I am a hobbyist woodworker and just finished a new workbench. The top is 3.5” thick and made of hard maple. Finished with OsmoX raw finish which doesn’t color the wood. Works beautifully. Picture attached.
I drilled 3/4” dog holes in the top and purchased Gramercy holdfasts. The holdfasts work in about the a 1/3 of the holes. The other 2/3 never get tight.
I sanded the inside of the holes to remove any finish that may have dripped down and roughed up to the holdfast stem with 80 grit paper, sanding circumferentially. I also dimpled the holdfasts with a punch on surfaces that would contact the tops and bottoms of the holes.
None of this worked. I believe that the combination of hard wood and thick top are keeping the holdfasts from achieving adequate friction. The fact that some are working and some not is a little bit puzzling.
The next step appears to be to counterbore the holes from the bottom to shorten the distance between the holdfast contact points. I am writing to see if anyone else has had this problem and ask if there are other possible solutions.
If counterbore is the only answer, I will this do with a 1” Fortsner bit. But Forstner bits are a slow go in hard maple. Centering the bit on a pre-drilled 3/4” hole will also be a challenge. I am thinking to mark the center of a 3/4” plug and tap it into the hole. After drilling the counterbore I will tap the plug out from the top and proceed to the next hole.
Is there a better or simpler way to do this?
Thanks in advance for advice.
Russ
Replies
Beauty of a bench! I'd take a long strip of plywood and make a guide for a 1" holesaw. Clamp under each dog hole, cut the hole to the depth you think will work and chop out the waste. Not as pretty, but who's gonna see it?
Edit: a plunge router on the same strip of plywood would serve the same way.
Hi Russ
My bench top is also 3 1/2" thick. It is made of European Oak, and the dog holes were made with a brace and auger bits. The holes were left unsanded. The finish inside is smooth-ish, but not sanded. The Oak is a coarser surface than your Hard Maple. I use Gramercy holdfasts, and never have a problem. In fact, they will hold with hand pressure.
Why are our benches so different? Also, why do some of your dog holes grip and others not? I suspect that smooth dog hole sides are partly the enemy, and that you may have some finish inside as well. Counterboring the underside may help as it will angle the shafts more - too tight a fit would exacerbate the issue of grip. Conversely, roughing the sides of the Gramercy is unlikely to make a difference as the grip comes from the wood and not the metal.
I demonstrated the power of grip in a short video: https://www.youtube.com/watch?v=OaI_E2Yv1O0&ab_channel=DerekCohen
My bench top uses rectangular dogs along the edge, but round dogs holes in the centre. You can see the coarser Oak here below.
Regards from Perth
Derek
The holdfast grip comes from the friction (and hence the pressure) between the holdfast shaft and the wood of the hole it's in. If either one is slippy, it reduces the grip for the same pressure applied via the whack of mallet on the holdfast top.
I have both Gramercy holdfasts (which have very smooth shafts) and some others of identical configuration but made so that the shafts have a very rough finish:
https://www.workshopheaven.com/simon-james-holdfasts-pair-with-free-19mm-auger/
The latter grip much more readily that the Gramercy holdfasts. If the Gramercy gets some oils from one's hands, they can become less inclined to keep their grasp of the hole. The Simon James items always grip, even with only a firm hand-thrust on their tops.
Another factor might be the stiffness of the shafts. The grip in the 'ole comes from the pressure and friction applied by bending the shaft slightly with the mallet-blow to the top of the holdfast. If the holdfast shaft is so springy it very much wants to go straight again, this will make it lose any grip it has more readily.
How uniform is the "temper" of the holdfast shaft across different examples of the same item?
Shortening the length of the hole from underneath, by drilling a larger diameter stopped hole concentric to the 3/4" exit hole under the bench, will also help, as others have said. But it seems a bit of a nuisance to have to do this for several holes. Personally I'd buy better holdfasts. :-)
The Gramercy shafts could be more roughed-up (80 grit sandpaper isn't going to make them very rough) but that too seems a bit of a faff. It might be more help to thoroughly degrease them and to avoid touching them with bare hands, as even your own skin can exude oils that will lessen the grip of an almost polished shaft like those of the Gramercy.
