Vectric Wizard
Posts: 1687
Joined: Sun Oct 24, 2010 7:28 pm
Model of CNC Machine: homebuilt 4'x2' (Mach3+G540)
Location: Guelph, Ontario

Re: Toolpath

Post by PaulRowntree »

I believe the lookahead is unrelated to other settings, and I don't know of any reason to have it low. It won't make much difference on long straight cuts, but curves should get a boost.
Paul Rowntree
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Vectric Wizard
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Model of CNC Machine: Gerber System 48,Denford Triac Modified
Location: Crossgates, Scotland

Re: Toolpath

Post by martin54 »

mlk1950 wrote:Hi Martin, I do it all from the keyboard and it's wired via usb as is the mouse. What do you mean by "Look Ahead"? Even though I've been carving with this machine for about 5 years, I still have tons of stuff to learn. What I don't understand is why would it be carving just fine and then just plunge into the wood like that. I am wondering if it's an issue with the controller board, which is connected via parallel port. Problem is I would know where to begin troubleshooting that.
If you've been using it for years without issue that is why I am inclined to believe it's a mechanical problem rather than software related, if Mach3 settings haven't been changed although the machine possibly wasn't set up for optimum performance it was certainly good enough for you to produce what ever work you have done on it.

Are you sure it was cutting fine before it plunged? Could be that the z axis had already moved a bit & you just hadn't noticed.
When the bit plunged into the wood I don't suppose you noticed what mach3 was reporting the z height to be do you? Because a lot of the lower priced routers use stepper motors rather than servos the systems are open loop rather than closed loop, this basically means that the true position of the axis is not known. The controller tells it to move a set distance & then assumes it has so when steps are missed the axis ends up in the wrong position but the control software doesn't know that.

Have you checked for backlash or any free play on the z axis at all? Try zeroing the z axis & then performing a lot of rapid z axis movements & then check the zero again. Can you move it up & down freely by hand with no power on the machine or is there any binding anywhere?
Check where the motors connect that any grub screws are tight & if it has those aluminium spring type couplers that the couplers aren't broken.
I had a problem like this a while ago & it was caused by the z axis motor itself, it was one of the old slo syn type round motors which was pretty old, over time the magnets in these motors deteriorate & when that happens problems start. My problem was solved by replacing the motor with a more up to date nema 23 motor but the problem you have could very easily be completely different.

I don't know why the default look ahead setting is set so low either, maybe something to do with the computers available at the time mach3 was developed.

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