petermichaux wrote

<JJJ> wrote in message news:390f5141.12967200@news.jetlink.net...
>> I understand what your saying I am a machinist by trade .
>> and Ive worked on some cheap cnc's and it is possible in some
>> instances to program around backlash
>> I would try to make sure I was off the part and move in the direction
>> to kind of get the backlash out before final cutting

That's exactly what I was getting at. Good way of putting it.

>> This was on a cnc lathe with about 10 to 15 thou of backlash thats
>> alot

Sure is a lot for cnc!

>> I'm wondering about backlash and the steppers missing or skipping
>> do you think there is any correlation

I'm not positive but I don't think so. For unexpected table movement the
table moves until the backlash is out of the screw. Then the nut is resting
on the screw and the stepper motor's holding torque will hold the table in
this position. However if the table moves very quickly there could be
sufficient table momentum that the stepper motor couldn't hold the table
when the backlash is out. This might cause the stepper motor to rotate a
step or two. High torque motors would probably emliminate this problem
completely.

I have emailed with several people that make a living using stepper motor
mills and lathes to do very precise work. They all say that they have
virtually no problems with stepper skip.

>> I'm still considering Bill Wainwrights servo system I think its about
>> 1800.00us dollars

It is $1800 for the 100 oz-in motors and $2000 oz-in for the 600 oz-in
motors. If you can afford it then it looks great! I am not sure but the
Camtronics system might be the same one. I just think that the extra $800
might not be necessary to spend. I'd rather spend it on tooling. If I had a
knee mill I would definitely consider a servo system.

The thing about these servo systems is they are only sort of closed loop.
The encoders read whether or not the *motor* turns when it is supposed to.
However if their is backlash in the screws then the computer won't know if t
he table moves unexpectedly as we discussed before.

>> I sure didnt know there was this much to this whole thing.

Me neither! I thought it would be way less involved. Just the advice on
mounting timing belt pullies was a little overwhelming. People really have
opinions about how things should be done. Some people that don't pay the
bills will only settle for the best. Others who pay the bills have explained
what you can get away with and still achive good results.

>> What I would really like, is to see a retro mill/drill run with my own
>> 2 eyes. maybe I am making more out of this than I need to.

I was wondering if I was making too much out of this about a week ago. I
don't think so.

>>
>> Joe

What brand of mill do you have?

Peter