Mortise and Tenon:
The mortise and tenon joint is one of the strongest joints a woodworker can use. It also resists movement in any direction. I am in the process of building a new workbench and want it to be the most solid, sturdy, functional bench I can make (Currently the wood for my bench is sitting on stickers acclimating). So when it came to which joint I should use, the mortise and tenon joint won hands down. For the front rails I will use drawbored through tenons. The end assemblies will be drawbored but the tenons will not be through; I want the front posts smooth and flush with the bench top. After reading many magazines articles, online articles and forums these are the general guidelines I will use:
- Wide: 1/3 the width of the thinnest part of the joint.
- Deep: Over 1/2 of the mortised piece. A through tenon is the strongest.
- Tall: The tenon should be 1/2 the height of the board leaving both shoulders at 1/4 the height.
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Drawbore:
1. Drill a hole through the mortise close to the edge where the tenon will be inserted.
2. Drill a hole in the tenon just offset of the hole that was drilled through the mortise – toward the shoulder of the tenon about 1/32.
One way to achieve this is to use a forstner bit to drill the hole in the mortise. Then insert the tenon, insert the forstner bit in the hole and tap it with a hammer. This should leave a mark on the tenon. Then measure up 1/32 from the mark toward the shoulder of the tenon and drill a hole through the tenon using the forstner bit.
3. Insert the tenon into the mortise.
4. Pound the peg (dowel) into the hole which will draw the tenon deeper into the mortise.
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Tips:
One source recommends applying glue to just the peg. I plan on applying glue to both the joint and the peg.
From what I have read it is best to limit the number and size of the pegs so you don’t weaken the joint. I could not find any hard and fast rules on this but I would think the combined size of the pegs should be around 1/3 of the width of the tenon. I will give an update with the size I use when I complete my bench.
Put a small bevel or chamfer on the end of the peg by rolling the end over sandpaper at a 45° angle.
One tip from David Charlesworth is to drill completely through mortise. This helps prevent the surface grain from splitting out on the far side and removes the need to put saw kerfs in the peg. Once the long peg is driven home a short dummy peg is inserted in the far end to cover the hole.
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References:
The Pegged Joint, Exposed – from Fine WoodWorking.com – via Matthew Teague
Drawbore Joinery — via WoodworkingTips.com
Dowel plates used to make hardwood pegs — by David Charlesworth
-See “My bench frame” section.
Woodworking Magazine Weblog – via Christopher Schwarz
-See “Wedged Tenon v. Drawboring”
Drawboring a Mortise & Tenon Joint – via Loren Hutchinson
A Treatise on The Haunched and Drawbored Mortise & Tenon Joint — by Bob Smalser
