Question about mortises and stability - Woodworking Talk - Woodworkers Forum
 
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post #1 of 4 Old 12-03-2015, 11:02 AM Thread Starter
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Question about mortises and stability

I'm in the process of building a crib out of Ash. The posts are currently going to be 6 quarter ash, the rails are 5 quarter, and the slats are 4 quarter. So the posts will be about an inch thick, the slats 3/4", and the rails somewhere in-between.

I'm using the image below just to illustrate what I mean. Structurally, it'll go about like the picture, although my rails will be 3" wide or so rather than the inch pictured. (I'll add more flair, too ) The uprights will be about 3.5" wide (rather than the 1.5" or whatever this crib has).

I have two questions I'm hoping somebody can help with.

The first is I'd like to make it come apart into 4 sides, so I can store it flat. I was planning to have the four long rails (two on each side, screwed in in the picture) be through tenons (~ 2" tall, 1" wide) with a hole, so I can push them through and secure them in place with a decorative piece of wood through the hole, if that makes sense? I attached a side view of what I'm trying to explain.

My concern with doing that is whether the mating surface will be sturdy enough, in terms of diagonal flex. Basically, on each end of the crib, I would have 4 tenons, where the tenon is 3" tall, 1" wide, and goes through a mortise that is about 1" deep. Without further support and without glue, do you guys think that'll prevent diagonal flexing? Is there a different approach to take there?

My second question concerns the mattress support. I could take the cop out and buy the spring frame, but I would rather just use a solid piece of wood - maybe make a flat frame of the ash, cut a rabbet, and put a piece of plywood in the middle. Attaching this board to the posts is the question at hand.

Most of these designs use a screw on each corner and the metal rails. I was considering doing a shallow (1/2", maybe 3/4" deep) but fairly wide (probably 2" or so) mortise on each corner, and having my mattress support have a tenon that mates up to it. Again, I would plan on not using glue, so I can pull it apart - will this be strong enough?

If anyone can give any input, I'd really appreciate it. Thanks!

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post #2 of 4 Old 12-03-2015, 11:34 AM
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Your new design with the the mortises will be strong. It's really over-kill. Assembly using high quality bolts will be sufficient like in the picture. A child usually leaves the crib at 30 lbs, so there is no use in building it strong enough to jail an adult.
The bolts will allow for quick disassembly.
If you go forward with the mortise and tenon design, it can also be disassembled for flat storage.
The picture shows the mattress support bolted to the frame, this adds more strength to the assembly.
The bed is attached at the top, the bottom and center (mattress support).

Last edited by Toolman50; 12-03-2015 at 11:45 AM. Reason: Bolts over screws for assembly
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post #3 of 4 Old 12-03-2015, 12:39 PM Thread Starter
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Quote:
Originally Posted by Toolman50 View Post
Your new design with the the mortises will be strong. It's really over-kill. Assembly using high quality bolts will be sufficient like in the picture. A child usually leaves the crib at 30 lbs, so there is no use in building it strong enough to jail an adult.
The bolts will allow for quick disassembly.
If you go forward with the mortise and tenon design, it can also be disassembled for flat storage.
The picture shows the mattress support bolted to the frame, this adds more strength to the assembly.
The bed is attached at the top, the bottom and center (mattress support).
I always overbuild everything, it's an addiction.

Ok, I guess 8 tenons (2 per corner) even without glue and even only being 1" long should still hold the crib solidly square, then? My main fear wasn't having it fall down, but being able to push a corner "in" and make the whole thing into a trapezoid or rhomboid sort of shape.

And, that's a point - maybe what I should do is screw in my mattress support, so that it's removable and helps hold the whole thing together.

Thanks for the input!
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post #4 of 4 Old 12-03-2015, 04:13 PM
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If you hinged the corners of he crib, the bed could be folded when the mattress platform was removed. (You mentioned using a solid plywood platform).
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