Lataxe
Have the same problem, the top is 3 1/2 inch maple, counterbored the hole from the bottom and roughened the dog, still does not hold. Looking forward to solutions.
Plugging the hole and reboring like you mentioned doing is a really good way to do that. I've done that many times , usually to correct some mistake. A tappered reamer might accomplish what your trying to do as well.
A standard 7/8" or 1" metal bit would center in the 3/4" hole well enough for a counterbore on a surface that will not be seen. As MJ said, not pretty, but quick and easy, no guides or alignment issues.
I had the same problem with my bench, 4" thick maple top. I counterbored about 1-1/8" from the bottom of the hole for a net thickness of just under 3" at the dog hole.
The Grammercy holdfast are excellent and work like a charm. There was no need to coarsen up the existing.
To counter bore, just bore a hole in a piece of scrap stock with the forstner bit you are going to use, clamp or tack it over the hole you want to enlarge and drill.
Thanks to everyone for taking an interest in this problem and offering good suggestions. I was reconciled to counterboring eight dog holes to get the holdfasts to work. Not looking forward to that.
But in reflecting on the reply from lat_axe, I rethought how much effort I had made to maximize friction. I had coarse-sanded the contact surfaces on the holdfasts and medium sanded the dog holes to remove any finish that might have dripped down.
This morning I went back to the holdfasts. I staged a series of roughening steps from a little to a lot to see what effect that would have. I used a Dremel tool and standard accessories. I tested the hold in all of the holes at each step and tool a photograph of the holdfast surface after each step. These pictures are attached in order of steps below.
The first picture is the starting point: hand sanded with 80 grit sandpaper. What shows below the surface dimple is the top back of the holdfast where. it contacts the top edge of the dog hole. I applied the same process to the lower front of the holdfast where it contacts the bottom edge of the dog hole (no photos). The final picture shows the Dremel tools I used.
Step one was coarse abrasion with a sanding wheel (looks like about 60 grit). I abraded both the holes and the top and bottom contact surfaces of the holdfast with this tool.
Step two was abrading the holdfasts at the same locations with a medium coarse grinding wheel. Didn't do anything further to the dog holes.
Step three was abrading same surfaces with a burr. Each abrasion path in these steps was circumferential to the holdfast.
One by one, loose dog holes submitted and held. After the last step, all of them held.
Gramercy holdfasts are indeed smooth so might need more abrasion than others to hold in fairly deep dog holes in hardwood. But the lesson to me is that aggressive abrasion is a possible remedy for others who might have this same problem.
Thanks again for your input.
Russ
It's a mighty fine-looking bench you have there. It sounds like you have resolved your problem but just for what's it's worth I too had the same issue with my newly built bench and Grammercy holdfasts. Coarse sanding took care of it for me. I used like 80 grit and hand sanded aggressively.
BobE
I’ve had the Grammercy holdfasts for a few years. My bench is a skosh under 4”. Had the same problem. The is (used to be) an article or advisement on tfww’s website about the issue. Their suggestions for benches over 3” (IIRC) is to 1) bore a 1” dia x 1” deep relief hole on the bottom side of the bench for each hole. I used a forstner chucked into a hand drill on my back. 2) Rough up the bitey side ( under the hook at the bottom of the shaft) with a coarse file or even a hack saw. I really like those holdasts n these two little modifications made them solid as a rock.
When you think about it it makes sense. The deeper the bench the lower the angle of the “bite” for the bottom end of the holdfast.
Hope this helps.
Thanks again for advice from the Forum.
I continued to investigate alternatives to counterboring the underside of the dog holes to achieve better hold for Gramercy holdfasts in my bench.
Another woodworker with a similar bench material and thickness as mine shared his solution. He densely dimpled his Gramercy holdfasts in the areas where they contact the dog holes. This raised multiple sharp edges that better gripped the wood.
I tried this and it works beautifully. The holdfasts grip firmly now in all the dog holes when they are simply dropped in. One whack with a mallet and they are set.
This may not solve everyone’s individual situation, but it saved me from counterboring, which would have been a last resort.
Hope this helps someone else.
Russ