Hi everyone, I am trying to better understand the z-zero methods. I am used to using the method from the top of the workpiece, but I want to switch… I watched Eric’s videos about the difference, and I want to define the thickness of material at the bottom of a pocket, say leaving a consistent amount at the bottom of a rabbet no matter the thickness of the plywood. I am not succeeding! When I set up a new job in Aspire and reference from the table surface the entries in the pocket tool path setup seem to me to the be the same as when you reference from the top of the workpiece. Start depth = 0; cut depth = 1/4" say. If anyone could clarify this for me I would really appreciate it.
That’s correct. In aspire you define the material dimensions. The z zero is just a reference point. So if you’re using 3/4" material with the z zero set at the spoilboard, your cut would start at 0.75" above the z reference. If you define the z zero as the top of the material, then the cut would start at 0.00". It doesn’t change the depth of the cuts you define, unless you define the cut start height incorrectly for what you are trying to do. Take a peek at the little diagram that details the cut parameters at the top of the toolpath menu, it lays it out pretty clearly.
Thank you. So, if we are working with plywood that varies, say around .735, there is no way to define the bottom of a depth of cut as a fixed amount above the spoil board, say 3/8"? I need to keep thinking about my depth of cut from the top is what I am understanding. (in my example my depth of cut is .36)
Video for reference: https://youtu.be/-dk5WDKdWBQ
Thanks Eric. I watched this, and am not understanding why the entry numbers are still from 0 at the top of the workpiece. I thought the number line would be flipped, to set the bottom of the pocket. There is no way to define the bottom of a pocket referenced above the spoil board? I appreciate it.
naPS pretty much covered it, but I’ll try to explain again:
If you set your Z zero to the bottom of the material and your material is 1" thick in CAM your bit will be held up .5" ABOVE THE TABLE to make that .5" pocket.
If your material is 2" thick the same thing will happen, the bit will be held .5" above the spoilboard to make that pocket (so it will be cutting a LOT deeper)
If you set your Z zero to the top of the material and you have a 1" thick piece of material the bit will move down from the top of the material .5" to make that pocket. So in that scenario your bit will still be .5" above the spoilboard to make that pocket.
If you used 2" thick material, you zeroed to the top your bit would move down to 1.5" above the spoilboard to make that .5" pocket in the material.
As I say in the video, for cabinetry you certainly want to zero from the bottom of the material so your rabbets and dados are always a consisten thickness.
I’ll add my thoughts… A long time ago I took a woodworking course on “reference edges” and it helped my understanding a lot. Basically, you measure from where the measurement is measured from.
I.e. if you want a dado to be 1/4" deep regardless of how thick the wood is, you measure from the top. If you want the wood under the dado (the part that’s left) to be 1/4" regardless of how thick the wood is, you measure from the bottom. If you want a 1/8" reveal, you measure from the reveal side, not the hidden side. Etc. If you do it right, you never have to measure the wood, because it never matters.
It doesn’t matter where “zero” is, it matters where you measured from (the reference). You could tell your CAM you working on the top of a 3/4" piece, touch off the bed, offset your Z so that zero is 3/4" up, and you’re still referencing the bed. HOWEVER, if you touch off on the wood itself, you are now referencing the top of the wood instead of the bed (bottom of the wood).
Sometimes it also helps to think “How could I do this so I could run the same job with either 3/4 or 1/2 inch wood, and still get correct results?”
I skimmed the answers so maybe someone said this: If you z-zero off the spoil board you can put your depth of cut whether pocketing, drilling, or profiling to “Z-(thickness you want left)” so if you want 3/8" left between the bottom of the material and the bottom of your hole/etc you would enter “Z-0.375”.
On most machines, a more positive Z value means the cutter is more higher up relative to the work (i.e. for us, “spindle up” but for a knee mill, it might mean “table down”). So if you set Z=0 at the surface of the spoilboard, that would mean that any negative value of Z will cut into the spoilboard.
For your example, if you touch off Z=0 at the spoilboard and want to leave 3/8" behind, you’d want your Z to be +0.375 while cutting, not -0.375. That’s at the machine’s display; your CAM software might do other things “for your convenience”.
Thank you everyone. I like the logic, I am just having a hard time getting my machine to execute. So, to keep it really simple, in aspire, z-zero from machine bed in job setup. Now, if I have a 1" thick workpiece, and I want a pocket to cut 5/8" deep, leaving 3/8". Start depth = ? and Cut depth =?
I have tried it several ways, and my machine wants me to start with 0 at the top. Rich may have answered by actually entering a formula in cut depth? I appreciate the patience.
I don’t use Aspire (I use Fusion) but… if you can tell Aspire that Z=0 is at the bottom of the workpiece (In Fusion, I’d set the origin point to one of the bottom corners of the wood, for example) then all your numbers (at the cnc machine) should be as if you stood a ruler on the table - you want to cut from the top of a 1" piece down to 3/8" remaining, so you’re cutting from 1" away from the table to 3/8" away from the table, or start at Z=1.0 and end at Z=0.375.
But Aspire might offer convenience functions that confuse things. If you start with “I have a 1in thick piece and want Z=0 at the bottom” it might still ask you about “depth” of cut or “how far down from the top” etc (Fusion has lots of these options - I could say “3/8 from the bottom” or “5/8 from the top” and if I change the size of the wood it does the right thing). It will do the math for you so don’t be confused when you get to the machine and the numbers are different - the CNC machine doesn’t know about “depth” or “thickness” it only knows about where it is.
If in doubt, touch off your Z=0 at three inches above the table and run the job, and imagine what it would actually cut. Sometimes watching what it does is easier to understand than the written word.
You’re overthinking this…
If you have Aspire set to Z zero at the bottom of the material, and you have the thickness of the material set correctly in Aspire, in CNC12 your Z zero should be set on your table. To do this you simply set it to zero.
A quick way to do this is in the Set Part Zeros>WCS table. Just find Z and set it to 0 and run your job.
I’ll try that. Thank you, DL