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Blow forward bolt, presssure and springs

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Re: Blow forward bolt, presssure and springs

Unread postAuthor: jrrdw » Fri Mar 20, 2015 8:55 am

What kind / brand and size of lathe do you have?
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Re: Blow forward bolt, presssure and springs

Unread postAuthor: Ianbuckwell » Sat Mar 21, 2015 1:55 pm

It's an old Myford ML7, think it is late 1940s!!! Its an English manufacturer so not sure if you will have heard of them. Not sure what size it is, I will take a photo of it. It isn't perfect, but I think operator incompetance doesn't help things. Hoping in near future that my dad is going to get a more modern smallish lathe, something like an Emco.
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Re: Blow forward bolt, presssure and springs

Unread postAuthor: jrrdw » Sat Mar 21, 2015 2:51 pm

Hoping in near future that my dad is going to get a more modern smallish lathe, something like an Emco.


I like what you got right there better than a Emco. Some elbow grease to clean it up and you got a nice lathe. From the pic I'm guessing 10X22 on the size.
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Re: Blow forward bolt, presssure and springs

Unread postAuthor: Ianbuckwell » Sat Mar 21, 2015 7:44 pm

Really!? I was hoping a new lathe would allow greater precision and accuracy, I must admit considering it is 65 years old it does OK. Think I need to practise along with a modified design to improve my project, I have ordered a 100mm long 1/2" bsp brass extension tube that has male threads one end and female the other, I will remake the bolt in delrin (as run out of brass) initially but this time only have one step in it for the spring seat rather than 2, I am also going to buy a brass fitting which is threaded one end and straight 15mm tube the other in the hope that it will be more precise than my current air inlet piece which is soldered into a threaded fitting. If I get chance tomorrow I am going to cheat and try chemical metal epoxy to bond the air inlet into place so that I don't need to pull it up tight on the threads and see what happens.
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Re: Blow forward bolt, presssure and springs

Unread postAuthor: jrrdw » Sun Mar 22, 2015 6:46 am

Ianbuckwell wrote:Really!?


Oh Yea. You probably have a fair amount of tooling already, there for won't have to rebuy all that like you would if you buy a new lathe.

I was hoping a new lathe would allow greater precision and accuracy, I must admit considering it is 65 years old it does OK.


Not ANY low cost hobbyist machinery that I know of. It's a trade off, price / quality.

Think I need to practise along with a modified design to improve my project


To most of us it's still practise! L0L :bigsmurf:

I will remake the bolt in delrin


Tough stuff but flexing might happen with the thinner diameter.

I am also going to buy a brass fitting which is threaded one end and straight 15mm tube the other in the hope that it will be more precise than my current air inlet piece which is soldered into a threaded fitting. If I get chance tomorrow I am going to cheat and try chemical metal epoxy to bond the air inlet into place so that I don't need to pull it up tight on the threads and see what happens.


Brass fittings are rarely true and to thin walled to fix. It's my only real con for using brass fittings as chambers.
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Re: Blow forward bolt, presssure and springs

Unread postAuthor: Ianbuckwell » Sun Mar 22, 2015 7:37 am

Thanks for tips, I have noticed that with brass fittings, the threads never seem straight, guess it isn't helped by the course BSP threading either. The fitting I have found is very thick walled compared with most, my calipers won't reach past the threading but I am guessing the I.d. is maybe 18-19mm whilst externally it is 25mm it is a real solid lump, just hope it isnt tapered internally, cant measure it as one end has a star shaped socket internally for tightening which will need removing when I get my 100mm long one. I hope to be able to keep the bolt wall thickness enough to stop any flexing, if not it can just be used as a prototype to get dimensions correct. If this all doesn't work I will just use some thick walled aluminum tube, just means I have to try and thread it straight this time! Thanks again for the advice the more I can learn from other peoples experiences the better.

I have resorted to epoxying the fitting in along with thread most the way checking the bolt can move freely, this version will never take the pressure I was wanting, I am going to use 200psi, but at least it has been a learning experience.

Update- it now works the bolt moves nicely forwards and backwards, really feels like I have got somewhere!
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