Half-Round Router Bit - What Am I Doing Wrong?

[Matt Culik]

I have a 3/4" half-round router bit WITHOUT a guide bearing. I'm trying to put a bull nose on a 3/4" piece of birch plywood that's going to be used as a painted shelf. Was doing some test cuts and am losing my mind trying to figure out what I'm doing wrong. This is my first time using this kind of bit.

I have it mounted in my router table and the height seems perfect. HOWEVER...

I'm trying to do small passes like I normally do, but am finding that when the workpiece comes out the finished side of the router bit, it's no longer against the (straight/planar) fence. This isn't a problem for the first half of the work piece, but things become unstable towards the end and I keep gouging my workpiece.

It seems like my only option is to make the bullnose in one, full-depth pass where the center/deepest part of the router bit recess is flush with the fence.

Am I thinking about this correctly? That's a lot of material to remove in one pass!

Thanks in advance!

[Mel Fulks]

My guess is you are cutting on a plywood edge. It would be better to glue a strip of real ,solid wood onto the plywood. That will make a
much smoother surface .

[Greg Quenneville]

I think you could do it in one pass, but the surface finish may suffer. I use a round straight rod* helpful to align the fence to bullnose cutters to minimise snipe on the trailing end.

*never discard a dead printer without salvaging the ground round rods inside. Very useful things.

[Mike Burke]

Matt, it's hard for me to explain but, you must be taking material off the front edges for it to be shy or off the exiting fence a little. Here is a video that might help. I have a done a bull nose on bench tops before , on solid wood, and haven't had much trouble. It take some pretty precise setup thought to get it just right. They do make " Bullnose" router bits that might help. I hope this helps some.
https://www.youtube.com/watch?v=AeCOhn37zRE

[Lee Schierer]

If your bit is actually a round over bit, then lower the bit slightly and move the fence forward toward the work piece to leave a small flat area on the edge of your work piece. You can clean this up with your final sanding.

The other option is to use a split fence where you adjust the out feed side so it is slightly closer to the work piece than the in feed side so that it supports the cut area right from the start. The split fence will prevent the snipe you are getting with your present setup.

[Patrick McCarthy]

I think i would lower the bit so that it is only cutting 3/8 or so, and then flip it over and do the other 90 degree edge (if you want a bullnose). You should be “rounding over” or softening just the 90 corner of the two faces, not creating an entirely new 3/4 face. Hope that makes sense.
Step back and think if you were doing it with sandpaper. You would attack the 90 degree edge to soften it, but would not go full width. Then flip the board over and attack the 90 degree edge on the other side.

A cut edge on plywood might take more work to finish and prep for paint, than just gluing a hardwood strip to the front and shaping it. Good luck. Patrick

[John TenEyck]

Either do as Mike said or make a shim and glue it to the outfeed side of the fence. The thickness of the shim = the gap you are getting between the outfeed fence and finished bullnose when the workpiece is still tight against the infeed side of the fence.

The first option requires you to leave a tiny flat on the workpiece; the second option does not. However, the workpiece will be narrower than it was before you routed the bullnose by the thickness of the shim.

John

[Rod Wolfy]

Assuming that you're using a router table, are you using a feather board to keep the piece up against the fence for the entire cut?

[Myles Moran]

I used a thumbnail bit on a table recently - similar to your bullnose but but slightly less depth. When I set it up, I used an edge guide on my router because the table was too big for the router table (but same idea here). I made 2 passed to take off the edge because it was hickory, but otherwise I would have made 1. Then I got the bit as absolutely close to making a full cut but leaving a really really narrow uncut section - maybe about 1/32 or less. Once I had the guide setup I made a pass on all the pieces for the table top.

That small unrouted section was quickly touched up with a sanding sponge and after a few passes you'd never know I cut it slightly short.

[Rick Potter]

I suspect you are cutting the full surface of the piece, which means you are basically getting snipe at the end of the cut.

If this cut is the way you desire, try cutting a practice piece for about 3 inches and stop and turn off the router. Look carefully at the outfeed side of the router fence. There should be a gap where the piece does not touch the fence. Find a spacer that fits that gap, formica, cereal box, etc. Clamp it to the fence, and continue the cut. It should now work.