Veneer Replacement Technique

[Don Stauffer]

The reason I'm thinking a CNC router is that I could only replace the burl veneer and leave the 2" frame at the outside. The edges and corners of the frame are where I noticed it's not flat.

The other thing is one could actually make the top flat with the router, using the lowest point as a reference and routing the rest to the same height. Then as a second operation, route the area for the veneer. Probably using 3 of the 4 corners to form the plane for the router would work since the corners are probably lower than anyplace else.

[Bert McMahan]

Before you start building a CNC take a straight edge and check the table for flatness. I doubt it is perfect, and a CNC has no way to measure imperfections within the parameters you are describing.

Actually, lots of CNC controllers can do a probe scan of a surface and adjust their profile based on actual surface height. It's mainly used for printed circuit boards, which need to be engraved only through a thin layer of copper. You will want to make sure the CNC machine you buy actually has this feature, but it's available on even very cheap models. The touch probe is as simple as a piece of conductive material (like a flat piece of copper or aluminum) to which you connect a wire and lay on your part. Another wire is connected to your frame, and the machine drops the tool down and detects when the tool touches the part. You do this with the spindle off, of course.

[Brad Shipton]

Bert, I am aware of that, but not in the price of the different machines he listed. The controller to collect that data is more expensive than the machines listed, and you need software that creates the 3D surface.

[Bert McMahan]

Bert, I am aware of that, but not in the price of the different machines he listed. The controller to collect that data is more expensive than the machines listed, and you need software that creates the 3D surface.

It's actually doable with the Shapeoko, one of the machines he mentioned. It's a little finnicky but not bad. The Carbide3D controller will accept a probe input, and since his part is wood you can make a probe with a piece of flat copper and a wire. You use a regular tool as the probe, which completes the circuit when it hits the target. The controller senses this and notes the position. Here's a fairly DIY way to do it:

https://hackaday.com/2014/12/12/mill...an-uneven-bed/

Here's some info from Planet CNC, which makes a 4-axis controller for about $175:

https://planet-cnc.com/how-to-use-moveable-sensor/

And how to use their Warp feature to compensate:

https://planet-cnc.com/how-to-use-warp-feature/

Basically, instead of doing the warping in CAD, they do it to already-processed Gcode. It's also doable on many of the very cheap controllers that will run GRBL.

It won't be quite as full featured as doing it with a full-on CMM but it's definitely not expensive and you don't need anything more than some free software.

[Brad Shipton]

That is interesting Bert. I am familiar with the industrial versions and own software that can make these type of surfaces. I think one needs to temper their expectations in this machine class. I have a 4'x8' machine that has frustrated me at times, and I expect there is a lot of learning to get all these steps to work. I am not sure I would do it for this table unless it was a family heirloom.

[Bert McMahan]

I expect there is a lot of learning to get all these steps to work.

Now that, I can agree with

[Mike Henderson]

In my opinion you're making this a lot more complex than it is. What I'd do is use a drum or wide belt sander to sand the panel flat. Then I'd lay up veneer with a veneer edging of the same species and color as the existing edging. Use whatever veneer and pattern for the center panel. You could even do a radial match if you want to be fancy.

Lay that on the flat panel, preferably using a caul and a vacuum bag. When cured, put an edge around the outside to hide the joint between the wood of the substrate and the veneer. Done.

If you can't do it and don't want to learn veneering, shop the job out to someone who does veneering.

Mike

[Phil Mueller]

If it were my table, I’d create a simple jig similar to a slab flattening jig and with a router remove all the veneer to just a HAIR below the existing solid wood border. Square up the corners with a chisel. I’d glue in new veneer...whatever pattern you want. For that size table you could make a couple of plywood or MDF cauls and clamp down the glued veneer. Put a layer of felt on one side of the caul that goes against the veneer to make up for the slight recess of the veneer (wax paper in between the felt and veneer).

If you have any gaps between the new veneer and existing edge, you could fill it, or I would run a small stringing inlay.

Once it’s all down, carefully plane/card scrap the existing edging down to level with the veneer.

[Don Stauffer]

3D printers have a similar feature, inaccurately called "mesh bed leveling".

[Don Stauffer]

Phil, that is almost exactly what I had in mind when I first made the post. But I got responses discouraging that plan. Your "slab flattening jig" was not part of my original idea, though. But I did think of it later, and then I thought basically all that is is making the router have a reference plane with the correct orientation to the table, and that made me think a CNC router would do the same thing.

What I'm discovering about CNC routers, though, is they would require I remove the top. I could try dissolving the glue, but your way could be done with the top still attached.

I'd be interested how you'd fashion the jig.

[Phil Mueller]

I’d have to experiment a little, but was thinking just a 3/4” frame, a bit longer than the table width with an opening in the frame that would allow you to see what your doing, but still give good support to the router base. If for example the opening is two inches wide (really just depends on the size of your router base), clamp it down, do a 2 inch area, then move it, do two more inches, etc. Not the quickest, but would get the job done.

If you have a router guide, use the guide against the outside of the table edge and do the perimeter of the veneer first.

Set the router depth to the thickness of the new veneer, plus the frame thickness, plus a hair deeper.

[Don Stauffer]

I see! Doing it in small sections allows the jig to be narrow enough to support the router on both sides. But it does seem like the frame would have to be supported on both ends to the same height no matter where the 2" area is, so it would have to sit on pieces that went all the way across the table. Something like:

Image1.png

[Phil Mueller]

That’s what I was thinking. And yes, the two frame pieces that sit on the hardwood edge of your table would need to be long enough to move completely from one side to the other. You could also make the router support pieces thicker if you want a little more support.