Drawbore Rules and Standards?

[cutter12]

Hi,

I have been searching the internet and forum to find some common rules regarding Drawbored Mortise and Tenon Joints. I have yet to find any information that explains sizes and positions of dowels in relation to the M&T sizes.

I have read that:

- The Dowel is generally half the thickness of the tenon.
- The offset of the hole in the tenon should be 1/16" closer to the shoulder
- Dowel sizes are 1/4" for cabinet work, 3/8" for heavy Furniture and 1/2" for large construction.
- The peg hole is located on a line 3/8" in from the mortise butment

How do people decide:

- Peg/Dowel diameter?
- The hole placement across the width and length of the tenon?
- How many Pegs to use per joint? one or two?

Is there a way to determine sizes and position of the pegs based on the size and dimensions of the M&T Joint?

 

[undergroundhunter]

As far as I'm aware there is no set fast rules. I usually go just under half way between the shoulder and the end of the tenon (hope that makes sense), if using one pin then go dead centre to the tenon, if using two then equal distances to distribute the load. I have only ever used 3/8" pegs but then I've only used drawboring on big stuff that is difficult to clamp. Overall is the pegs will be visible then I tend to go with what looks right to my eye.

Matt

 

[MikeG.]

Hi,

I have been searching the internet and forum to find some common rules regarding Drawbored Mortise and Tenon Joints. I have yet to find any information that explains sizes and positions of dowels in relation to the M&T sizes.

I have read that:

- The Dowel is generally half the thickness of the tenon.
- The offset of the hole in the tenon should be 1/16" closer to the shoulder
- Dowel sizes are 1/4" for cabinet work, 3/8" for heavy Furniture and 1/2" for large construction.
- The peg hole is located on a line 3/8" in from the mortise butment

How do people decide:

- Peg/Dowel diameter?
- The hole placement across the width and length of the tenon?
- How many Pegs to use per joint? one or two?

Is there a way to determine sizes and position of the pegs based on the size and dimensions of the M&T Joint?

None of that applies to green oak framing, where everything is much bigger (your "large construction" category clearly isn't for framing). In particular, the pegs are likely to be around 18 to 22mm diameter, but I have found a couple in old scarf joints which were well over 30mm diameter. The offset I use is never less than 3mm. The distance from the shoulders for the peg location is going to depend on the size of the peg, so a 3/8ths generalisation is simply wrong*. I also can't see any justification for relating the diameter of the peg (it isn't a dowel, BTW) to the thickness of the tenon. The most important dimension of all, how much tenon is beyond the peg/ hole, isn't mentioned at all, and it is on this that the long term strength of the joint is reliant.

*In oak framing it is almost always at least 25mm. Try to imagine a 22 diameter peg on a centre only 3/8ths (=8mm) from the edge of the timber with the mortise!!!

 

[MikeG.]

........ if using one pin then go dead centre to the tenon.....

Sometimes, for very good reasons, the tenon isn't central to the post/ stile/ rail from which it is cut, and a solitary peg not being on the centreline of the post/ stile/ rail looks most odd. So whilst you are generally right, there are exceptions. Further, with diagonal braces, and in particular arched braces, the centreline of the tenon can be a very long way off the centreline of the brace.

 

[Jacob]

Pins, draw bored or not, single or multiple, should be close to the shoulder. The idea is to keep the joint tight so any movement would be at the other end of the tenon. Otherwise the joint may open.
Appearance doesn't come into it!
MikeGs hints above make sense - peg/pin distant from the joint perhaps 1 1/2 to 2 times the diameter of the peg?

PS you don't need to draw bore at all if you can clamp the thing together easily and then drill/pin whilst clamped tight. Draw boring is effectively a way of clamping i.e. DRAWing the components together. Hence not needed if already tight.

 

[MikeG.]

........PS you don't need to draw bore at all if you can clamp the thing together easily and then drill/pin whilst clamped tight. Draw boring is effectively a way of clamping i.e. DRAWing the components together. Hence not needed if already tight.

This applies only to seasoned timber. In unseasoned timber, draw boring is a useful way of compressing the fibres a little to keep the joint somewhat tight even after the wood has shrunk, and is thus a critical element of the structural strength of the joint. Obviously, unseasoned timber joints aren't glued.

