Hi to all, I'm done assembling the lathe, the only thing I'm missing is the correct preload nut for the crosslide lead screw, it should be coming in next week. I was able to test the electronics and everything seems to work ok, I posted a photo of what the lathe looks like at this point, but I'm confident that it will be completed by the end of the month, and at that point I'll post a few more.
--- In SherlineCNC@yahoogroups.com, dtbarber@... wrote:
> I have created a photo album showing my approach for driving the spindle head with a stepper motor. Once approved by the moderator, I will add comments and more explanation.
> Regarding your question about how I am threading on the lathe, I use MACH3 and a single 60 degree lathe bit for CNC threading. There is a lot of information available about CNC threading with MACH3, but fundamentally, MACH3 uses a spindle index pulse to determine rotary speed and position of the material being threaded and advances the Z-axis the appropriate feed rate to generate the thread. The ability to track spindle speed and position allows threads to be cut in multiple passes, reducing tool loading.
> The process is simple but torque limitations of the standard Sherline motor results in inconsistent spindle speeds during the threading process. You probably have noticed that spindle speed can change during normal lathe turning processes. MACH3 adjusts to the changes in speed due to tool loading, but when speed changes are pronounced, adjustments in Z-axis speed can result in an inconsistent thread. I have made various modifications to my Sherline lathe to improve threading, including replacing the standard 20-TPI leadscrew with a 5-TPI leadscrew, which allows threading a higher than normal spindle speeds. However, I think driving the spindle head with a proper sized stepper motor is all that one really needs to do. With my current system, I remove 0.005" per pass in free machining steel and even when cutting 20-TPI threads in .5" material, spindle speed remains constant through out the threading process.
> More when the pictures are posted.
> --- In SherlineCNC@yahoogroups.com, Davide Ghelarducci <tuscanland@> wrote:
> > Hi Dan,
> > Â
> > nice to hear back from you, I've wired everything correctely so far, just need to wait for the connectors to arrive and I'm all good to go.
> > For now I'll go ahead with my plan about modifying the lathe, meaning I'll just use the threading attachment made by Sherline, driving the gears using the nema 34 stepper.
> > I was under the impression that the 425 oz/in would have worked as well, but just to be on the safe side I've opted for the more powerful nema 34.
> > I'm not sure how you are threading on the lathe, do you use the threading attachment in the same fashion that I plan to do, or do you thread using a mathematical formula combining spindle speed in conjunction with the appropriate feed rate on the z axis?
> > I sure would be interested to see your pictures when you have time to upload them.
> > Thanks for uploading the dxf files, I'll go look for them now.
> > Best regards
> > Davide