Machining Motor Casings

[DPatell]

My dad and I have undergone motor casing prouction, and it's proven to be a lot of fun. It's not too hard or expensive if you already have the machines. My dad enjoys working with lathes and metal, so we had the stuff on hand already.

The first casing that we chose to try was a 7" long 38mm. Turns out to be like similar to the Loki 38-220, and I have to give Jeff credit for the dimensions. Thanks for posting so much information on your site!

This has been a very good experience. It has helped my dad teach me how to use the lathes and gains us appreciation for the casings that you buy. You get what you pay for!

Here is a pic of the casing blank.

 

[DPatell]

Here is a picture (blurry) of the snap ring groove in the casing.

 

[DPatell]

Here's another pic of the snap ring groove with a snap ring installed.

 

[DPatell]

Here is an above view of the case with a snap ring installed, a much clearer picture.

 

[DPatell]

Completed forward closure.

 

[DPatell]

Graphite nozzle blank. 2" stock, it's not too great of quality, but it'll do.

 

[DPatell]

This is the nozzle almost done! All that needs to be done is to have it cut off of the extra, the exit cone machined, and an o-ring groove machined.

 

[DPatell]

Last for now is a picture of the forward end of the motor assembled.

 

[Evil Prince]

Dan, not to be a stick in the motor casing or whatever, but they can only be used for EX. Even if one were to use the "same" materials and anoidizing and machined them to the identical specs, NAR and TRA disallow certified motors from being flown in anything but the manufacturer's - or appointed vendor's - hardware.

 

[DPatell]

Yepp. I just used Loki's dimensions for the first casing we tried. The next ones will be my own dimensions and such. Thanks!

 

[GL-P]

Yeah, they are pretty cheap if you have the equipment. My dad made an H casing for Aerotech reloads. He doesn't have the equipment but there is a class he goes to that has tons of equipment. It hads screw closures and a little eyebolt in the top for a shockcord. Its got a thrust ring and and grooved ends like Dr. Rockets does. Looks almost exactly like Dr. Rocket's casings. The only problem is I had to launch under the the description "experimental". Should try some Pro38 casings.

 

[n3tjm]

Very cool. We have a machine shop in our garage.... but I don't use it. Belongs to my Dad.

A friend of mine offered to make me some cases if I send him the materials. I took him up on his offer, but I am waiting for him to come back from his honeymoon

 

[xenon]

Originally posted by Evil Prince
Dan, not to be a stick in the motor casing or whatever, but they can only be used for EX. Even if one were to use the "same" materials and anoidizing and machined them to the identical specs, NAR and TRA disallow certified motors from being flown in anything but the manufacturer's - or appointed vendor's - hardware.

FYI from the Dr. Rocket web site "Is this [Dr. Rocket] hardware Tripoli approved.....can it be used at Tripoli sanctioned launches?
Yes. The following is from Bob Sisk, chairman of the Tripoli Motor Testing (TMT) Committee:
" As long as reloadable motor hardware is made of the same materials and to the same specifications and tolerances as that used for testing, TMT will consider it acceptable for use by certified Tripoli members." The full text of the letter is available from Dr. Rocket at our company address."

 

[DPatell]

This case is designed to be used with experimental motors. I really wish I could go into detail regarding the propellent, but it's not allowed in this forum.

I do have loads for this case, and will test fire it once finished.

edit: Moderators, will I be allowed to post pictures of the static fire?

 

[AlexNUMB]

Originally posted by DPatell
I really wish I could go into detail regarding the propellent, but it's not allowed in this forum.

Yeah, that sucks...

Nice casings! Isn't it fun to learn how to use a metal lathe? My desire to do my own has gotten me to learn also. Good luck with your static burns!

One thing we have noticed using the coarse grain graphite is that slag tends to stick to them a little more readily than when using nozzles machined from fine grain graphite. It seems to grip the little pits in the surfaces.

YMMV...

