On 11/27/2010 11:48 AM, Bob La Londe wrote:
My Taig is wearing out. I've had it for just over two years and I would
guess its seen well over 1000 hours of run time. Probably over 2000. I
should probably save my time and energy and just jerk the spindle and
steppers for a new machine, but I hate to waste it completely. Its
biggest problem since day one has always been the quality of its Z-axis.

I think I have a design for a Z-axis retrofit for it all worked out, and
I have a question or request for clarification from some of you guys who
have built, retrofit, or modified your own machines. Everybody says you
need a brake on the Z-axis if you use a ballscrew or it will backdrive.
How much force does it take to back drive? I know the answer is probably
"it depends", but I was looking for a more general answer.
I have put a ballscrew on a minimill (I think equivalent to and X2) and
have had no problems with it dropping when power is off. This is with a
servo, even, not a stepper. So, I would not worry about this with a
reasonably fine thread pitch. If you do it with a 2 TPI ballscrew, then
it could be a problem.

You can use springs to reduce the weight of the Z to help the motor.

Jon