Drawboring

[Todd Zucker]

I would like to do drawbored mortise and tenon joints on a garden bench. This will be my first try.
Is this something I need to practice, or will it suffice to read 10 articles and watch 10 YouTube videos about 5 times each.
The joints are looking good, and i just don’t want to mess them up.

[Joe A Faulkner]

Not that hard. No practice necessary. Just take your time. Dry fit be for boring the hole in your tenon

[ken hatch]

I would like to do drawbored mortise and tenon joints on a garden bench. This will be my first try.
Is this something I need to practice, or will it suffice to read 10 articles and watch 10 YouTube videos about 5 times each.
The joints are looking good, and i just don’t want to mess them up.

Todd,

There is nothing hard about drawboring. Just remember you want the joint to pull to the shoulder, drill your holes and pound your pegs. If you mess up it is no problem just drill out the peg and make it a pegged joint instead of a drawbored joint.

ken

[Tom M King]

With holes already in mortise piece, dry fit tenon into mortise, use brad point bit (not in drill) to mark center location, dissassemble, and drill hole in tenon where you want it, taper end of long peg, and assemble. There's nothing hard about it, just don't overdo it. I've never seen a failed joint in drawbored large timber framed joints, but see many failures from drawboring in small pieces like old window sash.

[Jim Koepke]

With holes already in mortise piece, dry fit tenon into mortise, use brad point bit (not in drill) to mark center location, dissassemble, and drill hole in tenon where you want it, taper end of long peg, and assemble.

Wait! Something was left out. After marking the center of the hole, move the bit just a bit toward the shoulder of the tenon. The amount should be about the same as what we used to call a thin dime. That was back in the days of silver dimes that would wear through years of circulation.

The idea is to have your peg pull the tenon into the joint tighter. Too much offset and it could cause the tenon to split. Too little and it is just a pegged joint.

There should also be at least two or three times the diameter of the pin from the hole to the end of the tenon to resist an splitting of the tenon. More is better.

jtk

[Derek Cohen]

I would like to do drawbored mortise and tenon joints on a garden bench. This will be my first try.
Is this something I need to practice, or will it suffice to read 10 articles and watch 10 YouTube videos about 5 times each.
The joints are looking good, and i just don’t want to mess them up.

Todd, here is a complete primer from my website:








Below are the measurements used:

• The stretcher is 3” wide.
• The centre of the tenon is 1 ½ “ from the side.
• The 3/8” hole for the tenon will be ½” out from the shoulder. Allowance is made for this when determining the centre of the hole.

Use an awl to start the hole for the auger screw.







Boring the face side ...



Here you can see the exit hole. The auger bit relies on the lead screw to pull it through the wood. Once there is nothing to grip, it will stop cutting.



Now insert the bit and drill back the other way ..



And here is the final hole ..





Fit the tenon into the mortice. Since the hole is 3/8”, take a 3/8” brad point bit and use it to mark the position of the hole on the tenon cheek.





Here is the result …





Now mark the position of the hole for the cheek about 1/16” closer to the shoulder. This distance is arbitrary. It depends on the bend characteristics of the dowel. A hardwood will flex less and so you would not want to offset the holes more than neccessary. Here I am using Tasmanian Oak, the same wood as used in the frame. It has good flex.





Drill the offset hole …







The amount of offset is evident when you assemble the boards …





Now you can grab a drawbore pin and use it to pull the boards together, either in preparation for inserting the drawbore pin, or just to see how they go together. Drawbore pins are not essential for this joint.

These drawbore pins are made by Veritas. They have tapered shafts that act as a wedge to draw the holes together and pull the boards against each other.







Insert drawbore pin and twist the handle to force the shaft deeper.

[Derek Cohen]

Let’s make dowels

Riven wood is wood that is carefully split along the grain. This creates a piece with greater stability.
What one does not want is to choose a board that looks like this! Use one that is straight grained.





To prepare a board for easier riving, first cut it to a smidgeon over the desired final thickness.
To split the board I simply clamp it in a vise and use a large and hefty chisel as a wedge.







Chamfer the ends in preparation for the dowel plate.





The dowel plate is from Lie-Nielsen. These come in both metric and imperial. One could simply drill a series of different sized holes through a steel plate, but LN save much time and effort, and I very much doubt that I could make one as precise as this. They write: Holes machined with 6-degree clearance taper on underside, holes are straight for the first .025" (6.35mm); so this tool can be sharpened many times without increasing the size - but at 60 Rockwell it probably won't ever need sharpening.

Begin by using a hole one size up (or closest to the riven blank you have). Drive it through the dowel plate with a mallet or hammer.

Tip: keep the dowel vertical and, depending on the straightness of the blank, use short rather than long blanks to minimise the edges catching unevenly.







Here is a result ..



Note that some do not use round pegs, but prefer tapered square-sided pegs. All good ... whatever you prefer. They all work.


Putting it all together

We are ready to wack the dowels into the joints.

Step one is to chamfer the ends so they do not catch inside the joint.







Step two is to pull the joint together with the drawbore pins (see earlier).

Step three is to drive the dowel through the joint….







…. Until it is comfortably past the other side.





The final step is to saw the dowel flush.







After planing or paring the stub flush, this is the result ..




