Probe calibration

[kprice1658]

I've used cheap probe for a year that has been pretty reliable - at least with repeatability. I only really use for workpiece setup, using the Mach probing screen to set X,Y &Z.

I've started doing 2 piece parts and notice they are off slightly when assembling them. That led me to actually check the starting work offset location against an edgefinder and found its off about .007 -008 in X and .004-.005 in Y.

I remember reading somewhere that when entering the Tool 99 diameter thats its not always what you can measure. Mine measures .1375 - which is what I have entered.

I tried to play with the diameter setting, changing it both ways to see if I could make up the difference from what I'm seeing with the edgefinder. Didn't work as I expected.

I ran the Comp Probe routine form the manual and it shows X off .004 and Y off .0037 according to the difference between position 2 and 3.

I use a dial mic setup against the probe tip and have it adjusted to less than .001 movement while spinning the probe 360 degrees.

I'm sure most of the problem is the quality of the probe, but the repeatability has been very good when doing tool height settings. It has the 3 adjustment screws for adjusting, but I'm sure its not as delicate as a $1500 probe.

If I can get the X and Y setup to be right - I'll be happy with my $100 probe.

Whats the best way to get this accomplished?

Kevin

[justgary]

Kevin -

Can you offset the probe repeatably? It would seem that the ball position is not as important as the whole probe's touch position (where it indicates an edge, even if the ball touched 0.004 earlier). That is what you really want to center, so try offsetting the probe until it touches (electrically) as uniformly as possible.

Also, the effective diameter of the touch position may differ from the physical ball diameter (and may even be an ellipse). I would think that you want to use the effective radius, not the physical radius.

You can also leave the probe alone and do the offsets in your head, then subtract them every time you touch off of something. Just remember the offset when approaching from each cardinal direction.

I don't have a probe, but I thought that Mach allows you to set up those kind of offsets.

Good luck,

- Just Gary

[mayhugh1]

kevin,
If you have access to a lathe you might turn a ring gage. Turn a piece of brass or whatever to 1-1/2" diameter or so and carefully face an end and then carefully bore a hole through it about .75" dia or so. The exact diameter isn't important but it needs to be perpendicular to your faced end. Measure the id carefully and then clamp the gage to your table. Use the Tormach probing routine to find the center of the id, and it will set automatically set the x-y axes to zero at the center of the gage. Then carefully move the probe in all four directions until the contact light illuminates and note the coordinates of the touch points. You can then adjust the radius value in the tool table until the probed points agree with the radius of the actual id. - Terry

[kprice1658]

JustGary,

Thought about just adding the difference everytime I offset, but I'd like to make the adjustment permanent - I don't need something else to remember every run :-)

Terry,
I ran through that setup just to see what the actual difference was. I should add 1/2 half the difference to the diameter of the probe to make up the difference?