Thread: Cutting circles with router - tear out

Don't know if it is possible . . . .

Drill the hole for your trammel point all the way through and flip the panel to cut with the router.

Make the cut twice. The first cut is 3 or 4 MM larger than the desired size. The second cut is the actual cut.

Make the first cut with a band saw, again a few MM larger and then the final cut.

Make the cut where you're getting the tear out as a climb cut. Just make the climb cut very thin and really hang on to router as it going to want to climb through the cut.

Would a down cut bit make a difference? It might slice across the grain more.

From the underside with a nail as my axis for the circle jig, I cut through 40mm blackbutt using an Upcut spiral router bit. Using an upcut bit from the underside meant the top side was being sheared "down" towards the underside. Resulted in a nice finish. Took it in 4 passes.

For smaller circles, I just make a perfect MDF template. Then using a dual bearing flush trim bit in my router table, I double sided tape the template to the solid timber stock and shape it. Only cutting down the grain, flipping the board over for each quarter circle as required.

For larger circles, dining tables for example, I use a router trammel and of course I rout against the grain for two out of four quarters of the circle. It leaves a pretty average edge finish for sure. But since it is just a dining table, I clean up the edge with a block plane in a few seconds and the job is done. Spiral bits will give a better finish, but better is still "pretty average".

Originally Posted by qwertyu

Any tips on how to get a cleaner cut when cutting above circle? the blue section?

You're cutting into the grain there, so the absolute best way to do it is to flip the thing over so you're cutting with the grain for that section. Not always practical though.

Originally Posted by rrich

Make the first cut with a band saw, again a few MM larger and then the final cut.

Always remove as much waste as possible before going to the router; your bits and motor bearings will thank you and smaller cuts don't tear out as much.

Originally Posted by rrich

Make the cut where you're getting the tear out as a climb cut. Just make the climb cut very thin and really hang on to router as it going to want to climb through the cut.

This will also help, but I would only ever do it with a template and bearing because if it starts to grab you can pull away. With a trammel-type jig, the router is fixed to the job and, if it grabs, it will start running circles around the whole thing faster than you can blink. Did it once, never again.

Originally Posted by Fuzzie

Would a down cut bit make a difference? It might slice across the grain more.

Up cut or down cut will slice equally well, the only difference is whether the breakout is on the top or bottom.

Originally Posted by elanjacobs

Up cut or down cut will slice equally well, the only difference is whether the breakout is on the top or bottom.

This is true if you're only cleaning up a cut edge. Using a downcut bit there will be some upward force exerted by the bit on the router. If you're taking a full bit diameter cut with a downcut bit in multiple passes the upward force can be very considerable. For full depth cuts in one pass the best result will be achieved with a compression bit regardless of whether you're doing full bit diameter cuts or just cleaning up an edge. Once you get the compression bit started in a single pass full bit diameter cut the waste is ejected out the previously routed groove so the problem of the waste having nowhere to go is greatly alleviated.

#1, make sure your router bits are sharp .... especially the very end.
#2, make light cuts near the surface
#3, use no smaller than a 1/2 inch router bit for this work.