I have a 20" plate with 2 holes in it. How do I measure the angle between them from the center accurately

Question

2 holes, They're both near the edge. I want the angle of between them measured from the center of the plate very very accurately, possibly even to minutes seconds if possible. Is there some engineering trick or tool that will help me accomplish this. A regular protractor is too inaccurate.

Thanks

Answer 1

I assume that you do not have the center marked? If that is the case, Find a machine shop with a CMM. A good prototyping machine shop will usually have one, and if not, some other very accurate QC tool.

A CMM is a very accurate computerized measurement device. It is not uncommon for these to be accurate to less than 0.010 mm. That should be plenty good enough for you to get accuracy on measurement to inside of seconds of a degree.

If you have a mill... you might set it up with a dial gauge and use that to measure the part.

Answer 2

Other than using a CMM you could make pins that are a slip fit for the holes and then use them as guide pins. Then take a vernier protractor and mesure them. Bring a magnifying glass though because those suckers are hard to read. Then of course you have the formulas above that you can always employ.

My method would also require you to make a construction hole in the center of the plate.

Answer 3

First, take a ruler and line up the center of the plate with the first hole. Then find the place on the rim that is colinear with the hole and the center. Do this for the second hole as well. Measure the distance between the two points on the rim, and call this distance s. The angle will be = sin^-1(s/20),

i.e., sin(angle)=s/20.

Answer 4

Sin20 + the arc of tan of your angle.