Saturday, July 28, 2012

An angle gauge for a wet grinder

I have always admired the Tormek (q.g.) wet grinders, made in Sweden. These things use a 25-cm synthetic sandstone wheel running in a water bath. The water makes it impossible to overheat the tool, which is the curse of the high-speed dry grinders. Tormek has an extensive online presence, with many useful instructional videos. They also have a large number of extremely useful accesories. The drawback is that they are extremely expensive.

So some time ago I acquired from (q.g.) an Asiatic knock-off of the Tormek. I call this a TSO (Tormek-Shaped Object). It is about a quarter of the Tormek price. But their accesories leave something to be desired. Of all these accesories by far the most necessary is their angle setter. It is necessary to grind tools at precise angles. My grinder comes with a clever, but basically inferior, gauge, which broke when dropped, rendering it useless. The Tormek WM-200 (q.g.) is far superior. So I downloaded the instruction manual for the device, a PDF file, thinking maybe I could emulate it. Lo and behold, on page one of this PDF file is a full size (maybe) drawing of the thing. If it isn't full-size then it it close enough for Chalupy work. Hmmm. What have we here?
What we have is page 1 of the aforesaid instructions. Close scrutiny will reveal that the gauge is a sort-of rectangle with two moveable widgets. At right, the angle setter. At left, an extremely clever cam that allows you to compensate for wheel wear. As you grind, so does your wheel shrink. Do not be deceived by the knobs. They are not at the pivot point of either the setter or the cam. Obviously the widgets pivot somewhere else. You can find the pivot points with a ruler by very carefully extending the graduation marks on the drawing. You do this on the paper copy. So then you have a pivot point. Then you take some clear plastic which I happened to have, and basically trace the outlines of everything on to the plastic. Be sure to mark the pivot points on your cutouts. Cut it out any old way. I used a jigsaw. Cut oversize. Then I started filing. Note that the important things are (1) the angle setter point and the pivot point must be aligned. After that you can shape the angle setter any old way. (2) The cam profile is important. Trace it carefully. It may not be circular. Then drill holes at the pivot points, and use small screws (I used 4-40 hardware store screws) to assemble. By tightening up on these screws, I did away with the original's knobs.
When all was said and done I realized I had cut the angle setter undersize, so I remade it. Plastic, after all, is cheap; especially when it is found. I have traced out the angle and wheel diameter scales onto the plastic. So when you use it, set the cam to the measured dimension of the wheel. Mine is still at 250 mm close enough. Then set the angle to what you want. Here 25 deg.
And now it's all downhill. Set up your jig so it exactly coincides with the underside of the angle setter. Any questions? Refer to the WM-200 literature! It's online. Today I sharpened a rounding plane blade (25 deg) and an axe (45 deg). Without this gadget I would have been lost in space. Most useful gadget I have made in a long time.

And now, to forestall the patent Nazis: It is true that the WM-200 is patented. It is also true that under US patent law it is perfectly legal to make a copy of a patented thingamabob so long as you do not offer it for sale, i.e. for your own use. Please note that I am not in any way, shape, or form offering this thing for sale. So there.

But there does remain the question of what to call it. I don't want to violate trademark laws. So I will call it the angulometer.

1 comment:

  1. Ned job. I agree that this is an excellent design. Two comments:
    - the flat that should sit on the gouge or chisel is rather short. I've made one with a longer flat to make it easier to see any error.
    - the angle you're interested in is the bevel angle at the cutting edge. So, if you were to use this gauge to set the platform angle, as, for instance, Stuart Batty shows his being used, you must add to the set angle an offset for the thickness of the gouge/chisel. For a 6" wheel this is about 0.75° per mm of the length of the bevel (if hollow ground). For instance, I want to set my platform for grinding an 8mm thick skew chisel to 40° bevel. Each side is 4mm thick and has a 20° bevel relative to the axis. A 4mm thick 20° hollow ground bevel is about 10mm long, so you need to set the platform about 27.6° to the stone, not 20°.
    I'm not saying you were getting this wrong - only that others often get it wrong.