Breaking Quarter-Inch Shank Router Bits Using a Dovetail Jig

If your jig won't accept half-inch-shank bits, you may break a lot of bits working with plywood. March 10, 2008

For those of you who make dovetail drawers using multi-core plywood such as Baltic birch, Appleply, Europly, etc., I was wondering if you have a problem with your router bits breaking off. I have been using 5/8" 11 ply Euro maple to make my dovetail drawers using a hand router and a Reliant dovetail jig. I have been having bad luck with dovetail bits breaking. At first I was using the low cost ones I got from MLCS - they work great on solid wood, but shear at the shaft on the plywood after milling maybe 8-10 4" drawers. Then I decided to upgrade after a dozen or so breakages and went with the CMT bit. These broke too, but they broke at the knuckle between the shaft and the cutter. Then I went to Whiteside - these felt much better than the CMT bits, but I only got about 6 drawers from one before I had to put in another; these also broke at the joining area between the shaft and the cutter. By the way, 1/4" shaft and a guide collet. I cannot use a 1/2" shank on this dovetail jig. Frustrated.

Forum Responses
(Solid Wood Machining Forum)
From contributor E:
I haven't had that problem, but I upgraded to an Omnijig some years back and use 1/2" shank bits. Assuming you're not forcing the bit through the cut too fast, maybe the plywood is just too dense for dovetails? I guess what you need to decide is how much are you going to spend on bits before upgrading to a jig that allows you to use 1/2" bits. I can generally get a half dozen kitchens or more out of a bit before having to replace it.

From the original questioner:
I would run 2 years or so on the same bit using solid wood like maple or poplar. But this plywood is almost solid glue because there are so many plies.

From contributor J:
I used the Omnijig 24" with 1/2" shank bits. The 1/4" shanks will fail in no time. I recently bought a 15 spindle Dt, so the Omnijig (almost new) is on the market.

From contributor T:
I had that problem years ago. I found that a cheap single edge carbide tipped router bit worked well and eliminated the breakage. Believe it or not, the best one I could find was a Craftsman bit - no lie. Try it out - I guarantee it will cure your problem cheap. I now have a Macoser unit, but I remember those days well.

From contributor F:
Another vote for 1/2" shanked dovetail bits. Even with the Omnijig, the engineers knew the 1/4" shank bits will break, but that's what they supply with a new jig. I broke the two original bits and switched to 1/2" shank with no further breakage. Just too much torque involved in routing plywood dovetails for a 1/4" shank.

From contributor G:
1/2" shank. Never broke one in apple ply or anything.