CNC or Router for Trimming Veneer?

It's hard to understand exactly what you are trying to do but it makes me want to say "Think. There must be a harder way"
Not meant as an insult. It's just that veneer is so easy to work with without all the setup effort.

@shipwright I'm simply asking if trimming veneer (the kind you apply) with a router is an issue.

I guess you could hold down the veneer with tape and try to CNC shapes with it. Since you know how to program a CNC machine you might consider using an inexpensive laser cutter instead for cutting out shapes in veneer. I think routing thin sheets of veneer the bit might tend to catch the veneer and the edge might flop around unless it is taped down well.

I just straight cut veneer with a special straight edge I made from a design used by Paul Schurch.

You have to match the bit to the application. You want to ensure the router bit shears the correct direction and the wood fibers being cut are being supported.

Like Shipwright says, it's hard to understand what you're trying to do.
If you could supply us with a sketch or a better explanation it'd be easier to make recommendations.

I want to apply a wood veneer to MDF. Then I want to run that veneered MDF through a CNC (or router) and do both the cut and the essentially the veneer "trim" in the same operation.

Oh, you can probably do that. If you can do plywood you can do veneered surfaces. Make sure your veneer is glued down properly and I wouldn't anticipate any problems.

If it's just square parts, it's much easier to cut your blank, then use a down shear trim bit to trim veneer.

I want to apply a wood veneer to MDF. Then I want to run that veneered MDF through a CNC (or router) and do both the cut and the essentially the veneer "trim" in the same operation.

- wilschroter

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This is easy to with the the right bit. If the veneer is face down, use an upcutter. If the veneer is face up, use a downcutter. If the veneer is on both sides and a clean cut is necessary on both faces, use a compression spiral.

I want to apply a wood veneer to MDF. Then I want to run that veneered MDF through a CNC (or router) and do both the cut and the essentially the veneer "trim" in the same operation.

- wilschroter

This is easy to with the the right bit. If the veneer is face down, use an upcutter. If the veneer is face up, use a downcutter. If the veneer is on both sides and a clean cut is necessary on both faces, use a compression spiral.

- JAAune

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^^^Basically what he said.^^^
I would add that I wouldn't hesitate to use a compression spiral in any of those three scenarios. Because the shear is toward the center and will keep everything nice and smooth.

This is easy to with the the right bit. If the veneer is face down, use an upcutter. If the veneer is face up, use a downcutter. If the veneer is on both sides and a clean cut is necessary on both faces, use a compression spiral.

- JAAune

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I have always been confused about using compression bit on a CNC. Do you use it just for a last clean up pass? It would seem to me that if you are using it to cut out a pattern, until you reach the down cutting spirals, it will try to lift the veneer on the top?

Compression bits do tend to chip the upper veneer while ramping down into the material until the downcut spiral reaches the wood. There are many ways to avoid that and it's up to the operator to decide the best approach. One method is to do a zig-zag ramp so the bit is climb-cutting long enough to let the bit get into the wood before it reverses direction. Another method is to plunge part way before ramping. A third is to cut the part 1/32" over-sized then do a full depth cleanup pass.

It is certainly possible to replace a downcutter or an upcutter with a compression bit in most scenarios. From a production standpoint, it's often desirable to use upcutters wherever possible as they're much cheaper, run cooler and improve dust extraction. Compression bits really shine when doing single-pass cuts at high feed rates which provides fast, clean cuts and maximum bit life.

Thanks for the clarification. When you said trimming veneer I thought you meant just veneer. If it's properly glued to a substrate it's a totally different thing.

Compression bits do tend to chip the upper veneer while ramping down into the material until the downcut spiral reaches the wood.
- JAAune

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I always set the ramp-in at an angle to the perimeter of the part so that wouldn't happen. So as the bit descends at an angle to the spoilboard, it's also getting closer to the perimeter. Does that make sense?

Once it reaches the perimeter, the upshear is cutting up, and the downshear is cutting down. No chipout. It even works for the worst possible material for chipout: melamine on particle board. Man~! I HATE that stuff. It chips if you look at it funny.

self delete Laser

I always set the ramp-in at an angle to the perimeter of the part so that wouldn t happen. So as the bit descends at an angle to the spoilboard, it s also getting closer to the perimeter. Does that make sense?

- Underdog

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Yes. That makes at least 4 solutions to stop compression bit chipping. I believe VCarve calls it lead-in and we use it occasionally.

Most of our plywood/veneered panel cutting is done with down-cutters since the CNC is equipped with pressure rollers and a vacuum table so the spoilboard is usually enough to prevent chipping on the bottom.

Thanks for the tips on using the compression bits.

Wouldn't it be easier with a hand held router and a flush cut bearing bit?

Intro to Ramps and Leads - Part 44 and 45 - Vectric For Absolute Beginners