Saturday, November 18, 2017

Making a set of eccentric drawbore pins.

I like to drawbore. But I haven't got any drawbore pins. This hasn't stopped me in any way, but once in a while I have thought that it might not be a bad idea to have some, so that I could test fit the joint before gluing and inserting the pegs.

I read a bit up on the various ideas behind it on the Internet, and it seems as there are a two models normally employed, both tapered along the length of the protruding part of the steel:
One version has a cylindrical shape of the tapered part  all the way.
The other version has got a not completely rounded shape of the tapered part. (popular called eccentric)

I guess that the eccentric model can either be of an elliptic shape, or it could just be a circular shape with part of the perimeter moved inwards.

I am going to try to make a set of drawbore pins based on the last idea. I can't really see any advantages of a pure elliptical shape over the flattened circular shape, but there is a lot more work involved in making a tapered elliptic piece of steel compared to the flattened model.

After a bit of testing to try our some ideas I had regarding how to do it, I ended up with this way of getting the wanted result:

First a piece of steel is mounted as usual in the 3 jaw chuck, and the far end is supported by the live center.
I adjust the compound rest to a 1 degree taper, meaning that the including taper will be 2 degrees.
I then take some passes only using the compound rest, to make a tapered section. I stop when the thin end is approximately half the diameter of the steel rod.
I then have to move the main apron to continue the taper. That is because the travel distance of the compound rest is only 2.75".  Once I have completed the taper to its final length, I stop.

The next step is to remove the old hole for the live center, so I can make a new one.
The new hole is made eccentric by adding a distance piece under one of the jaws in the chuck. In this case the distance  piece is an old washer.
I leave the washer in place and make sure to orient the steel bar in the same way, and again use the chuck and the live center.
The eccentric mounting of the live center and the washer between the steel bar and the jaw now causes the entire piece to be wobbling in the lathe. Or more correctly it is eccentric mounted with a throw equal to the thickness of the washer.

I bring the turning tool into contact with the piece and repeat the process of making a small taper. I removed 0.6 mm (3/128") while making this second taper.

The result is a nice and shallow taper and if the piece is rotated there is a slight difference of the aforementioned 3/128".
As far as I have understood the idea of this is that you insert the flattened part into the drawbored holes, and then you twist the tool to tighten up the joint.

I am going to try to  harden the drawbore pins before making some octagonal handles for them.

So far I have made two sets, 4 - 8 mm (5/32" - 5/16") and 5 - 10 mm(25/128" - 25/64")

Eccentric drawbore pins

Turning the taper

Getting ready for making the pin eccentric.
Note the washer between the left jaw and the workpiece.

This should show that there is a flattened ace on the pin.


  1. Good stuff Jonas. I've only done a few drawbored M&T joints and (like you) never had drawbore pins to use. I'm not even sure why they help. Can you comment on that? Seems like if you drill your holds appropriately, you don't need pins to line things up properly.


    1. Hi Matt

      As far as I have understood, the idea of the drawbore pins is that they will allow you to make a dry assembly of the joint before adding glue and without using the pegs.
      That way you can correct any issues on e.g. the shoulder of a tenon etc.
      Some say that it also helps by easing the way of the peg into the holes.

      My main reason for wanting to try them out is so that I can make a test assembly without using clamps, and see if all fits.

      Chris Schwarz made a set using drift pins, and he is my main source of information on the subject.

      I think that I need to make a set of drawbore pins that are an even larger diameter too, but I haven't got the steel for that out here, so I'll try to get that done at some point at home. But these should be fine for most furniture work that I do.

      There seems to be a bit of disagreement whether or not regular cylindrical tapered drift pins can be called drawbore pins, but I wouldn't care much about that. The important thing is that they work. I just like to experiment with a metal lathe, so that is why I made mine eccentric.


  2. These look cool. I look forward to hearing about them in use.

    1. Hi Brian
      Thanks, I think I need to invent some sort of project that requires a bit of drawboring, so I can test them.