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Messages - alenz

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Pete, I too have seen some unexpected results when using Absolute IJ mode. These gcode snippets all run on my machine, even tho the last two should not. Strange that Mach will error on a very small end point error while other times it will allow over ½ inch.

This cuts an arc in Absolute IJ mode, center at X0 Y0.5,  radius 0.5, as expected.

G00 X0 Y0
G01 X0 Y1
G02 X0 Y0 I0 J0.5
G01 X0 Y0

Now change the J to 0.25 and it also runs, but makes a spiral;

G00 X0 Y0
G01 X0 Y1
G02 X0 Y0 I0 J0.25
G01 X0 Y0

For an even more interesting curve change the Y to 0.5;

G00 X0 Y0
G01 X0 Y1
G02 X0 Y0.5 I0 J0.25
G01 X0 Y0

Can anyone else get this code to run? If so maybe a neat way to cut spirals?

I’m running R3.042.027 and should mention this came up while trying to help a poster on another forum.


General Mach Discussion / Re: Fixtures, Offsets, Origins & Suchlike
« on: March 03, 2010, 11:50:25 PM »

In regard to the above post, it is assumed that the circular recess in the fixture is centered at X0, Y0. The Gcode for cutting the recess would include something like this:

G00 X(radius) Y.000 Z0.000
G01 Z-(depth of cut)
G02 X(radius) Y0.000 I-(radius) J0.000
G00 Z0.

General Mach Discussion / Re: Fixtures, Offsets, Origins & Suchlike
« on: March 03, 2010, 11:02:13 PM »
 As for centering the plastic gear, you might want to consider this method. Cut a circular recess in a piece of  MDF (or similar)  with the X & Y DRO’s zeroed.  The recess should be approx ½  the thickness of the gear, (or deep enough to get a positive registration). Start out with the diameter undersize and enlarge until the gear is a snug fit. Now clamp the gear in the recess and it will be centered with respect to the gear teeth which should be more accurate than indexing off the center hole.  The center will be at X0, Y0 assuming the DRO’s haven’t been disturbed during the process. For clamping, drill and tap a couple holes in the MDF and use strap clamps. 

As for drilling two holes 90 deg apart, here is one way. Align the vise fixed jaw with the X-axis and clamp a temp stop to fix the X dim in the vise. (If the stock is small enough maybe use the machinist square to align the stock with the side of the vise). Now after touching off a corner and drilling the first hole, just rotate the stock and clamp it (against the stop, or square) and you have retained your reference, i.e., the stop in X and the vise fixed jaw in Y.


General Mach Discussion / Re: Chinese Digital Caliper Magnetized
« on: February 19, 2010, 09:51:16 PM »
Hi Daniel, I can’t tolerate magnetized tools so I bit the bullet and gave the calipers the full treatment. Good news, you were right, it didn’t do any harm. And now I can say from experience that they (at least this one example) can be safely demagnetized.

General Mach Discussion / Chinese Digital Caliper Magnetized
« on: February 18, 2010, 11:17:38 PM »

I have a Chinese digital caliper that the tips have somehow become magnetized.
Question: Will pulling it thru a demagnetizer destroy it?
I’ve tried cautiously putting just the tips in the demagnetizer.  It weakened the magnetism and didn’t seem to affect the operation, but I am a bit leery about demagnetizing the entire caliper.
I posed this question on another forum but no one knew for sure.
Thanks for any info.

General Mach Discussion / Re: Rotary axis zeroing problem
« on: February 17, 2010, 05:55:42 PM »
Thanks Russ and Tweakie, my bad. Sometimes the longer I look at the obvious the less likely I am to see it :(. There was no reason for an A word in that line, (although  I still don’t see why it did what it did since it was already at that position).
Thanks again,

General Mach Discussion / Re: Rotary axis zeroing problem
« on: February 17, 2010, 04:46:20 AM »
There appears to be another bug in the rotary axis that bit me. The following code drills 4 holes 90 deg apart and works as expected one time but one time only. Hit cycle start the second time and it goes bonkers. On line N110 it goes backwards a full revolution but worse yet the Z travels down concurrently. NOT GOOD. This was with Rot 360 rollover and Ang Short Rot on G0 both checked but other combinations do the same thing. Exiting and restarting Mach is the only way I know to get back to normal.  I did discover that adding line N25 G92 A0 will cause it to work every time but that shouldn't be required. (But it might be a clue).

N10 G00 Z.050
N20 G00 X0 Y0
(N25 G92 A0)
N30 #1 = 0
N40 M98 P10 L4
N50 G00 Z.25
N60 G80
N70 M30

N80 #1 = [#1 + 90]
N90 G00 A#1
N100 G01 F20
N110 G81 Z-0.25 A#1 R.025
N120 M99

 I would be curious to see if this can be repeated on someone else’s machine. It is repeatable on 2 PC’s here.
Thanks, Al

General Mach Discussion / Re: Drifting in the Y axis
« on: December 17, 2009, 10:19:06 PM »
I seem to recall a similar instance being reported which was a result of the step/dir being set to high when it needed to be set low, (or vice versa). A step would sometimes be lost when the direction reversed. I think the fix was to check (or uncheck) the low enable in Config > Ports & Pins > Motor Outputs and then go to Config > Homing/Limits and check/uncheck the Reversed block to get the proper direction back.  Probably a long shot and I’m just going on memory :)

Or perhaps a way to turn off "Caps Lock"? <VBG>

General Mach Discussion / Re: Strange circle problem
« on: December 07, 2009, 09:14:42 PM »
David, that is a perfect description of Y-axis backlash. But since it happened all of a sudden, then that implies that something in the y-axis has suddenly come loose. Perhaps jogging the Y and watching/listening may help find it.
This assumes that you didn’t originally have backlash and were using backlash comp. That’s another story.

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