How to Flatten Cupped and Twisted Wood | ToolsToday

We posted a short video flattening some walnut and 
got a lot of questions there about how to set this   up on the CNC with a cupped or twisted board.
So I figured I’d go into that setup a little   more on this video. Basically I’ve got these 
walnut pieces sitting here, and cut off the   piece that I didn't need.

I’ll save that for a 
future project. You can see how bad this piece   is cupped. There's also a bit of a twist to 
it and I’ll show you how I deal with that.  So we'll take it over to the 
bandsaw and rip it down the middle,   as removing the material like this would remove 
way too much and leave me with basically nothing.  Bandsaw works perfectly for this because it 
doesn't pull the pieces like a table saw would or   bind at all. So it doesn't really care 
about any of that.

So now we're left   with two boards and you can see just how much 
material was saved there. But we still do need   to deal with that twist that is in the board.
So I’m setting up a fence here on the CNC. This   will just be for something to put some pressure 
up against, and you can see that twist there.  So basically I’ll shove a shim underneath it 
until it doesn't rock anymore.

That just puts   some pressure around. And then we'll use some side 
pressure with just a few pieces of scrap plywood   and some brad nails into the waste board. And 
this piece isn't going anywhere. It's being   held in nice and tight. So we can pick up the 
RC-2255 flattening bit. This is a three-wing   insert carbide flattening bit. We'll zero off 
of the highest area and then do a full pass,   just removing anything just to make sure 
that I don't have any unexpected high areas   and end up crashing the CNC or anything like that.
So you can see it just skimmed that top and   removed those high points. And then we'll do 
steps down until we end up with a perfectly flat   top surface.

So essentially as long as the piece 
doesn't move the head of the CNC is parallel with   the waste board. So it's going to create a flat 
surface. You could definitely do this with like   a jointer and a planer in a shop. Unfortunately I 
don't have one so this is the way that I do that.  So we'll remove those from the CNC, get 
everything cleaned out underneath, and then get   them put back down to flatten the other side.
We don't need any shims or anything since the   other side is already perfectly flat.
And again we'll take steps down   until we end up with a nice flat surface. 
So we can end up with two parallel surfaces.  I had a little bit of fun with the dust collector 
on the CNC going around picking up all the extra   dust.

But anyways as you can see here there are 
a couple areas that I missed, but I only need   a three inch wide board so this will work great.
This is another way to do this if you don't have   a CNC. This is just a router flattening jig, and 
it's essentially the same principle as a CNC. So   I can just hold everything down in place and 
then I’ll use the same RC-2255 flattening bit   and we'll go through and make passes, going across 
the grain since this is a really wide piece.  You essentially have the same thing as 
the CNC. You have two parallel surfaces;   the router’s riding on one and creating that 
parallel surface with the slab that's sitting   there, since everything is moving 
nice and square with each other.  So anyways that is another way to 
do that and it works really well   if you don't have a CNC.

And you can see 
the results here are pretty spectacular   as we have a perfectly straight piece.
So I’ll show you a quick version of doing   that on another one. We'll hit all the high spots. 
We'll get everything going down at a step a time,   and then we'll end up with a nice flat piece. So 
we'll flip it over and do the exact same thing.  So the walnut grain is absolutely beautiful. So 
it's always really cool to see. As you can see   there are no ridges on the piece at all. Those 
are the lines that are created when going back   from climb to conventional cutting, similar to the 
lines that are created when you mow your grass.  Hopefully that provides a little bit 
of insight on how you can get pieces   flattened on the CNC as well as on a router sled.
But hopefully you guys enjoyed it.

We'll catch   you guys back out here in the next 
one. Have a great day everybody..

As found on YouTube

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