Draw Boring Technique




This is a little “mini-tutorial” about the technique of draw-boring. This technique uses dowels to reinforce mortise & tenon joinery. The only difference is, the holes in the tenon are “bored” slightly offset, so the tenon is “drawn” into the mortise as you drive the dowel into place (hence the name).

I used this on the workbench trestle bases that I made for Woodguy1975, and also for my own workbench project.




HOW IT’S DONE


First, the M&T joints are all fitted. This includes grain and color matching the pieces, etc — the project needs to be dry fitted exactly the way you want it to go together. Once that is all completed, all the pieces are marked with a pencil so they can be taken apart and put back together the same way. I just numbered the joints.

Next, the pieces are marked for the locations of the dowels. I did this while the project was assembled, to avoid confusion. The project is then disassembled, and the mortises are bored out for the dowels. I drilled from the inside faces of each piece, and drilled all the way back into (but not through) the outside face.



Next, the project is re-assembled, and the locations of the holes are transferred onto the tenons. You could use a dowel center finder or an extra drill bit for this, but since I don’t have those I just marked them with a pen:





The holes in the tenons are bored just slightly off center – probably less than 1/16″ – toward the shoulder of the tenon.



This leaves a little “meat” on the outside of the bore hole when the M&T is re-assembled – it looks a little exaggerated in this picture because of the angle:



The dowels are cut long enough to reach all the way through and engage on the far wall of the mortise. The leading end of the dowels are chamfered slightly to help get them though:



During the assembly phase, the M&T joinery is glued up and assembled just as usual. Glue is applied to the dowels, and they are nailed into place with a hammer. You have to be careful not to drive the dowel in too far – you could blow out the back wall of your mortise!

Finally, it’s just a matter of cutting away the excess from the dowel, and smoothing it all out with a plane and/or sander:



One of the biggest advantages that I see with this technique is that the project can be assembled in stages, without using any clamps at all. The dowels draw the joints tight — you can see the glue squeeze out while the dowels are driven into place. As long as the shoulders of the tenons are square, the assembly will be pretty well self-squaring.

1 comment:

  1. Great site and even better walkthroughs. Keep it up!

    ReplyDelete