Motor retainer and centering ring

[ttabbal]

I wanted to try making one. I spent enough time on it that I would have come out way ahead to buy a commercial one, but it's just part of the build.

It holds 29mm reloadable motors in a 38mm tube. It also acts as a thrust plate to direct the force to the outer tube. In this case, it's overkill, but might as well.

It also keeps the motor in place for the ejection event so it doesn't go flying.

My first go at making "spec" matching threads on the lathe. 1 3/8-20. Worked well. Thread wires for the external, matched the internal to the part. I had to grind an internal threading tool. Interesting clearance problems inside the bore.

It will be glued into the tubes with jb-weld. Reminds me, I think I'm out....

 

[Sparweb]

Thanks for posting.
I just bought a lathe not long ago and at the time, the idea of making rocket motors didn't even cross my mind.
I used to make lots of rockets and enjoyed a few Estes kits again when my son was that age.
Now...
...You're putting ideas in my head.

 

[mikey]

You did a nice job on this! Threads look good but the knurl could maybe use a little work.

 

[ttabbal]

Thanks! Yeah, the knurl was a bit off. I need to work on getting better results with that. I think part of it is the wheels are the chinesium that came with the lathe. And I just need to practice. I've only used a knurler a few times. I don't mind terribly as it's the part of the rocket that hits the ground first when it comes down normally, so it will get dinged up a bit.

I also "discovered" that a knurler can make a threaded part REALLY tight! I ended up needing a pipe wrench to get it loosened up. That didn't help the finish, but I learned that I need to not do it that way. I wind up with a facepalm moment on most projects.

 

[ttabbal]

Thanks for posting.
I just bought a lathe not long ago and at the time, the idea of making rocket motors didn't even cross my mind.
I used to make lots of rockets and enjoyed a few Estes kits again when my son was that age.
Now...
...You're putting ideas in my head.

Thanks. The part above isn't actually a motor, it holds the motor in the rocket and directs the thrust to the outer body tube. It's a bit like the hooks in the Estes kits, just more reliable for larger setups with larger ejection charges. I do have plans to make motor cases, but I've been distracted with other things lately. If you have a club near by, stop by a launch and see some of the projects people are doing. There are some really interesting things out there.

 

[mikey]

Thanks! Yeah, the knurl was a bit off. I need to work on getting better results with that. I think part of it is the wheels are the chinesium that came with the lathe. And I just need to practice. I've only used a knurler a few times. I don't mind terribly as it's the part of the rocket that hits the ground first when it comes down normally, so it will get dinged up a bit.

I also "discovered" that a knurler can make a threaded part REALLY tight! I ended up needing a pipe wrench to get it loosened up. That didn't help the finish, but I learned that I need to not do it that way. I wind up with a facepalm moment on most projects.

Are you using as bump knurler or a scissors knurler? Knurling is one of those things in machining that is very much tool-dependent.

I assume the material you're using is aluminum? If so, then those parts can gall really easily and then be a biatch to separate, especially if you cranked down on a knurled knob to tighten them. A little bit of anti-sieze on the threads will help.

 

[ttabbal]

The tool is a camjack I built. I cranked it down a bit hard to start. I had to loosen it to enable the spindle to turn, I last used it in stainless and went a little nuts. The wheels are the ones that came with the bump knurler. Likely not great, but they don't seem horrible either.

Yes, 6061 aluminum. I thought of the antisieze after it was on there really well. I was concerned I damaged the threads, but they check out with the wires and fit well, so I think that's alright at least.

I have another part to make in aluminum I'd like to knurl, so I'll be doing some practice runs to try and get a better knurl. I'm planning on knurling before threading, so I won't have the knurler tightening the threads at least.

 

[mikey]

Sounds like a good plan. Aluminum flakes like crazy so try to make the knurl in one pass.