intersecting mortises

[Noah Wagener]

If you two rails meeting in the same post, how do you control blowout on the second mortise you chop or is it not a concern?

[Isaac Smith]

For me, it depends on the scale of work. In something like a Roubo style workbench, it wouldn't bother me too much. On smaller work, you can put in a sacrificial tenon to back it up while you chop.

[Bob Lang]

Whenever I make mortises, a major concern is leaving enough material so that the piece containing the mortise (or in your example mortises) is structurally sound. If making the mortises removes so much material that the part is compromised, or the method of making the mortises is violent enough to cause damage I would redesign the joint or find another method.

Bob Lang

[Derek Cohen]

This is part of my chair build. Drilled and pared. Do it gently. You can add packing into one mortice when you remove waste in the other (I did not need to do so) ...

Rotating a leg … the mortice for a side stretcher (the right side faces towards the floor) …





Continuing clockwise …





… and finally we see the mortice for the front stretcher …






The tenons are split to intersect one another ...





Regards from Perth

Derek

[Chris Griggs]

For me, it depends on the scale of work. In something like a Roubo style workbench, it wouldn't bother me too much. On smaller work, you can put in a sacrificial tenon to back it up while you chop.

This is what I do. A little blowout doesn't matter, but you don't want to destroy the glues surface with. Just plane down a scrap and stick it in there to support the fibers.

[Shawn Pixley]

Noah,

I do mine just like Derek. If you think you'll blow through, drill it first and pare to square it up.

[John Crawford]

A few of the woodwrights shop episodes available online discuss this, and are always fun watching as well.

I think "standing desk part 1" has intersecting mortises, and he talks about blowout:

http://video.pbs.org/video/2365021451/

[Warren Mickley]

The method I use takes some skill, but is probably faster and neater than some of the other suggestions.

First, imagine the L shaped mortise as three regions: the two side mortise regions and the overlap region in the corner. The worst case is where you make a full depth mortise on one side (or even a little deeper). Then when doing the second mortise the chisel suddenly breaks through and makes the mortise sloppy on the inside, not the end of the world. If you could somehow end the first mortise right at the edge of the overlap region, then when making the second mortise the chisel would always be supported by the material in the overlap region and would not suddenly jump.

What I do is make the first mortise go just a little (half or less) into the overlap region. I do this by eye or by feel; you could measure. Then when I make the second there is still some material to support the chisel and breakout is minimal. Also I can see the side wall from the first mortise so I have a good gauge of the depth I have to go. So I am not overshooting either mortise.

[Sam Stephens]

this is my method as well. i miter the tenons.

What I do is make the first mortise go just a little (half or less) into the overlap region. I do this by eye or by feel; you could measure. Then when I make the second there is still some material to support the chisel and breakout is minimal. Also I can see the side wall from the first mortise so I have a good gauge of the depth I have to go. So I am not overshooting either mortise.

[george wilson]

I used haunched mortise and tenon joints just like Derek's in a mahogany table I made. As Sam mentioned above,the tenons came in so deeply,their long ends were mitered at 45 degrees to fit in for maximum depth and gluing surface as is usual on some good furniture.

[Adam Cruea]

I had the idea to do the mortises like Derek pictured above. I have a craft table I'm making for my wife where the 2 aprons would meet in one leg and I was trying to figure out how to M&T the joints.

Good to know I wasn't smoking crack when I thought of it. I might try George's method, too, with the 45 mitres.

[george wilson]

I learned the joint from old Mr. Simms about 1970. He's the one whose tool chest Roy had on his show.

[Noah Wagener]

thanks all,

I think I'll try what Warren said with a dummy tenon thrown in for good measure. I do not have sharp drill bits or know how to sharpen them. I usually get blowout when i drill through something. For future reference, is there a particular type of bit that is least prone to blowout? I did try drilling the first mortise i did but had trouble drilling overlapping holes. I slide into the adjacent hole even using a lead screw bit.

I can not do mitred tenons because the long rail tenons (it is a workbench) are through tenons so they can be wedged and unwedged and the bench broken down. I did not know about pegged tenons like the ones used in that The Woodwright's Shop video above.

[Adam Cruea]

I use a forstner bit for most of my drillling and don't get blow out. When you're close to the other side, the center should poke through just a little for you to line up with when you flip the piece. Other than that, I've found that you can go very slow and make a nice clean hole with a forstner and not get blow-ouw, too.