Originally Posted by
SteelFred
Hi!
I have a Craftex CT089 13x24 lathe and I've set the gears up to cut 8TPI according to the chart inside the gearbox door. These gears are M/N=28/35, A/B=35/28, C/D=30/48 where the numbers refer to number of gear teeth. The speed is 110 RPM, material 1" aluminum rod. I did a test cut and the thread is indeed 8 threads per inch. The problem I'm having is synchronizing each subsequent cut to the same thread. The chart indicates to close the halfnut when the TDI is at "2" only. My procedure is to zero the crossfeed against the workpiece and never touch it again, move the carriage and compound feed to the thread start and zero it, set the feed towards the headstock for a right hand thread and engage the half nut when the dial indicator is at "2". After the cut, the half nut is disengaged, the compound feed is pulled back, carriage rolled back to start, compound feed another 0.005", then wait for the "2" before engaging the halfnut. I've tried many times, and also using all the other thread dial indicator numbers 1-6 but with the same bad result- nothing synchronizes. I've noticed that the half nut will engage a total of 17 times even though there are 6 divisions on the thread dial indicator, so it becomes difficult to engage on an exact division. The leadscrew has 5TPI while the dial thread indicator has 17 teeth. Any ideas on what could be wrong here? I'd also be interested in any links to the math behind all this. Frustrating start to cutting my first thread. Thanks in advance!