View Full Version : threading, I know you hate it...

10-28-2007, 04:12 PM
If you are threading a screw or internal... If you stop the lathe, then reverse the direction, Start the lathe up and increase the cut, won't the thread continue in the opposite direction? Or will backlash screw you up? I am threading for the first time. Just getting the appropriate gears in the right spot has been a Royal pain in the a**. Of course the damn phone is ringing as soon as your hands are covered with grease.... Any help is greatly appreciated. You guys have been great teachers and friends though you didn't know it. Fred

paul r taylor
10-28-2007, 04:23 PM
When you start cutting the thread set your dial to zero. When you are done with first pass, disengage and start over with a deeper cut.
This is what the screw thread dial is for.

10-28-2007, 04:30 PM
I do this all the time and it's not that big a deal.

- Set the compound to 29.5 degrees
- Set the 60 degree point cutting tool perpendicular to the work
- Advance the cross-feed to present the point to the work, zero the dial
- Move the carriage to clear the work on the right side (you will be cutting right to left)
- Advance the compound feed a couple thou
- Set the half-nuts and do not unset until you are finished
- At the lowest possible RPM, begin cutting. Kill the power just as the cut is at the leftmost side of the work (you did cut a working clearance, right?)
- Back out the cross-feed one full turn, put the machine in reverse, turn it on and return the cutter to the beginning again. Do not disengage the half-nuts.
- Return the cross-feed to the original zero, advance the compound feed again, put the machine in the forward direction, turn it on and make another cut.
- Repeat as necessary. On the last cut, advance the cross-feed, not the compound feed so that the cutter cleans both sides of the thread.

Disconnect the half-nuts and admire your threads.

Here's a video showing it exactly: http://youtube.com/watch?v=0q_q53wsyHU

Oh yeah - and one of these can help put the cross-feed back to zero very quickly:

tony ennis
10-28-2007, 04:41 PM
I've seen that video, it's cool. Notice that he comes within a hair of crashing the cutter on the 2nd or 3rd pass, lol.

Very instructional.

10-28-2007, 04:57 PM
Yep - I wish for that reason my lathe had a brake on it.

paul r taylor
10-28-2007, 04:57 PM
While not disengaging the half nut will work, it is extremely slow. You can disengage the half nut , move the carridge back to the starting point and reengage the half nut. The numbers on the thread chasing dial, 1-4 are for doing this. If you are making an even number thread you can engage on any one of the numbers. If you are making an odd number thread the you have to engae on either 1 or 3.

10-28-2007, 05:15 PM
In the case of my lathe there was no threading dial until I made one. Even so it can't be used when cutting metric threads so the reversing method is necessary. Not usually a problem for folks with "real" lathes.

paul r taylor
10-28-2007, 05:19 PM
You're right. When making a metrictric thread on an american machine you have to leave the half nut engaged. This is also true when when making a half thread.

Alistair Hosie
10-28-2007, 05:30 PM
I cant get the thread cutting video to work it cuts out before it starts making the cut.Alistair

tony ennis
10-28-2007, 05:34 PM
Alistair must have some of them kerosene-powered interwebs.

Your Old Dog
10-28-2007, 05:48 PM
well as a neophyte on thread cutting the biggest thing I took away from the video is that it took him 11 passes to cut his thread. Maybe that's my problem, I'm doing it in 3-5 and getting ratty looking results. I did shim up my cutter bit and introduced a little back angle to the cutting edge and things are looking much better. Well, I mean you won't slice your hands open if handle the threads :D

10-28-2007, 06:01 PM
3 to 5 passes is fine for a 20 TPI. The guy in the video could use a little oil.

10-28-2007, 06:46 PM
Thank You Guys!!!

10-28-2007, 06:51 PM
I cant get the thread cutting video to work it cuts out before it starts making the cut.Alistair

You probably got a virus when you downloaded those free books.

Just kidding - couldn't help it :p

10-28-2007, 10:17 PM
Call me lazy, stupid and even late for dinner but this is how we all should thread. ;)