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Topics - cooke86

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General Mach Discussion / in need of help!!
« on: October 12, 2016, 02:31:43 PM »
Hello all,

I have a small cnc mill and am having quite a strange problem that I really need help with....

I have been using the machine for a couple of years now with no problem, but recently decided to change my CAM software to fusion 360. I like Fusion 360 better as it is a all in one package. I used to use CamBam to create my gcode and all was fine.

Recently I have designed a part in Fusion 360, a new hoover fiting for the mill. Through the CAM tab in fusion made the required toolpaths and outputed the gcode using the "mach3mill.cps" postprocessor. I ran some simulations before and it all seemed fine.

 
Now comes the problem....

The Cam tab in fusion360 has 4 process's, 3 cut fine but on the 4th it starts to drift on the y axis.

1. A slot around the outer edge.(2mm endmill)

2. 4 Holes for magnets.(6mm endmill)

3. 2 large holes. (6mm endmill)

4. The outer shape. (6mm endmill and Here's the problem)

It appears to drift upwards on the y axis by about 1mm on each pass around the outer edge. I have ruled out backlash and am 99% sure that its not missing steps. (If it is missing steps its doing it in exactly the same places, Everytime I run the code and only on the last toolpath.... VERY unlikey) It is as if it happens gradually over the course of one time around, There is at no point a recognizable "step". What I dont understand is why it can cut everything else fine but not the outside cut, In my opinion it has to be a software/ gcode problem.

I have also let the gcode file run until the end (cutting in the air) and once it was done told it to return to zero, Once it returned the y axis was off by about 10.5mm.

This is really strange to me for a few reasons:

1. The machine has worked fine for along time using code from cambam.

2. The machine apears to be missing steps, However Every time I run the code the result is the same. The first three processes cut fine then on the fourth it slowly drifts with no noticable missing of steps.

3.The machine very rarely misses steps.

I could really use some pointers as I am at a loss currently and dont know where to look next. ???

I have also posted the problem on the fusion360 forum, thinking it was a cam problem. But the code appears to be fine. here is the link to that post where there and files and photos: http://forums.autodesk.com/t5/computer-aided-machining-cam/possible-bug-with-cam-gcode-output/m-p/6615681/highlight/false

Thanks
Luke

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