View Full Version : Flush trim bit question

01-22-2018, 03:01 PM
Once in awhile i get tearout or bearing scars while flush trimming the top or back.

Currently using a 3/8th 9mm diameter bit. Will a larger diameter flush trim bit help with less tear out and bearing scar. For example a larger 1/2 inch or 3/4 inch diameter bit?

01-22-2018, 03:18 PM
In my limited experience those are two separate issues. A larger bearing or moving the router more quickly may help prevent scarring, but a larger bearing probably won't help so much with tearout and moving quickly will likely make tearout worse. To avoid tearout, avoid moving the router in the direction a tearout chip will go (start from that direction and move in), move at a moderately slow but steady pace, and perhaps consider a spiral down-cut bit.

Michael Smith
01-22-2018, 05:05 PM
I belive the larger the cutter the more tearout you will get not less. A spiral bit will give you less tearout. With a spiral downcut being the one that should give you the least. You should only get scaring from the bearing if it is not functioning properly.

01-22-2018, 05:53 PM
I use a 1/2" bit but I start with a larger bearing and run the router in the climb cut direction. I then change to the 1/2" bearing and only have a small amount to remove, again a climb cut. It is harder to control the router when climb cutting but much less chance of tearout. I use a nylon coated bearing to reduce marking the sides.

01-22-2018, 07:23 PM
As an alternative, don't forget that a simple well sharpened thumb plane will take care of trimming back those back and top over hangs in a jiffy with less danger of a tear out. I'm not against power tools and use them all the time, but this is an area where I like to get up close and personal with my uke. I love seeing the curls come off and the skritch-skritch sound. There is a danger with this method though in that you can gouge your sides by mistake which is not a good thing. Not good at all. I also put 2 or 3 coats of a 1 pound shellac cut on the edges before I cut. Makes things much more forgiving and less stress. Also it is much quieter. Very meditative. Try it.

01-23-2018, 01:01 AM
Got it thank you. Yeah im using the stewmac routing method to prevent tear outs.

Didnt know they made nylon bearings, will look into that.

Yes i also shellac before routing , and i also used mini plane to flush trim before i bought a laminate trimmer. Maybe ill go back to old school and just do it by hand again.

01-23-2018, 01:05 AM
Maybe it could be my bit. I was using a bosch brand bit with almost flawless trimming. I bought this new cmt brand one same size , and it really tore the top and bearing scars on the first use.. Easy fix is to router it out for binding .