Uneven table compensation

[crane550]

Hi all,

I know the proper way to handle this is to fix the table, but for now, does mach3 offer any kind of uneven table compensation? For example, I have one corner that is about 1/32 of an inch off. When I V-Carve down to that corner the change in my carving changes dramatically, that the width of my path is exactly off by twice the Z error. (Assuming 90* bit)

Any way I can tell my software "that corner is high/low?"

[Superman]

I'll suggest to try looking at it from another direction

-Can you place your material in a way that would seem flat from the cutter's point of view instead of fixing the machine or NC code

ie place packers underneath to jack-up the stock while running a dial indicator across the top ( dial indicator is held by the spindle collet, DO NOT turn the spindle ON, or you'll find it on the other side of the wall )

[CarveOne]

Originally Posted by crane550 Hi all, I know the proper way to handle this is to fix the table, but for now, does mach3 offer any kind of uneven table compensation? For example, I have one corner that is about 1/32 of an inch off. When I V-Carve down to that corner the change in my carving changes dramatically, that the width of my path is exactly off by twice the Z error. (Assuming 90* bit) Any way I can tell my software "that corner is high/low?"

That might seem like a useful feature, but I'm pretty sure that Mach3 has no utility like that at present. It might require that you use a touch probe to create a reference height map database file of your table top every 1/2" or so, then create another height map database file of each piece of material that you intend to cut after it is fastened down to the tabletop, then use the software feature to generate gcode that compensates for the height map database file differences at each coordinate in the area that you are going to cut.

Bottom line is - surface plane your table and "make it right". It's a whole lot easier and faster and less problematic.

CarveOne

[ger21]

You may be able to do it with the formula functions, but as CarveOne said, the easiest way is to surface the table flat.

Surfacing the table should be one of the first things you do with a new machine, and may need to be done periodically to maintain a flat table

[eloid]

Originally Posted by ger21 You may be able to do it with the formula functions, but as CarveOne said, the easiest way is to surface the table flat. Surfacing the table should be one of the first things you do with a new machine, and may need to be done periodically to maintain a flat table

yes resurface table top complete flat relative to you gantry, end result ...you will have a " your" table compensation if you like apply/ screw a temp. spoil brd on top of it, remachine as need... etc

[analogman]

Subtle twist on the other suggestions: bolt down a spoil board and then surface the spoil board. Use lot of bolts. I use a 1 1/2" bottom surface bit from grizzly.

This method works extremly well. After a spoil board surface I can engrave anodized aluminum which would really mess up if the surface was off by .002

[crane550]

Originally Posted by analogman Subtle twist on the other suggestions: bolt down a spoil board and then surface the spoil board. Use lot of bolts. I use a 1 1/2" bottom surface bit from grizzly. This method works extremly well. After a spoil board surface I can engrave anodized aluminum which would really mess up if the surface was off by .002

Already done!

[eloid]

Originally Posted by crane550 Already done!

sound like you lossing steps in your steppers and your spoil brd is wave as a result of that issue.

[crane550]

Originally Posted by eloid sound like you lossing steps in your steppers and your spoil brd is wave as a result of that issue.

?

Not sure I follow...

[eloid]

Originally Posted by crane550 ? Not sure I follow...

stepper motor are open loop, if there not sized/ tunned/overloaded/
feed rate set to high, the motor will drift..... resulting in missing steps

[otto_pjm]

If you want to go the code compensation route, have a look at this thread. I believe the end up with code for both EMC and Mach. The process is to take you g-code, height probe around it in a grid and average the heights, then update the code to cut as if the board was even. It's being used with extremely small bits for PC board cutting. It may take awhile to probe if you have a large area, but should be able to compensate, if you can't level / tram the surface to your spindle.

Pete

http://www.cnczone.com/forums/showth...t=82628&page=8