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Author Topic: Pocketing and Island avoidance issue, need help  (Read 14718 times)

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Offline 2bits

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Re: Pocketing and Island avoidance issue, need help
« Reply #30 on: April 21, 2009, 10:22:26 PM »
I'm running behind tonight and will try and get to it.  While I don't have a dial guage I got thinking I do have a digital calipers that seems to be pretty accurate.  So I rigged up a portable vise and hooked it to the gantry and recalibrated again (5" runs).  According to the calipers, it was way off, so much so I wonder if the specs for the machine I got are correct.  Originally I was cutting while doing the mach3 wizard, measuring and entering that value and eventually did some manual calcs and entry for fine tuning.  So anyway, I thought I'd try this (wish I had the change to buy some good precision tools), when done, I cut a 1" square and was with .010.  From there I have tweaked manually and got a 1.0 square +-.002 (for now???)  So now I'm currently recutting the file from Graham to see what that does, then I'll try your files. It's getting late, so will see how much time I got yet tonight.  Thanks!  By the way, for tweaking, is going off a 1" square correct?

Offline 2bits

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Re: Pocketing and Island avoidance issue, need help
« Reply #31 on: April 21, 2009, 11:13:28 PM »
Sorry, out of time tonight to get to the files you want me to cut.  I'm beginning to wonder if this system can and will hold a calibration.  Do I need to spend the money and get a dial guage with a block setup to dial this as close to 5.000 as possible? If I'm 5.006, is that enough to throw this off when cutting the island from .175 to .148?  I'm picking 5" right now because my calipers only go to 6".  I know the dial guage would be the most correct, I'm just wondering if I'm spinning my wheels, because I'm not getting an exact true measurement.  Or, is there something wrong with my controller or motors where I'm skipping or gaining steps at random?  Even with the calipers, it would vary +-008.  Sunday after playing with it all day, I had finally successfully cut twice to spec, and the last two nights the calibration seems all over the place.  I don't know if it's because I don't have the right tools or if there's something wrong with this unit.  Once calibrated, should I expect the same measurement everytime or within say .003?  At this point, I don't think there's any point in cutting test files until I can get the calibration stable.
Re: Pocketing and Island avoidance issue, need help
« Reply #32 on: April 21, 2009, 11:49:55 PM »
I have an old Bridgeport and am happy with +-.0005. From what I can see of your machine, +-.002 or +-.003 should be reasonable.
A six inch caliper should be just fine at those tolerances. One thing to think about is when your Z axis is all the way down you will have the
most potential for deflection errors. Try mounting your material to be cut as close to Z zero as possible leaving just .2" clearance.
For testing Try this file. Remember to subtract the tool diameter from 5" for the measurement. The file cuts 1/2" around each corner.

Offline Graham Waterworth

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Re: Pocketing and Island avoidance issue, need help
« Reply #33 on: April 22, 2009, 03:23:38 AM »
If you are +-.003 over 5" then over the 24" travel of the machine you can be .040" out and dimensions will not be consistent.  It must be and can be spot on.

Try putting the calculated figures in again.  When you change a steps per setting you should restart Mach3 and then do your checks, if you are not doing that that may be why you are getting strange results.

Graham
Without engineers the world stops

Offline 2bits

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Re: Pocketing and Island avoidance issue, need help
« Reply #34 on: April 22, 2009, 09:21:52 AM »
Because of the design of this system and using 1.5" bits, there is not enough travel to as far as required, so I had to raise my sacrificial board 1.25" from the get go  which puts me alot closer to Z zero. 

Graham, thanks, I was not restarting Mach3 after changing steps, so I'll give that a try.  Tonight I'm also going to install Mach3 on a newer, faster pc and try that as well just to rule out the pc I'm currently using.  It's at the minimums and seems to run it ok, but it's 1 more thing to rule out since this seems to be such a strange issue.

Offline 2bits

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Re: Pocketing and Island avoidance issue, need help
« Reply #35 on: April 22, 2009, 09:38:39 PM »
Alright, grabbed new pc, downloaded and installed fresh copy of Mach 3.  Got my portable vise and digital calipers out, ran calibration on each axis using the Mach 3 utility for 5" moves.  I did this until I got 4.999 on X and 5.000 on Y and then I did it 5 more times getting consistently 5.0 +- .001  Even if my calipers aren't the high dollar ones, it consistently gave me close results.  So at this point you would think everything is good to go.  Restarted Mach 3 and cut Grahamns file, results are:  Outer dimension of pocket; expected 1.0 got 1.025, Inner Island dimension; expected .175 got 1.50

It's .025 off, how can it be off .0125 on each side when i did sufficient calibration to get 5.001?  I did another calibration check, 5.001, It's like calibration and cutting are two separate entities, neither one has anything to do with the other.  What's unique about this .025?  it's always been off in this area, .020 - .025.  On the controller, if it's supposed to be 1/8 step, but it was strapped for 1/2, or vice versa, would this be real obvious, or could this be a reason? Or maybe the controller is just bad in some way?  Pc is ruled out, software is ruled out (CAD/CAM and Mach 3), gcode issues ruled out, system appears to be able to calibrate, but fails with .025 overcut consistently.  Motor to lead screws coupling is tight, can't change the threads per inch, no backlash noted especially when it's .025 over all the way around.  New Router, less than 4 hours on it, new bits, no runout detected.  This doesn't leave much but the motors and the controller.  And it would be real nice if the builder would return my emails!

Mark
Re: Pocketing and Island avoidance issue, need help
« Reply #36 on: April 22, 2009, 10:54:36 PM »
If you set Jog to 1" increment and hit X jog 5 times how far does it move?
Re: Pocketing and Island avoidance issue, need help
« Reply #37 on: April 23, 2009, 02:44:13 AM »
It has probably been mentioned before, but the backclash compensation is turned off?

Have you tried the test I suggested in reply # 22?

That little test should say something about the hardwire and calibration issues.
Run the last cut in the same direction as you do when you'r pocketing the final small diameter cut.
« Last Edit: April 23, 2009, 02:48:31 AM by SteinarN »

Offline 2bits

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Re: Pocketing and Island avoidance issue, need help
« Reply #38 on: April 23, 2009, 09:14:13 AM »
SteinarN, backlash compensation is off and I did run that test, but it was off because of the same issue I'm having right now.  Calibrate X and Y which appears to be correct, but when cutting it's off by .020-.025.  I'm at work right now, so I don't have the numbers I recorded, I'll post the results when I get home tonight.  I didn't get around to mentioning it earlier because I was ticked off it was still wrong after calibration and it basically ended up the same as all other test cuts.

MachineMaster, I'll check the 1" jog tonight as well when I get home.  Sure glad this is a hobby venture, I'd be out of business by now trying to get this up and running to make a living.

vmax549

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Re: Pocketing and Island avoidance issue, need help
« Reply #39 on: April 23, 2009, 10:33:38 AM »
2Bits, are you SURE the bit is .118 and NOT .143??

IF you have the machine calibrated correctly then The only way I can see "your " error happening is IF the bit is .025" larger than you think it is. That is the only way I know to cut oversize in both interior and exterior cuts on the same setup without tool comp being applied and there being NO runout on the bit.

AS a further test setup your caliper and do a simple 1" move at slow feedrate. did the caliper show it to be exactly 1".

What were the settings in motor tuning (steps per inch)

Just a thought, (;-) TP
« Last Edit: April 23, 2009, 10:40:55 AM by vmax549 »