I have been working on tooling in preparation for a CNC router build. I have built several screw type clamps but found them difficult to use. The problem was that, when tightening the clamp, the part I was clamping would tend to move out of position. Once tight, the clamp could not be adjusted without first loosening it. This Instructable describes an improved design that overcomes both of these shortcomings.
Step 1: Materials
I use a wire rack as a welding table. These clamps, along with a piece of drilled angle iron, work well as a guide rail to hold parts in position. Depending on what you are clamping and to what you are clamping you may need to modify the design appropriately.
1 @ 2" O.D. 3/4" I.D. washer
2 @ 1 3/8" O.D. 9/16" I.D. washers
1 @ 1/2" O.D. x 1 3/8" long piece of hot rolled steel tube
1 @ 1/2" O.D. x 1/2" long piece of hot rolled steel tube
1 @ 5/16" x 1 1/4" long piece of threaded rod
1 @ 5/16" nut
1 @ 1/4" x 1 7/8" long piece of hot rolled steel round
1 @ 7/8" O.D. x 1" long spring
Step 2: Assembly Part I
In this step you will use one of the smaller washers and the shorter piece of steel tube.
Place the small washer on your welding surface. Center the short piece of steel tube inside the washer. Tack weld the steel tube to the washer.
Step 3: Assembly Part II
In this step you will add the threaded rod and larger washer.
Place the large washer on your welding surface. Center the washer/tube assembly inside the large washer as shown. Tack weld the threaded rod to the steel tube. It may be easier weld a nub on one end of the threaded rod to hold it place.
Weld the threaded rod to the steel tube, the steel tube to the small washer and the small washer to the large washer.
Step 4: Assembly Part III
Bend a 1/2" section of the spring at a 90 degree angle to the coil.
Drill a hole through through the small washer adjacent to the large washer. Thread the bent section of spring through the hole. Weld the spring from the opposite side. Be careful when welding the spring as the current from the arc welder can melt it. That's why I recommend welding it from the other side.
Step 5: Assembly Part IV
In this step you will use the remaining small washer, nut, longer steel tube and steel rod.
Place the small washer on your welding table and place the nut in the center. Weld the nut to the washer.
Drill a hole towards one end of the steel tube large enough to accept the steel rod. Place the steel tube on top of the nut with the drilled hole on top. Weld the tube to the nut.
Push the steel rod into the steel tube and weld it in place.
Step 6: Using the Clamp
The image above shows a set of clamps installed on the base of a tapping machine I am working on but I have also used them with a single piece of angle iron. Paired with a drilled/slotted piece of angle iron they can be used to position components on your welding table or as a drill press rail. If you look closely at the image you will see that I have drilled holes through the angle iron and cut a flat spot on the larger washer to prevent it from turning.
Screw the nut assembly onto the threaded rod from underneath until the spring begins to compress. The tension of the spring will hold the part steady, yet allow it to be repositioned if necessary. Loosen or tighten the nut to vary the tension. Once everything has been positioned where you want it, tighten the clamps until positive contact is made.