Zeroing off Machine Bed

[FoothillFurniture]

Can't figure something out? I have my part thickness set at .8 and zeroing off the machine bed. I have the cut depth at .8 and I'm using a touch plate to zero my Z. When I run my cutter goes into the spoilboard by about .125"? Can't figure out why this is happening. Touch plate settings for thickness of the plate are correct. Any ideas?

I have just started this new setup because I want to keep the spoilboard unmarred as long as possible. I thought this would help. Zeroing off the machine bed and setting the cut depth to .8. My part is actually .78 thick, so I though if I started slightly above and it went down .8 it should just skim the spoilboard? Is this correct?


Thanks

[Adrian]

I can't see anything wrong with the file. The only way it should be cutting into the spoilboard would be if one of your toolpaths was set to cut more than 0.8" deep which they aren't.

I would suspect something up with the z-zeroing side of things at the machine/control software end or the spoilboard is a long way off level.

The fact that you're using different thickness material won't matter as you're zeroing to the spoilboard. It would if you were zeroing from the top of the material.

[dakotablue]

If your touch plate is spring loaded, it may be depressing some when the bit contacts it. Lower your probe speed a bit. I,m assuming you accurately measured the thickness of your plate.

[SteveNelson46]

I always set the material thickness in the software to as close as I can get it to the actual thickness of the material. It just give me a good base to start from. Then other adjustments are much simpler. I don't know what control software you are using but most have a command line. After zeroing the bit to the spoilboard type "Z0" on the command line, or the equivalent command for your control software, and see if the bit just touches the spoilboard. If it does, then at least that portion of the setup is correct.

When using a cut that goes all the way through the material I just use "Z=" to set the depth to the thickness of the material. the machine always leaves about .001" skin. That almost always works for me. Even if it cuts into the spoilboard a little then "oh well". After all, it is a spoilboard.

[FoothillFurniture]

Thanks guys, This is a 4x4 DIY ball screw machine with plug and play electronics system from CNC Router Parts (AvidCNC now) and Mach 4. I am using their touch probe which is spring loaded, but I don't see that it's depressing the plate when it touches. The only thing I can think is that the thickness of the probe is wrong in the software, but it has always worked fine when zeroing on the workpiece.

[sharkcutup]

This may be dumb founded question but I must ask:

If the system works fine zeroing from workpiece why change it?

Sharkcutup

[FoothillFurniture]

Not a dumb question. I make this part several times a day. I wanted to be able to have a g code file set to .8 depth of cut and not have to change it. So, I can plane my parts to .78, have a spot set up zero'd in X and Y in G55 that I can automatically go to zero off the machine bed once and cut as many parts as I want. Zeroing off the material doesn't really work for this as even planed wood can be off by a little and I would have to zero Z for each part. Trying to eliminate that step if I can. I know it's just one step, but it would save me a lot of time cumulative.

[SteveNelson46]

I'm not sure about Mach 4 as I use WinCNC. It remembers the X Y and Z 0 setting even when I shut down the machine and computer. If this is the case with your machine why not just set Z0 to the spoilboard, mount your blank, run a planing pass to set the thickness then machine your part and forget about using the planer. Unless, of course, I'm not understanding the problem.