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/diy/ - Do It Yourself


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File: 1.22 MB, 2100x2850, eploded joint and isometric overview.png [View same] [iqdb] [saucenao] [google]
2800015 No.2800015 [Reply] [Original]

I'm making a workbench from salvaged construction lumber. The legs and lap joints are already cut, but I need a strong joint for the shorter stretchers going depthwise. They are just long enough to reach between the legs, but not long enough for tenons. At first I thought of just a butt joint with really long screws, but then I came up with using large dowels instead.

According to the tests of based autist Matthias Wandel, screws sink into the wood as they fail, but dowel joints perform almost on par with mortise and tenon.

The dowels are 20mm in diameter, the stretchers they go into are 60x95mm, legs 75x90mm and the long stretchers 45x60mm.

I plan to glue and screw the laps, though I would prefer not to glue the dowels into the legs, but instead pull them together with long structural screws. This way I could "flat pack" the bench if I need to move it.

So my question is, would all the dowel, screw and counterbore holes packed into the lap joint weaken it significantly? And could I get away with no glue on the dowel joints?

>> No.2800021
File: 120 KB, 3508x2480, Bench Assembly Drawing 1.png [View same] [iqdb] [saucenao] [google]
2800021

Here's the joint test I mentioned: https://woodgears.ca/joint_strength/index.html

You can also see how my design would fit together in picrel.

>> No.2800023

>>2800015
> According to the tests of based autist Matthias Wandel
There is a lot of cool autists out there.
One of the most brilliant of them was testing screw and bolt holding in wood that was tapped with threads.

He found that adding crazy glue to the inside of the threads made them A LOT stronger. Brilliant idea. I forget who it was though, it was years ago.

>> No.2800030

>>2800023
I think I saw that somewhere as well.

> wood that was tapped with threads
Do you mean he tapped machine threads, and used bolts instead of wood screws? That sounds really interesting.

>> No.2800130

>>2800015
I don’t know what you’re making but I don’t think this is what you need. Too many components for very little added strength, 3x20 mm dowels is pretty much anlways overkill unless you’re Dusty Lumber Co. Don’t pull the end grain with screws like that either, it’s a terrible connection even worsened by putting them so close to the corners. 3x8 should do fine any day

For one you can disassemble you’d normally want to glue the trestles, and the top, and remove the connecting horizontal beams to take it apart. This way you’d still have a flat pack. Then put some carriage bolts instead of screws.

>> No.2800319

>>2800015
yes extra holes weaken it
you could get away with using no glue if your dowels are perfectly snug and tight but I wouldn't recommend it to be honest

>> No.2800480

>>2800030
> tapped machine threads?
Exactly. I’d tap them again after the cyanoacrylate cures. You still want beefy threads though… course. And you want the thread depth to be as big as possible.
You can tap big ass lag bolt threads and those massive deck screw threads just by cutting a slit through the threads of a spare screw or bolt with a dremel.