holdfast in square vs round holes - unscientific test

[merrill77]

My Gramercy holdfasts from Tools For Working Wood arrived yesterday. I had already build a tiny workbench surface for testing. It is 2 7/8" thick with a round hole and two square holes. One of the square holes is 45deg to the other - I am curious if the angle has any effect on holding power on the square holes. The holes are as close to 0.75" as I could get - a micrometer is needed to measure the error.

I followed TFWW's recommended break-in for the holdfasts (de-grease and sandpaper), dropped my test bench into my tail vice, grabbed a few scraps and started pounding away. In this very informal test, I found that the holdfast held very well in both square holes. Much better, in fact, than the round hole - I had to hammer the holdfast multiple times to get it to hold in the round hole.

This is probably all the evidence I need that square holes are fine, but I am still considering getting a scale and doing a more scientific test with varying bench thicknesses.

 

[MarkE]

Did the orientation of the square holes have any affect on the holding power?

 

[merrill77]

Did the orientation of the square holes have any affect on the holding power?

Not as far as I could tell, but as I said, this wasn't very scientific, yet. I just pounded the holdfast and pulled the board as hard as I could. The board did not budge in either of the square hole orientations. Until I setup something that objectively measures the force required to break the hold, I can't draw any conclusion beyond than that the seem to be about the same.

 

[MarkE]

That's close enough for me. It's good to know that the options are there for if/when I build my next workbench. Thanks for testing. :icon_thum

 

[ehpoole]

IIRC, the thickness of your bench/table AND the tolerances of your holes (square or round) will play a big role in holdfast performance. The thicker the bench and tighter the hole the worse they will perform because the holdfast's holding power depends upon them canting a bit within the hole, generating tension and locking them in place against the top and bottom edges of the bench/hole. For this reason, a hole the allows no freeplay (i.e. same width/diameter as the holdfast) will have poor holding power, whereas a hole with some freeplay will hold much better (though too much play is also undesirable).

You may well find that slight adjustments in the diameter/width of the hole relative to the holdfast's diameter and bench's thickness yeild dramatic improvement (or detiororation) of the holdfast's holding power.

I am looking forward to your future data.

 

[kooshball]

This may be my issue... My syp bench is a bit proud of 3" thick with 3/4" holes and I can't get these holdfasts to hold anything. I cleaned them and scuffed them with sandpaper and it helped but not enough to bring things to the functional level.

I am thinking of removing 1" of material below the bench to thin it out in the hole area...so we will see...

IIRC, the thickness of your bench/table AND the tolerances of your holes (square or round) will play a big role in holdfast performance. The thicker the bench and tighter the hole the worse they will perform because the holdfast's holding power depends upon them canting a bit within the hole, generating tension and locking them in place against the top and bottom edges of the bench/hole. For this reason, a hole the allows no freeplay (i.e. same width/diameter as the holdfast) will have poor holding power, whereas a hole with some freeplay will hold much better (though too much play is also undesirable).

You may well find that slight adjustments in the diameter/width of the hole relative to the holdfast's diameter and bench's thickness yeild dramatic improvement (or detiororation) of the holdfast's holding power.

I am looking forward to your future data.

 

[KenOfCary]

I am thinking of removing 1" of material below the bench to thin it out in the hole area...so we will see...

To thin the material, just take a 1-1/2" Forstner bit and enlarge the 3/4" hole from the bottom about an inch deep. But you probably already figured that out.

I was going to do that but my Gramercy Holdfasts are working fine in my 4-1/4" thick bench with 3/4" round holes, but I had to do a lot of circular sanding on them first. It seems the more I use them the better they stick. Maybe the holes I'm using are getting worn since I tend to use the same holes repeatedly.

BTW, the bench started out 5" thick but with shrinkage and leveling ended up a little over 4" thick, but I digress.

- Ken.

 

[kooshball]

When I was at the woodwright's school recently for a joinery class I noticed that the holes in the benches for these same holdfasts was almost 7/8" in diameter and they held like crazy. I was able to pound out entire mortises with a pig stick and never have to retap the holdfast; all with an oversized hole.

 

[eyekode]

I recently picked up a LV holdfast. It has a couple advantages: longer reach, serrated shaft, and applies pressure with a twist of the knob. I didn't think I would like the knob but the pictures don't do it justice. It is huge and turns so smoothly! It takes me less time to spin the knob then to find my mallet (even if it is on the bench .

It also works better on my sliding deadman. I still like the gramercy's but the addition of the LV is nice.

Salem

 

[bluedawg76]

I have a pair of the gramercy hold fasts and in my bench (+3" thick, 3/4" square holes), 1 has an incredible grip and the other just ok. For most work they both work well, but the times when 1 fails is when jointing a board with bench plane (force tangential to the bench). For example, if I'm face jointing an 8" wide board, I'll place a secondary board such as 1/2" mdf along the far long edge of the board so that I can plane across the grain or diagonally. I use the holdfast to hold down the secondary mdf board. A couple of full width shavings with the plane and the mdf support starts sliding off the bench no matter how hard I pound in the holdfast. That's a good suggestion regarding slightly enlarging the holes. Although at first it seems couterintuitive, I think providing enough space to "cantilever" the holdfast is more critical than the bench thickness.

Sam

 

[KenOfCary]

I recently picked up a LV holdfast. It has a couple advantages: longer reach, serrated shaft, and applies pressure with a twist of the knob. I didn't think I would like the knob but the pictures don't do it justice. It is huge and turns so smoothly! It takes me less time to spin the knob then to find my mallet (even if it is on the bench .

It also works better on my sliding deadman. I still like the gramercy's but the addition of the LV is nice.

Salem

I also have one of the Lee Valley HoldFast's as well as the two Gramercy's and totally agree with you. Both are super useful.

- Ken.