[maker4444]

I had a first attempt with 18mm plywood yesterday, using a 6mm 2 flute upmill and cutting in two passes. Cut slow as per Gwizard for Fine Finish.

I was naive: the results were pretty horrible!

- overheating from sawdust buildup (despite strong compressed air jet);
- very hairy top face, somewhat hairy bottom of cut;
- generally a poor finish on the cut faces;

Any general suggestions as to how to do better much appreciated.

But in particular I'm concerned about making 6mm wide slots through this 18mm thick wood.

Any ideas how I can make deep, narrow slots whilst beating the sawdust and avoiding hairyness?

(And not having to stand by the machine holding a jet / vacuum !)

[ger21]

Try one of these, making 3 passes. Rough the slot on the center, and do a full depth finishing pass removing the last .5mm.
5MM COMPRESSION ROUTER FEM 1" CUT .150 UPCUT LENGTH 1/4 SHANK

Even then, unless they are razor sharp, you'll still get some minor fuzzing on the edges. If your slots run perpendicular to the grain, the fuzzyness will be worse.

[Routerfiend]

Hi
You might have better luck by using a 1/8 single flute to pierce the top few layers . It tidies up the top edge then you can hog out the bulk of the material without any problem.

[maker4444]

@ger21 that's insightful. Now I have a plan!

I guess plywood is not the best thing to cut on a router.

Whereas Trespa (phenolic resin board) comes out perfectly.

What sorts of wood give a really Nice edge finish?

[Routerfiend]

Plywood comes in various grades the tighter laminations like Birch faces ply are usually pretty good but a remedy for the cheaper ply`s is to make up a pva solution ( Wood glue & water) and paint it on the surface that you want to cut ,either over the whole sheet or locally where you need the cut. This bonds the surface and stops a lot of the shredding that you are seeing. The weaker the solution the better for the first coat and then a more robust coat to finish. Give each coat a half hour to dry & you`re good to go.

[maker4444]

Fantastic. Going off to study ply. Thanks!

[Zorbit]

You can use a two flute carbide downcut tool and a sacrificial MDF bed underneath. Cut it in three passes, with the last one going 2mm into the MDF. The cut will be excellent when the MDF is new, as it is properly supporting the back of the ply. As the MDF becomes worn out the cut quality will deteriorate, but you can re-surface it. Note though, a re-surfaced MDF bed will never be quite as good as the virgin one was, the surface is softer and not as flat.

[maker4444]

Didn't know that would work.

Thanks @Zorbit!