Regards from Perth

Derek

[David Eisenhauer]

As you have been told, drawbored M&T joints are easy enough to create and Derek's step-by-step tutorial (as always) is an excellent primer. IMO, the main thing that can go wrong when drawboring is in using too-long, store-bought (non straight grain or riven stock) dowels and yellow glue when driving in the pegs. If your peg is tight to drive (from a larger offset of the drilled holes and/or use of yellow glue) it is very possible to break the pegs when driving them in before reaching full depth. Using straight grain dowel material and liquid hide glue (much more "slippery" than standard yellow glue) will greatly help prevent this, along with not having the dowels an extra 3"-4" longer than required. Making your own dowels after riving the material out for dowel-forming may seem like an extra PIA step, but it greatly contributes to success. I tend to use liquid hide glue for all of my M&T work just to aid things sliding together, as I have had yellow glue M&T failing to fully seat during final glue up after a successful dry fit up ahead of time.

[Todd Zucker]

All very helpful, especially the tutorial. I don’t know why I waited so long to get a dowel plate, but I guess it is time.

I was planning on using West System g-flex epoxy, since the bench will be outdoors. My recollection is that, even though it is thick, it is kind of slippery.

[Alan Schwabacher]

Epoxy will be fine. One thing you can do as a shortcut to Derek's clear description is to choose a bradpoint bit for marking where to drill the tenon that is smaller then the hole. If you place it against the edge of the hole nearest the shoulder while you mark, it will mark the needed offset. Just use a drill bit smaller than the hole by twice the desired offset.

The most important thing is to make the offset in the right direction, so it pulls the joint together rather than pushes it apart. If it's easier for you to envision that with the joint apart, do it Derek's way. If it's easier to see with the joint together, you might want to try my suggestion.

[Robert Hazelwood]

The advice above is good and pretty much all you need to know. I can add a few points:

-If you can, drill the holes in the mortised piece before you create the mortise. That will avoid having to deal with blowout inside the mortise. The blowout is not a big deal, but you have to go back and pare inside the mortise to clean it up, and the mortise walls will have torn out sections. You will get a neater result if you drill first.

-A brad point bit will work to mark the tenon, but transfer punches are ideal. A cheap set is all you need. Whatever you use, you only need to lightly tap to create the mark- if you make the mark on the tenon too large and deep it is difficult to clearly mark the offset, and tough for your drill bit to reliably find the correct mark on the tenon since the two marks will sort of overlap.

-A pair of dividers is a good tool to mark the offset, especially if you have a bunch of tenons to mark that require the same offset. Just set one point in the transfer mark, with the other point towards the tenon shoulder, then pivot the dividers towards the shoulder to create the offset.

-In dry wood I would use an offset of 1/32 to 1/16 unless the dimensions of your pieces are very large. This is sufficient to draw the joint closed, but prevents unwanted excitement when driving the pins home.

-So far all of my drawbore pins have been oak dowels from the box store. You can usually find a handful of straight dowels in the bin...look for dowels with the fewest cathedrals (grain runout). Then cut out the best portions and use those as your pins. I've not had any break.

-To create the taper, if you have more than a handful of pins to do and you have a belt sander and cordless drill, chuck the dowel in the drill and make the taper on the beltsander. Ideally the taper should be fairly long and gradual, especially if the mortise walls are thin. When the backside mortise wall is thin (say 1/4"), there is a risk of the tip of the drawbore pin contacting the inside wall of the bore hole and tearing a chunk out of the backside of the mortised piece. This is the only problem I've ever had with drawboring, and it can be avoided by limiting the drawbore offset, and creating a longer taper to prevent the point from contacting the inside wall of the bore hole before it exits the other side.

-You also want to chamfer the butt end of the drawbore pins to prevent them from splitting as you drive them home. If I'm belt-sanding the tapers, I will just create the chamfers that way too, which is very fast.

[Robert Hazelwood]

Epoxy will be fine. One thing you can do as a shortcut to Derek's clear description is to choose a bradpoint bit for marking where to drill the tenon that is smaller then the hole. If you place it against the edge of the hole nearest the shoulder while you mark, it will mark the needed offset. Just use a drill bit smaller than the hole by twice the desired offset.

The most important thing is to make the offset in the right direction, so it pulls the joint together rather than pushes it apart. If it's easier for you to envision that with the joint apart, do it Derek's way. If it's easier to see with the joint together, you might want to try my suggestion.

That's a clever idea, and would eliminate a step in the process. With a set of transfer punches it would be easy to find the correct punch for any offset.

[Bill McDermott]

Todd, A consideration... No one will see the inside joints, so if you are using hand tools to cut the shoulders, error by going a little heavy on the inside. That way the pin will draw the outside should tight up against the leg with no interference from the inside shoulder. Or, just do everything perfectly. Remember to leave the clamps on the rack )if it goes together square). That's the best part of draw-boring. By the way, I made my dowel plate from 1/8th" mild steel I got at HD. It works fine for the few dowels I pound out. Sharpen by sanding though a few grits on the face that is the edge.

[Todd Zucker]

Good suggestions. I have been getting into hand tools lately. Doing the joints on this project mostly with hand planes, chisels and hand saws, and the shoulders are close but not perfect. I was going to a dry fit of the entire bench, and then troubleshoot each joint once I can see how everything comes together. I suspect that going heavy on the inside of the shoulders will fix most of the issues. With epoxy, it should also help fill any gaps inside the joint.