Cutting a Double Start Acme Thread 

They make thread gages for acme threads just like the ones for unified national/ISO threads (60 degree thread form). They are used in much the same way. Grind a bit, check the angle, grind more, check, get really close, check, make a small adjustment and screw it all up, curse a bunch, start over. The big difference is that acme threads have a wide flat on the end of the thread that is very different in size depending on thread pitch. Actually, UN/ISO threads have a flat too, but it is quite small and you can get away with using the same tool to cut multiple thread pitches. Not so with acme threads. The acme thread gage has numerous notches on the sides to help you grind the correct flat. If I get a chance, I'll shoot a short video on it. Great question! Thanks for watching!

Hi Jeremiah. I put up a video showing the acme threading gage. You can find it here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-K0mcGgGS5m0.html

@@StuartdeHaro i saw it. Perfect explanation. Thank you

@@JeremiahL you're very welcome! Thanks for the question.

It is really fantastic.

I'm starting to feel the pressure actually. I've got one more scheduled and one being edited right now. Then I've got to start filming like a madman.

@@StuartdeHaro I can imagine. Have you thought about doing some live streaming like Richard Holdener does? Maybe a video every other week and a live stream on the off weeks? Either way, keep the content coming. I've been watching a ton of machining videos since you have started this.

@@bwcordes I've thought about it. I'm not sure I'm properly set up for it though. I'll look into it.

Not necessary in brass. Mostly not necessary in steel either.

@@electech3339 indeed, if cutting a 6tpi perhaps but more regular threads quite unnecessary.

@@chrisstephens6673 Agreed. I generally only infeed at an angle if having trouble with finish or chip control. And try threading at 0.5 TPI... Especially for internal threading, often need to cut every thread surface separately - and sometimes split even *those* into halves!

@@electech3339 have you seen a "clapper box" threading tool? If not take a look at my video about screw thread cutting, so you think you know an easy way, showing an up dated victorian design.

@@chrisstephens6673 nope, had not seen that style, very neat. I have seen the spring loaded style ones that shoot back out of the cut once they're triggered. Those need to be reset after reversing back out past the end of the part. Those are pretty cool too, and don't require any relief groove.

Interesting. I've never heard that. The Monarch will cut down to 1.5 TPI with a 4 TPI leadscrew. I'm pretty sure my lathe at home will do 4 TPI and it has an 8 TPI leadscrew and it is pretty light.

@@StuartdeHaro I've read it in a few older books written in the U.K. And those were from well respected authors so I'd assume there's something to it. And most lathes with change gearing there thread charts I've looked at never seem to list any thread pitch less than the lead screw pitch. More industrial type lathes are a different animal though. Hardened and ground helical gearing will obviously take a lot more than the light weight spur gears mine have.

@@StuartdeHaro My home lathe has an 8 TPI lead screw as well and will cut 8 different threads between 4 - 7 TPI. The key words here are '_older books_'. South Bend's book "How to Run a Lathe" caused me quite a bit of grief when I first tried single pointing threads on that lathe. Following the information in that "older book" on using the threading dial was a disaster when applied to my more modern lathe. Using the chart in the owners manual however works just fine.

I could have. The thread pitch is very coarse though and I think that would have made it even harder to get a good measurement.

Probably, but I think it wouldn't be too bad. The groove at the end gave a lot of room.

Yep. 4 TPI double start, so the machine was actually set to 2 TPI.

And no tailstock support? And the thread relief being fully cut before threading? I feel like I'm missing some vital piece of information, what gives?

Sorry, I just read my own comment and realized it could be misinterpreted as being nasty. I'm not critiquing, just looking to learn something I don't understand

@@jpsimon206 brass is really only grabby when drilling, and just when the drill starts to break through the other side. I never use cutting oil when machining brass. It doesn't stick to the tool like aluminum. It won't wear down a tool quickly like steel or stainless. The thread relief was actually a critical feature on the part that slipped into a channel on the mating part. I could have machined it in later but honestly didn't think about it. The thread was quite short and stout so I didn't think tailstock support was necessary.