Need Help!- Lathe spindle speed and lathe facilities

[GuntisK]

Hi everyone!
I've got a question for those who use lathe with TCNC. How often do You use different speeds of spindle? Is it so essential to have a full set of different speeds for example from 50 to 2000 rpm? Will it be ok if lathe is operating only with three speeds- 2920, 973 and 335 rpm and if I use M50 to read the speed into program? What about cutting of different types of thread in this case?

[The Blight]

For thread cutting, you will end up using several different spindle speeds. It can also be nice for different tooling types like drill bits and cut-off tools.

Are you worried about setting up the digispeed chart? You can get away with only specifying 3 values and speeds. I believe TCNC will figure out the values in between, but it will be a linear calculation. I also believe that a more detailed map will give you better connection between the speed you choose, and the actual speed. I have not tested this enough to say exactly how it works.

My advice is to just take some "air chips" and test it. Did you order the Digispeed XL?

[GuntisK]

Problem is in replacing old DC 11kw spindle motor with 10kw AC motor. Lathe has three positions of gearing- 1:1; 1:3; 1:9. Freq.converter is too expensive for me, so I thought about using only three speeds which can be achieved using that 3-phase AC motor and set of standart gearing (its an old cnc lathe if You remember ). Only thing Im worried about is: what my lathe will be capable of?

[The Blight]

Oh! So the spindle will not be controlled through TCNC. Yeah, you can get by with that. TCNC will be able to figure out how fast the spindle is turning with the index pulse configured.

I remember you working on a old lathe, and I went to look for the topic. Found the pictures of your ATC. How fast is your spindle?

[GuntisK]

Originally the speed range were from 20 to 2240 rpm. It seems to me that now the best thing would be installing that AC motor. Today after some thinking I found a possible way to bring to life that DC motor only thing is that it could take some time. Need to carry out some experiments.
And yes- ATC now is assembled, now Im working parallel on ATC controller.