Almost all of us with woodworking vises have experienced the annoyance of racking. This phenomenon occurs when an object is held in one end of the vise with nothing to balance the load on the opposite end (at left). As a result, the vise closes unequally, resulting on an angled jaw, poor workholding and, eventually, damage to the hardware.
People have come up with all sorts of ways to prevent this. Some are simple, some are complex, and some are downright bizarre. Most involve some way of supporting the opposite end of the vise jaws so that alignment is maintained. One method that I still use in my tail vise ( which is just a face vise at the end of the bench) is a series of stepped blocks to fit any gap that may present itself. The biggest problem with them is that they tend to fall out when you open the vise. However, they have three virtues: they’re fast, they’re free, and they can be made to fit any gap.
My favorite technique for face vise work involving flat stock held on-edge in the vise is the use of T-blocks (at left). These consist of pieces of stock of varying thicknesses with a crosspiece attached to the top. As shown, these slip into the opposite end of the vise jaw from the workpiece and keep the jaws parallel. These allow you to repeatedly open and close the jaws without having to look for the spacer on the floor as often happens with step blocks. In effect, the vise works something like a leg vise laid on its side. I have these pieces made up in the common widths from 1/2″ to 1 1/2″, and store them at the end of the bench. If I’m working with stock of an odd thickness, it’s no problem to slap one together from an offcut.
If you’ve got a method to prevent vise racking that you’d like to share, leave a comment.