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Just started to get "dents" at the plunge point

Just started to get "dents" at the plunge point

Postby shobley » Sat Dec 09, 2017 4:19 pm

I just noticed that I am getting a dent at the plunge point of a cut path, and yet simple drilled holes come out just fine.
It suggests that the spindle is flexing when plunging, but would not explain why holes look OK.

Does anyone have any suggestions for how to diagnose this further?
All I'm asking for is BlackToe, with a laser beam on its head...
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Re: Just started to get "dents" at the plunge point

Postby ShenValleyCNC » Thu Dec 14, 2017 4:59 am

Difficult to diagnose without being there. If I understand correctly, you get a small impression in your surface at the start of your cut path showing the bit wandered a bit before plunging into the material? But drill holes appear to be clean with straight in plunge.

The way to resolve this is to do tests. First eliminate the mechanical. So the usual stuff looking for freeplay applying manual pressure. One thing that comes to mind here is to try and precisely measure where the center of the drill hole is and where it should be. You might find it appears ok but is off by just a hair indicating some movement.

Mount a piece of wood, plunge and do an x move for a few inches, raise, move it over a some and cut a parallel line in the opposite direction. Compare the two. Then do the other axis to see if the problem shows up. For instance, if you stoop to eye level with the material surface as the bit makes contact, you can see if it maintains perpendicular or if it "drags" or wanders.

Running the code and then stopping it repeatedly, moving over a bit and restarting it and watching very closely will allow you to observe when it makes the dent and if it appears to be a programmed move, or something amiss.

I can read GCode a bit, I look at it see if it says something wrong at the beginning of the cut which could indicate a software configuration issue. Your lead in code might skim the surface before a plunge. If you have some pre-processor code entered into your code generator and it got munged, it might be writing this problem into your file every time.

I have seen software simply generate wrong gcode when something gets written into the design file that you can't see. I go to the offending point in the design window, move or delete an item or recreate it, regenerate the gcode and see if the problem goes away.
It always takes longer than you expect, even when you take into account Hofstadter's Law
Hofstadter's Law
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