of rocket fuel are you pressing?

Some types of fuels are easier to remove from a stainless steel spindle.

There are materials you can put on the spindle to make it easier to remove after pressing.

 

Mikeee

[btdk34]

I will be using some type of charcoal-cooled black powder variant. Last year I experimented with KNO₃-Sucrose rockets with great success, but they only lasted a few days due to their hygroscopic property. These are my first real black powder rockets!

 

I've heard that you can apply vegetable oil or a similar oil on the spindle first, but this will affect the performance of course. I think I would prefer to use a 'dry' spindle (not adding any oils, etc.), which makes it seem like brass is my best option... but I am still open to the possibility.

[mikeee]

You shouldn't have much problem with black powder rockets removing from the spindle.

Some whistle & strobe fuels are pressed at high pressures which can be difficult to remove from the spindle.

There are several mold releases that you can polish the spindle with to ease removal.

If your spindle has a slight taper that solves most of the problem of removal.

 

Mikeee

[btdk34]

Good to know. I am planning on having a 1^o taper on the spindle. Any more, and I fear the diameter will become too small and break after much use.

[dagabu]

You may want to consider 1.5% on the spindle, the tip will be just fine. If you have access to a Menards hardware store, pick up a can of Jig-a-Loo for the spindles if it gets really tight. I find that brass is really easy to pull out from whistle where SST and Al are a bear.

 

Brass releases even better after it tarnishes some so don't shine it up all the time, just let it be black. Al and SST have to be shined and have lube to release properly, I wish that all the spindles were brass.

 

Your convergence and divergence seem to be OK but the thrust curve BP motors make is not going to be enough of a gain to make up for all that extra clay you will need to make the 45° divergence. In order to actually make use of the thrust, you would need to design a longer throat such as this:

 

http://www.jacobsrocketry.com/general/graphics/de_leval.JPG

 

What we are able to make from pressing clay in a single increment makes little improvement but ANY bell (divergence) will help with erosion and over-pressurization. I think you would do well to build or buy a thrust stand to test your theory.

 

I will be bringing at least one test stand with me to PGI for testing by anybody that wishes to use it and should be ready for limited production before Christmas. Price TBA.

 

-dag

Edited July 22, 2012 by dagabu

[californiapyro]

you can do a 2 degree taper without worry, that is fairly standard. Have you used the rocket tool sketcher for a design?

[btdk34]

Dag, I think I will have a really hard time not wanting to polish the brass all the time! I'll keep the Jig-a-Loo in mind too. I'll probably make a spacer to eject the rocket so I don't have to twist it off if it is too difficult.

 

Cali, both you and Dag convinced me to increase the spindle taper to either 1.5^o, and possibly even 2^o. Although if I use a 2^o taper, the tip is less than 1/16" diameter! Is this something to worry about? I guess by the time I am ramming at this point, the spindle is already being supported by the core already made...

 

I've used the rocket tool sketcher a few times to get a general feel for a design, but never used it as a final design. If you select the 'BP Core Burner' option, it automatically makes the tube length 10x the tube ID. I'd prefer it to be a bit shorter, say 8x instead of 10x. Plus, I quite enjoy designing it from scratch (I use adobe illustrator for the design).

[btdk34]

Just saw your update, Dag. Did you mean 15^o divergence, or 45^o convergence? Either way, what sorts of angles would you recommend then?

 

To clarify, I'll show some pictures of my plans so far. The attached image shows a 45^o convergence with a 15^o divergence, with the total nozzle height ~3/8".

 

The tube is 3" long (the picture cuts it off), with a total spindle length of 2". Is this too short for a tube this length? I'd like to leave room for delay and a clay header.

Edited July 23, 2012 by btdk34

[dagabu]

Just saw your update, Dag. Did you mean 15^o divergence, or 45^o convergence? Either way, what sorts of angles would you recommend then?

 

To clarify, I'll show some pictures of my plans so far. The attached image shows a 45^o convergence with a 15^o divergence, with the total nozzle height ~3/8".

 

The tube is 3" long (the picture cuts it off), with a total spindle length of 2". Is this too short for a tube this length? I'd like to leave room for delay and a clay header.

 

Your drawing looks great, the spindle looks just like the SLD Universal Hybrid design. It looks like you used the long winded screamer selection for the spindle length? Yes, a spacer is a great material to use. I am looking at ACME brass screw for a removal tool but the spindle for a 3 pound motor would run $50.00.

 

A word on clay bulkheads: The only times a clay bulkhead needs to be used is when short timing, high thrust and/or a heavy lift is used. For 90% of rockets, there is no need to use a clay bulkhead since the delay is more then enough to hold the thrust. BP (standard) burns about 3 seconds an inch, a bulkhead should be at least one motor ID (that changes in very large motors) in depth so your motor with 1/2" of delay will give you the bulkhead and delay you want for a simple heading and just add more delay for a longer coasting if using a report.

 

-dag

Edited July 23, 2012 by dagabu

[btdk34]

Cool! I actually picked a 2" total spindle length arbitrarily. It seemed to look nice inside the 3" tube length, giving enough space for what I thought should be the delay charge and clay bulkhead.

 

Out of curiosity, what is SLD Universal Hybrid design? I've been a longtime lurker here, reading lots and trying to learn the basics of rocketry. I don't really understand how universal tooling works for various fuels... I would imagine different types of fuel need different core lengths/widths, etc... care to explain?

Edited July 23, 2012 by btdk34

[WonderBoy]

Oh a test stand you say? I will definitely be taking you up on that offer. I have been very curious about how much thrust I am getting with my motors.

