On Drawboring

[Tom King]

From the Timber Frame Engineering Council:

can't get the link to work.   Sorry.   You have to go here, and open the different pdf's.

https://www.tfguild.org/timber-frame-engineering

[RichardA]

I don't think drawboring for timber frame would be any different than what I/we use when building furniture.  You'd just require a bigger hammer.

[Tom King]

That's about right.  I thought it was interesting that they have some general rules to go by as far as layout, and spacing.  They also show a number of ways to mark the offset.

[drzaius]

I did some experimenting on draw boring a few years ago. For 1/2" white oak pins in hard maple, 3/32" offset was the sweet spot. I cut the test joints in half and it was cool to see how the pin threaded its way through the offset. One of the joints with too much offset broke the pin & the sharp point went through the maple like it was a nail. I wish I'd taken pics of them.

[RichardA]

16 hours ago, Tom King said:

That's about right.  I thought it was interesting that they have some general rules to go by as far as layout, and spacing.  They also show a number of ways to mark the offset.

I use the center point of the drill I used to get the first holes.  Mark center, then depending on the size of the pin, I go toward the shoulder, anywhere from 1/16th to 3/32. I would think that in timber framing, you'd want to move your mark the distance of your shoulder gap plus a 1/16th or so to pull it as tight as possible. And the best part, is glue is unnecessary, unless you wear a belt and suspenders.

[Chestnut]

Yep that site is really interesting. It'd be a lot of fun to design and build a timber framed structure.

[wtnhighlander]

5 hours ago, drzaius said:

I did some experimenting on draw boring a few years ago. For 1/2" white oak pins in hard maple, 3/32" offset was the sweet spot. I cut the test joints in half and it was cool to see how the pin threaded its way through the offset. One of the joints with too much offset broke the pin & the sharp point went through the maple like it was a nail. I wish I'd taken pics of them.

I suspect species makes a significant difference. The one and only breadboard table I have built has draw-bored pins all the way through. Walnut on walnut. I tried at 1/16" offset and could not drive a 3/8" dowel through without breaking it or splintering the hole. Had to take it down to a shy 1/32".

[Tom King]

I never knew that the part towards the end of a tenon, beyond the peg hole, was called the "relish".

I have some 1-1/2" pegs, that I took out of an 18th Century timber frame, that have more than a half inch bend.  I think we're talking about a bit more offset than furniture parts get, and some timbers are so large, you don't want to have to put them together, and take them back apart.

These big pegs are best riven, because otherwise they're likely to break from the bending stress.  Also, even though the frame may be green, the pegs need to be dry to whatever the normal air dried moisture content is for wood where they're going to end up.  Here, that's 12%.  

[drzaius]

4 hours ago, wtnhighlander said:

I suspect species makes a significant difference. The one and only breadboard table I have built has draw-bored pins all the way through. Walnut on walnut. I tried at 1/16" offset and could not drive a 3/8" dowel through without breaking it or splintering the hole. Had to take it down to a shy 1/32".

I think you're right. White oak is really tough wood. One needs to pay close attention to the grain as well.

One thing I did to ease entry of the pin was to round off the business end of it I relieved the edges of the entry hole in the tenon & the back hole of the mortise. Without that, I doubt if I'd have gotten away with much more than 1/16". 

I was surprised by the force with which the joint is pulled together. No clamps needed at all.