Problem making metric threads on a Jet GHB1340A lathe

dougcasey · 2005-10-04T16:13:52+00:00

This lathe is advertised as being able to cut english and metricthreads. I have had no problems making english threads.According to the manual, in order to do metric threads you must do thefollowing:Change gears - i.e. for a 1.5mm thread, select the two 48 teeth gearsand run one on the 120 main gear and run the lower on the 127 gear(machine has 120/127 double main gear for converting to metric).Select the proper combination of levers - i.e L,T,A,C according to thechart printed on the front of the lathe.Disengage feed selector to the "O" posotion.Now, when cutting english you use the dial indicator andengage/disengage the half-nut lever. On metric, the manual says toengage the half-nut lever and leave it engaged during the whole processof cutting the thread.However, the manual fails to tell you how to stop the machine at theend of the cut so that you can reset the depth on the cross-feed. Youcannot reverse the direction of lead screw travel as suggested by anauthorized jet technician for three reasons. One, there's a largewarning on the front of the machine telling you not to do this. Two,it doesn't work since you are temporarily changing gear teeth whenmoving the selector know, therefore you are off when reversing andcoming back into the cut. Third, changing the lead screw directiongoes from cutting right-handed to left-handed threads when changingdirections.It seems that the procedure involves leaving all gears continuallyengaged. Then you cut the forward/reverse lever on the apron sectionto the neutral position to cut power to the travel. The head continuesto rotate due to momentum until it comes to a rest and the magneticlatches release on the motor. Then you back out the cross feed, jogthe machine backwards using the jog button, reset your depth and doanother cut. This appears to work, but what do you do to stop thedrift after stopping? If you need to thread a half inch piece that hasa 1/4" relief and then projects into a 60 degree bevel towards...

Oct 04, 2005 23 Replies

Rate this thread:

Robert Swinney 20 years ago

Re. hand crank: I used a tail pipe expander from HF as the axel part for the hand crank. I made 2 of these, one for the rear of the spindle and a smaller one for the 5-C collet tube when it is in the spindle.

Vote

Eric R Snow 20 years ago

Jim, The main reason for a brake is to stop the machine in an emergency. It sure has saved my butt a few times. Eric

Vote

Eric R Snow 20 years ago

Bob, Since I make my living on my machines I tend to see thing in a daily use production mode. For just occasional use a hand crank is probably better. That said, if I was doing it for a hobby, I'd put on a three phase motor and a brake. That's just me, and it reflects my experience of working in machine shops for so long. Cheers, Eric

Vote

Robert Swinney 20 years ago

Point duly noted, Eric. Thanx.

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required