holdfast hole "issue"

kezzer · 5 Nov 2013

Gents & Ladies,

I'm nearing the end of my 1st big project, the split top roubo bench and have created myself a problemette that requires a bit of sense to solve.

I have bought 3/4" benchdogs and holdfasts and have test drilled a couple of 19mm holes in some stock just to see the "fit" of these clamps. For me, they were a little on the tight side so have gone with 20mm holes for the holdfast holes in the leg. Problem is, they will not hold fast, they won't grip. I did try a test for them in 2" stock which worked fine but it seems in 3.5" deep legs and I'd assume, my 4" top the holdfasts won't grip. Not a problem for the dogs since they sit in with a side spring.

What I'm looking for is a remedy. I will obviously do the top with 3/4" holes. Yes I could drill more 3/4" holes in the leg but is there something else I could do with the holes I have, maybe add some 1mm or .5mm shims that may help or even with the holdfasts, they are Sjobergs Holdfast ST03 from Axy?

Thanks in advance.

Keri

marcros · 5 Nov 2013

counterbore the holes if they work in 2" stock, but not 3 1/2. I seem to recall that they are designed to work in around 2 - 2 1/2" best.

Phil Pascoe · 5 Nov 2013

Make a templet and re-bore the holes a few mil larger on the underside, so that the "working depth" of the hole is 65mm - 70mm or thereabouts - the holdfast contacts the bottom of the 19mm hole, not the bottom of the timber.

kezzer · 5 Nov 2013

Thankyou, I've just experimented with the shims option and a little wedge based shim from the rear also works nicely, just would be a bit fiddly when used in earnest and the idea is for a quick mallet smack and the piece being held is solid.

Will try the counterbore/template option though, sound like what the doctor ordered.

Many thanks.