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Things I hate: Gouging my own eyes out with a spoon, and being pulled away from a project for more than a couple days.
It’s been a week since I’ve been able to devote any time to the legs of my workbench. This morning I sneaked into the shop and hid there for three hours. My plan was to start mortising the top to receive the legs. The legs, meanwhile, had other ideas.
These legs are still a little wet. They’re not squirting like FreshenUp gum, but they are a little moister than I like. After I cut these honking-long joints and departed for Indiana (and then New York), the joints dried out a bit in my absence and a couple of them twisted a little.
So I fetched my big Buck Bros. chisel this morning and pared away. They’re in good shape , for now. But you can bet that tomorrow morning I’m going to bust my hump to get the legs driven into the top.
– Christopher Schwarz
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Dave,
I’ve written a lot about drawboring and used it a lot. It’s great in the right application. Should you drawbore delicate cabinet doors? Nope. How about workbenches? Probably. Wet stuff? Yes. Stuff too long for your clamps? Absolutely.
Is it risky to use? Yup. Apply it wrong and you’ll ruin your day.
Timber framers live and die by the technique. Woodworkers use it in limited applications.
Just my 2 cents.
Incidentally, the Timber Frame Engineering Council has the following to say (taken from http://www.tfguild.org/publications/tfec1-07.pdf
3.1.2.1 Holes for pegs shall be sized such that pegs are held securely by friction after installation, but pegs shall not be damaged by crushing, mushrooming, flexure, or splitting as they are driven into the hole.
3.1.2.2 Draw boring shall be permitted where it can be demonstrated by full-scale or prototype tests or extensive experience in use that wood splitting in the tenon and damage to the peg do not occur and that the strength of the connection is not compromised.
It is certainly the case that drawboring can cause a joint to fail, so the size/location of the peg and the amount of offset needs to be weighed against the size of the joints, the amount of "meat" left on the tenon and mortise, the species of wood, etc.
Tests have shown that pegged joints in general are actually weaker than a well-made glued joint without the peg. (Presumably due to the preload and the loss of glue area.) One or more pegs can be useful if the joint is already plenty strong and we want it to last longer than the glue.
Drawboring in particular can be useful if you don’t have long enough clamps or if you don’t want to glue the joint at all.
On the subject of mortise/tenon, I note that you’re a fan of drawboring.
Quoting Goss from "Bench Work in Wood" page 110 –
"The practice of drawboring is not to be commended, and, if indulged in at all, great care and discretion must be exercised. In many cases, it puts a strain on the joint which is nearly equal to its maximum resistance, and but little strength is left to do the work for which the joint is made. Frequently, the mortise or tenon is split and rendered practically useless."
So, what’s the straight dope on drawbores?
Do they still make FreshenUp gum??
From what I remember, it ranks right ahead of Fruit Stripes for flavor retention.
Can I use the "they twisted overnight" excuse for when i cut something crooked?
Get a hold of some I-beam clamps, and some strong helpers to tighten them down. If necessary, use a caul across the bottom of opposing legs, and across the top of the bench. A long enough caul means you can add more clamps, and while it feels like folly, it works.
Once the clamps are on, and TIGHT TIGHT TIGHT, then use a mallet on the bottom of the legs.
The tension on the clamps is a whomping pre-load. The mallet is just to overcome stiction.
Hump busting is only reserved for panic mode. And that is only reserved for getting assemblies back apart when thing go awry.
At least, from underneath, you can sneak in a few wedges, and fill a gap or two.
We’ve been doing a fair amount with greener wood for chairs and toys. There are benefits, to be sure. But I don’t do green dovetails. 😉