multiple parallel through mortises


aliebling

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I'm building a bench where a center shelf is joined to the middles of the side walls by 4 through mortises (the tenon side looks like a really big finger joint).  I cut the mortises first, but wonder if anyone has any recommendations/best practices for fitting the tenons.

 

I laid them out based on the mortises (but extra point, figuring I can trim the ends after they fit), cut them out (probably too conservatively) and have been paring them back with a chisel (due to the lack of space between them cannot use a plane), but it feels like it's going to be hard to keep the ends nice and square and beautiful. Having to make four of them all fit just makes it worse.

 

Advice?

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Sorry yes...here are some photos.  it wouldn't let me post them from my phone earlier.

 

One side is now done and the fit is great, thought it's not perfect.  I did it with lots of straight edge marking, chiseling, test fitting with clamps (which showed the tight spots on the wood) and more chiseling.  I can live with the results, but a more reproducible technique would be nice.

 

 

 

 

20200919_165838.jpg

20200919_095658.jpg

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I think you did well by cutting the mortices first. Careful layout is key, of course. To keep the fit precise, a 'paring block', just a square piece of stock clamped along the cut line, will give your chisel more registration surface to help keep it square.

If the shelf isn't too long to fit, I'd probably use a box joint style jig on the tablesaw to cut the fingers. Honestly, your cuts look pretty good. When you glue it up, mix sanding dust from the side walls into the glue, it will help disguise any tiny gaps around the tenons.

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Those are llooking good.  When I do such things I clamp the tenon board to the mortise board such that the end of the tenon board cover about half of the tenons and then scribe marks for the tenons by place an exacto knife against the inside face of the tenon and making a deep scribe mark (nick) on the corner of the tenon board.  Then use a square to extend the lines with a scribe (exacto knife) as needed.  Even then I cut conservatively and then pare to the scribe lines.  Test fitting as I go.  Be sure to mark which side of the board is up.

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Thanks all...my procedure was more or less what Ronn outlined and it worked pretty well.  I'm happy with it.  The top of the bench attaches to the walls with dovetails, so I need to test fit everything and hope the top (with dovetails) and the shelf (through mortices) match in length.  wish me luck!

 

After that, the last bit to do is a support between the shelf I just finished and the top (with the same kind of through mortices above and below) so I've got one more chance to practice these.

I'll post up some photos when it's done!

Note: I didn't want to cut these on the table saw due to the length of the board...and because part of the plan for this piece was to do all the work by hand.

 

P.S. Definitely mortices first.  anything else would have been madness.

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9 hours ago, aliebling said:

P.S. Definitely mortices first.  anything else would have been madness.

I am definitely mad then. I much prefer to cut the tenons first. I find it a lot easier to mark the mortices from the tenons than vice-versa, especially if the mortice board is thick in comparison to the size of the tenon so that the mortice is a deep hole.

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I think my feeling about mortise first comes from doing these all by hand.  I feel much (much!) more confident chiseling out a perfect mortise and then paring down a tenon to fit it than I do freehand cutting a perfect, straight, square tenon.

 

If I was cutting the tenons on a table saw (or was a better freehand tenon cutter), then I'd feel comfortable cutting the tenons and using them as a template for where to cut the mortises.

 

Machining the joint with a table saw, drill press, and router I'd lay out both sides and I don't think it would matter much which I did first.

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17 hours ago, aliebling said:

I think my feeling about mortise first comes from doing these all by hand.  I feel much (much!) more confident chiseling out a perfect mortise and then paring down a tenon to fit it than I do freehand cutting a perfect, straight, square tenon.

I work totally by hand also. I don't cut the tenon first when I cut a "normal" M&T, such as with a leg and rail, but I do for the type of joint you are doing. I think that is purely for ease of marking out. As always, accurate marking out is crucial and I find doing the tenon first and marking from it much easier than accurately transferring sizes from the middle of a panel to the end of a board.

 

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