Gunsmithing Threading 25 tpi

[crumpmd]

My friend has a flash hider with bayonet lug off a german rifle. He wants me to thread a surplus barrel. The threads are closest to 25 tpi as far as I can tell. I have no metric gauges to measure threads. It may be metric threads.
I can't cut 25 tpi on my lathe. I can change gears and cut metric. But I have no way to check it when I cut. Any ideas? What mm pitch is closest to 25 tpi?

 

[230grRN]

Re: Threading 25 tpi

Well there's 25.4mm in an inch so I'd say you have a thread with a 1mm pitch.

 

[jwSubMOA]

Re: Threading 25 tpi

You really need to get some metric gauges. Take it to a machine shop and they can check it for you. Do you know how to cut metric thread? It's a whole bunch different than standard threads.

 

[crumpmd]

Re: Threading 25 tpi

Thank you.

My lathe, when set up for metric, cannot use the thread dial and must leave the half nut engaged until complete. This is looking like a PITA job. I may not be able to complete this with my machine.

 

[mcfred]

Re: Threading 25 tpi

You can just use the flash hider as a makeshift thread gage. Just keep cutting until it fits, assuming that you KNOW it's the right pitch. Or if you have a tap of the same size you can tap an extra piece of material and us that to verify your cut threads.

Otherwise get the metric gages and do it right.

My friends give me headaches with their projects too. Lots of ad hoc and reverse engineering...

 

[ugsly]

Re: Threading 25 tpi

When cutting metric & Standard, I cut a thread relief grove and then run the lathe in back gear and thread off the end of the barrel when I can. Makes it a little easier.

Kc