Good morning folks!
Work benches provide a solid and flat work surface to increase the effectiveness of both hand and power tools. With the help of vises, clamps, and holdfasts a woodworker can ensure their work piece will not shift or fall from the weight behind a strike or swipe. Today I am focusing on what I thought was an utter phenomenon: the holdfast.
First let me explain what a holdfast is the best I can. A holdfast is a hook shaped piece of metal that is placed into a hole in the bench and on the work piece. With a single strike on the top of the holdfast the work piece is “clamped” to the workbench tightly enough for several operations. The strike on the top will wedge the rod into the dog hole giving the holdfast significant holding power. When done, a simple strike to the back of the holdfast will loosen it and allow you to take out your work piece.
Holdfasts aren’t a typical item sold at any home center. In fact there are only a handful of companies that produce these vintage clamps and only a select of those make quality versions. Lee Valley and Lie-Nielson make their own version but their style don’t quite do it for me. Instead I went with toolsforworkingwood and their version produced by Gramercy Tools. The quality and the price cannot be beat; $35 for a pair. They come highly recommended by professional and hobby workers both for their durability and holding power.
Next I needed to drill 3/4″ holes into my bench to accept the rod of the holdfast. So I brought out my brace and 3/4″ auger bit; unfortunately I couldn’t get the proper leverage to drill into the top without getting on top and putting my shoulder on the pivot of the brace. My bits are probably dull which attributes to needing more body weight. As soon as I drilled out the last hole I ran in and yelled to my wife, “Come see my bench! I wanna show you my holdfasts!” I put a work piece down on the bench, placed a holdfast in the dog hole and gave it a solid smack with my mallet. I was excited and relieved to know this process was done; until I touched the work piece and it slide around as if it were on ice. After all that work the holdfast failed to hold; I was sickened and without a solution. The holdfast was already a mystery to me and now when I thought I knew how it worked and did everything correct, the whole thing blew up in my face.
That is when I went looking for a positive solution and found that the wedging action depends on the angle made when striking the top of the holdfast. The longer the dog hole, the more real-estate the rod interacts with which in turn decreases the angle of the wedge. I needed to increase the angle and it could only happen by lowering the amount of rod interacting with the dog hole walls. It is a Pythagorean Identity for my mathematician friends; the wedge angle is determined by the ratio of the opposite side and the adjacent side. When the adjacent side decreases (the dog hole wall) while the opposite remains constant (distance between the dog wall and the closets point on the rod at the top of the bench) then the angle of depression will increase strengthening the wedge and overall holding power. In short I somehow needed to shorten the depth of the dog hole.
Before I started chopping into my freshly build bench I thought I would try my theory out on a piece of cut off. I bore a dog hold; on the dog hole I scribed a 1 3/4in square and began to cut them out 2 1/4in deep. I wasn’t worried about making the square perfect nor the depth perfect. These weren’t meant to be precise joinery but isn’t just needed to be a thickened dog hole to trick the holdfast into thinking the bench was only 2 1/2in thick instead of 4 3/4in thick. And guess what? It worked and I was ecstatic! I then took about 4 nights to cut out the same faux holes on the bottom of my bench for each of my dog holes.
Thank you following along with the build. Stay tuned for more projects from the PlaneOleWoodShop. If you have any questions or advice for myself or other viewers please feel free to leave a comment below.