Since I received my Benchcrafted Roubo workbench a year ago, my woodworking life has tremendously improved. My new and heavy bench (I wrote about it here and here) has 1” holdfast holes that can be fitted with the excellent Crucible tools ductile cast iron holdfast that Chris Schwarz makes. The 1” holes and the monumental Crucible jig work like a glove in hand and the extra heft that this massive “candy cane” helper is endowed with is an advantage over lighter-body holdfasts.
But as it happened, I own a few ¾” shank holdfasts, and two of them, the discontinued bench duck hold down from Veritas, are my favorites. I want to note that the shanks of the Veritas holdfasts (including their standard Holdfast) are threaded to increase friction inside the hole.
Since ¾” holdfasts can’t fit into a 1” hole, I began exploring ways to resolve this inequity. I contemplated between a sleeve that would drop into the hole and one that would be affixed onto the shank of the narrow holdfast.
After a few sketches and an internet search, I opted for mounting the sleeve over the shank.
While searching the excellent McMaster-Carr catalog, I found the perfect candidate to experiment with – an aluminum sleeve with an internal diameter of ¾” and an external diameter of 1” (Item # 9056K36). After receiving the sleeve, I held it in a machinist’s vise and corrugated its face with a cold chisel. Then I drilled a hole and taped it to accommodate a ¼”-20 set-screw I had on hand.
I installed the sleeve over the shaft and gave it a try. It worked beautifully!
Now that I am happy with the results, I will improve the prototype and make another sleeve – this time with additional set screws that will be installed flush with the sleeve’s surface.
McMaster-Carr’s catalog offer such set screws, and here are two options to consider:
A short ¼”-28 set screw: #91301A140 and a narrower 12-24 set screw: #91375A241
The catalog also offers a steel sleeve which I haven’t tried, but I believe would work well: item #7767T371
It would be interesting to see how this sleeve solution works on ¾” holdfast that had not been threaded in the method that Veritas chose. If the set screws do not provide adequate friction on smooth-body holdfasts, I will drill a dimpled hole to accept the set screw and provide it with a positive anchorage. In that case, I would ensure that the set screw is long enough to penetrate the dimple while still having enough purchase on the tapped threads.
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