Drawboring: How much offset is enough?

[Matthew Hutchinson477]

First attempt at drawboring today. Long story short, I don't think I used enough offset because inserting the dowels did not close up the gap in the joint nearly as much as I expected. The tenons are about 2-3/4" x 3/4" and I used 1/4" dowels with 1/16" offset. It's red oak.

On a side note, apparently some folks think the dowel should be pretty close to the tenon shoulder. I placed mine halfway up the tenon cheek because I didn't think it mattered. Does it?

When I dry-fitted this mortise and tenon before glue-up the gap was pretty tight. Not perfect but as close as I can usually get. After glue was added this was the result:
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It isn't terrible but it's noticeably looser and the drawboring didn't seem to tighten it up any more. Did I just not use enough offset and should I have used bigger dowels?

[Jim Koepke]

The distance from the shoulder shouldn't have much effect on pulling the joint together.

One problem with putting the dowel further away from the shoulder is the pin can cause the area of the tenon away from the shoulder to split out. That may be what happened here. Another possibility is the offset hole was drilled on the wrong side of the dowel hole. That would have the effect of loosening the joint. (DAMHIKT!)

Finally the dowel needs to be tight in the holes. This is why often people rive and make their own dowels for draw boring. A tapered pin helps to start in the bore hole and needs only being driven until the joint pulls together. Any excess is then cut off.

jtk

[Hasin Haroon]

1/16" is plenty for red oak. I would only go larger than 1/16" for softer wood like pine, and only for huge tenons (like a workbench). If it is actually farther apart after drawboring I think what Jim said about the hole being on the wrong side might be what's happening here.

[Matthew Hutchinson477]

The distance from the shoulder shouldn't have much effect on pulling the joint together.

One problem with putting the dowel further away from the shoulder is the pin can cause the area of the tenon away from the shoulder to split out. That may be what happened here. Another possibility is the offset hole was drilled on the wrong side of the dowel hole. That would have the effect of loosening the joint. (DAMHIKT!)

Finally the dowel needs to be tight in the holes. This is why often people rive and make their own dowels for draw boring. A tapered pin helps to start in the bore hole and needs only being driven until the joint pulls together. Any excess is then cut off.

jtk


Thanks Jim.

I shoulda mentioned--these are through tenons so I can see the end of the tenon. Definitely no splitting. And I know the offset was in the correct direction. Only because I marked the first one in the wrong direction and caught it right before getting the drill out...

Maybe my dowels aren't tight enough. Since I used a hand drill and my steadiness isn't exactly perfect, it's possible that my dowel holes are slightly over 1/4".

[Jim Koepke]

it's possible that my dowel holes are slightly over 1/4".

That would be another cause of what you are seeing.

It is also a good reason for using riven and tapered pins. Then the hole size accuracy isn't as important.

Though in reality many of my draw boring was done with store bought dowel stock and drilled with a brace and a bit sized for doweling.

jtk

[Patrick Chase]

First attempt at drawboring today. Long story short, I don't think I used enough offset because inserting the dowels did not close up the gap in the joint nearly as much as I expected. The tenons are about 2-3/4" x 3/4" and I used 1/4" dowels with 1/16" offset. It's red oak.

How tight was the joint when you marked out the starting point from which you offset? As much as I hate to admit it, this is one of those instances where one of those Dubuque wedge-grip clamps might come in useful. You could use one of those to close the joint so that your offset has consistent "meaning" (if the joint doesn't fully close when you mark out then you may have to adjust it based on how much of a gap you see).



On a side note, apparently some folks think the dowel should be pretty close to the tenon shoulder. I placed mine halfway up the tenon cheek because I didn't think it mattered. Does it?

It does if you get too close (say, less than 4 peg widths) to the end of the tenon. You have short grain "fault lines" on either side of the peg in that case, i.e. the tenon can fail in shear on either side of the hole, allowing the peg to pull straight out. If you have to choose between having the peg close to the edge of the board or close to the tenon end, then put it close to the shoulder since you're supported by cross grain there.

[Phil Mueller]

I’m looking at the photo enlarged, and frankly, it looks pretty tight. There is a slight gap at the right side, but it also appears quite tight through the center area. From what I can see, it looks like maybe the gap is just a reflection of the fit. Oak has such open pores that an open pore next to the shoulder could seem to be a gap. Unless you can get a piece of paper between the joint, I’d say it’s good to go.

[Robert LaPlaca]

I would say that getting the dowel into a 1/16” offset drawbar in red oak should have been somewhat of a struggle, was it tough to get the dowel in the joint?

[Bob Leistner]

I looked at the picture as Phil did and I wonder if it is more that the shoulder is slightly out of square.That the inner edge is tight. The draw bore looks to be good from here

[David Eisenhauer]

I am also with the crowd that says 1/6" is way plenty offset in red oak M&T joints of that size. I probably go more towards 1/32" most of the time in smaller (furniture) sized hardwood M&T joints. Did you use yellow glue? I have had M&T joints dry fit nicely than fail to pull together as tight when glueing up with yellow glue. Although, it seems that a drawbore would fix that. At any rate, I now only use liquid hide glue for M&T joints. Run your square up against the existing shoulder and see if there appears to be something off as others have suggested, but then plane, sand or scrape the joint and move on. It will be one of those things that will catch your eye more than anyone else's. It really is not that bad.

