Rounding error on Circular Milling Operation
What do you get if you post using dump.cps, just curious.
Mark
Mark Hughes
Owner, Hughes Tooling
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Post?
Best guess on my part is since it's cutting your hole diameter+tool diameter in half to .09375" the post is rounding it in tenths since that's all the machine will take for code. Could be location tolerance.
Can you share the part? Have you looked at the toolpath (expand toolpath, right click on the size and select View Toolpath)?
I'd guess this is partly down to using incremental arc centres, not sure if there's any way to work around that in the post.
Mark
Mark Hughes
Owner, Hughes Tooling
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One thing I noticed was the locations and I wonder if that's something in the rounding issue.
What happens if you make a duplicate and post it in metric? The higher resolution may yield a closer to nominal result.
Edit: you could also try making another setup and aligning the holes along an axis and see if the post changes to see if the center position has an effect.
I think this is a rounding error in the post.
This is what I get with a post set to absolute arc centres.
I think the problem is incremental position are calculated in the post with jOutput.format(cy - start.y, 0) so there's more room for a rounding error to creep in.
Mark
Mark Hughes
Owner, Hughes Tooling
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Does your control have a code for ABS arc centres, Mach3 has G90.1?
Mark
Mark Hughes
Owner, Hughes Tooling
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@ the Fanuc comment
Yes, it does support R words. I just hate departing from uniformity. My day job shop uses Esprit and I've never seen this occurrence. Not to say it doesn't happen, but I've never seen it in the 8 years I've been there. I can ask the programmer on Monday if he ever had to do anything about it.
To be fair, if you actually need to hold that .0001" tolerance (well, more like ±.0001"), it should probably be done on a Yasda 
I understand trying to keep code the same as what you're used to, but sometimes we are forced into situations that are less than optimal. Another workaround idea: change the hole diameter to .1876 and see if the arc changes in the post. Comp it with Stock to Leave and see if it still shows up. Just trying to find out what it's rounding and where.
Pretty sure this is indeed a post rounding issue.
In most posts there is a line like this at the top:
tolerance = spatial(0.002, MM);
0.0001 inch is 0.00254 mm so if your post processor tolerance is left at it's default it's allowed to be off by that much.
Haven't tested your file with a tighter tolerance though so it might not help. Worth a try I think.
Laurens Wijnschenk
3DTechDraw
AutoDesk CAM user & Post editor.
Found out the hard way is the best way to win.
Looking at the dump file these are the numbers being used onCircular, format seems to be IJZ XYZ
For the first hole the difference is 0.093749939926027 and the second 0.0937500150184932, you'd think they should round to the same number. I'll have to experiment with the post and see if I can get it to output as comments before any rounding.
250: onCircular(false, -3.4488647941529282, -0.8355995238296628, -1.4050000108133152, -3.368114861916369, -0.8355995238296628, -1.4050000108133152, 5)
sweep: 90deg
radius: 0.08075
251: onMovement(MOVEMENT_CUTTING /*cutting*/)
251: onCircular(false, -3.4618648018423968, -0.8355995238296628, -1.4050000108133152, -3.368114861916369, -0.8355995238296628, -1.4050000108133152, 5)
sweep: 360deg
radius: 0.09375
275: onCircular(false, -0.860216110710084, -0.6383743436317744, -1.3549999927911232, -0.7794661033810593, -0.6383743436317744, -1.3549999927911232, 5)
sweep: 90deg
radius: 0.08075
276: onMovement(MOVEMENT_CUTTING /*cutting*/)
276: onCircular(false, -0.8732161183995525, -0.6383743436317744, -1.3549999927911232, -0.7794661033810593, -0.6383743436317744, -1.3549999927911232, 5)
sweep: 360deg
radius: 0.09375
Mark
Mark Hughes
Owner, Hughes Tooling
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