drawbored MT joints for workbench

[Chris Henke]

I am making slooooow progress on my first workbench build. It is a roubo style bench made mostly of fir. I finished the tenons for the stretchers and started putting holes in the legs to drawbore the tenons when the bench is assembled. Another in a long list of stupid mistakes: I didn't research the best practices for drawboring BEFORE I started drilling holes. Most of the info I've found suggests putting the drawbore holes about 3/8" from the tenon shoulders, but I drilled holes in the legs either 1.5" or 2" from the shoulders, so that's going to put the drawbore pegs right in the middle of the tenons (the tenons are 4" wide by 2.5-3" long by 1/2" thick). I have NOT drilled the holes in the tenons yet, just through the mortises in the legs. Each of the holes is 1/2" thick to accept oak dowels, which I also now realize is a little on the large side for drawboring.

So my question is how to proceed from here, which I think really depends on just how likely it is that I will split the tenons when I drive the drawbore pegs through. It is not likely, then I will just proceed with the current holes and 1/2" pegs. If there is likely to be trouble, then I could potentially just re-drill new holes closer to the shoulder of the tenons and then just put a plug in each of the first holes to fill it up.

Thanks for any advice!

Chris

[Steve Voigt]

Chris, i'm not sure about the chance of splitting the tenons, but it doesn't seem that likely. My main concern is the 1/2" tenons. Are they double or single? If single, they are much too thin to resist the stresses they will be subjected to on a bench, imo. If you look at chris schwarz's various plans, the tenons are like 2 - 2&1/2 thick. I recommend you use additional methods of securing the top, like lag-bolting it to stretchers. I think i would just skip the drawboring.

[Chris Henke]

Thanks, Steve. To be clear, I'm referencing the tenons on the stretchers for the base. There are also much thicker tenons that mate the the legs to the top. I do wish now that I had made the tenons on the stretchers thicker than 1/2", though I already have the mortises cut in the legs, and I'm not sure how easily I could widen them. Thanks for your advice,

Chris

[Adam Cruea]

Thanks, Steve. To be clear, I'm referencing the tenons on the stretchers for the base. There are also much thicker tenons that mate the the legs to the top. I do wish now that I had made the tenons on the stretchers thicker than 1/2", though I already have the mortises cut in the legs, and I'm not sure how easily I could widen them. Thanks for your advice,

Chris

I used 1/2 inch drill holes on my hickory bench to drawbore the stretchers into the legs and the legs into the sled feet.

I made sure my holes were right in the middle of the mortise. So for my 4" legs, I measured 2" in from each side to center the hole on the through-mortise and them made two holes about 3/4" in from the edges of the mortise and tenons.

I had no cracking or splitting and the thing seems bomb-proof and honestly, quite solid.

[Charles Wiggins]

Chris,

If i were in your shoes I'd probably get some scrap and recreate the end of the stretcher and the mortise section of the leg and try it and see what happens. I am assuming that they are fir since you referenced that. I don't have much experience with fir so I don't even have a clue whether it will have a tendency to split or just deform when you drive those 1/2" oak pegs.

[Jim Koepke]

If you can make the mortise and tenon a bit bigger you might want to try this.

If you do not make the draw bore offset to radical, your current set up should also be fine.

jtk

[Randy Bonella]

+1 with Jim, My bench is Doug Fir and I used 5/16" pegs to draw bore the MT joints. DF deforms pretty easy so odds of splitting I think are pretty minimal as long as you don't have a large offset and the MT joint is pretty snug. I don't think location relative to the edges matters much, and you really don't need much of an offset for this to work. My offset was about 1/16", give or take a little. Make sure that you taper the leading edge of the peg enough for it to slip into the offset holes. Also if you plan on gluing that joint put a little glue on the peg just before you place it and drive it home. The glue acts as a lubricant but you need to drive it in pretty quick as it starts to make the peg expand. If you are not going to glue the joint then use a little bee's wax on the leading edge of the peg. That also helps so you don't have to pound so hard to drive the peg home.