 

[Jacob]

........PS you don't need to draw bore at all if you can clamp the thing together easily and then drill/pin whilst clamped tight. Draw boring is effectively a way of clamping i.e. DRAWing the components together. Hence not needed if already tight.

This applies only to seasoned timber. In unseasoned timber, raw boring is a useful way of compressing the fibres a little to keep the joint somewhat tight even after the wood has shrunk, and is thus a critical element of the structural strength of the joint. Obviously, unseasoned timber joints aren't glued.

I didn't know that. Makes sense.
Using dry wood the most frequent need for draw boring is with stair strings to newel posts. Very difficult to clamp. Sets of three or four 5/8" diameter pins for this purpose, used to be basic essential joiner's kit

 

[custard]

For furniture at least the pins should be riven and never from kilned wood. They then curve around the hole off-set, exert their own pressure to close the joint, and will never subsequently drop out.

This video pretty much follows the method I use.

https://www.youtube.com/watch?v=Qa8K_CH3eaI

Draw bore pins are useful for angled components that are difficult to cramp (think of the stretcher on a hayrake table), but you can make your own or improvise, you certainly don't need fancy Lie Nielsen jobbies.

 

[Phil Pascoe]

In my old house the sashes weren't drawbored but they were pinned ............ with twigs, that when dried fell out when the paint peeled. It was all that held them in.

 

[Jacob]

In my old house the sashes weren't drawbored but they were pinned ............ with twigs, that when dried fell out when the paint peeled. It was all that held them in.

They may have looked like twigs but I guess they would have been riven as per custard's description above.
They can mysteriously work their way out of the hole if paintwork neglected. Quite common on neglected joinery. The reason being: they start as squarish riven pegs but by the time they have been driven into a round hole the leading end has been squashed to a round section but the hole has been stretched wider at the near end on the side from which they are hammered in.
Result: slightly tapered peg in a slightly tapered hole.
Then with alternating pressure from expansion when damp and dry again they will ratchet themselves slowly outwards back the way they came. May take years. Draw boring would make this impossible as the peg ends up locked with kink in the middle where it goes through the tenon. But not necessary on painted work.

 

[Phil Pascoe]

They were twigs - you could see where the pith had dried out.

 

[Jacob]

They were twigs - you could see where the pith had dried out.

OK then I guess the originals had already flown the nest and someone replaced them with twigs. Afterall the original maker wouldn't have been short of a few scraps for a few pegs. But who knows? :lol:

 

[cutter12]

Thanks everyone for your replies. I have been a little slow replying as its been a bit crazy since the storm.. no electric for a few days...now just flakey internet.....

Siince my original post I have been reading what Charles Hayward has to say....

He says that the hole 'should be within 1/4" of the edge, though the exact position depends upon the size of the work. For heavy work it can be more'.

Unfortunately he does not expand on this point.

I am making a workbench and have three sizes of joints that I want to drawbore. The wood is just softwood (spruce or pine probably).

Joint A

Through Tenon - 73mm wide. 29mm thick.
Mortise - 69mm deep into 69 x 95mm leg

Joint B

Through Haunched Tenon - 83mm wide. 29mm thick.
Mortise - 69mm deep into 69x95mm leg

Joint C

Through Double Tenon - Overall width of 163mm. 23mm thick. The haunch (?) between the two tenons is about 44mm wide and protrudes 24mm from the shoulder.
Mortise - 95mm deep into 69x95mm leg

What dia pegs would you use? How close to the shoulder? How many pegs per joint?

 

[Jacob]

Unless you have a clamping problem you don't need to draw bore any of them.

 

[cutter12]

They are not the neatest joints and I do have limited clamps ....... and I really really want to drawbore them all...... a bit 'belt and braces' maybe. I made a couple of things for the hall (a bench and a shelf unit) using drawbore and now want to explore it further. I did enjoy wacking the pegs in

 

[Phil Pascoe]

^^^ +1. I used cascamite for the open time and as I only had two sash cramps I joined the end frames first, then bolted the cramps together and pulled the joints up one rail at a time and pegged them so I could move on the next. Draw boring is making work if you have an option.