Re: [CAD_CAM_EDM_DRO] CNC edgefinding/touch probe update

Is the acu-rite probe magnetic? I have had occasional repeatability
problems with a regular edge finder and a slightly magnetic work piece. A
wipe with isopropyl alcohol should solve the cleaning issue. Watch out for
burrs.

At 08:52 AM 2004/02/09 -0700, Kim Lux wrote:

>I ordered and received the edgefinding touch probe that I spoke of last
>week. Specifically, we purchased an Acu-rite 38-80-00-155, which is an
>electrical contact type probe (ie between the probe stylus and the
>workpiece). The probe is self centering, with a 0.5" shank (ie works
>with R8 collet mills...) and a 0.2" diameter tip. The stylus has about
>1/2" of movement in each direction in case of over run. THe probe cost
>$250, plus shipping. I have no affiliation with Acu-rite.
>
>There are less expensive touch probes on the market, but:
>
>a) they are usually battery powered and visual, ie they light an LED.
>b) they don't readily tie into a CNC controller, although they could be
>made to...
>c) most have a 1" shank, ie they won't fit an R8 mill.
>d) most have a 0.4" sensing ball, which is too large for a lot of holes.
>e) most don't do Z axis touches. The Acu-rite does.
>f) most have limited over travel capability.
>
>We mounted the the touch probe in our CNC mill, which is running
>TurboCNC as the controller. TurboCNC had a G50 command for center
>finding a hole. The G50 routine had a few bugs, which I fixed. I also
>added a G51 routine for center finding on a protruding shaft and a G52
>routine for edge finding on an ... edge !
>
>I've got mixed feelings about the performance of this setup. First, the
>Acu-rite touch probe itself works well, ie it centers itself well, has
>good over travel capabilities, etc. No problems there.
>
>The issue I have with this setup is that it utilizes an electrical
>connection between the workpiece and the probe to sense when the edge is
>"touched". In my (limited) experience, one must have perfectly clean
>parts in order to get repeatable results. One can get Total Indicated
>Runout measurements of 0.0004" on a hole, but it might also take 3 or 4
>centering efforts to achieve that.
>
>I'll continue to refine our edge finding efforts. If anyone has any
>advice, I'm all ears.
>
>--
>Kim Lux <lux@...>
>
>
>
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