Introduction: Over Center Clamp
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
- 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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