Over Center Clamp


Introduction: Over Center Clamp

About: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying posting things I have learned and done since I got my first ...

I need an over center clamp, also known as a push/pull toggle clamp, for holding a piece of wood while drilling with a pocket hole jig. The price at a large local hardware store is about three times what I think it should be. I decided to try making my own.


  • Angle iron
  • 1/4 inch steel rod
  • 3/8 inch bolt and nut
  • 1/8 x 3/4 strap iron
  • 1/8 inch rod
  • 3/8 inch washer
  • 3/4 inch plywood


  • Angle head grinder and cutting wheel
  • File
  • Wire welder
  • Spring clamps
  • Drill press
  • Hole saw

Step 1: Cut and Weld Angle Iron

I cut two pieces of 3/4 inch angle iron to 4 5/8 inches in length. I aligned them and placed 3/4 inch strap iron between the two pieces for a spacer. I welded 1/8 inch rod across each end of the angle iron to hold them in the correct position.

Step 2: Prepare Guides for the Bolt Piston

I drilled two 3/8 inch holes in the 3/4 inch strap iron and cut them to make squares with the holes centered in them. I slipped the bolt through the holes and placed them on the top edge of the angle iron. (See the second photo.) Weld the squares to the top of the angle iron pieces.

Step 3: Prepare the Bolt Piston

I removed most of the bolt head and welded a piece of 1/4 inch rod across the end of the bolt.

Step 4: Make Connecting Pieces

I cut two pieces of 3/4 inch strap iron so that I could drill 1/4 inch holes through both for connecting the bolt piston to the handle linkage. The distance between the holes is about 1 inch.

See the second photo. I added the dimensions I used to remove guesswork for anyone who wishes to duplicate my clamp. All dimensions are in inches. The bolt piston is 3/8 inch in diameter, and 3 1/2 inches long. Note: The 15/16 inch dimension between the black line and the olive green line could be a little greater, perhaps 1 inch or 1 16 or 1 1/8 inch, but then the angle iron base would need to be a little longer, too.

For the sake of clarity, green to yellow 1 9/16 inches, yellow to blue 15/16 inch, orange to black 3 1/4 inches, black to olive green 15/16 inches (or a little greater).

Step 5: Make the Handle Lever

I used 3/4 inch strap iron to make an "L" shaped handle linkage and drilled a 1/4 inch hole in the lower handle end. I ground the weld beads flat.

See the second photo. I located the exact place to drill the hole in the end of the handle by placing it into the angle iron assembly and drilling through the angle iron assembly and the handle.

Notice where I ground a recess in the top of the angle iron so that when the clamp is closed, the knee action will be below a line that runs from the axis for the handle and the axis for the connecting pieces on the bolt piston.

Step 6: Fit the Axle for the Knee Joint

The knee joint is the center of three axes. Make certain no movement of the pieces will be obstructed. Locate the place for the knee axis hole and drill. Insert a 1/4 inch rod section. Weld the two 1/4 inch rods nearest the camera. Do not weld the axis on the bolt piston.

Step 7: Add a Stop

If the bolt piston retracts too far, the lever movement will lock up. I added a piece of 1/8 inch rod to the bolt to act as a stop. Be careful to make sure the stop does not interfere with the necessary range of motion. I welded the "C" onto the bolt piston.

Step 8: Add a Pad

I cut a plywood disc with a hole saw. Then I drilled out the center hole so it is about two drill sizes smaller than 3/8 inch. This makes it possible to thread the plywood disc onto the bolt piston threads. A nut and a washer back up and support the plywood disc. Drill mounting holes in the angle iron. Mount the clamp and adjust the plywood pad. Lubricate with oil or grease.



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    21 Discussions

    I know I should have quoted this looked similar,But not quite as complicated.

    1 reply

    I know I should have quoted this looked similar,But not quite as complicated.

    I know I should have quoted this looked similar,But not quite as complicated.

    I know I should have quoted this looked similar,But not quite as complicated.

    I know I should have quoted this looked similar,But not quite as complicated.

    I know I should have quoted this looked similar,But not quite as complicated.

    Boy that sure looks similar to a Norwood saw blade setter. ;-)

    1 reply

    I have not seen one of those, but the principle is probably very similar.

    Great clamp Phil. I built mine pretty much the same as yours but mine doesn't lock properly, what's the key to getting these to lock?

    5 replies

    Thank you for looking and for your comment. I would say two things are needed for the clamp to lock. One, draw an imaginary line between the first and the third pin in the linkage, the second pin needs to go over that center line just a little when the clamp is in the lock position. Two, the adjustment on the clamp needs to be tight enough when clamped, but not too tight. I hope this makes sense. I wish you well with your clamp.

    thanks for the quick reply. You're right about the position of the linkages, I played around with mine and got a nice positive clamping action although mine is a little finicky. I expected a stronger clamping action and that was part of the problem. This is not a cam action clamp from what I can see, what forces are at play that make this work? Also notice that you've used it for a pocket hole jig and that is my intention too. How has it been working for you and what range timbers does your clamp work for?

    I have to confess I have made very few pocket holes, but the jig seems to work fairly well. I set the clamp back from the fence with the idea I could insert a piece nominally two inches thick, but add a shim piece 3/4 inch thick and clamp 3/4 inch wood for drilling. That works, but I had to play with the adjusting nut on the pad so both thicknesses fit by adding or removing the shim piece. It is not clamped as tightly as I had first planned, but it is adequate for drilling a pocket hole. I could have really used this pocket hole jog and over center clamp a few months ago, and will surely use it sometime in the future.

    As for how it works, the clamp is adjusted so it is just a little too tight. You force it just a little to get the knee action go over center. Even when over center, there is enough tightness to hold the work with sufficient force.

    If yours is finicky, I am wondering if the knee action goes too far over center or not far enough. Does the clamp sometimes break open as if you had released it? That would mean it he knee action does not go far enough over center. Does the clamping action feel tight when moving the handle, but the work is a bit loose when the knee action has gone over center? That would mean the knee action goes too far over center. You should be able to correct either situation.

    thanks for the detailed reply you've addressed my concerns. My situation is the first one you outlined in your 3rd paragraph. Great idea with the shim. Thank you for your help and thanks for the great instructable, I've been looking for how to make a push pull clamp for years and yours was the first detailed one I found.

    if the knee action needs to go a little farther over center, that should be easy to fix. I would go slowly with a file until it was just right.

    Thanks, Bill. I added an image in step 4 with dimensions I used for someone who wants to make one of these without working out exact dimensions on his or her own.

    I don't know if "cam action" is the correct term. I mean the clamping force due to the mechanical advantage of the linkage increases as you move the lever forward.

    Wow! craziness. another gem phil. Hinges, toggle clamps... Regardless of the price at the store, the bigger price you pay when buying anything is the missed chance to understand and to have the capacity to be able to make whatever the item is. The welding definatelly takes it up a notch. I recently bought a wire welder but havent set it up yet. Ive never done any welding before. What type of welder did you use for this project?