For more information on sash clamps, see our beginner site Common Woodworking.
This post is for Matthew who asked me about the red sash clamps I use in my workshop. He saw them on the videos and in my book. This was my reply:
You can buy the 24″-48″ sash clamps in this style for between £7-£11, which I think makes them good buy. I will post some tips on my blog tomorrow with pics about them so others benefit from your question too. These clamps feel somewhat cheap when you first pick them up but the actually work well. I retrofit mine by inserting a strip of wood inside the clamp full length. I cut the wood for a snug fit but not too tight as the more the wood enters the greater the bite. This one change exponentially changes the feel of the clamp and makes it rigid so that it actually removes any tendency to torque, which was a definite problem with them before. These clamps, regardless of colour, are all made by the same Asian maker. In the UK they are sold under several makers including Silverline and Faithful and are also available from Axminster who claims them as theirs, but all of these companies buy from the same maker and put their name on them. I also superglue 1/4″ plywood pads on the heads to cushion and that works great.
Here is how to retrofit the clamps. Now these clamps are very common and you may think as I did that they are cheap feeling but this work really changes them and makes them to where you will wonder how you lived without them. Now I know that they are not heavy enough for some work, but these are just about the only ones I have used for 15 years. I have I-bar clamps for heavy framework.
Cut the wood to fit. The fit should be snug bit not too much as the wood will increase in resistance as the wood deepens into the extruded aluminum.
Cut the wood to the end of the aluminum and dimple the aluminum with a nail set to secure.
Wax the working head between the two shoes and the bar to prevent binding.
Cut pads of ¼” plywood the same size as the shoes.
Apply superglue to the pad and spray shoe with accelerator. Press two together and hold until set.
Repeat to second shoe and clamp together and tighten quickly so pads and shoes bed down tightly. Sometime in the future the pad may separate, but this method works well and the pad is quickly resituated.