Machining to a fixed thickness from touch off?

[Mark Bolton]

Ive been chunking away on this and as with all my questions Im assuming the answer is brutally simple but...

I am trying to come up with a way to surface panels to a fixed thickness from their thickest point. These are either solid wood slabs or panel glue ups and Im tyring to come up with the fastest way to drop one on the table, touch off from the thickest area (visually) and then machine to a fixed/pre-determined final thickness after flattening the first side.

So for instance with a panel glue up I input the work piece into VCpro with a shape slightly larger than the glue up. Set a pocket toolpath with fly cutter set to a pass depth of say .010, Z on top, and a cut depth of anything, lets say an inch. Auto Z off the thickest portion of the part (say the panel has a hump in the middle or a high corner, I auto Z off there). Then start. The program runs .010 passes cutting air the first couple on a portion only hitting the highs and then we get a full clean up of the panel abd stop the program. Now flip the panel, auto Z again off the thickest area of the job visually, and now I want to machine to lets say .8125 and stop.

Using WinCnc and VCpro, is my only option to touch off and then create another toolpath setting the material thickness at the height of the touchoff and toolpath it that way? Or is there a way I can zero off the spoil board and set a start height via touching off and machine to .8125 and stop? If that makes sense.

Was hoping to come up with a work around where say I had a 48" x 48" slab that was thick and thin, I could set the start height and machine to .8125 off the spoil board and stop in .010 passes. The last pass would of course have to be whatever was required if the start height wasnt evenly divisible.

I guess this would require some sort of toolpath in VCpro that would allow me to start at any point I wish in Z, and machine to .8125 which I guess doesnt seem possible.

Sorry for any confusion.

[NormanAlbert]

Hi: If you have Mach 3 you could use one of it's programs based on the piece your working on.

[4DThinker]

When I'm wanting the material thickness to be a set dimension after pocketing out I zero the bit on the spoil board, but instead of using "0" I enter the negative value of the material thickness I set in Vcarve. Then if the top of the material is uneven I still end up with the board and pockets exactly the thickness I want.

4D

[FixitMike]

If I understand you correctly, you are correct in saying that what you are wishing for is not possible using Vectric programs. The toolpath files do not take into account the actual material on the table, they only assume that the material is as described when you set up the toolpath in the program.

If this is something you do often, then you could set up different toolpaths for different material thicknesses, and use the one that suits for the 2nd side.

[nicksilva]

When I'm wanting the material thickness to be a set dimension after pocketing out I zero the bit on the spoil board, but instead of using "0" I enter the negative value of the material thickness I set in Vcarve. Then if the top of the material is uneven I still end up with the board and pockets exactly the thickness I want.

4D

everything 4D said. bottom to top.

[Mark Bolton]

4D,
Thanks, That gets me on track. As already posted its understood VCpro has no idea whats going on on the table only whats input. I think my solution is going to be to have the VCpro file open at the machine, touch off, document that height, and input it into the VCpro model and tool path from that point. Going to give it a go here in a moment.

Thanks for everyones input. My brain gets all twisted up with the myriad of options and possibilities.

[Mark Bolton]

If I understand you correctly, you are correct in saying that what you are wishing for is not possible using Vectric programs. The toolpath files do not take into account the actual material on the table, they only assume that the material is as described when you set up the toolpath in the program.

If this is something you do often, then you could set up different toolpaths for different material thicknesses, and use the one that suits for the 2nd side.

Thanks Mike,
Thats what I was thinking of doing initially but it would get a bit tedious having different files for different panel sizes and thickness increments in the .010 range.

We are surfacing with a large fly cutter and the depth of cut threshold when running pretty fast isnt very forgiving. Once the part is down to and even thickness we can run wide open but on the first few passes watching for high spots. We just got a pendant on line which makes a WORLD of difference being able to be there for the first pass and throttle back the feeds and then once we know were clear just run it wide open and leave it be.

Thanks so much for your input.

[Pete Cyr]

Is there a reason you would not set zero to the CNC table top and machine a fixed dimension to make the glue-up a standard thickness?
Why bother trying to find the high spot on the panel if you going to machine it flat?

[ger21]

I would touch off to the low point, and just program to remove a small amount, like .01".

[tomgardiner]

Touch off on the high point and surface with a pocket of a depth greater than your worst case scenario. Set pass depth to .01" or so and run the program until the surface is flattened then stop. A bit slow but no adjusting the files.

[Mark Bolton]

Is there a reason you would not set zero to the CNC table top and machine a fixed dimension to make the glue-up a standard thickness?
Why bother trying to find the high spot on the panel if you going to machine it flat?

This would apply to rough sawn glue ups, over sized glue ups, as well as surfacing irregular slabs. I figured I'd need to find the high spot if my tool wasnt capable of hogging off all the material in a single pass. We are surfacing with a large cutter and the pass depth would have to be within its capacity so assuming a panel may be glued up at .980" or something like that and needs to come down to .8125 in .010 passes it would require ma couple passes.

[Mark Bolton]

I would touch off to the low point, and just program to remove a small amount, like .01".

We do that when we can but often times the high points on a panel or surfacing a slab are much larger than the tool can take in a single pass. That was the thought of touching off on the high and then surfacing to the final dimension in passes that work for the tool.