--Alex

 

[DPatell]

Yea, I love working with machines. It gets me out of in front of the computer every now and then!

I'll just have to do some extra cleaning with the nozzles, no biggie. The price was definately right though! I personally got mine from www.GraphiteStore.com

 

[n3tjm]

In my opinion, I think EX is a valid and wholesome endeavor for the experienced and legal (old enough to be leagally responsible) rocketeer. TRA has an EX program, and in my opinion, NAR should come up with one too. Before 1994, reloadable motors were taboo... now... anyone flying anything above G is pretty much limited to reloadables. Hybrids are now here. So many new things coming up... which is good. Remember.... it's up the hobbiest that become the great inventors of the world .

 

[AlexNUMB]

Originally posted by DPatell
I'll just have to do some extra cleaning with the nozzles, no biggie. The price was definately right though! I personally got mine from www.GraphiteStore.com

Yep... That's where we get ours also.

If you are using much aluminum in the formula, "cleaning" can involve a utility knife and 20 to 30 minutes of chipping at the converging section... The price on the medium grain graphite is sure nice, tho!

--Alex

 

[DPatell]

For future reference, I am 16. My dad supervises and works with me whenever I do anything regarding propellent or casing making. He is TRA L2 and has a LEUP.

I've had to do quite a bit of chipping already with the loads I flew at LDRS from Loki. This one may be a little more difficult, but if needed I imagine that I could even lightly use sand paper to remove it after I chip off the majority. It's no longer a fire hazard since it's burned.

Thanks for the kind words and all the help guys, anything else is welcomed!

 

[Evil Prince]

Originally posted by DPatell
... with the loads I flew at LDRS from Loki...

Don't you mean YOUR DAD flew?

 

[Ryan S.]

Word of advice, rather than scratch your nozzles after, simply put lots of grease on them before. I little push and the whole peice of slag usually comes out, in my case, it does in the perfect shape of the convergance cone. The way to do it is to push on the slag with a jewlers screwdriver from the throat outward, that way you are pushing the slag in the direction it is weakest, If you push towards the throat it will be much easier

I have never had a problem removing slag, I had a somewhat tough peice once, (just a square on the convergance cone) I hit it with some windex and the problem was solved

 

[midpwrguy]

Dan
I can show you a few things thats helped me in making some of the cases I've done. One thing I think helped alot.Is to turn a spacer that holds all your nozzles and bulkheads in the same spot
In the chuck. I done this by turning it smaller than a 29mm nozzle or bulkhead. This has a shoulder on it that stops at the back of the chuck. Most lathes have a hole that runs out the back side of your lathe. Here's a picture of it

 

[midpwrguy]

Here's the chuck with the spacer installed.

 

[midpwrguy]

This one just show's. How it looks with a bulkhead. By having this all my bulkheads and nozzles are held in the same spot in the chuck.

 

[midpwrguy]

One more thing I came up with. Is some adapters to hold the case for cutting the sprial snap ring groves and to polish the cases. Theses where just turned out of solid bar stock. It has two shoulders cut into it. These will fit the 29mm and 38mm ID. One end is held by the chuck. And the other is centered with the tail stock. Picture

 

[midpwrguy]

In the last pic. You can see the marks made by the chuck.
This shows the one I use for the tail stock end. The inside has been turned on an angle to fit the taper of the tail stock.

 

[midpwrguy]

This is what it looks like with a casing on them.

 

[midpwrguy]

Here's a picture of just a few that I've been turning. The small case is a 16" 24mm case.

 

[AlexNUMB]

midpwrguy--

Wow! That's a great tip. Thank you for posting it!

I haven't done casings on my little Logan lathe yet, but I have done end closures. It is kind of annoying to have the nipple not be the same length as others (still functional, tho!).

--Alex

 

[midpwrguy]

Not only that Alex It gives me a solid STOP to work from. This is how I cut all my bulkheads and nozzles to the same lenght. Put the O-ring groves in the same spot.