Parallel guide chain mechanism
To make the chain mechanism, I used #35 chain and the sprockets are 10T with a 3/8 center. The chain is attached using two chain links. I had to do some metal working to create a few items: the brackets to hold the sprockets and a way of securing the chain at both ends.
I had a 1.5” rectangular steel tube in my scrap collection so I used an angle grinder with a cutoff wheel to make both brackets that hold the sprockets with 3/8 bolts. Big box store angle irons would be my second choice. I used 3 brass washers and a nut on the inside to center the sprocket and an outside nut to lock it in place. For the upper bracket I drilled the bolt holes so that the sprocket is close to the surface of the leg. I thought this would help keep the chain out of the way as it travels down the back of the leg. I may make a cover for it eventually.
I used a 5/8 bolt I abused on the bench grinder to attach the chain at the chop. It fits in a hole on the chop with a recess that hides behind the screw’s brass plate. I cut the bolt to length so it does not stick out of the chop and ground it to shape in about 30 minutes. I ground a centered flat part on the end and drilled a small hole through the flat part so that I could attach a #35 chain link that holds one end of the chain.
The lower bracket is attached to the leg under the shelf. The bolt holes for this sprocket are further away from the leg surface since the chain needs clearance here. Since the lower sprocket sits between the half lap on the leg and the hole for the linear bearing, there was not a lot of room to secure a bracket, and it would be subject to some serious forces. To address this, I made the bracket longer and cut a hole in it so the linear bearing can pass through. This allowed me to secure it over a wider area for strength.
The other end of the chain is attached to a ¼ hex bolt I modified heavily. I pounded the hex head flat, ground it to shape on a bench grinder, and then drilled a hole for the chain link. Its a little crude but functional. This bolt attaches to the “flanged shaft support block” on the linear bearing shaft. The tension on the chain can be adjusted using a nut on the bolt.
This shows how the lower part is put together. Clamping force and chop angle are controlled by length of chain, placement of the support bracket and the nut on the bolt holding the chain. I cut the chain as long as I could, then played with the other adjustments until I got a flat angle when the vise is clamped down.
if metal is not your thing, except for the bearing shaft side of things, this is very similar to the Ancora Yacht Service chain system that is available commercially (no affiliation but learned a lot from looking at their website).
The end vise is a quick release model I picked up on Ebay. I took it apart, cleaned it and painted it. I made a front face from my maple horde. I drilled some blind dog holes and put in a couple of bench dogs. The vise mechanism prevents through holes, so I came up with an alternative. The bench dogs have a small central hole drilled in them and a nut glued in at the bottom of the dog. I ground the head of some Philips machine screws flush to the thread. There is enough material left to allow a screwdriver to grip if there is not a lot of force involved. The screw goes into the central hole and engages the nut on the bottom. Tightening the screw down with a screwdriver pushes up the bench dogs when I want to deploy them. Unscrewing the screw allows the dog to be pushed down out of the way.
Wrap up – Dimensions
I designed this table, but did not pay much attention to dimensions. Everything is based on the decision to make the top out of ½ sheet of plywood (two glued up quarter panels) with edging. I used the pieces already constructed to determine the dimensions of the next pieces being built. The main parts of the bench are dimensionally amorphous. The legs and shelf can be any size you want and any relationship to the top is a design decision. I chose to make the shelf and leg footprints the same size as the top. The shelf could be narrower or shorter to give you an overhang. Even the two leg assemblies could be different dimensionally if you need a trapezoidal table for some reason. (i.e. back legs wider then front legs.) Want the legs canting front to back as well? Only the half-laps in the legs for the shelf need to change to the desired angle, (though the chop would be affected and the joint would no longer be flush).
Where to put the screw in relation to your guide and clamp point? A face vise in some ways is the opposite of an Archimedes lever (move the earth, but watch where you step). The forces from the acme screw are partially lost as a ratio of the distance of work to screw divided by work to guide. If the screw is 2/3 up from the guide and the work is clamped at the top of the chop you are loosing 1/3 of the screw force. This says that you should move your guide as far down as possible and make the screw to work height as short as possible. Guide height is usually constrained by how far down you want to bend to put a pin in. The distance from the work piece to screw limits the size of the board you can clamp. A 1” distance would maximize the force but would probably wobble with most boards since the grip area would be miniscule.
After mulling over this theory, I decided to put the parallel guide under the shelf, fairly low down and out of the way and the chain eliminates the need for bending. The canted leg increases the clamping surface that clears the screw for holding long boards vertically. I can clamp with about 2/3 of vise and still stay clear of the screw mechanism. For clamping boards horizontally, you can’t avoid the screw so I gave myself about 10” here. I may be over thinking this a little. The screw probably generates around a 1000 lbs of force and tweaking the dimensions will probably not buy you noticeable improvement in clamping forces, but if you can maximize things without a downside, you might as well go for it.
I added a leather pad to the chop face to further improve the grip.
I finished the whole bench with tung oil and a coating of wax. The main reason is to keep the surface less grimy and to resist glue. I started using the bench while it was still being built and was amazed how quickly sawdust and dirt accumulated on the surface that could not be brushed off. It got in the pores and stayed there. Luckily, I was able to sand most of this off in final finishing. This is not fine furniture, but would prefer it if it looks reasonably nice for as long as possible.
I carved my initials in the chop. Not essential but fun.
I added a green man to a recess I had in the hand-wheel. He is a Celtic god that among other things is responsible for artists and gives them energy for their work. I am not pagan, Celtic or an artist, but have no issues with getting some free energy and skill improvement whatever the source. Again not essential but fun.
In the future I will be adding some type of deadman and would like to find a way to add some wheels for mobility but have not figured out a non-clunky way of doing it yet.
I learned a lot by building this bench and I hope this blog provided some useful info for others contemplating this journey.
That’s the story of my bench. Its done and I am ready to use it to build some things.