Down cut or up cut sprial router bit?

[Lloyd James]

Hi,
I am routing a small blind pocket approximately 13/16 x 1 ¼ x 9/16 deep into a 1 ½ Sq.
Block of hard wood. The pocket is for a doll house type kitchen sink. I tried using a 5/16 Dia., 2 fluted straight router bit in my router table, but I am getting a rough finish on the walls. When I tried a test run with red cedar, I did get a smooth surface, but routing the hard wood I have trouble moving the wood with a smooth motion. Would it be better to use a spiral cutter? I do not know if I should purchase a down cut spiral bit, or an up cut spiral bit?
I can’t believe how much the price of the bits jump so much going from a ¼ Dia.
to a 5/16 or 3/8 Dia. bit. Thanks for any help.

[Rick Moyer]

I believe the general difference is the upcut is best for mortises, pulling chips up from the cut. The downcut should leave the cleanest edge. I only have two upcut spirals and have not had an issue with tearout. You will like using the spiral bits. Get a good one.

[Bryan Wellman]

I use the carbide upcut bits for cutting out templates all the time. The down will definitely give you a smoother cut, but you need to be more careful with bogging the bit because you will be pushing the chips down.


This was a good explanation...

http://www.newwoodworker.com/updowncutbits.html

[pat warner]

Shallow stages ~ 3/32/pass is called for.
Up or down spiral ok, & so is 1/4", see no 12 (http://patwarner.com/faq.html).
Chatter is from poor control not the cutter.
I won't ask you how you can handle a 1.5" square on a router table.
That has got to be one step away from the ER.

[Terry Beadle]

+1 on the liter pass... 1/16th or less. Also make sure to touch up the cutting edges of the bit with a diamond file. Sharp cuts smooth, dull or stained bits don't.