Best technique to round over tenons?

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Forum topic by Picklehead posted 11-22-2013 09:28 PM 3443 views 0 times favorited 9 replies Add to Favorites Watch
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1041 posts in 1893 days

11-22-2013 09:28 PM

Topic tags/keywords: mortise tenon shoulder router round rounding

I’m doing my first mortise and tenon piece, and I’m wondering what different techniques people use to round over tenons when making mortises with a router (1/4 inch in this case). My thought was to use a flush cut saw to cut a kerf at the shoulder of the tenon then use a chisel to split/shave off a 45 degree chamfer, starting at the end of the tenon and working towards the shoulder. That seemed to work in my pine test pieces, however on one piece I actually removed too much and narrowed the tenon a bit, which would allow it slip within the length of the mortise a little. I know I could do floating tenons, and I may in the future. My main concern is to avoid damaging the shoulder or face of the workpiece, so if I rasp it or something else how do I avoid that? Before I go reinventing the wheel and cutting kerfs in the shoulder of the tenon and sticking in thin protective pieces of cardboard, I figured I’d ask the people who know. (Or maybe I should be squaring the mortises by hand). Thanks for any advice.

-- You've got to be smarter than the tree.

9 replies so far

View JustJoe's profile


1554 posts in 2002 days

#1 posted 11-22-2013 09:43 PM

I just use a corner chisel to square the mortises, but if you don’t want to do that then just a few swipes with a decent rasp will round the tenons.

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View nwbusa's profile


1021 posts in 2250 days

#2 posted 11-22-2013 11:07 PM

Yeah, I also square out the mortise corners with a chisel. But I agree with JustJoe, if you want to round off the tenons, a rasp will do the trick.

-- John, BC, Canada

View theoldfart's profile


9611 posts in 2415 days

#3 posted 11-23-2013 12:26 AM

I’m going to echo Joe and John, use a mortise chisel to square the ends. Use a chisel the same width as your mortise and the chisel will follow the sides all the way down without twisting giving you a square end. I do this all the time except I hand drill to remove the waste, but the concept is the same. Good luck.

-- "With every tool obtained, there is another that is needed" DonW ( Kevin )

View Picklehead's profile


1041 posts in 1893 days

#4 posted 11-23-2013 12:51 AM

Thanks for the info. Guess I’ll make up some test pieces and see if I can rasp them properly.

-- You've got to be smarter than the tree.

View bondogaposis's profile


4682 posts in 2315 days

#5 posted 11-23-2013 12:54 AM

I’m one who’d much rather round a tenon that square a mortise. I use a chisel for the most part paring away a little off the corners at a time. I use a rasp too but you’ve got to be very careful that you don’t gouge the shoulders just keep the rasp away from the shoulder and finish up w/ chisel.

-- Bondo Gaposis

View Picklehead's profile


1041 posts in 1893 days

#6 posted 11-23-2013 01:55 AM

Thanks, Bondo. That sounds like a good mix of techniques. I’m leery of mucking up the shoulder, which would be visible on the finished face of the tenon board.

-- You've got to be smarter than the tree.

View MJCD's profile


540 posts in 2335 days

#7 posted 11-23-2013 02:27 AM

For something completely different…

I mount the tenon in a clamp, use a coin to create a half-moon tracing; use a razor knife to take off the bulk material, then sandpaper pulled down and back & forth to smooth the rough edges into a half-moon: works every time.

-- Lead By Example; Make a Difference

View MAKZ06's profile


69 posts in 1768 days

#8 posted 11-23-2013 02:35 AM

I always used a round over bit in my router table and get as close to the shoulder as I can. Then a sharp chisel run down the face of the tenon to the shoulder easily takes off the last little bit you can’t hit with the router bit.

View GOOD LUCK TO ALL's profile


418 posts in 1692 days

#9 posted 11-23-2013 02:39 AM

Cut the tenon 1/8” short, (the shoulder an 1/8” long) rasp the corners then cut off another 1/8” of the shoulder getting rid of any damage that may have happened from the rasp. Then just have to chisel the little saw cut left.
Just a thought, I’ve never actually done it.

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