Cutting Plywood with a router bit

My question is what cuts are you planing to make with a router bit.

Normally if you are trimming a side I’d only have the router bit cut maybe 1/16” or so. I’d cut almost to a line with a saw.

But again what kind of cut are you making with the router?

-- What happens in the workshop stays in the workshop. No wait that doesn't sound right. Karson Southern Delaware karson_morrison@bigfoot.com †

I think Popular Woodworking has an articule this month on using plywood router bits…

-- Never board, always knotty, lots of growth rings

To cut plywood without tear out you want to use a spiral compression router bit. It has flutes that are sharpened up cut and down cut so it compresses the wood fibers as it cuts leaving a clean edge. Or you could also use a down cut spiral bit if you don’t need both sides to be perfect.

-- David, South Windsor, CT "I love the smell of sawdust in the morning"

Hey Karson, Im not sure I know what you are asking. The panels are square shaped right now and I want to just cut a curve on the top. The only reason I want to cut them with a router bit attatched to a jig is so they will all be exactly the same. I have never had much luck cutting close to the line and then sanding them on my drum sander. Hope this helps, and thanks for the response. I will also have to check out Popwood, thank you for that.

Hey Brad Nailor, is that the name of the router bit, spiral compression, or is it the upcut spiral bit? Both sides do need to be clean. The way the bunk beds work is you use both headboards on the bottom bunk when they are together then you switched them around when you unstack them so you have to flip one of the panels. Kinda complicated because all the brackets have to be put on exactly in the same place on the legs so they can be switched.

I was of the impression, wrongly I guess, that they were already cut with the circle. So what you are trying to do is cut the circle edge with a circle cutting jig.

You could make multiple passes, cutting part way each time. A compression bit has the capability to cut without splintering on the edge. I’ve just never been a person to try to do everything in one pass. It’s easier to control when you don’t have to put so much pressure on the tool to get it to move.

Router bits will burn if you don’t have them move with a little speed. The material leaving the router bit helps to cool the bit. Cutting slow causes it to burn. Cutting fast is harder to push the router and the bit, and if something goes wrong it also goes fast.

-- What happens in the workshop stays in the workshop. No wait that doesn't sound right. Karson Southern Delaware karson_morrison@bigfoot.com †

I would do the following:
Create the circle jig for the router
Use the jig to draw the curve on the plywood
Use a jig saw to remove most of the material, stay 1/16 off the line
Use the router jig to finish cut the curve

What others have said about the 1/16”, but I’d also do the final router cut as a climb cut. Yes, it’ll be harder to control and the router may get away from you, so be careful and make sure that jig is firmly in place, but you’ll get a smoother edge, and as long as you’re only taking off a 1/16” or so it’ll be doable.

I’d consider taping the edges, but for that kind of cut I don’t know if you’ll just end up gumming up your bit.

-- Dan Lyke, Petaluma California, http://www.flutterby.net/User:DanLyke

Ok guys, thanks for the tips! Now, exactly what kind of router bit would be best, upcut spiral, downcut spiral, flush trim bit, etc?

To avoid tear out I used to sandwitch (top and bottom face) of the workpiece (the board) with sacrifical 1/8”
ply. Make 3 to 4 pases for 3/4” thick ply/board. I use normal straight bit .
Alternativelly, draw the curve line and cut using jigsaw and clean the machine marks with sandpaper.

-- masrol, kuala lumpur, MY.

If I were doing what you describe, I would use the jig and make two cuts. The first cut would be proud if the the radius you want and the second would be 1/32nd or 1/16th shorter as a clean-up cut and the set up would be repeatable from cut to cut.

I would us a straight 3 bladed bit steping it progressively deeper for each cut on the first go around. The second (clean-up) cut of 1/32 or 1/16th smaller radius would be cut in one pass. Use a steady feed rate, slow enough not to cause tear our but fast enough not to burn the wood or the bit.

The most important advise regardless of the set-up you use is to use a sharp bit. If you don’t have one, it’s time to increase your tool inventory.

-- Tom Landon, Lakeland, Fl. When you're through learning, you're through.

The bit you want to use is a spiral compression bit. That will give you a clean edge on both sides due to the way they sharpen the bit, it cuts from both directions “compressing” the wood fibers as it cuts. We used these bits along with up cut and down cut only in a CNC router. Always gave clean cuts in cabinet grade hardwood plywood. Just to make it easier on yourself you might want to cut most of the waste away with a jigsaw, and then use the router bit….just for ease of handeling..that has nothing to do with how the bit will cut. Unfortunately, cutting the waste off up to 1/16” off the line and using a regular straight bit doesn’t guarantee that you wont get tearout..it might help your chances but the way the bit cuts is what causes the tear out not how sharp it is or how much material it is cutting. Climb cutting helps also but you are still using the same straight bit. See one here at Rockler

-- David, South Windsor, CT "I love the smell of sawdust in the morning"