All,
As usual about the time I think I know what I am doing reality sets in. I wanted to make several bread bow knives. Fiddled around with some shapes and came up with a template. Laminated some Koa on both sides of a piece of maple. The maple being pretty stable keeps the Koa from potato chipping. I sanded the blank and cut it down to rough shape on the bandsaw. My plan was to use a tracer bit and finish the profile on the router table. I fed the piece in about 1/16 and it grabbed hard and nearly ripped it out of my hands. I tried a couple of more times with the same result. Moved to a 1/4" bit and got the same result.It appears that anything like the 1" depth of cut is not doable. I would appreciate any thoughts or work arounds.
As Stick mentioned, routing can be sensitive to the grain direction. I assume koa is pretty hard so it’ll be a stronger effect. Since you made your own plywood, it seems possible that the grain on one side wants to be routed one way, while the grain on the other side wants to be routed the opposite way. I can think of two things that might help:
Use a spiral bit instead of a straight bit.
Take off less at a time. I’d probably use something like WoodRiver - Router Bushing Set with Case - Brass - 10 Piece | Woodcraft so you can use the same template and swap out different bushings to get closer and closer to your template until finally you don’t use a bushing for the final pass.
I think you can address this by not taking the entire height of the piece at once. Aim to do it in 2 or more passes; do the first 1 or two with a top bearing bit (short height mortising bits are ideal for this) and take 1/4" or 3/8" cut each time. The last pass can register on the piece itself where you’ve already done a flush pass, or on the template.
Also, where possible use a spiral or compression spiral bit; they are much less prone to grabbing than straight bits are.
Top Bearing bits will allow you to control the height of the pass with your router riding on the pattern/template. The last pass can be done on a router table.
I agree with Craig in using a compound spiral bit, but in a larger diameter so that the cut will be a little more parallel to the grain. Also, using graduated size bearings, and working, taking very thin cuts should help. Maybe try some straighter grain wood instead of Koa to get your technique down. I have practiced with Koa many times and I’m still frustrated with grain direction! It’s such a shame that a beautiful wood is so difficult to work with, but when you are successful, it will be worth it!
Thanks for all the help and ideas. I bought a shorter bit with an up/down spiral. Took 1/8 passes and got it done. Probably change the shape of the handle as the boat tail design exposes too much end grain and still grabbed a little. All in all I learned a bit so it was very worthwhile.
