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.

 

[Rog02]

Hi Marv:

Just got to ask, when you sleep? You must stay up all night figuring this stuff out. LOL

I saw this on your webpage and the SC Club page, some time ago and downloaded it. I am in the slow mode of building a new angle guide for a Turner-Walker Bandsaw and am seriously considering using this instead of the graduated scale.

 

[mklotz]

You're supposed to sleep !?!

As I build models, I keep a list of things that need to be fixed, improved, solved, etc..
After completing a model, I'm usually tired of doing tiny precise stuff so I take a break by addressing some of the items on my list. By the time I address an item on the list, I've spent some time thinking about how to solve it in those boring moments we all encounter - dentist office, renewal line at DMV, SWMBO talking to me, etc..

Focusing on building a solution to the problem (as opposed to jury rigging something while doing another job), combined with the "dull time" pondering tends to produce a nicer product that provides some real positive feedback when it's used during the next round of model building.

 

[Tin Falcon]

Greenie:
Interesting tool for boiler makers and sheet metal work. Thank you for letting us know about them.
I do think that marv's has a use in the home model shop. I for one can not see using a two foot long angle gage to do a set up on my mini mill or mini lathe that is only two foot long.
Marv thanks again for sharing you Ideas and programs with this forum.
Tin

 

[BobWarfield]

I like it!

It makes me wonder why the Chinese or someone else isn't making one with a builtin caliper and slightly changed software that allows the angle to be read directly. Calipers are so cheap these days one could easily build on of these with a permanently attached caliper.

I guess clearance might be a problem, but vernier protractors are bulky too. Something like this with a digital readout would be extremely handy.

Cheers!

BW

 

[mklotz]

Bob,

Digital protractors exist,

http://www.fvfowler.com/protractor.html

although, AIUI, they directly measure rotation rather than inferring it from a linear measurement of chord length.

Any electronic angle measuring device is going to be a bit limited in utility by the need to have the electronic read head present. My skeletonized approach can be built in any scale so as to fit into almost anything that needs to be measured. With the measuring feature externalized, there's no bulk to get in the way of the measuring. The price one pays for this utility is the added time and mathematical effort needed to make a measurement. (I'm retired so my time has only the value I choose to assign to it. If my hobby were a business, I'd be long ago bankrupt.)

 

[wareagle]

Marv,

That is an ingenious tool! It's not often that I find myself needing to get angles that accurate, but with no more time than this little tool would take to make, it would be a worthy addition to my tool box. The math behind it may complex to some, but your program make use of it a breeze. Thanks for sharing!

W/E

 

[Powder keg]

Great tool Marv,

I remember seeing something similar for testing the center distance for gears. You would make the shafts so the gears "ran good" then measure the center distance and you could use that dimension for your part..

Wes