Dumb question #1 - protractors

[dbb-the-bruce]

Maybe not really a question so much as a puzzlement.

Shopping for a protractor - to date, I've been relying on other means for angle measurement - So the puzzlement is why both round head and square head protractors? Or more accurately, in what situation would a round head protractor be better suited than a square head one? I can't for the life of me come up with a use case where the round head wins.

Seems to me that having a square head makes it really convenient to indicate the set angle as a compliment and also from an orthogonal feature. IE. I'm assuming that the square head sides are produced square and parallel with a high degree of accuracy.

Am I missing something? is there any case where a round head is better?

-Dave

 

[Bob Korves]

A rounded protractor has the graduations on the curved edge of the protractor, so you can mark your work right next to the degree mark on the protractor. The round head protractor still has one straight edge for aligning it with a straight edge or line on the work. The square head protractor has four sides that can be used to align with the datum edge of the work for measuring angles, making it more useful in that regard than the round edge protractor. Both types have their places for differing needs. Machinists use many different types of protractors for the work they do, depending on the work at hand.

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[dbb-the-bruce]

I guess I'm being dense.....

I get that there are lots of different varieties of protractors. For the basic arm and gage type, the angle is indicated on the top side of the arm using the markings. Angle is between the base and arm.

If you swing the arm up around top, it doesn't look like there is any way to use the gage. You could have an arm with a hole and indicator mark so you could use it up on the topside but I've not seen this on simple gage/arm protractors.

I can see that you could mark at some tick on the top / rounded side - the mark would be 2 or so inches (gage radius) from the baseline - might occasionally be useful...

All this vs. a square head that you can line up a bunch of different ways.

Perhaps I just think too much (ha!)

-Dave

 

[cbellanca]

May I repeat there are no dumb questions. Make a choice from the above list to best suit your needs. the square edge has been more useful in the shop for layout work. I have used a curved edge protractor for drawings.

 

[dbb-the-bruce]

Thank you for confirming my thoughts - I can see how a round head could be better for drawing or maybe something like laying out a clock face. I'll probably get a square head that has a sliding arm for depth. I've got a tiny sliding depth tool that has a few major angles scribed on it and I find it incredibly useful.

Regarding drawing - I love mechanical drawing, but sadly no longer really need to do it ever. It seems like it's a dying art. In HS I took as much drawing as I possibly could. I knew that it would serve me as an engineer. I now use CAD for pretty much everything, but that foundation has paid off in spades.

Whenever I find old mechanical drawing books, I grab them just to look at. Some of the plates are truly amazingly packed with beautiful detail.

I just picked up a copy of "Rogers' Mechanical Drawing and Design"

-Dave

 

[kd4gij]

Easy one of each. And a digital angle finder while your at it. We are tool junkies right?