Tenons

[Casey Carr]

Finally got around to working on some tenons I’ve been meaning to cut for a few years now...how tight do they need to be? Takes a mallet to get it to seat fully. Through tenons on 1.75” square maple. As tight as they are, hoping the glue won’t need to do much.0363DC6A-D9A2-47CF-9C84-8C90DD91129E.jpgCF56B0F4-E6AA-4893-A5D4-D9FFDC9FBB04.jpg

Never done tenons before, so figuring out my jig and what all shortcomings it has was fun. And I decided I wanted double tenons like an idiot on the first try. Had to check that it was square to the table every time I swapped the wood around. Finally got it squared up and hopefully it will stay that way. Couple screws that hold the angle adjust screw weren’t tight, but then it made it a bear to tighten the adjustment handle without it throwing it out of square again. I took the horizontal handle off so I would quit pushing on it and instead just push the body. Think that was throwing things off as well. Was also swapping the t slot bar back and forth between the slots to get to the distances I was needing, but gave up on that and started measuring from the opposite side. That bothers me though as tolerances stack up. It’s a rockler tenon jig, are they all this frustrating?

[Patrick Kane]

I typically shoot for a fit that doesn’t require a hammer but doesn’t come apart when you shake on it a bit. In terms of how many thousandths of an inch that is, I have no idea. Sounds like your fit is a hair too tight. Like you need 1 swipe of a shoulder plane on each cheek.

[Thomas McCurnin]

I don't have this jig, but it is similar in design to my 30 year old Delta cast iron one.

I don't use my Delta jig much anymore. I'm not sure why, but it sits in a box. It was too fussy for me and I had to go through a dozen or so test pieces to get it dialed in. I've also tried to use the Leigh Jig, and got it to work and it was super-precise, but the learning curve is very long. Indeed, you've got to read a 50 page manual and watch a video and it helps to have two dedicated routers for the jig, one for the mortise and one for the tenon. So that jig sits in a plastic tub for now.

I've also used a radial arm saw with a dado blade and it seems to give me very good results without a lot of fuss. It will take a few minutes with a block plane, shoulder plane, or sanding block to clean things up. And there may be some hand chisel work, but it was faster than either the Delta or the Leigh jigs. I have also used my table saw with stop blocks and a miter gauge. The gauge has to be 100% square. These also need some clean up.

Check out videos by Paul Sellers for making them by hand. He is amazing and can pull out a tenon in about five minutes with a router plane. I've got to get one of those someday.

Lately, I build my own jigs, usually one-off jobs with a 1/4" MDF top fitted with a guide bushing slot, supported by a long piece of plywood, clamped in my vise. While constructing a one off jig is time consuming, it has an advantage of being very accurate and repetitive. Mine is very simple and generally a one-off jig. Do a google search for tenon jig under images and you'll fine some amazing tenon jigs that guys have made.

As for the tightness of the fit, it has to be tight enough that once inserted it won't fall out on its own, but is easily inserted and removed by hand. That seems to leave enough space for the glue. That's my rule of thumb, but others I'm sure will have better ideas than I have. Alas, some days I feel like an incompetent piker in the woodshop.

[Casey Carr]

Now I have to find a tiny shoulder plane that will fit between the tenons...kidding of course! I’ll hit it some more with a wide chisel. It seems to be the last 1/8” or so. Can’t quite tell what end it’s hanging up in though. I think some of it may be my jig being out of square slightly so the tenons are tapered? Maybe, I’ll check again.

[David Eisenhauer]

Casy, Thomas nailed it just above - tight enough to not fall apart (pre glue, test fit stage) when you hold the whole thing upside down, but not so tight that you need some serious hammer work to get it together. As to using/adjusting jigs, you may have hit on why many wood workers have drifted over to the hand tool side to hand cut their M&T joints. Sometimes it feels like we all need to become Brian H machine tool clones to dial in the machines to get two joints in a row to come together without lots of machine/jig tweaking. The main thing with tenons is that the tenon be square or parallel, not twisted. A too tight or too loose tenon can be fairly easily adjusted, but an out-of-square one requires lots more work to correct. The gap between the twin tenons is usually cleaned up with a chisel and it is usually planned for the gap to correspond to a nominal chisel size so that it is easily accessed.

[Carl Beckett]

Sometimes (especially hard maple) as I rock them back and forth putting it together, it puts a small shine on the high/touch spots. Then I know where to take material off.

[Brian Holcombe]

How did you cut the mortises?

[Carl Beckett]

btw - you might want to get a softer hammer. I use a bead filled one from HF.

Mashing all the wood fiber with a hard mallet will cause you some grief later on with finishing (even if you plane out the dents there will be compressed fiber underneath that could swell during finishing)

[Casey Carr]

The gap between the two tenons is 1/2”, so not a problem there for doing it by hand, but I chopped a couple of the mortises by hand. Was not a fast process for me. I think it was taking me about four hours to get through the full 1.75”. And it was very hard on my chisels. Edge looked serrated if I didn’t hit it on a leather strop after every few hits. Wasn’t the best at keeping the end walls vertical either, face walls were okay though. I wound up buying a Baleigh mortiser to finish cutting them after doing three or four by hand.

And this will be the base for a work bench, so no finish, and even where I’m hammering will be cut off when I round the edge of the bottom rail off.

[David Eisenhauer]

A serrated tip on the chisel meant that the edge was chipping. A fix for that is to increase the angle of the bevel face to the flat back. Mortise chisels are typically sharpened at around a 35* bevel to help prevent chipping and premature dulling. As you stated in the original post, you did not start on an easy first-mortise type. Rubbing chalk or even a pencil across the inside of the mortise before test fitting the tenon will reveal the tight spots on the tenon if the "shiny" spots mentioned above don't show enough. Use a narrow square down in the mortise to check for true 90* vertical mortise walls. Work the mortise over first to be sure it is as correct as you can get it, then adjust the tenon to fit that particular mortise. I used a Unisaw with a Delta tenon jig for years and had fairly good luck with fit up as long as I carefully prepped my stock prior to starting on the tenons. It was not uncommon to have to slightly sand/rasp/pare down a cheek to get it right though.