Month: June 2016

Drawboring Mortise & Tenons – Low Cost Roubo 4

With the joints all tuned up and ready for glue up, it’s time to drawbore all the mortise and tenon joints in the base. Drawboring pulls the joints tighter, strengthening them and reducing the effect of any slop in the joints. With the advent of modern glues and clamps, drawboring is not very common in furniture these days, but there seems to be a resurgence in interest in this centuries old technique. I find drawboring to be an easy way to add a lot of strength and character to a joint, so I use it whenever I can.

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Base ready for glue up and drawboring. Also, my extremely messy living room. 

Because the joints are pretty huge in this bench, I went with 3/8″ dowels. For regular sized joints 1/4″ would be a better option. The concept of drawboring is very simple. A 3/8″ (in this case) hole is drilled through the mortise, and the joint is dry fit. With the joint dry fit, the centre of the hole through the mortise is marked on the tenon. The joint is then disassembled, and a hole is drilled through the tenon, 1/16″ to 1/8″ slightly offset towards the shoulder. With the holes drilled, the joint is glued up, fit together and a peg is driven through the holes with a hammer or heavy mallet. The peg should go through to the other side, pulling the tenon shoulders closer to the mortise and tightening up the joint.

Drawboring the mortise and tenons in the stretchers

Drawbore pegs peeking through.

I always use hardwood dowels, in this case oak. I also like to use a contrasting wood for the pegs – drawboring demonstrates quality craftsmanship, so show it off! It is a good idea to whittle the pegs to a point before driving them in. I usually rub a little paste wax on the pegs before driving them through as well. I’ve had people tell me this is overkill – but then I’ve never had a peg  break on me or a drawbore attempt fail, so I’ll keep overdoing it.

On a project like a bench where you have a large number of joints to drawbore (in this case, 12), it’s vital to plan ahead. Once you glue the joint and fit it together, you have to drawbore the joint together quickly. I like to do them in batches – I went with the left legs and stretchers at once, and the right legs and stretchers at once, followed by the long stretchers to complete the base. This is also the point where you want to move the parts to the final location of the bench – it gets heavy and unwieldy after this. Like I mentioned earlier, this bench was meant for a room in my basement, so I moved it all downstairs. When you drive the pegs in, don’t be scared to put some heft into it. Give it a couple good whacks and you should see the peg poke through on the other side.

The photo above shows the legs being clamped together. You don’t actually need to clamp it, the drawbores will pull the joints tight enough. I didn’t clamp the other side.

Drawbored base showing the through mortise and tenons

Base complete!

With the base all glued up and drawbored, give it a few hours for the glue to dry, and use a flush cut saw to trim the excess off the tenons and the drawbore pegs…and you’re done!

P.S. If you are planning on installing a leg vise, you will need to account for that at this stage (or earlier preferably). I’ll cover that in a future post.

 

Posted by Prairie Artisan Woodshop in Builds, Split-top Roubo Workbench, 0 comments