Drawboring

[Shultzy]

I'm familiar with the drawboring technique but I'm not sure of specific details. I've attached a section through the oak newel post of my stairs, the string being the 27mm strip in the middle of the picture. I'd like to drawbore, from right to left through the newel but I'm not sure the size of dowel, the offset, or whether the 33mm width is wide enough.

 

[milkman]

Er I'm sure others will clarify but I did drawbore a stair I made at college. Think I used 3-4 mm oak pins on softwood. (it was half scale)
As to the amount of draw I wouldn't draw much, barely a millimeter. (I now work on timber frames and we only use a millimeter or two on 19mm pegs) The offset on the tenon should be 'to the shoulder from the face', a bit of a pithy memory jogger I know but it works for me!
Not sure about the distance from the edges for something this size so I'll leave it people with more experience.

 

[OPJ]

Assuming the string is also oak, I've had more success (in furniture making) when using a greater offset of something like 3mm. It sounds extreme but, in my experience, if you don't offset the holes enough, they won't have much of an effect at all. I'd try to make my own pins from straight-grained oak, instead of buying the cheap mass-produced beech dowels (...which you probably wouldn't be using on an oak staircase anyway! ;-)). You can very slightly taper of chamfer the ends of each dowel to help them locate in the tenon's holes and then, through in to the other side of the mortise. You're probably looking for 8mm dowels, maybe 10-12mm maximum.

As I said, though; most of my experience comes from making furniture on a relatively small scale. With large-scale joinery, things may be a little different...

 

[Shultzy]

Thanks Ollie, the string is redwood I think so there's probably a bit more "give". Using 8mm dowels on the 33mm section will leave only 12.5mm from the edge, is this ok?

 

[OPJ]

I'd say it should be okay - but, at the same time, I'm open to the interpretations of others with more experience... I've done it with less of a distance before (on a smaller scale), with both parts redwood, and it worked out fine. You certainly wouldn't want anything less than 10mm.

 

[Jacob]

String to newel is traditionally draw bored because you can't easily cramp at the stair angle and the tenons are sort of triangular and don't hold tight without help. One dowel at least in each tenon, 1/2 to 5/8" diameter.

 

[Shultzy]

Thanks Jacob, is 3mm ok as an offset. Is one ok with a few screws as well?

 

[Erasmus]

Based on a 90mm square newel and a 225 x 27mm string.

12mm tapered end straight-grained oak dowel, 3mm offset. Keep the centre of the bore hole on the newel 25mm from the shoulder of the string. Two dowels per string and one for a handrail. I wouldn't use screws. Beech dowel is okay for softwood

 

[Shultzy]

Thanks Erasmus.