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Author Topic: What is a good probe to use with Mach?  (Read 8909 times)

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Offline simpson36

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What is a good probe to use with Mach?
« on: January 19, 2010, 03:06:45 AM »
Now that I have an accurate machine, I am considering taking the plunge to probing/digitizing.

Wondering what people are using and how they like it.
Re: What is a good probe to use with Mach?
« Reply #1 on: January 20, 2010, 11:22:47 AM »
I just started probing myself, and opted to build my own probe.  great way to start and see if this is something you really want to invest money in.  i have been able to reproduce the fan for my router and i am working on some pistol grips for my Ruger.  Word to the wise, i tried to make  the NC(normally closed) probe work but it was pretty glitchy for me.  the parts and pieces went together fine, but the probe would #1. hang in the open position (it takes only the smallest piece of debris to keep your circut from closing) #2. "noise" in the signal giving me false points.

So i used the best parts of the designs i found and designed my own NO (normally open) probe. I have had good success with it so far. It really depends on what you want to accomplish. if high accuracy is important (.0002) then a commercial probe is the way to go, if you just need the basic geometry of the item and .01 is good enough i can post the design for my adjustable NO Probe and you can give it a whirl.

Also bear in mind that high accuracy while digitizing means LOTS of time for the scan. i.e. a 2.5 in X 3.5 in scan of my pistol grips @ .01 grid with a plunge of 20ipm took 10 hours, while the same scan at .05 took 1 hour 45 min to complete. the first gave me a good detail of something that i was not trying to exactly reproduce while the second gave me the basic geometry and allows me to model on top of it.

Hope this helps
Re: What is a good probe to use with Mach?
« Reply #2 on: January 20, 2010, 11:42:14 AM »
Simpson,

For surface probing, the "Arnie probe" (the one made by lister Arnie Minear, now sold by www.wildhorse-innovations.com) works great - it's very accurate and repeatable.  Though, like all such probes, it's a bugger to get calibrated accurately.   If you're looking for something to use for edgefinding, etc. for machine setup, I don't find that type of probe to be a good choice.

Regards,
Ray L.
Regards,
Ray L.

Offline simpson36

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Re: What is a good probe to use with Mach?
« Reply #3 on: January 20, 2010, 04:22:55 PM »

Thanks for the comments so far.

My primary want is for edge and particularly circle center finding. I have to do a lot of that and it is tedious, to say the least. The digitizing would be fun to explore if I had a probe, but it not a practical need for anything that I am doing at this time, other than plotting an off angle edge or an edge contour.

So if I could get a suggestion for edge and circle center finding, it would be much appreciated.
Re: What is a good probe to use with Mach?
« Reply #4 on: January 20, 2010, 04:57:59 PM »
Well, here's the conclusion I reached.  I've used a rigid probe for most of the last year.  But, Mach3, flaky thing that it is, *will* periodically screw up, and break the probe.  I've been through at least a half-dozen in the last year.  So, a probe with some "give" is, to me, a requirement.  But, the typical Renishaw-style probes have several drawbacks, when used for machine setup:  First, they have some travel after contact, but before switch actuation, and this travel is different at different angular positions.  Careful calibration is required to minimize the effects of this.  Also, they are very delicate, and difficult to calibrate.

I have a design for a contact probe with "give".  The probe itself will consist of a slender stylus with a 5mm ball bearing bonded to the end.  This will give a very precisely spherical tip.  The stylus will be supported by a spherical Delrin bushing about an inch above the ball tip.  The top end of the stylus will be supported by three springs, each with a tension adjusting screw.  By adjusting the spring tensions, the ball tip can be precisely centered to the centerline of the spindle.  The "switch contact" is simply the electrical contact of the ball tip to the work, so there is no "overtravel" - contact with the workpiece activates the Probe input directly.  If pushed beyond the contact point, the springs and spherical bushings allow the ball and stylus to swivel out of the way, so there's no damage.  Once the tip is released, the springs should push it back into perfect alignment.

This has no sensitive mechanical or electrical design aspects, so should be easy to build.  The *only* potential downside I can see is "stiction" in the spherical bushing can prevent the tip from self-centering.  But, with a little lubrication, and adequate spring pressure, this should not be a major problem.

The other option I've considered is simply making an insulated holder for a "wiggler" edge finder, but that would have to be manually centered after each contact, which would be very inconvenient.

Regards,
Ray L.
Regards,
Ray L.

Offline simpson36

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Re: What is a good probe to use with Mach?
« Reply #5 on: January 20, 2010, 05:59:20 PM »
The top end of the stylus will be supported by three springs, each with a tension adjusting screw.  By adjusting the spring tensions, the ball tip can be precisely centered to the centerline of the spindle.  The "switch contact" is simply the electrical contact of the ball tip to the work, so there is no "overtravel" - contact with the workpiece activates the Probe input directly.  If pushed beyond the contact point, the springs and spherical bushings allow the ball and stylus to swivel out of the way, so there's no damage.  Once the tip is released, the springs should push it back into perfect alignment.

Ray, your idea gave me an idea.  I'm going to try a couple of things and get back to you on this.

Re: What is a good probe to use with Mach?
« Reply #6 on: January 20, 2010, 07:39:31 PM »
The top end of the stylus will be supported by three springs, each with a tension adjusting screw.  By adjusting the spring tensions, the ball tip can be precisely centered to the centerline of the spindle.  The "switch contact" is simply the electrical contact of the ball tip to the work, so there is no "overtravel" - contact with the workpiece activates the Probe input directly.  If pushed beyond the contact point, the springs and spherical bushings allow the ball and stylus to swivel out of the way, so there's no damage.  Once the tip is released, the springs should push it back into perfect alignment.

Ray, your idea gave me an idea.  I'm going to try a couple of things and get back to you on this.



Simpson,

OK, but if you come up with something that works, you gotta share!  :-)

Regards,
Ray L.
Regards,
Ray L.
Re: What is a good probe to use with Mach?
« Reply #7 on: January 20, 2010, 07:41:04 PM »
Regards,
Ray L.

Offline RICH

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Re: What is a good probe to use with Mach?
« Reply #8 on: January 20, 2010, 08:11:20 PM »
FWIW,
There is info on making a simple probe and how to use it in Appendix E of the  COPYCAT  manual in Members Docs.
Of course you can also use a video cam.
RICH
Re: What is a good probe to use with Mach?
« Reply #9 on: January 20, 2010, 08:25:03 PM »
FWIW,
There is info on making a simple probe and how to use it in Appendix E of the  COPYCAT  manual in Members Docs.
Of course you can also use a video cam.
RICH

A video camera doesn't give you anywhere near the resolution of a good probe, though it's good enough for many operations.  And a rigid probe, like yours, *will* get broken at some point.  Mach3 is just plain squirrelly, and probing is perhaps it's least stable operation.  I've had it move in the wrong axis, or even multiple axes, as well as completely ignore the probe input, and keep moving long after the probe has made contact.  As far as I'm concerned, a "forgiving" probe is absoutely required with Mach3.

Regards,
Ray L.
Regards,
Ray L.