Sjoberg Holdfasts problem

[Silverbirch]

I`ve just taken delivery of a pair of Sjobergs bench holdfasts, like thesehttp://www.axminster.co.uk/sjobergs-holdfast-st03-twin-pack to fit the 19mm round dog holes in my bench. Unfortunately, the instructions that came with them say that they are suitable for benches with 19mm dog holes,but with top thickness up to 40mm. Mine is 70mm thick. Having tried them out, I can confirm that it is indeed the case. They don`t work.
So, my question is, does anyone have any suggestions how I might make them work? I could send them back, perhaps, but they were fairly cheap, so I don`t mind a bit of fiddling if there is a simple solution.
The legs are about 17mm in diameter and 220mm long, so plenty long enough.
I thought I could bore some holes through the legs, to take removable steel pins,which would bear against the underside of the benchtop when the holdfasts were tightened.
Any other (easier!) suggestions?

Thanks

Ian

 

[AndyT]

You need to enlarge the holes from underneath - to 25mm say - for 30mm vertically, so the effective thickness at each hole is reduced to 40mm. I hope you can get to the underside OK. You may need to temporarily plug your holes with wood so you can centre the 25 mm drill, depending on what sort of bit you use.

 

[marcros]

Exactly as Andy says, counterbore the dog holes from underneath.

 

[Sheffield Tony]

I have a pair of Sjoberg holdfasts and a bench from them to match. The top is only 28mm , but the holdfasts don't work terribly well in that either. I had assumed it was too thin !

A pair of Veritas surface clamps are on my wishlist.

 

[Peter Sefton]

Or you could use a punch to roughen up the back edge of the stem to increase grip.
Cheers Peter

 

[Silverbirch]

Thanks for the replies, guys.
I`ll try Peter`s suggestion of roughening up the back of the leg first, as that would be the most straightforward. If that doesn`t work, I`ll try Andy`s counterboring suggestion, although the bench is too heavy to flip over easily, so I would have to do the drilling lying on my back, coalminer style. Sounds like hard work!
I do have a Marples holdfast which fits in a collar in a fixed position. I`d hoped that the Sjobergs would be more versatile, enabling me to position them in various locations on the bench. Nothing`s ever straightforward, is it? :?

Ian

 

[AndyT]

I've just had another thought. Logically, boring out the top of the hole would have the same effect as boring out the underside. You could imagine it as equivalent to a 40mm thick bench with a 30mm thick piece of wood being held down onto its top, plus whatever you are really clamping.
So it could be worth doing some mock ups with scrap to experiment on, before you put on your hard hat and safety lamp.

 

[Silverbirch]

Yes, thanks Andy,that`s worth some thought too. As you say, I`d try it on some scrap first, though it would make any dog holes so treated non standard, and therefore less useful for other purposes, I think.

ian

 

[jim_hanna]

Just a suggestion. Would your supplier let you exchange the Sjoberg ST03 holdfasts for Sjoberg ST11 or Elite holdfasts.

The design of the latter two, seen here http://www.sjobergs.se/en/products/professional/234.php and here http://www.sjobergs.se/en/products/professional/ looks quite different from the st03.
http://www.sjobergs.se/en/products/hobby/

Bit more expensive but the professional holdfasts look a better design for a thick workbench, it shouldn't matter if your workbench is thicker than the length of the post which goes into the bench.

Regards

Jim

 

[Scouse]

Or you could use a punch to roughen up the back edge of the stem to increase grip

Thus

http://www.theenglishwoodworker.com/?p=1329

 

[Richard863]

Hi Ian
I had the same problem I filed a load of small nicks in the back no joy in slipping then filed nicks in the front. now all works well. I suppose I should have got a refund. But I needed something.

Richard

 

[Silverbirch]

Hi Richard
I`ll try that and see if it works for me. Thanks
Ian