[ernest dubois]

I like putting the peg hole fairly close to the shoulder, no further off then 1/4 tenon length. First off I want to ensure as much long grain as possible after the tenon's hole, this is called relish, to prevent blow out. Maybe if you are not experiencing this blow-out with the hole so close to the tenon's end, it's another indication of insufficient draw. With the hole closer to the shoulder you are drawing both halves towards each other, as intended, as the mortice side also flexes, instead of only the tenoned member being drawn into the morticed. I find it surprising and foreign that glue is being used with these pegged joints. The joint, once again, is intended to operate under continuous tension but this is no longer relevant when it gets glued making the peg in this instance nothing but decorative at best. Another basic purpose of the pegged joint is allow it being readily taken apart which with glue, it is not. Done right, the glue has no role and yet the joint has more than enough strength plus the added advantage of flexibility and being easy to take apart if need be.

[Matthew Hutchinson477]

Did you use yellow glue? I have had M&T joints dry fit nicely than fail to pull together as tight when glueing up with yellow glue.

This is precisely what happened.

[Matthew Hutchinson477]

I find it surprising and foreign that glue is being used with these pegged joints. The joint, once again, is intended to operate under continuous tension but this is no longer relevant when it gets glued making the peg in this instance nothing but decorative at best. Another basic purpose of the pegged joint is allow it being readily taken apart which with glue, it is not. Done right, the glue has no role and yet the joint has more than enough strength plus the added advantage of flexibility and being easy to take apart if need be.

Yes, I realize that many folks use the technique at least in part because glue is not needed. But this was my first time trying it so I wanted the reassurance. Once I get the process dialed in I'll probably start doing it without any glue.

[Matthew Hutchinson477]

Fun fact: (That many of you, maybe all of you, already know). Auger bits are slightly oversized!

For the first two holes I used a brad point bit but for the second two holes that go through the mortise I switched to an auger bit and 6" brace. My dowels are made with my high-tech dowel plate that guarantees dowels no larger than 1/4":
380090
Lie-Nielsen offered to buy my design for big bucks but I believe design is like art in that it is priceless.

It appears that I have found the culprit.

[ernest dubois]

Yes, I realize that many folks use the technique at least in part because glue is not needed. But this was my first time trying it so I wanted the reassurance. Once I get the process dialed in I'll probably start doing it without any glue.
My remark was in no way pointed but general, lots of commentators making off-hand references to glueing in combination with draw-boring. I wonder where it came from, C. Schwartz perhaps? I don't know.

[Joe A Faulkner]

I’m looking at the photo enlarged, and frankly, it looks pretty tight. There is a slight gap at the right side, but it also appears quite tight through the center area. From what I can see, it looks like maybe the gap is just a reflection of the fit. Oak has such open pores that an open pore next to the shoulder could seem to be a gap. Unless you can get a piece of paper between the joint, I’d say it’s good to go.

I'm with Phil. Looking closely at the edge of the receiving board, it looks like if you put a straight edge across that edge there would be a gap due to the open grain and/or perhaps minor void in the edge itself. Not to discount the auger bit theory.

[Malcolm Schweizer]

If you used glue, then the problem may be there was not enough room in the mortise for the glue and it pooped in the back of the joint, preventing the tenon from fully seating. This is especially true if you used epoxy, which has less compression and less absorption into the wood than yellow wood glue. No matter what glue, if the joint was especially tight, glue could have compressed into the back of the joint and prevented a tight fit.

Don’t feel bad- guess how I know all of the above! :D

Edit- that’s “pooled” and not “pooped”! Darned auto-correct.

[Jim Koepke]

Fun fact: (That many of you, maybe all of you, already know). Auger bits are slightly oversized!

This tells a bit about that:

https://sawmillcreek.org/showthread.php?131238-A-Bit-About-Augers

Usually auger bits are in the range of 0.015" oversized.

There are also auger bits that are DNO (Dead N*ts On) for doweling.


Edit- that’s “pooled” and not “pooped”! Darned auto-correct.

LOL! Didn't realize the typo (correction) until you mentioned it.

Glue as occasionally "pooped" on my efforts at woodworking.

jtk

[Matthew Hutchinson477]

That would be another cause of what you are seeing.

It is also a good reason for using riven and tapered pins. Then the hole size accuracy isn't as important.

Though in reality many of my draw boring was done with store bought dowel stock and drilled with a brace and a bit sized for doweling.

jtk

I actually have a piece of 3/8" A2 steel that I am planning on making into a dowel plate so good thing I figured this out before making said plate. If you were to make dowels to use with auger-bored holes would you think sizing up by 1/64" would be enough? Or would you go bigger?

[Jim Koepke]

I actually have a piece of 3/8" A2 steel that I am planning on making into a dowel plate so good thing I figured this out before making said plate. If you were to make dowels to use with auger-bored holes would you think sizing up by 1/64" would be enough? Or would you go bigger?

If possible multiple sizes would be made.

Another approach to getting good results is some dowel plates will have slightly oversized holes to pre-shape the dowels. They end up smoother that way.

If you are going to do a lot of doweling you might want to look for bits that are closer to actual size. My recollection is there are some Stanley Handyman bits in a Russel Jennings style that are dead on size. One problem is in many stores that sell dowels the dowels vary in size and are not always running with the grain like riven wood does.

jtk

[Patrick Chase]

If you used glue, then the problem may be there was not enough room in the mortise for the glue and it pooped in the back of the joint, preventing the tenon from fully seating. This is especially true if you used epoxy, which has less compression and less absorption into the wood than yellow wood glue. No matter what glue, if the joint was especially tight, glue could have compressed into the back of the joint and prevented a tight fit.

Both epoxy and wood glue are incompressible. The difference is that glue dries by evaporation and loses volume, whereas epoxy solidifies by cross-linking and doesn't shrink.