Poor man’s holdfast

[jim_hanna]

I was intrigued by the idea of using a batten with a birdsmouth notch to hold a piece against a single dog for planing after seeing a video demo (edit: found this again, it's at http://www.theenglishwoodworker.com/?p=1434) . It looked really effective at holding the stock for diagonal planing, yet the stock can be lifted and flipped over very quickly.
An essential for using the birdsmouth batten is some sort of holdfast to clamp it down to the bench.
The large solid metal holdfasts which you fix with a hammer are too pricey for me as is the Veritas Bench holddown with the screw tightening. The Axminster bench holddown is more reasonably priced but requires a collar to be inset into the bench.

Also all of the above have long stems which stick down below the bench when holding thin stock, I don’t really want to lose my underbench shelving.

I found some designs using an F clamp with the head removed and a swivel added to the end of the bar. Unfortunately any F clamps I have with a decent sized throat are much too big to go through my ¾ dog holes.

Then I found the Sjoberg QSh holdfast, it doesn’t protrude below the bench and looks a bit like an F clamp with the head removed and a kink in the stem to wedge it in the bench.

First attempt to make something similar saw me drill out the pin on a large F clamp to remove the head, then drill out another hole further up the shaft offset enough to give me a kink something like the catalogue holdfasts.

I used a bit of 12mm threaded rod inside a ¾ dowel for my first attempt, it bent like cheese as I started to tighten. Then I tried a bit of 12mm square steel with wooden facings cut from a dowel. Worked sort-of but was still starting to bend in use. Interestingly neither of them tried to rise out of the dog hole, the kink seemed to wedge them firmly in place.

Then I found an old ¾ UNF bolt I’d bought some time ago when I first got a lathe. My idea then was to shape the bolt to make a ¾ 16tpi tap to thread wooden faceplates. I never used the bolt, sticking a 3/4 UNF nut to a plywood circle proved a lot easier.
After knocking down the threads a bit the bolt is a good fit in my ¾ dog holes, it locks down the work solidly, total cost very little.

Regards

Jim

 

[Terry - Somerset]

I've not tried it, but a M12 rawlbolt may provide the basis for a cheap hold down - as the bolt is tightened the'shroud' expands to lock in the dog hole. The Screwfix ones require a 20mm drill for the hole (normally in brickwork/concrete) but may fit a 19mm hole in wood - or there may be alternatives on the market with slightly different dimensions.

Rgds

Terry

 

[Grit_monkey]

Here's one I made, it's the quickest hold down there is(I think so anyway).
http://www.youtube.com/watch?v=78xEGgKPlbc (This video is the first video I've made so it's poor, but it's only a demo to show my hold down/hold fast)
I found a Logarithmic spiral on Google images, printed it out then transferred it to a bit of scrap and cut it out. It is used in conjunction with a fixed piece the other side of the work piece which the work piece will be held against.
A larger logarithmic spiral can be cut out to give a wider range of movement to hold down a wider range of boards.
The idea comes from my main hobby, rock climbing where a piece of gear (called a cam unit) is used to protect the climber in the event of a fall, and works on a modified logarithmic spiral, it is placed in a crack in the rock face and when the climber falls it gets tighter, the same principal is used on the hold down, the more pressure the tighter it gets, but it's easy to release and there are no tools required to use it.

 

[jim_hanna]

I've not tried it, but a M12 rawlbolt may provide the basis for a cheap hold down - as the bolt is tightened the'shroud' expands to lock in the dog hole.

I haven’t tried a rawlbolt in wood either, my worry would be that once expanded it might be difficult to get out or that it might crack the bench top. I’ve seen a rawlbolt crack a concrete block wall when overtightened.
I have used an M10 rawlbolt, just the bolt without the expansion shroud, through the bench to hold my drill stand in place. I use a steel plate underneath the bench, a hole in one end big enough to pass the tapered end of the rawlbolt, a hole in the middle big enough for the tapered end to wedge itself and a 10.5 mm channel hacksawed between them for the shaft. It’s very easy to reach underneath the bench and slip the plate over the end of the bolt by touch, no need to struggle to get a nut on or off.

My holddown made from the F clamp and ¾ bolt was so useful that I’ve made a second one. Quite impressed with the 300mm by 120mm throat clamps (£ 9.99 from screwfix), equally good quality compared with some Irwin F clamps I have which were a lot more expensive. 300mm is probably longer than is required for a bench top holdfast but will be a useful size if I ever build a bench with square dogholes and want to slip the heads back on to the clamps again.
The washer on the bolt is just an M12 repair washer drilled and filed out to ¾. It’s nothing to do with the wedging clamping action, it’s only there to stop the end of the clamp bar dinging the bench when I push the bolt into the dog hole (DAMHIKT)

Regards

Jim