Paul Chapman
Established Member
There's an interesting piece on Joel's blog about how draw bore pins work http://www.toolsforworkingwood.com/Merc ... &BlogID=78
Cheers :wink:
Paul
Cheers :wink:
Paul
Draw bore pins
- Thread starter Paul Chapman
- Start date
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Thanks Paul
Thats an interesting read, I have to say that I don't own any draw pins, but none the less a good information.
Thats an interesting read, I have to say that I don't own any draw pins, but none the less a good information.
mahking51
Established Member
Anyone know if the new LN ones have this offset taper?
Martin
Martin
Argus
Established Member
.
I noticed that the Iles pins are advertised with an offset or elliptical shank and I must confess to wondering why.
In practice, I don’t see how an eccentric lead-in section on the tip of the pin does anything for the quality of the joint or to ease the work involved, for that matter.
However, it is customary (with me, that is) to cut that sort of shape on the end of the dowel with a chisel before it is driven home.
I take Joel's point about the pin entering the holes as he describes on his blog, but I've never found it significant unless the hole offsets are too great.
A drawbore pin is used to both tighten and align a joint using a lot of brute force and exploits the tendency of wood to distort slightly under duress. The hole in the tennon is deliberately offset toward the shoulder by about 1mm from the hole in the mortise so that they do not align. Forcing the pin through both tightens the joint and deforms the holes sufficiently to accept the circular dowel. It also compresses the fibres along the mortise rim against the shoulder of the tennon, reducing the risk of gaps appearing when the wood dries out.
I have a few ‘old’ pins, acquired over the years and I've just had a look at them for this tapered shape. Some are factory made by Marples, Frost etc and others made by various blacksmiths. They are all pre-war (don’t ask me which war….), although they are tapered, the shanks are barrelled, in other words, they curve slightly along the length, while the cross sections are round all the way down as far as I can see. This true for all of them. I can't see any eccentric tapers at the tip.
The length, shape and graduation of the taper is what makes a proper drawbore pin superior to an adapted engineer’s drift pin, which is what tends to be used these days – it isn’t the same.
All of these pins have seen some heavy work in their time and continue to do so with me; consequently any eccentric shape at the end was probably knocked out of them years ago.
.
I noticed that the Iles pins are advertised with an offset or elliptical shank and I must confess to wondering why.
In practice, I don’t see how an eccentric lead-in section on the tip of the pin does anything for the quality of the joint or to ease the work involved, for that matter.
However, it is customary (with me, that is) to cut that sort of shape on the end of the dowel with a chisel before it is driven home.
I take Joel's point about the pin entering the holes as he describes on his blog, but I've never found it significant unless the hole offsets are too great.
A drawbore pin is used to both tighten and align a joint using a lot of brute force and exploits the tendency of wood to distort slightly under duress. The hole in the tennon is deliberately offset toward the shoulder by about 1mm from the hole in the mortise so that they do not align. Forcing the pin through both tightens the joint and deforms the holes sufficiently to accept the circular dowel. It also compresses the fibres along the mortise rim against the shoulder of the tennon, reducing the risk of gaps appearing when the wood dries out.
I have a few ‘old’ pins, acquired over the years and I've just had a look at them for this tapered shape. Some are factory made by Marples, Frost etc and others made by various blacksmiths. They are all pre-war (don’t ask me which war….), although they are tapered, the shanks are barrelled, in other words, they curve slightly along the length, while the cross sections are round all the way down as far as I can see. This true for all of them. I can't see any eccentric tapers at the tip.
The length, shape and graduation of the taper is what makes a proper drawbore pin superior to an adapted engineer’s drift pin, which is what tends to be used these days – it isn’t the same.
All of these pins have seen some heavy work in their time and continue to do so with me; consequently any eccentric shape at the end was probably knocked out of them years ago.
.
Joel Moskowitz
Established Member
Argus":21wsznjz said:
First of all the section on all draw bore pins is round not eccentric. The offset of the cone is what gives it the power. but the forcing the pin is exactly what a good pin lets you avoid. When I rotate my drawbore pins in a mortise they tighten up. Once finding the tight spot, rotate the more and they loosen for easy removal. THat's why old pins don't have hammer marks on them. THere is no forcing. Also if you use too much force you can blow out the pit of wood in front of the hole in the tenon. turning a pin is a lot more controlled then pushing, forcing, or banging.
ps - the LN told me himself that their pins have no offset.
