Making jigs is one of the most common tasks for most woodworkers. Sometimes they are simple, sometimes not, sometimes they are used once but often they are used over and over again. Some of the most common jigs are associated with out stationary tools, like bandsaws, table saws, lathes, drill presses and so on. Many of the stationary tools that we use have mitre slots the are used for a few things, like mitre gauges, feather boards and other accessories that utilize this convenient slot.
Table saws are often picked on for making jigs where the mitre slots is used and when making jigs, it's ideal to be able to have some mitre gauge blanks on hand, rather than having to stop and make these as well as the jig.
Over the years I have used wooden mitre gauge blanks and often been frustrated by the fact that when I first made the jig it was fine, but when I go back to use it some time later, either the wooden mitre gauge blanks have swelled so they won't fit in the slot, or they are so sloppy now I need to figure out some way of tightening them up. All of which is time consuming and detracting.
Some time ago I finally switched to plastic mitre gauge blanks. They are made from a softer white type of plastic that is easily cut with bandsaw, table saw and can easily be drilled and even hand planed, not to mention sanded. Of course the big advantage of plastic mitre gauge blanks is that they don't take on or emit moisture which means they are always the same size. This is great when you make a jig and want to use it later on because you can be guaranteed it will fit in the mitre slot.
I purchase the plastic from a cut-off bin at my local plastic store. I believe they refer to it as UHMW Polythylene (Ultra High Molecular Weigh) Polythylene Plastic, or simply just UH plastic. The stuff I purchase is slightly thicker than three quarters of an inch, so it means that I need to trim it to fit on my table saw, which suits me just fine. The product cuts easily and this way I can control exactly how much play I want in my mitre gauge blanks.
To cut the plastic I use a thin Freud 40 tooth, 7 1/4 blade. These are typically used in circular saws but because they also have a 5/8 arbor they can be used in table saws as well. I like this blade (or any similar blade) because it has such a thin kerf and makes a nice finished edge. The UH plastic is somewhat expensive so you don't want to waste it.
The first cut I make is cut the blanks to height. This is normally slightly less that 3/8 inch. If you can accurately measure you mitre gauge slots, I think you will find most of them are pretty close to this height. I always like to have my blanks slightly lower than the table which means that I cut them a bit undersized in depth. I have found that sometime over sized ones make for bad jigs to I error on the side of small.
After the blanks have been cut to depth I want, the next step is to cut them to proper width. With some UH plastic that I get, it seems ot have a sort of pebble finish on both sides. I would rather have sheer fine finish on mine which means I need to trim both sides of the blank. This is pretty easy but you need to make sure you are only taking very fine cuts each time so that the blanks don't get too thin.
I have also found that there is some variance in the quality of mitre gauge slots depending on the material used in making the tool top, for example some composite or plastic tops the mitre slots seem a bit wider while the steel tops the slots are a bit more precision. This variance can make a difference in how your mitre gauge blanks fit the slots.
If you want to purchase UHMW in sheets, and cut your own blanks and other plastic items, and cannot find a source locally, here is the link to the Amazon store that also provides UHMW Plasitc Sheet material in a variety of thicknesses and sizes
In a case where a blank is too thin in the mitre slot and can be a bit sloppy, one of our reader Jeff Rosati has submitted a brilliant description and plans for making perfect fit blanks. The idea is to cut a couple of half inch holes 2 inches apart through the width of the blank. Then between these two holes another smaller hole about 1/8 inch. Now, you need to cut a slot between the two half inch holes that also goes through the middle 1/8 inch hole using a fine pull saw or similar tool. This slot is best if it is cut right through the material just as the holes are. Once you have cut the slot now you need to install a small screw in the middle hole that will make the sides bulge slightly. It is this bulge that will make the blank tight in the slot.
Copyright - Colin Knecht