I'm using a CMT flush trim bit on 3/4" birch ply and am finding that the bit consistently shaves off the tiniest bit of wood from the surface it supposed to be "flush" with. Is this a problem with my bit, the plywood or not a problem at all (i.e. operating as designed)?
Cheers
Could you be pushing into the wood too hard? The bearing could be pushing into the plywood edge. Look to see if there is a indentation where the bearing traveled. This happened to me a couple of times until I figured out to let the router do the work; esp. on plywood and soft lumber.
dave
Not as uncommon as you may think: A trimmer that eats its templet. A little bait & switch and also the reason your cutter is trimming templet at the
I had a bit where the bearing was about 1/64" smaller than the diameter of the bit, that would be the first thing to check. If that's the case get out a diamond hone and make them the same size.
Other things which cause this problem is bit defelection, 1/4 shanks are more prone than 1/2" shank. Make sure that the bering is ridding as close the surface that you want to trim as possible. And don't extert a lot of force against or you'll bend the bit a touch just let the router do the work.
"Mitch" wrote
It could be a defective bit. I had this problem with an imported bit from Grizzly. Ruined a laminate job. They offered to replace the bit ... no thanks, gave me my money back but I still worked a day for free. Maybe I should write it off as tuition :>) CMT bits I've found to be of the highest quality so unlikely the bit but not impossible. Test by running the bearing against a very hard surface, like laminate. More likely the problem is that you are holding the router not _exactly_ square with the work or the bearing is crushing the guide material slightly. When you are ripping the ply make sure the blade is set exactly 90 deg to the face.
Hope this helps, Mike
Kenneth Burton, author of "Cutting-Edge Table Saw Tips & Tricks," prefers to use his table saw instead of a router for flush trimming. It's just a tall fence that attaches to his table saw fence, but the add-on fence doesn't go all the way down to the table. It sticks up above the table far enough that the part to be trimmed isn't against the fence. Burton writes that it's easy to line up and a lot faster than using a router. I think I'll give the technique a try the next time I need to flush cut.
-- Mark
Mitch, a late reply here; what I haven't seen others mention is how deep to set the cutter. I like to set the cutting flutes just barely deep enough to cut through the veneer/laminate. Just because they give you 3/8 or 1/2" of cutting flute does not mean you have to use it all, and setting it deeper than necessary make is much easier to tip the router or flex the bit/arbor.
Lastly, I know you shouldn't have to fix a router bit, especially a top of the line CMT, but in a pinch you can fix that bit by sharpening the flutes with a diamond hone. It won't take much.
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