Full Chisel Blog

October 9, 2012

Preparing a Holdfast to hold fast

During a Hand Tool Chat over at WoodCentral a few weeks ago the topic of clamping was discussed and holdfasts came up in the conversation.  We were talking about a proper sized hole and the desired thickness of the workbench for using holdfasts.  A 1 ½” thick top is minimum for a holdfast, although I have used mine on 1” thick apron of my bench; and 1/16” larger hole than the diameter of the shank of the holdfast seems to be optimum.  Slightly larger holes will work as long as the holdfast can jamb from the top of one side of the hole to the bottom of the other side of the hole.

The holes for holdfasts should be straight up and down and as smooth as possible on the inside.  This smooth surface on the inside of the hole gives greater friction than a rough hole.  Then someone mentioned that a Celebrity Woodworker had said that to improve the ‘workings’ of the holdfast to roughen the shank with sandpaper.

At that point I remembered one of my three holdfasts had rough scale from the forging process covering the shank and I don’t use that particular one because it is rough and will destroy a hole after some use.  I did use it in a pinch but was careful not to drive it too deep.  I had just been too lazy to smooth off the shank and my other two have very smooth shanks and I use them all of the time.

I told the participants of the chat that that was probably not a good idea, because that would turn the shaft of the holdfast into a file that would abrade the hole every time it was used.  I argued that the smoother the shaft the greater the friction, same as the hole in the bench.  You don’t want a rough shank you want a very smooth shank.

So I set about rectifying the situation with my third holdfast.  I clamped it in the vise and using a mill bastard file dressed the shank by ‘draw filing’ the surface.  The scale came off leaving the shaft bright.  I also collected the iron filings for making iron buff and as an ingredient in ‘cultler’s cement’.

Now all of my shanks are smooth and ready for use.

Stephen

5 Comments »

  1. And just who exactly was this celebrity woodworker? How can we shun his television program if we don’t know which?

    Comment by Brock — October 9, 2012 @ 7:59 am

  2. Someone somewhere is misrepresenting what the ‘celebrity woodworker’ actually said. He said “if your holdfast isn’t holding and the shaft is smooth, try scuffing it with sandpaper”. In other words, only try it if you have to. One of the vendors offers holdfasts which are quite smooth, not being blacksmith-made. In thinner benchtops they can benefit from light dressing.

    Comment by Chuck Nickerson — October 9, 2012 @ 10:55 am

  3. Stephen, do you use anything between the pad of the holdfast and the wood that you are clamping to avoid marring the wood? Holdfasts are simple and fast but having to always put in a buffer pad would be a bit of a pain. I suppose you could permanently attach a pad, perhaps glue on a thick piece of leather, but I don’t recall seeing any hold fasts with protection under the pad.

    I’ll probably ask this question at tonight’s, Tuesday Night Handtool Chat.

    Terry in Ottawa

    Comment by Terry in Ottawa — October 9, 2012 @ 4:55 pm

  4. Oh dear. I must have missed that episode of Celebrity Woodworker on HGTV? In any event. I side with Stephen. Holdfasts have to have smooth shafts else the bench hole become abraded and out of round in time. It’s the pressure fore to rear that holds it in place, not the roughness of the holdfast. If the holdfast is not holding, you’re not smacking it in hard enough. If the piece to be worked is too delicate, don’t use a holdfast.

    It all comes down to you can’t take shortcuts with simple properties of materials and mechanical engineering. Abraded metal on wood will abrade the wood.

    Comment by Gary Roberts — October 10, 2012 @ 8:36 am

  5. and if your benchtop is too thin, it’s the wrong benchtop for a holdfast

    Comment by Gary Roberts — October 10, 2012 @ 8:37 am

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