I’ve never owned a real strap clamp, making do with clumsy  ratchet straps and other less than ideal methods. But I recently bought one just to have on hand, and got to thinking that I should have a look inside to see how it works:

The mechanism looks more complex than it actually is – cleverly simple, in fact. It basically clamps down on the loose end of the strap and holds it while simultaneously pulling on the loop to cinch it tight around the object being clamped. I know, that sounds a bit complex too, but imagine it like standing on the ends of a rope while pulling on a loop around something with both hands.

Although it was not my intention when I bought the clamp, I thought it would be interesting to try to make a version made mostly from wood. So I spent a few hours working on a roughly put together prototype:

And tested it out:

And even without a top cover to keep the insides in, it still worked surprisingly well. So I took what I learned from the prototype and refined the design further, and drew it up in SketchUp to make plans.

To get started, I picked out a scrap of cherry to make the top and bottom cover for the clamp. I could have made all of the parts from maple, but much like my wooden bar clamps, I thought the contrast between the two species would be an attractive feature. The top and bottom cover need to be about 1/4″ thick, so after cutting the slices on the table saw, I planed them down to an even thickness:

I only needed one of the slices for the clamp, but having the other was helpful as a guide while planing the stock, as seen in this short video.

Normally I print the plans to work from, but my printer has died and I used my phone instead. It’s not as convenient and I like having the paper to write notes on about things that need to be changed or adjusted in the plan. I cut the top and bottom cover to size and marked the screw locations and the hole locations for the slot at the front:

I need to mention grain direction for this project, since it’s very important to the overall strength. Notice that the wood grain in the covers runs from side to side and the grain direction for each part (or groups of parts) is marked on the plan and should be followed.

To make the slots I drilled a 3/8″ hole at each end, and cut out the material between with the jigsaw:

Then cleaned that up and made it smooth with a file:

These slots are just there to hold the pad in place and don’t have to be perfect.

I used a countersink in my drill for each screw location on the top cover. Keep in mind these are #6 screws, so the head will be smaller:

I made the sides next and the grain runs along the length of these parts:

The two spools, the yokes and the block next, all made from maple. Again, the wood grain direction is important, but the spools can be turned 90 degrees (as shown) if it’s easier to make them:

The important thing is that it will be face grain to face grain when the parts are glued together. There are no end grain glue joints in this clamp, since that joint is unacceptably weak.

The front and back were cut out next. I find my mini table saw sled perfect for cutting these small parts safely:

The front needs a shallow counterbore to anchor the end of the strap:

The pad and retainer with the grain running vertical on both parts:

And finally the handle, made from that same scrap of cherry. It has a 3/8″ hole drilled all the way through for the lead screw and was shaped with a hand plane and then sanded smooth:

All of the wooden parts for the clamp cut out and ready to assemble:

I used regular wood glue to fasten the sides and front to the bottom cover, and used spring clamps while the glue dried:

A flat spot was filed into the handle end of the lead screw to help key it to the wooden handle:

I could then use epoxy to glue on the handle and the nut on the end of the lead screw:

While I do have a reasonable amount of faith in the epoxy alone to hold the nut on the lead screw, I went further and pinned it as well using the shank of the 1/16″ drill bit I used to drill the hole. This takes minutes and is very easy to do while the clamp is still in pieces.

This project is all about the glue ups – the retainer to the pad, and the spools to the lower yoke:

Now all I need to do is wait for the glue to dry fully before moving on to the final assembly steps:

After gluing together the rest of the parts and threading the strap through the mechanism (shown in detail in the video below), I screwed on the top cover and then set it out in the sun for a while to let the cherry darken a bit:

And here it is after the first coat of linseed oil:

 

I made a video covering the assembly of this clamp:

And if you would like to build one (or more) of your own, plans are available:

Strap Clamp Plans