I Need A CNC Threading for Dummies Book

[Glenn Goodlett]

I wish I knew why G76 would not work reliably. Also if I try to use the NFS wizard, which I like for most things, to cut threads, it tries to cut threads all the way through the stock and beyond. I just don't get it. And I'm certainly not above operator error or lack of understanding.

 

[JimDawson]

I wish I knew why G76 would not work reliably. Also if I try to use the NFS wizard, which I like for most things, to cut threads, it tries to cut threads all the way through the stock and beyond. I just don't get it. And I'm certainly not above operator error or lack of understanding.

I use G32 for single point threading and let the CAM program assign the passes and cut depths. Saves me from having to think

 

[MontanaAardvark]

I use G32 for single point threading and let the CAM program assign the passes and cut depths. Saves me from having to think

What CAM do you use? Among the things I'm looking for is CAM. Screw cutting in particular, but general lathe work would be useful, too.

 

[JimDawson]

Fusion 360

 

[JimDawson]

I have been using the Haas-turning post. Seems to work well. My son does most of the design work, then I take it from there.

 

[MontanaAardvark]

I have been using the Haas-turning post. Seems to work well. My son does most of the design work, then I take it from there.

Jim, have you ever tried a follower rest? A well set follower would keep the work from deflecting away from the cutter all along the cut. Seems better than my dead rest idea. With a dead rest, even if it keeps the end from moving, the center of the part could deflect away from the cutter. The longer the part, the more that ought to be a concern.

It seems conceptually like trying to turn something more than "a few" times L/D ratio. You know the work is going to deflect too much without one.

 

[JimDawson]

Jim, have you ever tried a follower rest? A well set follower would keep the work from deflecting away from the cutter all along the cut. Seems better than my dead rest idea. With a dead rest, even if it keeps the end from moving, the center of the part could deflect away from the cutter. The longer the part, the more that ought to be a concern.

It seems conceptually like trying to turn something more than "a few" times L/D ratio. You know the work is going to deflect too much without one.

No, I don't own one. If I need to support the work with a tailstock and don't have tool clearance to get in there, then I grind away tool bit or do something else to get clearance. This could mean making a special center to do the work. I think the smallest piece I have manually threaded on my lathe is 10-32 with with about 3 inches of stick out. I supported this with a center and stuck the tool out a long ways to get clearance.

I don't have a picture of the setup but here is the part



I don't have a tailstock on my CNC lathe so everything has to be close to the chuck. But I don't have much experience yet threading on the CNC, in fact I cut the first actual threads on it yesterday. It was pretty easy because it was 1.5''-18 thread about 2 inches from the chuck. Not a lot of spring there.

 

[MontanaAardvark]

No, I don't own one. If I need to support the work with a tailstock and don't have tool clearance to get in there, then I grind away tool bit or do something else to get clearance. This could mean making a special center to do the work. I think the smallest piece I have manually threaded on my lathe is 10-32 with with about 3 inches of stick out. I supported this with a center and stuck the tool out a long ways to get clearance.

I don't have a picture of the setup but here is the part

View attachment 283800

I don't have a tailstock on my CNC lathe so everything has to be close to the chuck. But I don't have much experience yet threading on the CNC, in fact I cut the first actual threads on it yesterday. It was pretty easy because it was 1.5''-18 thread about 2 inches from the chuck. Not a lot of spring there.

1.5-18? I'll bet there wasn't much spring there.

Thanks for the info.

An easy experiment would be to put something in the tailstock to act like a dead center. A piece of 1/8" diameter steel rod just long enough to clear the tools and with a point on its end ought to work OK.

Edit to clarify that to "... with a point on its end and held in a drill bit chuck"

 

[MontanaAardvark]

I think I've finally got it. Back in post #45, I talked about needing some sort of lathe center to keep the far end from deflecting too far away.

My live center is long enough, but wide enough that the cutter crashes into it, and my dead center seems narrow enough but is too short.

I was chatting with a friend by email and he suggested I take a broken drill bit, grind a point onto it, and put it in my tailstock chuck. I didn't have a broken bit handy, but I had a broken #1 center drill (1/8" dia. drilling portion). One end was broken off, so I ground the good end to reduce its ability to cut. It took me a couple of days to get around to doing everything, but I tried it today.

Bingo. After I pulled the cutter and dead center out of the way, a nut threaded on easily and felt the same all along the length. Unlike the others, not different along the length - too tight at the far end and too loose at the near end.



I still preform the brass on the manual lathe, cut it to major diameter, and I drilled the center to put the broken center drill in it.. Transferred everything to the CNC lathe, set my Z dimension, then started the cycle. First pass success.

Sharp eyed viewers will see that the my brazed carbide cutter's tip broke off, so the search for new threading bits stopped being academic and I need to get some good cutters, before I try other experiments.