Giant Twin-bar Clamps

I made these clamps for glueing layered strips of pallet wood into a single large piece, which will eventually be the top of my new workbench. I was so pleased with the idea I just had to share it!

As they are intended for a specific purpose and are expected to be left in place for quite some time (with around 36 layers to glue!) I decided to forget about trying to replicate normal clamps, and make some which don't need to be removed, and more importantly, don't need the strong right-angled joint between the bar and the clamping surfaces.

Supplies

Wood blocks. Miine are 4 1/4 inches x 3 inches x 1 1/2 inches, but the exact size isn't important. Fitting your project is important! These were cut from pallet pieces.

Wood lengths. I used strips from a lightweight pallet, 2 1/2 inches x 36 inches.

You need 2 blocks and 2 lengths per clamp. If you make wooden feet instead of metal ones, you would need 3 blocks per clamp.

M8 Studding (aka threaded rod). Use whatever size makes you happy. I wanted to get M10 but the hardware shop didn't have M10 Tee nuts, so I used M8. You could also use long bolts. It turns out M8 is a little flimsy, so use at least M10.

M8 nuts. 1x self locking nut, and 2 normal nuts per clamp. Again, bigger is better!

Pieces of angled steel. I won't say "angle iron" because you can really just use what you have. I used some old racking designed for shelves.

30mm wood screws. 6 per clamp, though you may need longer and you might prefer to use more.

Screwdriver, drill, 10mm drill bit. You might need an 8mm (or bigger) drill bit too if you don't have handy pre-drilled holes like me!

Steel cutting device. I used my shiny new angle grinder, beats the pants off using a hacksaw!

Steel joining together device. For me it's a budget stick welder. I hope you have something better!

Step 1: Make Stirrups

The clamps have 2 long side pieces, so they can be made out of relatively fragile materials and quick and dirty construction methods.

First take a block and a wood length, and use two screws to attach the end of the length (leave a bit of overhang) to the end of the block. I screwed into the end grain, otherwise it wouldn't have been wide enough. Across the grain would have been preferable. Put one screw in, then ensure the top of the block is perpendicular to the length, then put the other screw in. Since I was using pallet wood, I put the screws through the old nail holes.

Turn it over and attach the second length, getting as parallel as you can to the first one.

Step 2: Make Clampy Bits

Take a second block, mark the centre and drill a 10mm hole. Insert a tee-nut and whack it in with a mallet or soft face hammer.

Carefully choose the length of studding you are going to use. You need: enough at the top to fit in the drill chuck, or attach a handle to, plus: enough to go through the wood block, plus: sufficient adjustment need for your project (I gave mine a range of 2 layers), plus: room for 2 locking nuts, plus: room to go into the foot piece and fit a self locking nut on the end. This is a minimum requirement. In practice I found that more would have been better.

Cut the lengths of studding using your preferred method. get rid of any sharp bits from the ends. Screw the piece into the tee nut at one end, and a couple of nuts at the other end.

Cut lengths of your angled steel, long enough to completely cover the width being clamped. In my case this worked out as pieces of racking 4 holes long. Cut some more pieces to attach the studding to. I cut pieces just 1 hole long from the racking, and cut off the part with most of the hole in it on the long side. This proved to be a mistake as they aren't strong enough. Bigger is better!

If you are using conventional angle-iron, you will need to drill an 8mm hole in the smaller piece.

My metal has grey paint on it, so this needed to be cleaned off prior to welding.

Although welding is the most straightforward method of joining the steel pieces, it's not the only way. Since the joint is to hold it together more than to take any significant load, screws or rivets should be feasible, with suitable extra pieces.

Alternatively you could make a wooden foot for each clamp, using a big washer to take the force.

Hold a self-locking nut to the back of the hole in the smaller piece, and thread the piece of studding into it. Tighten it down so you can just see the end of the studding at the end of the nut. Screw the 2 locking nuts down to make a close fit, but so the studding can still turn. Turn them against each other to lock them together. A self locking nut won't work here because it can still turn when pressure is put on it from the clamp being tightened.

Step 3: Attach Clampy Bits to Stirrups

The final step requires you to have something to actually clamp, as they are assembled to size. Once the clamps are in place, you make major adjustments by unscrewing the top block and re-attaching it at the next position. Therefore it's important to make maximum use of the screw adjustment's range.

Fit the stirrup under the thing you are clamping. In my case this is actually a large beam which is acting as a level base for the work.

Estimate the amount by which you will need to tighten the screws between fitting the layer you are glueing, and full tightness of the clamp. Extend the screw to this amount less than maximum extension, position the layer you want to glue (or a substitute spacer), then with the clamp foot resting on top, screw the top block in place. You should only need 1 screw on each side.

Once you have your clamps in place, retract the screws a bit, glue and fit the layer you are clamping, tighten the screws with your fingers to stop things moving around, then fit each one in your drill chuck and tighten.