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Hello

Just wondering if anyone uses their CNC machine to thickness backs and sides or maybe tops. If so what cutter would you use?
Will it do well with figured wood? Just seeing if a cnc machine could replace a drum sander.

Thanks
Kevin

It would be possible, but I think impractical. Understanding workholding is a big part of CNC. How do you hold your stock firmly to the table while a router cuts into it and without cutting into your clamps?

The most likely solution for a large flat piece that needs to be faced is double sided tape (or masking tape and superglue). You would have to use quite a bit of it to be sure your piece doesn’t get ripped off the bed, lift off the table, or move. But you don’t know the final thickness before you cut. Each piece of wood is different. You have to cut, test, cut. Every time you would have to pry the piece off the table and hope it doesn’t break. Then peel the tape off, test, adjust your toolpath, tape back down again. It just isn’t practical. Also no matter how carefully you trammed your cutter, it would still leave ridges you would have to sand off.

Maybe there is somebody out there who can show us a good way to do it? I don’t see it, and I’ve had various desktop CNCs in my shop for about fifteen years.


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Thanks rlrhett your advise is what i am looking for - the practical concerns

Would a vacuum table work?

Possibly, but I’ve never seen a vacuum table on a desktop machine. I used an 5’ x 10’ machine that used vacuum to hold full sheets of plywood. The principal would be the same, just at a different scale. The big CNC had two 15hp motors running the vacuum pump and it sucked the vacuum right through a 3/4” MDF spoilboard. I don’t know what kind vacuum system you would need for a smaller machine.

I’m assuming you have a smaller machine, like a Shapeoko, otherwise if you had the space and money for a large $20,000 $50,000 CNC, you probably would just get a drum sander.


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right its a small machine and its not finished yet.

I thickness fingerboard and bridge blanks on mine--I use vacuum to hold down, and use the same kind of facing tool that I use for flattening out spoil boards. I've never tried doing tops and backs that way though--drum sander seems a lot more practical.

Dave

I never tried it but I spoke to a guy who once tried getting his CNC to handle thicknessing soundboards. He said it kinda works but it was inferior to using a boring old drum sander. The biggest issue is the CNC is rigid and wants to make things very very flat. The soundboard is thin and floppy and doesn’t want to lie perfectly flat and may have slight cup or other warping. So much hassle is involved with work holding to avoid the CNC cutting some areas too thin. Meanwhile you coulda just sent it through a drum sander a couple times, gotten the job done and moved on with your build.

Yes, you can use a CNC to thickness soundboards. Simply use the CNC to cutout parts for a drum sander.




sorry, couldn't help myself.

It could be done on tops using composite brads strategically placed and with a down cut bit.
That said, I wouldn’t recommend it….too risky. If a thickness sander isn’t available use a very sharp plane.