Using Gauge Blocks

A piece of scrap and a clamp can make your table saw safer. Click image to enlarge

Safety with accuracy

Text and photos by Tom Hintz

   If you are like most woodworkers, the simplest of things can cause and cure problems. In the case of a gauge block, using it can prevent problems. Not using it is asking for trouble. Since virtually every woodworker reading this probably has the materials needed to make a simple gauge block lying around in their shop, there is no excuse to not enjoy the extra safety it provides.

   A gauge block, as used on a table saw, is an extremely simple device that reduces the chances of your experiencing one of the most feared and dangerous accidents in woodworking--kickback. Unfortunately, to the new table saw user, using the miter guide and rip fence simultaneously, precisely what a gauge block prevents, may appear logical and safe. Of course, this is not true.

   The number of emails I receive on this one issue suggests this story should be required reading for anyone considering pushing the ON switch of their table saw for the first time.

Use It For Safety

Without a gauge block (Top) the cut off piece is trapped between the blade and fence. With a gauge block (Bottom) room is created for the cut off piece, reducing the chance of it flying out of the saw. Click images to enlarge

   Simply put, a gauge block is a spacer that prevents the workpiece from being in contact with the miter guide and rip fence simultaneously. Without the gauge block, the cut off piece of wood is trapped between the blade and rip fence. When this happens several things can occur, and none of them good.

   If you are lucky, the cut off piece will lay harmlessly next to the blade. If not quite so lucky, the spinning blade will slide the cut off piece towards you at somewhere below kickback velocity. Keep in mind that predicting the actual speed or precise direction the piece is impossible.

   It is important to realize that both of the above situations are sufficiently rare to make counting on one of them occurring rather than a full-on kickback foolish in a big way.

   The most serious, and not infrequent, result of trapping cut off stock between the blade and rip fence is kickback. The spinning blade can easily bite into the trapped wood and throw it out of the saw, often with tremendous force.

   Kickback usually happens so fast there is nothing you can do to get out of the way. The most common description I have received is the woodworker saying they felt and heard the kickback at the same instant.

Zero-Clearance Insert

   There is a perception that installing a zero-clearance insert somehow prevents this kind of kickback. In fact, zero-clearance inserts do nothing to prevent this kind of kickback. The forces present during a kickback can easily distort the blade to the side, forcing it into contact with the insert. When that happens, the blade will either gouge into the insert, or throw it up and towards you. Using a wider opening in the insert is not the answer, a gauge block is.

Extending the Miter Guide

   A recent email from a NewWoodworker.com viewer described an idea he had that turned out badly. He attached a length of wood to his miter guide to act as a fence that would sweep the cut off piece past the blade as he made the cut. He depended on this fence arrangement to replace the gauge block and had the stock contacting the miter guide and rip fence.

   While this actually worked (he lucked out) the first time, while making a second cut the cutoff kicked back, breaking a piece of the wooden fence off which became a second projectile. Fortunately, he suffered nothing more than a bruise and a couple of sore fingers.

Setting Up the Gauge Block

Set up correctly, the work piece is never in contact with the gauge block and blade at the same time. Click image to enlarge

   The most common gauge block is nothing more than a piece of ¾"-thick stock, clamped to the fence. Some use thicker material for gauge blocks because of the extra space it creates.

   The main point to remember when setting up a gauge block is to place it far enough from the blade so that the workpiece does not contact the block and blade simultaneously.

   To set the cut width, temporarily move the gauge block so it is parallel to the blade and resting firmly against the fence. Measure the cut from the gauge block to the edge of the blade closest to it, lock the fence down, and then reposition the gauge block near the edge of the table (closest to you) before clamping it in place.
   With the gauge block correctly positioned, the workpiece can contact it without touching the blade. Then, when the work piece is pushed forward it leaves the gauge block before encountering the blade. This is easy to achieve with most common sized lumber widths, but when the workpiece is too wide to clear the gauge block before contacting the blade, you should consider using a cutoff sled, panel-cutting jig or similar device that eliminates the rip fence.

Don't Be A Hero 

Make sure to use the gauge block to set the cut width. Click image to enlarge

  When each cut is completed, shut the saw off before trying to remove the cut off piece. The space created by the gauge block reduces the chances of kickback, but does nothing to protect your hands from the blade. Also, the cut off piece will be very close to the blade and any movement could initiate a kickback you might not have otherwise experienced.

Repetitive Cuts

   A secondary benefit of using a gauge block is being able to precisely cut many pieces to identical length. This is particularly useful when you nave to cut several pieces from a few boards. Set the gauge block and fence to the proper distance and you can cut your pieces with confidence they will all be the same size.

Partial Depth Cuts

If the board is too wide to prevent being in contact with the blade and gauge block simultaneously, use a sled or panel cutter! Click image to enlarge

Some woodworkers feel it is OK to make partial depth cuts, such as cutting tenon shoulders, with the work piece in contact with the rip fence and miter guide simultaneously. I believe that since setting up the gauge block is so simple, and just as accurate, avoiding this situation just makes sense. Even with a partial cut, it is possible for the workpiece to cock during the cut and produce a kickback. Taking the few seconds required to set up a gauge block is a very small price for the safety it provides.

   Using a gauge block is a fast, simple (and usually free) way to make operating your table saw safer without compromising accuracy. As is so often the case, learning to use even the simplest devices and techniques can substantially increase safety in our shops. Nothing is more important.

See our story on building a clamp-free gauge block - GO!

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