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Orthogonal mortises into a laminated post

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Forum topic by Jeff Mazur posted 11-06-2014 06:37 PM 817 views 0 times favorited 6 replies Add to Favorites Watch
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Jeff Mazur

69 posts in 766 days


11-06-2014 06:37 PM

Topic tags/keywords: question pine drill press chisel joining

Hi folks,

It’s my plan to build a loft bed for my son. The design involves, among other details, gluing up four tall corner posts from two or three (probably pine) boards, and joining them to the stretchers running between them with mortise and tenon joints. I’m a beginner and for some reason have an uneasy feeling about mortise cuts into the edge side of the glued-up post (especially) if such a cut straddles two of the component boards (i.e. cuts through the glue parallel to the faces. Have I any need for concern about this provided the glue-up is done right? (dead-flat, smooth, clean faces; sufficient and appropriate glue; proper clamping; proper drying time; etc.?) Anything to watch for while making the cuts? (I have no mortising machine, will be drilling with my press and cleaning up with chisels.)

I will add that the closest to a post end that this will occur will be about 6 inches (thinking in terms of the possibility that the lamination could split if cut too close to the end.) The posts will likely be about 4×4, accepting tenons from 2×6 stretchers. Of course, this issue is moot if I can find 4×4 untreated pine but I’ve not yet seen such a thing. Oh, I almost forgot to mention that the vertical position of adjacent stretchers will be staggered by a few inches to avoid interfering with each other or causing weakness at their common corner of the post.

Thanks in advance!

-- Woodworking is a beautiful, physical, cerebral, and noble art.


6 replies so far

View BinghamtonEd's profile

BinghamtonEd

2281 posts in 1831 days


#1 posted 11-06-2014 06:54 PM

The mortises will be fine if your glue-up is done well. I built a bed, not a loft bed, for my daughter. I did what you’re saying, except before I did the lamination, I used a dado set to notch out the middle board. When you glue it all together, the notched out middle board will create the mortise for you, with perfectly square sides. Just make sure you don’t spread glue on the locations that will be the mortise sides. I planed the center pieces of the lamination slightly thinner than the rails, so I could cut a shouldered tenon on the rails. I also drawbored the mortise/tenon (2 pins through each mortise/tenon). It’s solid as a rock.

-- - The mightiest oak in the forest is just a little nut that held its ground.

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Jeff Mazur

69 posts in 766 days


#2 posted 11-06-2014 07:39 PM

Ed, thanks – interesting idea, vacating the mortise prior to glue-up, sounds like it’s a worthwhile time-saver. Using the dado set seems to imply that the face-parallel joints would be through-joints (or at least the mortise would go through.) Not a terrible idea – I could include keyed tenons in the design instead of gluing or drawboring the joints, and not worry about the day that moving this huge beast comes :)

Small world, by the way – I, too am a software engineer.

-- Woodworking is a beautiful, physical, cerebral, and noble art.

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bobro

308 posts in 772 days


#3 posted 11-06-2014 08:13 PM

If you want to have more confidence in your laminations, you can run some dowels through them, as is done in laminated mallets and laminated hand planes. The physics of why this is so effective isn’t intuitive- it’s not a bolt for example- but it works. Plus instant functional decoration.

I’m experimenting with wedged work-holding systems at the moment, laminating scraps for prototypes: ran a dowel through a member that has a wedge passing through it and I’ll be darned if I could hammer the thing apart with the wedge, even with a hasty glue job.

By the way, if you use BinghamtonEd’s method of gluing up to make the mortise, you don’t want the glue in what will be the mortise as he says, and you also don’t want to starve the lamination in that area. So you can put some blue painter’s tape where the insides of the mortise will be, cut it to size with a utility knife. Then you can be freer with the glue and not risk skimping at those junctions.

-- Lao Ma: You are so full of anger and hatred. Xena: Everybody's gotta be full of something.

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Jeff Mazur

69 posts in 766 days


#4 posted 11-06-2014 10:11 PM

Bobro, thx, tape sounds like a good idea.

Regarding the dowel, even though it’s not a bolt, still prevents sidelong movement (shearing force), which must count for something. I may have to pull out my physics book and brush up, it can’t hurt.

-- Woodworking is a beautiful, physical, cerebral, and noble art.

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BinghamtonEd

2281 posts in 1831 days


#5 posted 11-07-2014 01:39 PM

Actually, the dado idea as I used it, the mortise is not be all the way through, but it depends on how you cut the notch. I think I’m not explaining it right…

When I cut the notches, the board was on its edge. When I laminated, I glued the boards face to face. This left a mortise that went about 1/2 into the leg. The width of the mortise would be equal to the width of the center piece, the length would be equal to the length of the notch, and the depth would be equal to the height the dado blade is set at. The width of the tenon would be equal to the width of the center piece of the lamination. This is why I planed mine a little thinner. If you’re working with 3/4” stock, and you make that center piece 1/2”, you will have a 1/8” shoulder on either side of the rail’s tenon which looks better and came in handy when drawboring (the drawbores pull the tenon shoulder tight).

If you were to cut the notch with the board laying on its face, and then glued face to face, you would have a through mortise. The width would be equal to the height of the dado set, and the length would be equal to the length of the notch.

I used knock-down bed hardware from Rockler for the side rails, so I could break the bed down. It’s solid. I used drawbores on the headboard and footboard because it provides a really solid joint, and I didn’t have clamps long enough to clamp across the entire headboard/footboard. It was my first time drawboring, and it was surprising how simple it was. Just cut the mortise & tenon to fit, then remove the tenon and drill through the mortise from the side. Put the tenon in and press it in tight, and use the tip of the drill bit in the existing hole to locate the hole on the tenon, and then shift it over slightly (I went with 1/16” max) and drill that. Put some glue on the joint, put it together, and pound the pegs home. No clamps needed and you know it’s a tight joint.

-- - The mightiest oak in the forest is just a little nut that held its ground.

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Jeff Mazur

69 posts in 766 days


#6 posted 11-07-2014 10:05 PM

Ed, I had a “senior moment” – I was thinking somehow you had meant a dado across a face. The explanation you just gave clears up a lot.

I like the idea of doing up the head and foot boards with drawbore, but this loft bed will be queen sized, as it is for my adult son and his girlfriend, and so transporting even an assembled head or foot board will be a chore due to the fact that they are both wide AND tall. So I will probably do something like leave the joints unglued and snug-fitting, then when assembled, draw and hold them tight with a threaded rod with washer and nuts. Each rod will be concealed in a slot bottom-side of its corresponding stretcher, and will come through its posts into recesses where the washers and nuts can be hidden with some sort of cap or tapered plug. (Got this idea from a Fine Woodworking video describing a beginner workbench project.)

I think one of the coolest things about my design is that I plan to use a pair of torsion boxes resting across the long stretchers as the bed platform, which will make on-site assembly simple yet will provide a secure and rock-solid place for the mattress to rest. Sideways sliding will be prevented by cleats inboard of the stretchers on the undersides of the torsion boxes. And when he breaks up with this girl, I can repurpose the torsion boxes as work table tops LOL!

-- Woodworking is a beautiful, physical, cerebral, and noble art.

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