Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: simpson36 on January 19, 2010, 03:06:45 AM
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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.
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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
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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.
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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.
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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.
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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.
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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.
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BTW - Here are the bushings I had in mind:
http://www.vxb.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=bearings&Product_Code=Kit7218&Category_Code=GE_Type
Regards,
Ray L.
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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
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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.
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Ray,
Picture is worth a thousand words! ;D
RICH
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Ray,
Picture is worth a thousand words! ;D
RICH
Exactly why my next one will capable of simply moving out of the way, then returning to its original position. Even re-making tips is a PITA, and very time-consuming, when you want the end-result to be on-center to within a few tenths.
Regards,
Ray L.
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OK, but if you come up with something that works, you gotta share! :-)
My idea involves an operation that carries some serious potential hazards if it is done incorrectly, so I am reluctant to post it on a public forum, but no problemo on the sharing it it works.
BTW, everything I come up with works . . .it's only a question of how many redesigns are needed to get there . . LOL!!
However, my special talent is taking something that works fine and 'improving' it to the point where it no longer works at all . . . :D
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Ray & Simpson36.
I have a nice probe just sitting in a box for a long time but have been reluctant to use it.
The COPYCAT center or edge finding worked quite well. I bent that probe when i used the wrong routine since one is ment for video and one is meant for a probe. Don't remember how accurately the probe found the center but was better than using video or a conventional edge finder. Say better than the runout of the tool end. The probe is rather easy to replace since the probe holder is placed in a collet chuck, piece of ground round is inserted, and only the end need be trued. This way you can have different end sizes or shapes if desired.
I never tried profiling something for 3d stuff, one of these days, just another learning curve to go through one of these days. So off to the side to learn something.
RICH
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Ray has my wheels turning now and I don't know about a few tenths, but less than .001 is probably doable and would satisfy my needs.
I can do a proof of concept really easily and then make a working prototype if the machining is successful. I don't have the high speed pullleys made for my new mill yet, so this project will have to wait. :(
The time eater is probably going to be learning the probe macros and how to use them.
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I made one but only used it for edge finding, had it dialed in to less than 0.01mm runout and it was very repeatable. Offices upstairs had a flood and it came down on my collet rack and flooded the probe and have not repaired it yet and miss it as I just use one ofthe sprung ball ones at the moment.
I will probably make another one but the adjustment I will do differently this time as it was rather finicky the way I had it before.
Hood
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How about something along the lines of a magnet that keeps the probe in positon, but breaks away when the force gets too high? I haven't really worked it out in my head yet... just blurting out ideas.
Himmay? do you really have that much squirrelleyness with Mach? I haven't done more than jog my machine around and run some sample programs, but it seems to do what I tell it to do (right or wrong, that is.) If you have posted examples of this going chaotic, please guide me to them.
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Memory again...But didn't someone already make-up a macro for a probe for centering a circle or square/rectangular piece of stock? A couple of years ago... ???
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How about something along the lines of a magnet that keeps the probe in positon, but breaks away when the force gets too high? I haven't really worked it out in my head yet... just blurting out ideas.
Himmay? do you really have that much squirrelleyness with Mach? I haven't done more than jog my machine around and run some sample programs, but it seems to do what I tell it to do (right or wrong, that is.) If you have posted examples of this going chaotic, please guide me to them.
Matt,
Yes, Mach3 really IS that squirrelly. It will work perfectly for days, or weeks, at a time, then do something stupid. I've had it do such things as:
1) Spontaneously simply stop executing a g-code program right in the middle. No E-Stop, no Stop, no FeedHold. It simply stops doing anything.
2) Spontaneously turn off the spindle or coolant in the middle of running a program
3) Decide, as it has recently, that G4 delays will ALWAYS be in seconds, rather than milliseconds, regardless of the configuation setting
4) Decide to ignore jog commands. For example, right now, my Z and A axes will not jog after an E-Stop, until I've jogged X or Y.
5) Decide to ignore spindle or coolant on/off commands
6) CV still does NOT work correctly on 3-axis helical moves unless acceleration/velocity settings on all three axes are virtually identical.
7) So many other things, I can't even remember right now....
Probing is, and always has been, particularly flaky. Most of the time it works fine, but every once in a while, it decides to move the wrong axis, or move it in the wrong direction, or move multiple axes, or simply ignore the probe input entirely, or do the probe operation correctly, then move the wrong direction on the retract. Pretty much all of these stand a very high chance of breaking a rigid probe, as they have done to me countless times. Just last week I had yet another tool ruined, along with two touchplates, when Mach3 decided to ignore the probe input, and it simply drove the tool right through the touchplate and into the workpiece with several hundred pounds of force, stalling the quill servo.
Virtually all of the bugs I've witnessed over the years have, eventually, been proven to be actual bugs in either Mach3, or the SmoothStepper, or the communications, or lack thereof, between the two. And, most have been fixed, or at least reduced in frequency of occurrence. But, I'm still running on almost a one year old version of Mach3 and SS plug-in, as I've seen problems in the later releases. At least the version I use are a known quantity. Hopefully, Mach3 v4, once it's out and de-bugged, will become a more stable platform, but right now it's got a long ways to go before it can be considered robust.
If you search here and the Yahoo Mach3 forum, you will find dozens, if not hundreds, of posts I've made over the years reporting the problems I've seen. While many people tried to blame many of the problems on the very slow PC I was using for quite a while, not ONE problem was ever definitively pinned on the PC, and the vast majority were PROVEN to be actual Mach3 or SS bugs, and most have since been fixed. It works FAR better now than it did two years ago.
Regards,
Ray L.
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Memory again...But didn't someone already make-up a macro for a probe for centering a circle or square/rectangular piece of stock? A couple of years ago... ???
I have "published" several sets of macros for doing edge finding, tool length setting, center finding, mid-point finding, measuring distance, etc, .etc. The most recent were posted a few weeks ago. Modulo the unavoidable random Mach3 bugs, these have worked perfectly for me. There will soon be a new Mach3 screenset, which will be the default screenset for v4, that has similar macros, based on mine, built in.
Regards,
Ray L.
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Oooo, smoothstepper. :o I ran one of those for about 1 day and made the switch to parallel ports. If you are familiar the smoothstepper "watchdog", as I'm sure you are, I can see how that would lead to lots of such problems. Not that I'm questioning any of your Mach problems, which I fully plan to read up on, but I wonder if you'd have better luck on parallel ports.
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Oooo, smoothstepper. :o I ran one of those for about 1 day and made the switch to parallel ports. If you are familiar the smoothstepper "watchdog", as I'm sure you are, I can see how that would lead to lots of such problems. Not that I'm questioning any of your Mach problems, which I fully plan to read up on, but I wonder if you'd have better luck on parallel ports.
Matt,
The SS has been responsible for relatively few problems, and things were no better with the PP. If anything, worse. The "Watchdog" has only kicked in a few times, usually as a side-effect of another problem.
Regards,
Ray L.