I'm looking for a way to use G31 to find XYZ on a mill with a metal work piece. I tried to rig up a simple 3V circuit outside of mach with a LED connected to a known diameter rod in the spindle and the work piece (aluminum). Thought process being when the rod touches the work piece the light comes on. I quickly realized that since the entire machine is metal this does not work since when you connect both alligator clips the circuit is complete instead of being complete only when the + rod touches the - workpiece. All my Google shows people achieving this on router tables where a short is created since the table or work piece is wood. Can this be pulled off in Mach on a metal mill? I have a touch probe,  but because of deflection it can't be repeatable.

How about fitting an insulating sleeve to the rod where it fits into the chuck ? (Turn down part of the rod, epoxy on insulating sleeve then turn it all true).

Tweakie.

This what I use on my mill.  The block is aluminum and insulated from the work piece with Lexan.  Could be any non-conductive material but it was what I had on hand.  The block is 1" thick and each leg is also 1".  When probing I use a 3/8" diameter dowel pin mounted in my spindle.  My probing script places the spindle centerline 1-1/2" from X0 and Y0 and changes the DRO's to reflect that. 

Hope this is useful information.

Excellent solution Tom.

Tweakie.

Echo Tweakie's  first reply.
Quick and dirty insulator could be some swrink wrap or even electrical tape.

BUT

Make one that has approx. zero run out. Then  check the run out at the end of the probe when held in the chuck or whatever.
Your probed locations will only be as accurate as the mills axis can move and the how the probe is mounted.
Maybe I am a little goofy about accuracy, my lathe probing  is +- 0.0002" repeatable and accurate, but can't duplicate that
on my mill.

BTW, To check probing accuracy just probe a know standard. You will quickly know what I said above.

FWIW,

RICH


 

Hi,
in industrial practice you would use a multi axis touch probe, the good ones are very accurate but VERY expensive.

This one:
https://www.homanndesigns.com/index.php?main_page=product_info&cPath=58_42&products_id=347&zenid=jebt2ol2047oqe9qf24e8ggs06
is more in my price range.

I doubt its as good as a Reinshaw but it sure does look the part. Has anyone used one like this and if so what do you think about it?

Craig

Joe,
Have a similar fancy one that sits in a drawer. 

Attached is one of the home made probes which  I use.
In use it's more accurate than the expensive fancy one I bought a long time ago that just sits in the drawer.
The probe tips are easily made or replaced. The bent probe tip is the result of operator error........!
Cost of new tip was approx a penny. 

RICH

So the fancy probe was tried on the lathe mounted on an attachment and let it probe a fancy handle.
So put it in a box for safe keeping.

Using  the led probe ( $20) I could quickly just find points that I wanted so the fancy handle could be drawn.
BTW, slightly modified the probe end so custom probes could easily be made.
After probing, just click a button on the screen and a dxf drawing is created. Have choice of dxf with points or lines, I prefer points to quickly draw the fancy handle. Then dump dxf into LT, or whatever, and the gcode to cut it is made. Easy and quick .......... usually

RICH

Hi Rich,
looks like cheap n' cheerful wins out over fancy....that's exactly what I needed to know. I'm not going to buy it...I promise....it just the
'Buy Now' button, I think calls to me when I'm sleeping.

On Friday I succumbed to a 'Buy Now' and spent $366.00 + GST on an Arbitrary Function Generator, I've been looking around for a while but
still this particular 'Buy Now' button seemed more seductive than most!

Craig

You can make your own ruby-tipped stylii as well. Much fun. See
http://www.cnczone.com/forums/calibration-measurement/321060-cnc-software.html#post1956342

Cheers
Roger