Furnishing a Sauna Suite #10: Suction-Fit Tenons

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Blog entry by DustyMark posted 02-10-2021 10:02 PM 444 reads 0 times favorited 0 comments Add to Favorites Watch
« Part 9: Routing Leg Mortises Part 10 of Furnishing a Sauna Suite series Part 11: Assembling Bench Frames »

My Technique

I’m a hobbyist, not a production shop, so my approach to cutting tenons to achieve a suction-fit might seem tedious. I cut the tenons with the sliding table and tenon jig on my table saw, a band saw and then bevel the edges of the tenons with a file. This technique only works well if your stock is absolutely true, square, and the exact same thickness.

Table Saw Work

My stock is 13/16” thick and I chose 5/16” mortises. That required a 1/4” deep cut on both faces of the board to establish the tenon shoulder. I raised the blade to 13/16” for the top edge and 1/2” for the bottom edge. I left a bigger shoulder at the top to avoid blowing out the mortise at the top of the leg. My sliding table came in handy for the long rails on the benches. I use an auxiliary fence to ensure all the cuts line up with each other around the tenon.

For pieces that clear the ceiling, I like to cut the cheek of the tenon with an adjustable tenon jig that slides in the table saw’s miter groove. This is extremely accurate. You can even sneak up to your final fit by inserting playing cards behind the wood to make 1/100” adjustments. There is a little play in the groove and I use this to my advantage by either pushing the jig to the outside of the groove to keep the tenon tight or pushing to the inside of the groove to loosen the tenon up. It works quite well. I always run a couple of test pieces from the same batch of wood to achieve the fit I want.

The long rails of the bench require the alternate approach of cutting the tenon cheek with a dado blade. I used a test piece to achieve the desired fit here as well.

Close-up view of the cut.

Band Saw Work

I cut the tenon waste with a band saw. This is drama free and safe.

I purposely cut the tenon smaller than the length of the mortise. I’ll then bevel the edges to fit with a file. This allows a place for the glue to squeeze out of the joint during assembly and makes clamping a lot easier.

Hand Work

Here’s a tenon before any fitting. Sometimes a cheek must be shaved down a bit or a shoulder evened up with a sharp shoulder plane. Only a few tenons required shoulder plane work in this batch.

Filing the tenon edges doesn’t take long at all. I settled on this approach 30 years ago and it produces strong joints.

Dry Fit Results

I shaved a little too much off of a couple of tenon faces with my shoulder plane. I plan to use polyurethane construction adhesive for assembly and that should fill in those areas. I also pin my tenon joints with dowels, so that will serve as a mechanical safety for each joint.

View of the changing room benches from the entry. I may need to install an extra leg on the back wall bench. I’ll wait until it’s glued up to see how much it flexes and creaks!

I’ll mortise in a shelf below to hold a fan.


Install braces between the bench rails.

-- Mark, Minnesota

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