Using the table as zero and having problems.

[knight_toolworks]

I need to figure out where I am going wrong. I have these wooden parts to cut where the thickness has to be exact. So either I run it through the planer and get it as exact as I can then change the toolpath to reflect that thickness or do it from the table so thickness is not as critical. Well if I can figure out how. Say using shopbot wizard and the nominal thickness is 1” I want to cut one part at .76 and another at .623 how to set it up with the table as zero. I can I do it so it will always cut that thickness even if the wood thickness varies a little bit?

[rob_bell]

I have a client who requires the pocket milling depths be of critical dimension from the bottom of the workpiece. He supplies the material and it varies a bit. So I wrapped the standard z-zero routine into one which zeros to the table then raises up to the general material thickness and re-zeros from there. Then it raises up another 1/4 to get things ready to go. Works great.

C2 ' standard zero to table,workpiece in place, vacuum on
MZ, 1.75 ' raise up to standard material thickness
ZZ ' re z-zero there
MZ, 0.25 ' lift up and good to go

[joe]

Robert,

Do you not have a CNC program like V Carve Pro or Insignia which will do all this for you?

What your are doing, while it will work fine, seems dated.

[harryball]

You should set your machine bed as 0, set your material thickness at .75"

Now, lets start with a actual .75" board on the machine.

If you set your cutting depth to .25" you will be cutting .5" above the table top. If you set it to cut at .75", you'll be cutting at the table top.

Now load a peice of wood that is .80" thick. If you cut at .25" you will still be cutting .5" above the table but deeper into the wood. Cutting to .75" will still cut at the table and thus all the way through.

Other than the fact that you need to be sure safe Z is above your wood thickness variations that's all their is to it.

If you loaded at .76" board and then did a surface routine at 0.0" it would true your board up to the exact thickness of .75"

I hope this helps,
Robert

[richards]

Robert,

Is the math correct? If 0.0 is the machine bed (top of spoil board) and the material to be cut is .75" thick, then the .25" setting would be cutting into the material .5", as you explained. However, if you set the height to .75", wouldn't you be just grazing the top of the .75" material? It seems that you would have to set the depth to 0.0 to cut all the way through the .75" material.

[joe]

I agree with Mike on this one. What software programs are you guys using?

[rob_bell]

I'll assume Joe's first post was directed at mine. My hand coded routine was a patch for an entire suite of files, approx 17 which I generated before I owned V-Carve Pro. Plus V-Carve Pro doesn't open STL. Those files were created based upon an assumption of a consistent material thickness. When that turned out to not be the case I wrote the zero to table fix. Sometimes old school is the way to go.

[harryball]

You're right, it was getting late... I meant to say cutting with a depth of .75" would yeild a board up to the exact thickness of .75" Good catch.

Robert

[knight_toolworks]

ok got it figured out I think. I thought of planing the sirface to the exact thicness too. though it would be a bit slow with a 1/4" bit if I was too lazy to change bits. this a part I won't make often so time is not critical. here is a pic of the piece.
7469