Holdfast Drilling Jig(s)
When making traditional-ish workbenches one of the considerations is making the holes for the holdfasts. I might have said “To holdfast or not, that is the question,” but in my experience a woodworking traditionalist either decides to incorporate holdfasts from the start or comes around to using them eventually.
As a general rule the hole for the holdfast is a smidge bigger than the shaft of the tool so that when the top is pounded to induce flexing tension the holdfast grabs the bench top firmly. As a practical matter virtually all of the holdfasts I know are available now use either a 3/4″ or 1″ hole. Getting the holes perpendicular to the bench top on two axes can be a nuisance some times, and in the past I have made a couple of drilling jigs on the drill press. However, over time both of these versions became wallowed out and somewhat less than fully helpful.
After returning from Arkansas where my older jigs got a serious workout I set to making another more robust and precision jig for fitting the Gramercy Tools holdfasts that I am so fond of. My main modifications for this were to lift its base up off the workpiece with plywood feet to provide exit for the chips, and bronze bushing sleeves fitted to the 3/4″ drill bit.
I drilled the hole for the O.D. of the bushings, then epoxied them in place. Finito.
Nice jig for perpendicular holes.
While I see the necessity for the two holes for a Moxon vise to be parallel (taking into account the play in the various parts) which is best achieved by having the two holes perpendicular to a same (geometric) plane, I don’t think it is necessary for holdfast holes to be perpendicular to the bench-top (or apron etc.)
There is an interesting article on the blog popularwoodworking.com:
“The _Mistery_Of_Holfasts”.
The stem of the holdfast must be askew in the hole anyway. As far as I understand the working of holdfast, the stem is like the tube of a pipe clamp while the bench-top acts as the lamellae of the pipe clamp sabot.
The trick of a rod askew in a hole is also used in the mechanism of the Horvater vises.
Sylvain
Agreed that the holdfast works by being askew and binding in the hole. A perfectly perpendicular hole allows that to occur equally at all 360-degrees of the compass rather than better in some angles than others.