Router Bit Question

[Andrew Kertesz]

If I were going to use a spiral cut bit in a router table should I go with an upcut or down cut bit? Or does it make any difference. My intention is to cut some box/finger joints if that has any bearing.

[Bill Huber]

I think it would be best to have a down spiral but I really don't think it would matter that much. I have an up spiral that I have been using and it works fine and has not caused any tearout, the reason I use it is because that is the only 3/8 I have.

[Joe Scharle]

I use downcut spirals for RT box joints. Seems to give smoother bottoms.

[Richard Coers]

A down cut spiral will want to lift the wood off the table, up cut pull it to the table. I never use down cut. I have used compression bits at work, but still prefer up cut at home where I am always working with hardwood. Occasionally working with plywood, the up cut still works great.

[Bill Huber]

A down cut spiral will want to lift the wood off the table, up cut pull it to the table. I never use down cut. I have used compression bits at work, but still prefer up cut at home where I am always working with hardwood. Occasionally working with plywood, the up cut still works great.

This is where I get my mind all screwed up, an up spiral bit when put in a table will now be pulling the wood down to the table.
So would that not want to increase the chance of tear out?

[Stephen Cherry]

This is where I get my mind all screwed up, an up spiral bit when put in a table will now be pulling the wood down to the table.
So would that not want to increase the chance of tear out?

That is the concept. A down cut compresses the top layer of wood down, into the cut, reducing the chance for tearing the upper layer of veneer. An upcut, brings it up, more effectively eliminating the chip. I use spiral upcuts with my inverted pin router (basically a fancy router table) and you really don't get much tearout. I have routed some pretty complex patterns, with right angles, and you just cut. I like the whiteside bits for 1/4 and up, and have used precisebits for smaller sizes. My impression is that downcut is more of a cnc tool for plywood, but I have no experience with that.