Why We Prefer a Tight Fit & an Untapered Shaft

Posted on 20 September 2016

The Crucible Iron Holdfast is patterned after a French holdfast that a friend of ours, Brian Anderson, discovered on a dung heap in a barn. Like many French holdfasts from the 20th century, this one had a shaft that wasn’t tapered. Additionally, the shaft was just shy of 1” in diameter – about .970” all along its length.

A straight shaft that is just shy of 1” allows this French holdfast – and ours – to work in benchtops from 2” to 8” thick, and to work with the pad up to 8” off the benchtop.

So why aren’t all holdfasts made this way? It’s a good question.

A holdfast with a tapered shaft has a number of advantages. It enters the workbench easily, it requires less raw material and it is easier to manufacture. These tapered-shaft holdfasts work fine in many situations, especially in benchtops thinner than 4”. But they rattle like loose teeth when pressed into service on a 6”-thick benchtop, or when the work you are clamping is more than 2” or 3” thick.

When we decided to make our holdfast with an untapered, .970”-diameter shaft, we knew it would require some trial and error. But everyone involved with the project, from our patternmaker to our foundrymen, were bemused by how much tweaking it took to get the right result, including numerous changes to the original wooden pattern, plus gating and risering to get the ductile iron to flow correctly.

When we finally got a holdfast to come out the correct size, Zack Erhart at Erhart Foundry sent me a message that said: “I think we’ve got it.” I ran over immediately – the foundry is about two miles from our office. I brought the holdfast back to my shop and realized that the only holdfast hole I had was 1-1/4” in diameter. I decided to give it a try.

It cinched down hard.

And that’s when I finally relaxed after months of wondering: Would this really work?

— Christopher Schwarz

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  • Karl A Ashley: January 14, 2017

    Nevermind, i just saw the other holdfast posts. Now to figure out how to get a couple to Australia.

  • Karl Ashley: January 14, 2017

    I understand modeling this on the original french one, and the continuous thickness the entire length makes sense, but is there a reason not to make one that fits a standard 3/4" dog hole? You’d lose some strength due to reduced width but would it really make that much of a difference?

    I’m still in the planning stage for my workbench, but I’d been planning to make my own dogs anyway. If this only comes in 1" thickness, i might just make all my dogs 1", so they can all use the same holes.

  • Robert : October 15, 2016

    I’ve also wondered about the flat of a holdfast not parallel to the bench, so I made one flat another angled, straight shaft,I can’t tell any difference in holding ability. The shafts on mine are intentionally roughed up, I do find a rough shaft helps grip. I use one in a 4" thick Doug fir saw bench, and a 3 1/2" maple work bench.

  • Andrew: October 04, 2016

    I’s curious as to why is the flat part of the holdfast is not more horizontal, or even all the way parallel to the table. How did you determine the angle? (Possible answer: That’s just the way they did it in France in 1910.)

  • Mark Gilsdorf: October 03, 2016

    I forged a Roubo-style holdfast for a client a few years ago and made the shaft straight as well.

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