Re: Any simple way to map ballscrews?

(Just-thought-of method in the PPS!)

Hello,

While perhaps not as accurate, putting the same money into a few sets
of 123 blocks and ground HSS lathe tool blanks will get you near the
same results.

IMO more importantly, they will find a lot more use in a typical
small homeshop than gage blocks; so they're not money spent for a one-
time use.

Of course, this advice will be good or bad, depending upon the level
of accuracy and precision you require of your shop, tools, and parts.
Point is, a guy calibrating a hjome mill or router can probably get
good enough results without the gage blocks...

Hope this helps,

Ballendo

P.S. Since you're looking for relative changes per unit, you can do
it even less expensively using a piece of grond bar cut into many
pieces and de-burred.

P.P.S. The least expensive extremely accurately sized items you can
buy are ball bearings. Choose a common size that will "fit" your axis
length(s). Line them up in a vee groove-- or with fences to make a u-
shape and you'll have much of the accuracy of gage blocks without the
expense. Use something between the last bearing and your measuring
tool that is flat and has parallel "ends".

Just thought of this!
Here's a further thought on this "peas in a pod" method.

1)Mount a drill in the spindle, and drill a hole in your added
calibration table, which is firmly fixed to the machine.

2)using CNC move 1/2 the diameter of your bearings, plus the ground
steel/keystock fence thickness, and then add 1/2 your drill bit size.
Drill a couple/few holes for pins to align the "peas" in their pod
accurately along the machine travel. Each length of fency needs two
holes for its pins.

3) insert drill blanks in threee of these holes--and set the keystock
fence in place, use another keystock to keep the balls from rolling
all over the place. (no balls yet.)

MAKE SURE EVERYTHING IS CLEAN!

4) UNPLUG the spindle motor!!!!

Version 1 method (uses indicator)

See version 2 below for without indicator technique

4A)now put an indicator in the spindle, and set it against the end
vertical drill blank. this is your "zero" point. (it will be off zero
by 1/2 the diameter of the drill size. FWIW, I'd use a stubby 135°
split point drill for the drill blank holes (screw machine drill)

5) Move the machine a bit down the "pod", add a ball bearing and then
come back to see how they "stack up" with this added increment.
You'll be reading directly the comps needed from the indicator.

6) repeat as needed til done.


Version 2 (no indicator available)

4A) Put a drill blank in the spindle.

5) move the machine down a bit, add a bearing, then come back but not
quite all the way you expect. (We want to leave aome space between
the ball we kjust added and the prior stack of balls. Each time we
will plan for the SAME amount of "theoretical space", but errors in
the machine will result in there being differing ACTUAL space(s).

5A) Use a feeler guage to determine this variable distance.

6) repeat as necessary until done.

BTW, could use dowel pins instead of drill blanks...

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@...> wrote:
>
> vrsculptor wrote:
>
> >Mach3 (and I'm pretty sure EMC) allows you to enter a leadscrew
> >compensation table to correct for errors in the leadscrew pitch.
Does
> >anyone have any sugestions on how to measure the error other than
> >using a dial indicator in the spindle, a block on the table and
inch
> >worming down the length of the table. I'm looking at using rolled
> >ballscrews that can vary as much as .007 a foot.
> >
> >
> Yes, you need a stack of gage blocks. You move one inch at a time,
and
> place
> another block in the stack, and using a dial test indicator, you
move a
> little
> bit until the dial reading is the same every time. The gage block
sets
> come with
> a 1, 2 and 4" block, and maybe you get two 1" pieces. Beyond that,
you
> have to
> make up a set of 4" blocks that match your 4" piece, or some other
scheme to
> get past the range of the set of blocks.
>
> Jon
>