Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: olf20 on March 07, 2008, 07:50:50 AM
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Hi all, hope everyone is doing well!!
When cutting some holes in a manifold plate I noticed that after the holes were cut that there was a small area that
was not cut on the final pass. Actually on each pass.
I was using a 1/4" endmill and cutting the a circle / hole about 2" in diameter.
It appears that the start point and the end point of the mill did not meet when the cut finished.
The amount was not great, just used a small file to clean up the uncut material. This happened on several cuts so
it was not a fluke.
I can post a portion of the file if needed, as the file is quite large.
Thanks for any help!
olf20
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Use the circle cutting wizard as a test and see if its the same, if not then its your code, if it is then it could possibly be backlash.
Hood
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If the problem was at the 12:00 or 6:00 positions, then check your Y Axis backlash. If it was a the 9:00 or 3:00 poistion, then check you X Axis backlash.
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How_are_you_cutting_the_hole_?
I-have_the_same_problem_If_I_use_the_pocket_function_in_Bobcad_but_if_I_just_make_my_cutting_path_
with_offsets_and_connect_them_then_It_cuts_fine.I_have_the_same_problem_with_a_circular_toolpath.
When_setting_up_your_path_make_sure_your_finished_edge_is_cut_with_a_complete_circle..
GaryV
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I have used Corel Draw, and VcarvePro, both with the same results.
I will try to used the circle wizard and see if I have the same problem.
I don't think it is a backlash problem as I have checked the machine several times,
but will check it again.
Thanks for all the response!!
I shall return.
olf20
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I started to reply to this last night but got my ********* in a twist trying to work it out. This is what I think happens.
This, I think is due to cutter width compensation.
The tool will start at X0 Y0 (which we will take as the centre of the circle). G42 is applied (which for a straight line effectively puts a - minus distance on the X and Y if required). The tool then moves to X2 Y0 to start the circle - it will actually move to X1.875 Y0 (allowing say 1/8 inch for a 1/4 inch cutter)
When describing a circle, GCode has to effectively errect a complete 1/8 barrier round the tool, because, unless it knows exactly which part of the tool is in contact (which takes some really serious maths (sorry Art if you have done it)) there is no other way of applying the offset.
We start to cut the circle, and the offset correctly applies the 1/8 barrier on the outside of the tool.
Unfortunately, as we get to X2 Y0 again, it is still applying it. It correctly stops at X1.875 but also applies it to the Y axis and stops at X1.875 Y-0.125.
Depending on how your GCode is written for each pass depends on whether the "shortage" gets over cut.
If the Code carries on and does another pass, it will be over cut, but say it retracts and goes to X0Y0, then comes out for another cut, the same "mistake" will apply.
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I am trying to use the circle cutting wizard. I can't seem to change the values without them reverting to the existing values. Can someone please explain how rouse this wizard?
Jim
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Hit the ENTER key after each entry.