Re: Re: Van Norman #12 Milling Machine

I probably would have left the Z axis alone, like you suggest, but my
machine came with a rack and pinion, with a lot of backlash already built
in. It seemed to have about 3/4 of a turn of backlash in the handwheel
alone. I didn't even bother to measure how much that is and proceeded to
just tear everything out, cut a 3" diameter hole in the top of the column,
placed a 1/2" blanchard ground steel plate between the column and base and
then mounted the ballscrew between top and bottom. If it had the acme
screw in there to begin with, it would have made things a lot easier. As
it is now, I have measured the Z and have zero backlash. I do plan on
doing contouring with it, so this is good.


Dan

At 02:26 PM 1/25/2000 , you wrote:

>From: tmay@...
>
>My name is Terry May, I been mostly just keeping quite and learning since

I joined the list.

> I have been following Dan's discussions about upgrading his RF-45 since

this is the machine I have and would also like to convert to CNC.

>My question for the group is, have you considered and rejected leaving the

Z axis on these types of machines acme thread instead of converting to
ballscrew? It seems to a beginner that backlash would not be a problem
because of the weight of the head and if better positional accuracy was
needed replacing the original acme threaded rod with a precision rod would
do the job. I would think that most of the cutting forces would be 90
degrees to the z axis and it doesn't seem like enough force would be
generated in that axis to overcome the weight. Perhaps if you were making a
sloping cut this would not be true. Am I missing something obvious to those
with more experience?

> The advantage to this approach is that it would remove the requirement

to provide power off protection or counterbalancing.

> Thanks in advance for considering my questions.
>Terry May
>