Introduction: Foot Activated Opposable Thumb Third Hand Clamping Device

I’ve got plenty of rigged up third hand devices to help hold things while soldering electronics.

They are fidgety to get them to hold everything exactly in place. When all you need is something to just clamp down on a wire or workpiece to get that soldering done...

Here is a solution but allows you to control when to clamp down and how much pressure is applied with your foot. Much better than some weak alligator clips or heavy spring clips which take a lot of effort to manipulate.

Step 1: Backpedal a Bit...

Adapt a set of bicycle brakes to use as the clamping mechanism. I used a set of side pull brakes but you can also adapt center pull or side mounted BMX style bicycle brakes.

The great thing about this is that the mechanism is already engineered for you and produced with factory machined parts.

Pro tip: Do not source your brakeset from a bicycle that will be used. I just purchased a spare set online.

Instead of clamping down on a tire, you can clamp down on the object you want to hold like in our need case, loose wires for tinning or maybe a strip of neopixels or a tiny circuit board for soldering.

A great way to use up scrap pieces of wood around the shop, build the mounts for the bicycle brakes to be turned into a clamping device. Although, you would still end up with smaller scraps of wood to save.

The hand brake lever will be mounted on a stable footboard to use as a foot pedal. Since the brake handle is built with a round clamp that is supposed to wrap around a round handlebar, I used a dowel mounted to an upright in the pedal board to simulate the handlebar.

I also built a platform piece to make a larger pedal pad so it would be easier to operate the brake lever with a foot press. The pedal is attached to the brake lever with tie-wraps that go through holes drilled in the side of the trough that the lever sits in.

You can also adapt the pedal foot mechanism to be mounted on the underside in front of your workbench or table so you can activate it with the knee when you press against it. They have these knee controls on industrial sewing machines where you can lift the presser foot without moving your hands off the workpiece of if you need your hands to operate a pair of scissors or holding a soldering iron. Like any mechanical device you learn to use, the convenience of the foot pedal is great once you get the feel for it.

Step 2: Hold on a Sec...

I used the rear brake since it had a shorter mounting bolt than the front brake unit.

It mounts to a crossbar in the bicycle frame and came with some curved profiled mounting spacers to fit a round bar.

I made the upright support post from a dowel that could substitute as that bicycle mounting bar. The post is glued into a fitted hole in the board for better support.

When mounted, I added a stop piece for the brake arm to help with leverage in using the brake as the cable is pulled and to keep it in useable position if it came loose and rotated on the upright post.

The bases should be heavy to keep it from moving around everytime the brake cable is pulled. Instead of wood, you can use the heavy dense material that cutting boards are made from, wood or plastic.

Step 3: Keep Calm and Solder On...

You can leave everything in it's bare wood state or give it a more durable finish. You can make it with a nice wood that develops a patina over time if you want fancy.

All the edges and corners were rounded and sanded.

I found a can of wood stain that I have never used in my paint can collection. I got it a long time ago when water-based stains first came out. It was expensive for that type of formulation so I picked up a can that I spotted on the clearance shelf. I didn't realize it at the time but I thought it was just a can of clear poly but it was a tinted stain that someone had returned to the store. It turns out it's a nice shade of TARDIS blue. Hmmm.

Water based stains/finishes go on a little thinner so you have to apply several coats for good coverage and even color. Darker colors may take 3 or more coats to get it looking nice.

Sand lightly and wipe off the sanding dust between coats.

It still looked kind of bare after the stain so I printed up a sticker and glued that in place. I coated it with glue to decoupage it.

Step 4: The Jaws of Life...

Since the brake jaws don't completely close so that the rubber brake pads touch each other, I made an extension from some aluminum bar stock for one of the brake pads.

You could probably just put a block of wood there but I had a piece of aluminum strip laying around that wasn't used. I'll spark some joy into it by putting it to use.

I used a hacksaw to cut a piece to length. Drilled some holes to mount it on the brake arm and a hole to accept the existing brake pad bolt. I just clamped two pieces of wood around the strip and bent it with body weight. I don't have a metal bending brake and didn't want to start pounding it with a hammer in a vise late at night. A file and some emery cloth smoothed out the rough cut edge and deburred the holes that were drilled out.

Adjust the position of the pads so they align when the brake is pressed to close. Adjust the cable slack. There is also a fine adjustment nut on the brake.

I added a cable clamp to secure the brake line to the base board just to tidy things up.

Tape up the free end of the brake cable or get a crimp on cap so you don't get poked with it.

Fine tune the brakes so you like how they feel when used.

Take it for a spin.

Add some rubber feet on the bottom or apply non-skid tape if the clamping device or the pedalboard slips when in use.

If you find the pedal too high up, build a platform wedge to bring the foot up more level with the pedal.

So make your own opposable thumb third hand clamping device to use.


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