View Full Version : First successful threads cut on lathe!

05-13-2006, 02:43 PM
Well i've tried once or twice before and always managed to cut double threads or screwed something up...but today i cut my first successful threads on the lathe! I cut 1/2 -20 left hand threads for an adapter for a new mini-bike project. It was alot of fun! It was intimidating at first, especially w/ no half nut disengagment. It was always sort of a guessing game to get it to a shoulder just right but once i got the hang of it it wasnt bad. Just wanted to say thanks to everyone here - i read alot of old posts about threading before trying; alot of good info out there!

05-13-2006, 04:10 PM
No Half nut disengagement? what do you have?

05-13-2006, 04:40 PM
doing them WO a half nut.......... :eek:

05-13-2006, 06:09 PM
Good going Fastrack!

Threading is one of those operations that you get better at every time you do it. If you have to single point a bunch of the same part in a production run it will make you an expert on that thread, fits and finishes.

As for continuous engagement of the lead screw, there are some folks who say that it is the best way to make sure a thread is precisely cut. What you do is to back the cross slide out one turn and simultaneously reverse the lathe, letting it run bacwards until your carriage is past the end of the part. Then, feed the cross slide back in to zero, and set your compound feed in about one and a half thousanths. Keep doing this until you are close enough to check the thread with a nut or go/no go gage.

Personally, although I have used this method, I still use the threading lever most of the time. I guess it is just "operator's choice."

Jim (KB4IVH)

John Stevenson
05-13-2006, 06:10 PM
Depends a lot on the lathe.
One one of mine that's a pig to reverse [ stop wait restart etc ] I do use the 1/2 nuts but on the others that have decent revers, either electrically or clutches I leave the 1/2 nuts closed all the while and reverse back.
Most threads are usually short 1" to 2" and keeping in mesh saves a lot of time waiting for the right number and also piece of mind.

Some threads I do are quite fine and only 1/4" long or so, in these cases i put the machine in neutral and pull the chuck round with the key, then wind back by hand.
At a 1/4" long to a shoulder this is definitely quicker ;)


05-13-2006, 06:22 PM
I read right over the
disengagment part :mad:. I was astounded that he could cut it with advancing the carriage by hand!!!! Now that I have reread he is not my hero :D

05-14-2006, 01:47 AM
hehe I've tried cutting threads by advancing the compound and/or the cross feed by hand. This works for about two or three passes at which point i enevitably screw something up. With my little Smithy lathe i have to run it as close to the shoulder as i feel comfortable, then shut it off and back out the cross feed. Then i reverse the motor, shut it off again, push the cross feed in to just over zero for my second rough cut and move my compound in just a little and make the cut again. Keep doing this until i get it cut so it tends to be a slow and nerve racking process because you have to wait for the cutter to come to a stop so you have to guess where it will stop before it goes past the shoulder and really screw something up :)