Sine bar protractor

[mklotz]

Reading a conventional protractor to any decent accuracy always tries my patience. So, I built a sine bar protractor. As can be seen, in addition to the measuring arms, it has two rolls, similar to those on a sine bar.



An offset half-lap hinge allows both arms to close flat against each other.



In use the device is set (or read) with calipers reading the separation between the two rolls.



The mathematics for converting between angle and caliper reading are a bit complicated, so I wrote a program to do the dirty work. It's available in the PROTRAC.ZIP archive on my page.

[mklotz]

Here's a diagram that details the associated mathematics...



The numerical values for R, d, delta and zeta apply only to my particular implementation of the design.

[AussieJimG]

Thanks Marv, that looks like a useful device.

Jim

[steamer]

Slick tool Marv!

Dave

[ScroungerLee]

Thanks Marv.  Great idea.

It looks easy uhhh useful.

Lee

[steamer]

Ahh don't let the "squiggly lines" bother ya Lee.   Like lots of things , it looks far worse than it really is.

Do you have a desk top calculator?....I'll walk you through it if you think it useful

PM me if you want to give it a go.

 

Dave

[mklotz]

Lee,

Perhaps you missed it but there is a program (PROTRAC) available on my page to do the math for you.  The diagram and derivation that Neanderthal Dave dismisses as "squiggly lines" is there merely to show how the math embodied in the program is determined.

[steamer]

Ah Marv!   Top a the morning to ya!

How are you bud!....I'd wave but my Knuckles hurt.

Dave

[mklotz]

I'd wave but my Knuckles hurt.

LOL. 

Cave floors are very abrasive.  Move to the swamp where the ground is mushy.

[chucketn]

Marv, on your protractor, are the rolls drill rod? Are they hardened?

If I made the protractor using drill rod for the rolls, tapped them for attachement, and then heat treated them to keem them from being marred, would the tapped threads stay the same size?

Chuck

[steamer]

I'd wave but my Knuckles hurt.

LOL. 

Cave floors are very abrasive.  Move to the swamp where the ground is mushy.

Oh why didn't I think of that! .....oh yea......!

[mklotz]

No, they're not drill rod nor are they hardened.  They're some stainless slugs I had lying around the shop.

I doubt the device is accurate to better than a minute or so.  So it's not worth going overboard in its construction.  OTOH, how often does one really need to measure angles better than that.  If you did, you wouldn't use a protractor.

[ScroungerLee]

Thank you for the offer to help steamer, and sorry about the knuckles

Marv, you have so many nice programs on your site that yes, I did forget about that one.  I think I have used it before as I have some of your other very useful programs.

Lee

Edit: it must have been your sine bar program I used, not the same one is it?