Using the MicroDial Rise Over Run Scale

Setting a cut with the MicroDial Tapering Jig is pretty straight forward when you know the angle you want to cut, just set the MicroDial at the end of the jig to the number you want. There are 80 pre-sets to choose from between 0 and 10 degrees. But if you do not know the actual angle such as when tapering a table leg, you need to set the jig based on how much you want to remove. This is when you need to use the Rise Over Run scale.So, what exactly is rise over run?

All tapers are a cut made along the angled side of a right triangle called the hypotenuse. This triangle (your taper) is defined by the length of the cut (the run) and the width of the stock to be removed (the rise). So if you have a 2” square leg blank and want to taper all four sides down to 1-1/2” at the foot, your rise needs to be 1/4”. The Rise Over Run scale in the center of the TJ-5000 has 32 pre-sets to remove from 0” to 2” of stock in 1/16” increments. These rise measurements are for a 12” run. So, to cut a 1/4” wide taper over 12”, you want to set the Rise Over Run MicroDial to the red number 4 on the scale. This is 4/16ths, or 1/4”. The 4 mark is red so use the red pointer on the MicroDial and let it settle into the provided pre-set hole. Be sure to secure the lock knob once the cut it set. The scale will provide an accurate 1/4” cut on a 12” long taper. But what if your taper is not 12” long? We can account for that with a bit of easy math.

Think about your taper cut; the longer the angle extends, the wider it gets. The setting that cuts a 1/4” off along12” (1/4” rise over 12” run) will remove 1/2" if the cut is 24” long. So if you need to make a taper 24” long with a 1/4” rise, the angle needs to be halved. Use the 2/16ths setting in black on the MicroDial. The settings are proportional in either direction. A 6” run would require the angle to double using the red 8/16ths setting.

Do in your head for simple conversions, but for odd angles, just use this formula: Divide 12 by the actual run you want to cut, then multiply the rise by that answer. So an 18” taper would use the yellow 3/16ths mark since 12/18 = 0.66 x .25 = 0.165 which is closest to the yellow 3/16” mark (.0187) on the scale.

Remember that the taper gets wider as it gets longer and you should have no trouble knowing which way to adjust the Rise Over Run scale on the MicroDial Taper Jig whatever the actual length of your cut. The TJ-5000 will do the rest for you providing accurate tapers the first time, and repeatable tapers every time.