 

On topic: I use stainless steel for nearly all of my spindles. I do usually apply some sort of "lube" though. I usually just rub some wax on the spindle and buff a tiny bit with a rag, Jig-A-Loo is a good option as well. Stay away from oils and vasoline as it will decrease performance.

 

Using the tool sketcher, in the same dropdown menu that allows you to pick "BP Core Burner" etc. you can pick "Custom" and then enter the dimensions that you want. Although I applaud your Illustrator skills, I am not a fan of drawing in Illustrator.

 

 

WB

[dagabu]

Cool! I actually picked a 2" total spindle length arbitrarily. It seemed to look nice inside the 3" tube length, giving enough space for what I thought should be the delay charge and clay bulkhead.

 

Out of curiosity, what is SLD Universal Hybrid design? I've been a longtime lurker here, reading lots and trying to learn the basics of rocketry. I don't really understand how universal tooling works for various fuels... I would imagine different types of fuel need different core lengths/widths, etc... care to explain?

 

Your design with the built in divergence is the UT design. That's exactly what they look like, good job.

 

The Universal Hybrid Tooling is one spindle, only the fuels and the nozzles change. There was over 11 different motors that could be made with the UH set as of last year and there is a pamphlet of sorts that Lee Bussy over on Passfire put together with all the text. This single set makes BP to Chuffers to long winded whistles to strobes to the work horse, the nozzleless BP rocket.

 

You could, if you wished to, make a strobe rocket with your set. It is perfect for the job.

 

-dag

[dagabu]

Oh a test stand you say? I will definitely be taking you up on that offer. I have been very curious about how much thrust I am getting with my motors.

 

On topic: I use stainless steel for nearly all of my spindles. I do usually apply some sort of "lube" though. I usually just rub some wax on the spindle and buff a tiny bit with a rag, Jig-A-Loo is a good option as well. Stay away from oils and vasoline as it will decrease performance.

 

Using the tool sketcher, in the same dropdown menu that allows you to pick "BP Core Burner" etc. you can pick "Custom" and then enter the dimensions that you want. Although I applaud your Illustrator skills, I am not a fan of drawing in Illustrator.

 

 

WB

 

It's an all-in-one design, Peret is doing all the hard work and I am playing assembly monkey and if I can get a break from stuff in life, I will have two fully functional units ready to use on site.

 

-dag

[btdk34]

Thanks! And I think I understand... so essentially, the only thing that changes is the nozzle throat height/convergence angle?

 

Someday, I hope to build an electronic test stand too. That would be incredibly useful!

[dagabu]

Thanks! And I think I understand... so essentially, the only thing that changes is the nozzle throat height/convergence angle?

 

Someday, I hope to build an electronic test stand too. That would be incredibly useful!

 

Noooooooo, the tooling stays the same, spindle, rammers, all of it. Only the fuel changes. Click on the link, the underlined words for the booklet for more explanation.

 

-dag

[btdk34]

Oh I see. When I click on the link, I seem to be getting the "Not Found" error...

[dagabu]

Thanks! And I think I understand... so essentially, the only thing that changes is the nozzle throat height/convergence angle?

 

Someday, I hope to build an electronic test stand too. That would be incredibly useful!

 

Too bad you don't get the PGI bulletin, Danny just finished a write up on a test stand built from available parts, this one will only be available for purchase finished and ready to go.

 

-dag

[btdk34]

On a side note, anyone have tips for lathing parts? I am still fairly new to turning parts, and I would like to know if anyone has advice relating to turning spindles (e.g. which part of the spindle to turn first, turning speeds for brass, etc...) Edited July 23, 2012 by btdk34

[dagabu]

I sure do (go figure, huh?), I made all sorts of mistakes when I first started and after long talks with Rich, Ben and Steve (I only remember half of my conversations due to Strohs poisoning) I now understand that the base of the spindle should be finished first. That means you will have to decide what the base will be like, will it be tapered, straight walled, drilled and tapped, four spring pins holding it, threaded etc?

 

I make my bases with a .5" hole for all my spindles and a set screw coming in from the side of the base to keep it from turning. The bottom of the spindle is drilled and tapped for a 1/4" x 20 bolt. Both of these operations are done in the lathe. The the spindle base is turned down to .5".

 

I flip the spindle around and use a live center to hold the unchucked end. I then turn the part that enters the tube down to the tube ID. I then turn the material down to the widest part of the finished spindle after measuring and marking the material. Once that is done I measure and turn the spindle above the divergence down to the end of the taper.

 

I then adjust the cross slide miter to the divergence angle and turn the divergence then adjust the slide miter to the base angle, turn that and move on to the spindle taper.

 

I step turn the spindle down using the the feed and cross feed only as it saves time and is fast. I then adjust the cross slide miter to 1.5° and finish the spindle starting at the base.

 

Remove the live center and sand the spindle assembly with 600 and then 1200 grit wet dry paper. Use Mothers Mag Polish to shine it up, it works on all metals.

 

-dag

[btdk34]

Cool! Thanks for the very in-depth description. Unfortunately, my school's lathe only has a 3-jaw chuck, and so if you cut a part, take it out, then re-chuck it, it is no longer the same center as before. I'll see what I can do to workaround that though. I'm getting my brass in a few days, I'll give it a whirl and let you guys know how it goes.

 

Also, quick question about the rammers. When the rammers are fully inserted up to the "no-pass lines", should there be a bit of clearance between the spindle and the rammer hole? Or should they exactly match? Just wondering what "typical" sets do.

Edited July 23, 2012 by btdk34