1/2 birch ply frayed underside edge

Hey guys and gals,

Quick question, when cutting ply with a downcut but the topside is perfect but the backside is a frayed mess. Without doing a ton of research I’m guessing I may need to cut a little deeper through the ply?

If not what am I missing / what do y’all do to keep the underside from fraying.

Put an image to see what you toking about ?.

Most likely you need to completely and smoothly support the plywood at the bottom — alternately, rather than downcut, for throughcuts use a compression bit? (will require careful adjustment of feeds and speeds)

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I’ll have to wait for my next cut and I’ll toss one up. At work right now.

Yea I probably need to buy a 1/8 compression finally. I’ve been using it alot more lately than the 1/4.

I guess the only way I’d explain it is… Using an upcut on plywood the fraying you get. Like that but on the bottom

What’s underneath the plywood? if it’s solidly supported that should prevent fraying.

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I feel like it is but I guess it might not as well as I thought. I usually have 3-4 clamps down in it on the sides.

Should be plenty, is the wasteboard all cut up? In theory it should only be able to fray if there’s nothing supporting the wood underneath.

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Plywood is very rarely flat… clamps around the edge might not be enough.

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Unfortunately splintering with plywood with thin veneer is common. You can improve the final product by cutting the exterior perimeter about 1/8" larger than you want, and then do a 100% depth final pass. An alternative is to not cut all the way through with your CNC, and then use a flush cutting router bit with a roller and your manual router.


Down-cut bit is good for good quality top surface, and up-cut good for bottom. Roller bearing trim bits are neither up or down cut, but have 100% vertical cutting edges.


Appreciate it! I still need to buy a 2nd router for now I want a cordless but the router and then batteries and a charger costs a good chunk. I may just detach my cnc router and use it.

Get a compression bit. I cut 3/4" red oak plywood constantly. I started out using upcut and downcut bits, but also found they caused fraying on either the top or bottom. Other people here commented about the quality of the surface (spoilboard) directly below your material. They’re right. The smoother/flatter it is the better since, as someone said, plywood, 1/2" for sure, tends to bow. However, I let my spoilboard get fairly chewed up before replacing it, but with a compression bit I have little to no problems with fraying. In my experience, the only time compression bits cause fraying is when they start to dull. It’s gradual, but helps me know when it’s time to buy a new bit.

Compression bits are a bit more money, but well worth it. And don’t be enticed by some of the cheapo bits you may find out there. Buy the better stuff. I use Whiteside and am happy with their products for the money.

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Yea my spoilboard needs some spots replaced. The fraying isn’t always bad. I guess it’s never bad just on smaller stuff it takes a while to sand. I use an Amana bit and it’s pretty new so I don’t see it being dull yet so I’ll check the spoilboard first.

I use one of these on 3/4” maple plywood:

Works like a champ! I forget speeds/feeds off the top of my head, think maybe 100/50 0.125 DOC at 20,000rpms? I posted it around on the forum somewhat recently, not currently at my PC to check.



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