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Forum topic by rrc124 posted 12-04-2017 02:46 PM 1286 views 0 times favorited 7 replies Add to Favorites Watch
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rrc124

3 posts in 232 days


12-04-2017 02:46 PM

Topic tags/keywords: joints mortise and tenon table

For my first woodworking project I’d like to build a polygon shaped, heavy duty work desk. I’ve modeled the desk with all necessary pieces in Fusion 360.

I’d love to get general feedback on my design. More specifically I do have some concerns:

1. I wanted my mortise and tenon joints connecting 100x60mm rails to 100x100mm legs to have 50mm deep tenons with pegs for strength, and my 90 degree joints do accommodate this. Unfortunately due to the polygon with 135 degree angles, I need to adjust my interior joints to only 30mm deep tenons without pegs. Gluing them together, will the joints be strong enough?

2. I don’t have room for the mortise on the outside 135 degree legs so I can add additional rails where the table top sections join. Will this fatally weaken the structure?

3. I’m uncertain about my thin (6mm high) and long (800+mm) mortise and tenons on the table top sections. My thinking here was to one up biscuit joints and add strong connections, but I have no idea if this makes any sense at all.


7 replies so far

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Lazyman

2188 posts in 1444 days


#1 posted 12-04-2017 04:27 PM

A couple of observations before getting into your other questions…

You didn’t mention what the intended use of this desk is. Those are some pretty beefy legs for a desk and a lot of them. The aprons are pretty beefy as well. Might be overkill unless you expect to have 1000 lbs sitting on top of it. Also, if you expect to have a chair sitting inside the cove, there are way too many legs in there to be able to use it comfortably. Not sure you can even get a chair between the 2 center legs and even if you can, you will be constantly bumping your knees and shins with lots of swearing. Purpose of the U-shaped desk is to be able to pivot around so you would want no legs on the inside of the cove which might warrant a completely different design approach.

Also, I think that the height is too low, especially with those 100mm aprons. With 622 mm legs, that only yields a clearance of 522mm or about 20 inches. The top of the seat of my desk chair is about 21 inches above the ground. Might be suitable for a children’s work desk but then way too beefy for that purpose.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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rrc124

3 posts in 232 days


#2 posted 12-04-2017 09:37 PM

Thank you for the excellent feedback! Let me try to address your points:

- This should be a general purpose workshop desk. I intend to have a laptop with docking station and monitor, keyboard, and mouse in one section, a soldering station in another section for electronics, and a glue gun, Dremel, etc. for small jobs in another. I intend to be sitting the entire time. I would want it to stand up to some odd hammering, sawing, whatever, but I do not intend to do any heavy duty jobs on the desk, especially as its height is for sitting and its odd shape is for slotting into a room exactly that shape and size, leaving only the center accessible.

- I wasn’t able to find any dimensional guidance on a work desk of this odd shape, I overbuilt everything because I was not sure what dimensions would be strong enough. It’s good to hear that you consider the legs and aprons oversized because it gives me some leeway to reduce them. Do you happen to know a good resource for sizing these things?

- It’s a great point about there being too many legs. I do intend to sit in the cove. Are there other support mechanisms which would clear the space for legs, but keep the tabletop well supported? I definitely would want to pivot around, but I’m struggling to find a good reference for designs that would support this. I have “The Complete Manual of Woodworking” where I learned about mortise and tenon joints, but I’ve found it surprisingly difficult to find more general table material covering anything beyond basic oval or rectangular designs either online or in the TOCs of books I’m checking out.

- Agreed on the height. In my woodworking book they suggest a height of 650mm from floor to desk surface, but I didn’t properly account for the clearance underneath. Unless I’m prepared to raise the overall height, it seems my only option is to reduce the size of the interior rails surrounding the cove and/or reduce the tabletop thickness. Similar to the above, I need to look for more designs that would continue to support the tabletop while freeing up space and maintaining enough strength.

I think I need a different design.

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Woodknack

12100 posts in 2437 days


#3 posted 12-04-2017 09:52 PM

Agree with everything Nathan said. It’s a really solid design for a work table but not for a desk.

What you need are two solid bases or legs on the outside ends, one large top made from a nice veneered plywood, and either a wrap around support or you could do legs/aprons for the side opposite where you sit. The chair side would be open. (basically it would be supported on 3 sides) You could make the top from solid wood but it would be tricky. Being your first woodworking project, I would build it from plywood.

-- Rick M, http://thewoodknack.blogspot.com/

View Lazyman's profile

Lazyman

2188 posts in 1444 days


#4 posted 12-05-2017 01:35 PM

Think about designing it as 2 desks joined by a bridge between them to form the U shape. I agree that plywood is the way to go rather than trying to edge join a bunch of boards. Just plan to use some sort of veneer or strips of wood to cover the edges. If you use a strip that is 1/2” (12mm) thick, you can more easily round over or at least soften the edges to make it more comfortable against your arms. If you simply google U-shaped desk images, you will see that most commercially available desks use sheet goods for the legs as well. They often use one that runs the length of each side that is set in from the edge that replaces the aprons to support and stiffen the work surface and prevent sagging. You could instead just run a board down the middle, similar to your aprons in the current design, to provide the support needed. If you need an area that can handle a little more weight or pounding for example, you could use a cabinet to support one or both ends. Put some shelves or drawers in the cabinet to give yourself some storage.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View LittleShaver's profile

LittleShaver

339 posts in 677 days


#5 posted 12-05-2017 01:56 PM

If this is being built for a specific wall configuration, I’d consider L or angle brackets attached to the walls at studs to support the bulk of the table and only add legs at the ends of the interior U. Install all the bracing and supports, then drop the top into position and attach. I’d also consider using plywood and maybe beefing up the edges to appear thicker. As I work alone, weight and configuration is a consideration. I’d probably make the top in 2 or 3 sections just so I can handle it.

A great resource for figuring spans and loads for different configurations and wood species can be found by searching for sagulator.

-- Sawdust Maker

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rrc124

3 posts in 232 days


#6 posted 12-09-2017 10:57 PM

Thank you everyone for the feedback! I’m still playing around with much of it, but I wanted to post one design which follows the advice to remove the interiors legs and seek to add some sort of support going through the center. In this design I was imagining something like a steel bar running across to support the center of the plywood desk top. In case my link to the model doesn’t work anyone, here’s a render:

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Woodknack

12100 posts in 2437 days


#7 posted 12-09-2017 11:20 PM

Much better.

-- Rick M, http://thewoodknack.blogspot.com/

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