07-30-2012, 09:09 AM
Make sure that the compound feed is parallel to the trailing edge of the bit. 29 degrees isn't the same on all lathes (some start at 0, some at 90). Handle towards your belly, swing right to 45 and then back 15. It'll say 30 or 60. Whichever, but it's very important that it is parallel to the trailing edge, if you are feeding with the compound.
You can kinda see the needed clearance angle by eyeballing things - hunker down and look at the thread from the side, see if your toolbit has enough clearance. At that pitch it will need a lot.
This might be a good time to practice the art of picking up a thread, rather than scrapping the part. Disengage the back gear so the spindle turns by hand and with the halfnuts engaged, fiddle the bit in where it needs to go, minding the backlash, then back the compound out until it's clear of the work, and zero the crossfeed dial. Turn the spindle by hand, watching the tool as it enters the cut (cutting air). If all is well, then resume threading.
You can kinda see the needed clearance angle by eyeballing things - hunker down and look at the thread from the side, see if your toolbit has enough clearance. At that pitch it will need a lot.
This might be a good time to practice the art of picking up a thread, rather than scrapping the part. Disengage the back gear so the spindle turns by hand and with the halfnuts engaged, fiddle the bit in where it needs to go, minding the backlash, then back the compound out until it's clear of the work, and zero the crossfeed dial. Turn the spindle by hand, watching the tool as it enters the cut (cutting air). If all is well, then resume threading.