Machine Screw Pull-Out Capacity 2

[Gerrha]

I am a retired scientist and off/on for many years I planned to build a small liquid fuel rocket engine. My son recently got me interested again so I am back working on the project. This engine will never leave the ground. It is for fun and also for my son and I to learn many new things along the way. As a starting point, the design will have a combustion chamber with a round injector plate on the top. They will be bolted together. These parts are fairly small, less than 3" in diameter, so the screws also need to be small as in #4 through maybe #8. Our current design would use 8, 6-32 socket-head cap screws with a thread engagement of 1/2". The material is copper, and the chamber pressure is 500-psig. The thing will be operated remotely, so if it blows up no harm will be done, but the point of the project is to learn what is required for a proper design. This bolt arrangement has become a question for me. It looks good on paper, but from an engineering consideration, is our bolt arrangement adequate or not?

I have searched many sources and cannot find this type of information. However, it must be out there somewhere. Could someone please help us with this?

 

[Gerrha]

Would there be a significant difference with a 6-32 helicoil? Would they not also be screwed into the copper substrate?

 

[MintJulep]

Would there be a significant difference with a 6-32 helicoil? Would they not also be screwed into the copper substrate?

Larger diameter --> smaller stress.

 

[Gerrha]

I could also just bump up to 8-32. I think there is room for that switch, and that 8 of those ought to be more than sufficient.

 

[SnTMan]

Helicoils might also be desirable if you disassemble / reassemble repeatedly. No wear on the copper threads.

They could also likely be retro-fitted if found to be needed.

Regards

Mike

 

[Gerrha]

Yes, I can see the logic for helicoils if there would be repeated assembly/disassembly. That probably does not apply to this situation and as you said, they could be installed later.