I always thought I wanted a precision angle finder. I finally decided to make my own. The photo shows it in use to check the angle of a rafter in my attic. This is a very easy project, but some precautions need to be followed to guarantee the accuracy of the tool when finished.

Step 1: Tools and Materials

Materials

A plastic protractor
A piece of wood
Some screws
A piece of wire or a long finish nail and a hex nut
Magnetic cabinet door catches (optional)

Tools

A table or radial arm saw
A rule (and a square)
An electric drill or drill press and bits
A countersink bit
Screwdrivers
Clamps
A file
A pair of pliers to bend wire, or a welder to weld a hex nut to a finish nail
A level
A grinder

The photo shows a commercially available angle finder. It reads 360 degrees. A protractor has readings for 180 degrees, but that will be no problem for a reason explained later. While the commercial version is not expensive, it is more fun to make your own.

(The photo is from Lowes.com.)

Step 2: Cut a Piece of Wood

I used a piece of 1 x 4 clear pine I had from another project. The two long sides must be exactly parallel to one another. I used a caliper to check. If you have a good table saw accurately calibrated, you should have no trouble.

Saw your piece off to be a little longer than the base of the protractor, and so the corners are exactly square. Check with a good square and by measuring the diagonals. These things really need to be very accurately done, or the whole tool will be compromised.

The square is a larger tri-square I have long wanted. See this Instructable for how I made it.

Step 3: Clamp the Protractor to the Wood

Once you are satisfied that your piece of wood has long edges exactly parallel and the corners are exactly square, rest the piece of wood on a flat surface. Place the protractor against it and let the protractor rest on the same flat surface. Gently clamp the protractor to the wood. Be careful that nothing moves during the clamping process.

Step 4: Fasten the Protractor to the Wood

With the clamps firmly in place, drill and countersink for two wood screws that will hold the protractor to the wood.

I chose to locate the screws at 45 degrees on each side of the protractor. Because they are countersunk, the screw heads are slightly below the outer surface of the plastic on the protractor.

I considered painting the wood white or placing paper under the protractor to make reading the angles easier, but decided it was not necessary.

Step 5: The Pointer

I planned to use a simple piece of straight wire with a round loop bent onto one end for the pointer or indicator. But, we moved a few weeks ago and I can not find that wire. I have a welder and decided to use it. My pointer is from a 2 1/2 inch finish nail with a hex nut welded to its head. Here you see a piece of 1/8 inch steel clamped in a vise. The head on the finish nail has been filed flat so it will stay in place easily. The finish nail and a #8-32 hex nut are held in place by spring clamps so I can weld the nut to the nail.

Step 6: Finish the Pointer

I welded from both sides of the nut and ground the welding joints as flat and smooth as possible. I drilled the hole in the nut out to make a smooth surface inside. That is so it can swing on the smooth part of the screw in the photo as freely as possible.

Step 7: Attach the Pointer

I drilled a hole at the center point as marked on the protractor. The hole in the protractor needs to be large enough for the shank of the screw. The portion of the hole in the wood needs to be a little smaller so the threads on the screw grab the wood.

I placed a washer under the pointer. I did not make the head of the screw tight against the hole in the pointer, but made certain it is loose enough for the pointer to swing freely.

Step 8: Calibration Check

Does the angle indicator show "0" degrees when resting on a level surface? I used a level, but the surface was not level. So, I placed a thin wedge under the level until the bubble was centered between the lines. (See the first photo. I turned the level end for end to be certain it was reading accurately, too.)

See the second photo. The pointer is correctly calibrated. If the pointer did not read correctly, I could bend the nail just a little near its middle to get an accurate reading corresponding to the level.

Step 9: Using the Angle Finder

The first photo shows the angle finder in use to read the angle of a rafter in my attic.

The commercial angle finder shown in step 1 is graduated with readings for 360 degrees. But, it does not have two parallel edges. I can place my angle finder under or over an angle to be measured. The first photo shows a reading taken from under that angle. The second photo shows a reading taken from above the angle. All you really need to know is how many degrees off of a horizontal or a vertical surface the angle is. The third photo shows the angle finder used with the side as the base for measuring a more vertical angle.

My angle finder does not have magnetic bases like the commercial version does. But, I could easily acquire some magnetic catches like those used inside cabinets to retain a door. If I put two on each side, I could attach my angle finder to a metal surface.