OBTUSE ANGLE SET UP GAUGE
When you sharpen your own chisels and wood turning knives, you’ll find it necessary to set your grinder or sander support table to different angles for different tools. Of course, you’ll find it necessary to repeat the previously set angle, to avoid removing valuable steel from the tools, and to get consistent cuts.
Setting up a tool rest of a grinder or belt sander to grind a specific angle presents a challenge because you can't use triangle templates (see first photo), angle gauges like I use in the steps of this ible, or similar set up tools.
You can use a bevel gauge. To do so, you’ll have to set it to the angle you need for the tool you’re sharpening. You can do this using a protractor to set the bevel gauge, then use the gauge to set the tool rest of the belt sander or grinder. This requires two steps, two tools and trying to set an angle twice.
Another quicker and more simple method is, use an obtuse angle template with the angle you need.
Unfortunately, obtuse angle templates aren’t easy to come by. Even on line. If you do find them, you may not be able to buy an angle template with the angle you want or need. Or you may not like the material its made from or even the size of the template. Your best bet may be to make your own gauges, since they are easy to fabricate.
To make your own set up angle gauges, you'll need the following:
1) Safety glasses.
2) Hearing protection.
3) An adjustable angle protractor.
3a) A protractor
3b) An adjustable bevel gauge.
4) Something to mark the material for cutting:
- An awl, knife or other sharp, pointed tool can scribe lines into plastic and aluminum surfaces.
- A fine tipped, felt pen.
- A sharp or mechanical pencil
NOTE: Choose the means of marking the material which works best for you. For example, the sharp point of an awl or knife works well for marking plastics that have had the paper removed. A fine felt tip pen may also work. A pen, fine point felt tip or a pencil works well for plastics with the protective paper still on. Any of the above may work for, or for marking wood, Masonite, aluminum or other material.
5) A tool which can cut the plastic, aluminum, wood, Masonite, or medium density fiberboard [MDF] you’ve chosen for your templates:
a) For long cuts in aluminum, plastics, wood and things like Masonite, I use my table saw with a fine tooth blade (e.g., 60 or more teeth on a 10" blade).
NOTE: If you are cutting aluminum, you can cut it with a table or miter saw, but will need a fine toothed, carbide blade. Specialty blades designed for this, with specialty tooth settings, are commonly sold where blades are for sale. You may find it handy to have around for other aluminum projects, like cutting your own miter slot guide rails for jigs.
b) If the pieces are not so short they pose a danger holding them by hand or with a clamp, I’ll use my motorized miter box.
NOTE: The smaller the pieces being cut, the more dangerous saws become. When cutting small pieces with a motorized miter or table saw, it becomes even more important to use clamps and, in the case of the table saw, to use a sled to carry the pieces.
c) For cutting smaller pieces of material, I prefer the band saw, which may be the safest and easiest to use.
NOTE: In the course of cutting some plastics, melted plastic will build up under the cut and catch on the saw blade opening (throat). You can clamp a piece of Masonite or other thin material on the side of the blade you are holding the material from, to raise the plastic enough so the melted plastic won’t catch. The raised be should be about 1/8" away from the blade, so the melted plastic doesn’t catch on it either.
d) If you have a hand held scroll saw, it can work just fine for these cuts. You will need a metal cutting blade and you will need a means of holding the material, if the pieces are small.
6) A method for smoothing the edges and fine tuning the angle:
a) A drum disk sander or edge sander, which is my go to method of smoothing the edges and adjusting the angles.
b) A belt sander
c) A course flat file at least 12" long.
7) If the sandpaper or file you used to smooth the edges and adjust the angle was very coarse, you’ll need a pad sander to knock off some or all the roughness.
8) If you want a polished edge, you’ll need a method of buffing them:
a) A buff pad you can mount on your drill press.
b) A buff pad you can mount on your lathe
c) A buff pad you can mount on a grinder (it MUST be able to spin at the RPM of your grinder;
d) An actual buffer, similar to your grinder and dedicated to buffing.
e) A hand held tool you can use to buff, like a die grinder, a Porter Cable random orbit [RO], variable speed sander-polisher with polishing head, or a Festool ROS with a polishing head.
1) Plexiglass, acrylic, Masonite or thin (approx. 1/8") aluminum.
2) 150 grit sandpaper
3) Polishing compound (I have very good luck with the red jewelers rouge).
Step 1: Setup Gauge Layout
1) Determine what size you want to make your gauges. For example, I chose five inch sides for mine and stayed in that ballpark size.
2) You can cut your material to the width you are going to make your gauges (e.g., five inches, as noted above) at this time, or you can move to the next step and make these cuts at the same time you are cutting the angles of your gauges.
3) Set your adjustable protractor [or bevel gauge] for the angle you want to transfer to your material (e.g., 30º, 35º, 40º, 45º, 50º, 55º, 60º, 65º, or 70º).
4) Lay your adjustable protractor [or bevel] on the material with the square plate of the protractor against a flat edge.
5) Mark your line in whatever fashion works best for you and the material you are using (e.g., scribe, knife, pencil, or felt tip marker).
6) If, instead of parallelograms you are going to do a different angle on each end, such as 30º and 35º, set the adjustable protractor up for the next angle and mark it opposite from the one you just marked. NOTE: If you, like me, used colored Plexiglass or Lexon, drag a pencil (carpenter’s pencils work good) across any scribed lines to make them stand out.
Step 2: Cutting the Gauges
1) The short, sweet and simple of it is, cut near the lines and as straight as you can. Any roughness of the cut will be touched up on the next step (sanding)
Step 3: Final Shaping, Sanding and Smoothing
1) Once you've made all your cuts, clean them up using a drum-disk, edge or belt sander.
2) After the edges are smoothed to the grit of the sander, check the angles of one or the other side, then, lightly, touch up the front or the back of the straight light until the angle of your gauge matches your adjustable protractor.
3) If you are doing a different angle on the opposite side, flip the gauge around, so you are dealing with the other two edges. Then, again, lightly touch up the front or the back of the shortest run until that side matches your adjustable protractor setting.
4) Once your angles are correct, if you are using plastic, and if you want to smooth or polish the edges, sand them using 150 grit paper. You can go finer sandpaper if you desire. Doing so will make polishing easier, but it may not be necessary to use a finer paper, if you have a good buffing system.
5) Once your edges are smooth and again, if you’re using plastic, buff them using a fairly hard wheel and the red rouge. Polish at about 1,500 RPM for quick results.
Step 4: Label the Angles
Whether you made parallelograms or gauges with a different angle on each end, labeling each angle would be a good investment of time, so you can tell, at a glance, what angle a given gauge is.
In addition to labeling each angle, I make a partial circle joining the two parts of each angle to make it clear which parts of the gauge I or anyone in my shop has to work off of to set something to the angle indicated.
The partial circles [drawn using a circle template, jar or whatever] are large enough I was able to scribe the angle inside the circles.
SIDE NOTE: Monitors and televisions can be salvaged to provide some nice, thick acrylic for projects like this.