A Sliding Door #3: Mortising, part 1

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Blog entry by Mark Kornell posted 11-02-2014 03:01 AM 1476 reads 0 times favorited 0 comments Add to Favorites Watch
« Part 2: Milling maple lumber Part 3 of A Sliding Door series Part 4: Mortising, part 2 »

Spawn of Satan broke through the gates to hell last night. And this morning. Not too difficult, really, if some human forgets to close the gate all the way.

The cat “screamed and leapt” at the dog, according to my daughter. Kind of like a Kzin, I thought. Needless to say, I sense there’s some urgency to get the door done.

Here’s what the current “gate” looks like

Not sure that the shoes are adding anything.

The track will be fastened to the ceiling. There are 4 or 5 joists it will cross, so plenty of places to put lag bolts.

For joinery, I decided on doubled loose tenons, 1/4” thick. The plan calls for 56 mortises, and I’ll be using a router.

I can plunge 2” with the 1/2” bit, but 1 3/8” with the 1/4” bit. Therefore a doubled 1/4” loose tenon joint would have more glue surface than a single 1/2” joint.

If I were building a typical side-hung door, I’d want to make the mortises a lot deeper. 3”, at least. But because this door will be top-hung by the stiles, the joinery to the rails does not have to resist racking. Each rail will simply have to support a vertical load, and pretty light at that – the weight of the rail plus some of the weight of the glued-in panel directly above. You could probably argue that anything more than stick and cope joinery is overkill. Overkill is underrated.

First, I lay out the placement of the rails onto the stiles:

Then flip the stiles onto their edge and lay out the mortise plan:

The middle 4 rails are all 4 1/2” wide. Allowing for a 1/2” deep groove for the panel, I end up with mortises that are 3” long.

Not shown, but the top rail is 5 1/2” wide, so the mortise will end up being 4” long.

Also not shown, the bottom rail is 9 1/16” wide. Doing that as a single, fully glued-in joint would pose some wood movement issues. So I decided to make 4” long mortises at the bottom of the rail, which will be fully glued. Above that will be 3” mortises with the tenon allowed to float. This will endure the rail stays aligned but be able to move.

The mortising jig is pretty simple:

But to get the mortises in the right place, you need to create spacers. This pic shows the calculations:

The jig was built so the centerline of the mortise being cut is 1 3/4” from the fence. So in this case, the centerline of the back mortise is 1 1/16” from the front edge. Subtract 1 1/16 from 1 3/4 to get an 11/16 spacer:

2/1000ths out. I can live with that. The critical part is that you need to always clamp the jig and spacer to the board from the same side.

So clamp the jig and spacer in place to visually check the placement:

Yup, that works.

Getting ready to cut the first mortise:

I really like that DW735 router, btw.

Change the spacer, cut the second of the pair and check:

28 mortises later, both stiles are done:

Setting up to cut the mortises in the end of the rails. I really need to get my bench finished, but in the meantime, this kind of face vise works well:

I just need to mark the center of the mortise, as that is how I align the jig. And remember to clamp the jig to the correct face of the rail.

Set up to plunge:

And… it is supper time. I’d rather not plunge mortises in the end grain and let them sit for a couple of days so I shut it down. Might get back at it tomorrow, but for sure on Monday.

-- Mark Kornell, Kornell Wood Design

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