My apologies to anyone opening this post expecting to read about a stunning antique or news of my latest furniture-making exploits. No, this post is about a persistent technical topic that came to a head this morning with the arrival, in my in-box, of eight similarly headed emails.
There seems to be a conundrum that perplexes a great many woodworkers, who, while in the planning or building stages of a new workbench, cannot determine what thickness of bench top to opt for, or if they have settled on a thickness, cannot determine whether their holdfasts will grip in it satisfactorily.
For the popular Gramercy holdfasts (of which I have a couple), those offered by North American blacksmith, Peter Ross – and possibly others, the optimal hole diameter for 3″ – 4″ thick bench tops is 3/4″.
In 3/4″ diameter holes, the holdfasts won’t grip reliably in timber less than 1-1/2″ thick (my softwood bench’s aprons are 1-1/2″ thick and the holdfasts work admirably) and they tend to bounce out of timber much thicker than 4″.
If your bench is one of those increasingly popular mass-of-railway-sleepers-on-legs creations, then it’s simply a case of boring slightly larger diameter holes in the top to get the holdfasts to grip. Dismally, I’ve heard of people retrospectively counterboring the undersides of 5″ – 6″ thick tops, a couple of inches deep, in order for the holdfasts to gain traction!
With such extreme bench tops I would suggest trying a holdfast in a 13/16″ diameter hole in a bench top off-cut before attacking the bench proper with the Jennings.