From: Pork Products <porkprod@yahoo.com>

Hi John,

Thanks for both emails you sent me. More very good
stuff.

Last night I measured the backlash on my mill. I set
up a system much like the ball bearing system you
mentioned. I had an endmill in the spindle and used
the vise as the work.

Using a thickness gauge I placed the endmill 0.003"
from the vise and then rotated the handwheel in the
oppsite direction 0.02". Then I remeasured the end
mill to vice spacing. The spacing would be 0.023" with
no backlash. In the logitudinal direction the spacing
was only 0.0145". This means the backlash was 0.0085",
correct?

0.0085" logitudinal feed backlash
0.0220" crossfeed backlash
0.0005" spindle feed backlash

The cross feed backlash is quite large.

I was reading the catalogue for ball screws from a
company called Ball Screws & Actuators Co.
(http://www.ballscrews.com/default.html)

They have ball screws that will fit my machine and
several ball nuts from which to choose:
--Standard Ball Nuts (no more than 0.007" backlash,
2.89" long)
--Standard Ball Nuts (no more than 0.002" backlash,
2.89" long)
--Preloaded Ball Nuts (zero backlash, it is 6.08"
long)

I will phone about pricing for these on Monday. I
assume the price increases with decreasing backlash.
The Preloaded Ball Nuts are very long.

Any rough estimates on how much two of these with
screws would cost in the US? $100, $250, $500, $1000,
$2000, $5000, ...?

Of these three types what do you think the minimum
quality I would need?

Is zero backlash an absolutely essential feature? (I
could probably live with 0.002" backlash if the price
was greatly reduced.)

How much backlash is there in your ball nuts?

What are some good brand names for which to look?

The ball bearing zeroing idea is a good one. I would
like to know how others do this. May I post your
method on the cnc news group to start off the tread? I
will give you credit or anonymity if you like.

How often do you zero the software. Once per work
piece or after each cut?

Do you experience much stepper motor skip?

I will also check archives for the people you listed
who have recently converted to CNC.

Thanks again,
Peter