Setting z height correctly?

Machines (Original/PRO) How To
1

I’m sure this has been asked a million times, but for the life of me, I can’t find the answer here.

I am cutting 18mm plywood. I measured it out to be .72 using a digital caliper. While the number may change slightly due to plywood thickness, I’ve always set the thickness to the caliper in Carbide Create. I zero off the top of the plywood, and I Probe XYZ successfully.

When I set it to “Use Stock Bottom” when doing the cut out pass, it randomly either cuts completely through the plywood and into the wasteboard by one or 2mm, or randomly doesn’t cut through it completely at all.

I don’t know what I’m doing wrong. I’m trying to cut out small cabinets for my shop which should fit on the 1/3 sheets I’m cutting out but each piece fits on the 1/3 sheet. (48x32). Someone mentioned setting the Zero Height to go off the Bottom (aka wasteboard) but when I try that, it carves nothing but air, seems about 2 inches too high…

Any advice on how to either 1) reliably cut to depth or 2) how does setting the Z work from the bottom/wasteboard level???

Thanks,

Wayne

edit I should be more clear that when I measured .72 with the caliper on the latest sheet I cut yesterday, it cut 1mm into the wasteboard (I just measured), on some sheets it’s .708, on some sheets it’s .715, but I guess that’s just variance in sheets of plywood…

2

I’ve tried three different digital calipers and they’re always pretty much dead same…

3

Hey Wayne,

the workpiece zero coordinate in your virtual 3D model has exactly to be at the same position on your real workpiece. If you define it at the bottom of your virtual 3D model, you got to probe or manually set zero coordinate at the bottom (machine bed) too.

If your Z height varies randomly when using the same g-code toolpath, you may have the Z plunge issue.

Also be sure that your touch plate dimensions are correctly set in the CNC controller.

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4

Thanks. I’ll check into the Z plunge issue, and yes, I know that I’m being a little too worried about the wasteboard. The items I cut yesterday came out just fine using a compression bit.

It’s just a little OCD of me to think I must be doing something wrong if I consistently cut into the spoilboard…

Followup question. If I wanted to set the Zero Height from the top of the wasteboard (aka “bottom of the workpiece”) do I do that using the Onefinity probe, or is that something I need to do via the paper method? I’m just a little unclear as to why – when I try setting it with the probe (full side down, notched side up), it starts cutting air high above the work piece. Maybe I’m doing it wrong…?

Wayne

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In this case you use the XYZ touch plate upside down, on machine bed. Thickness of the touch plate will be subtracted automatically.

6

Best practice is to always set the Z Zero position to the wasteboard, that way you will probably never cut into it.

You set the Z zero position in your CAM software, but you have not mentioned which software you are using.

If you use VCarve, it would be Create new file → Job setup, then tick Machine bed.

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7

Hi Tom,

I’m using Carbide Create, but I’ve tried setting it to Zero Height off the bottom (meaning top of the wasteboard) using the probe but it still starts cutting thin air about an inch or two above the top of the wood.

Today, when everyone in the house wakes up, I’m going to try setting zero height to the bottom, then manually set the Z Height using the paper method and see if that fixes it. It may be that the silly thing isn’t subtracting the height of the probe from it’s calculation when carving. I haven’t changed settings for that, so it’d have to be the default that’s out of whack maybe.

Thanks,

Wayne

8

When i was starting it helped me to sometimes to dry run the toolpath with the spindle off and an empty wasteboard, or run it 10 mm above the work.

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9

Do a sanity check. After zeroing the machine manually move to the zero positions. When moving to the Z axis that’s zerod off of the spoilboard move away from the project and lower the Z axis until it’s just touching the spoilboard. The zero axis position should be very close to 0. If it isn’t then you did something wrong. If it is and you’re cutting air then most likely your gcode is faulty. If the cut starts off good and then goes wrong recheck the zero positions. If they moved then you have an issue like a bad connector, stepper motor loose, or (Z axis only) the bit is slipping.

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