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1. ## Improvised tangent bar

This post is more in the nature of a solution looking for a problem. For a long time I've been noodling how to build a tangent bar, an angle setting tool that would, like the sine bar, convert a linear measurement into an accurate angle. The advantage of such a device over the conventional sine bar would be the fact that it could, hopefully, incorporate a bar moved by a precision screw to replace the block stack of the sine bar. This would make it a self-contained instrument without the need for an external height setting mechanism as is the case with the sine bar.

I'm sad to report that so far I haven't pictured a design that didn't have some flaw that would tragically affect its accuracy. However, while rehashing the problem in the shower, I did have an idea - the one presented here - that might have some utility for someone.

My idea revolved around the notion that the typical combination square (CS hereafter) already has everything needed to be a tangent bar. The CS head forms a right angle with the scale and the scale makes one side of the triangle length adjustable. (In the picture below, the CS has been laid against a ruler to form the triangle of which I speak.) The tangent of the angle opposite the CS head is given by:

tan (angle) = (CS head length) / (CS scale length from CS head to ruler)

or, inverted:

(CS scale length) = (CS head length) / tan (angle)

So, to set the angle we measure the CS head length and divide that by the tangent of the desired angle to obtain the amount by which we must expose the CS blade to set the angle.

On the CS shown, the head length is measured to be 3.777 in. Dividing that by tan(30) yields 6.542 in. Now we need to convert .542 in to 32nds (curse the inferial system to hell). 0.542 *32 = 17.34. So, I set the exposure to 6 & 17/32 + a smidgen ("smidgens" are 1/1776 th of an inch, another inferial nonsense unit, this one with patriotic overtones.)

To check the angle, I placed my precision 30-60-90 block in the angle and it fits very nicely.

So, certainly not as accurate as a sine bar although probably better than a cheap protractor. Does it have a use anywhere? Good suggestions are welcome.

2. ## The Following 4 Users Say Thank You to mklotz For This Useful Post:

Jon (06-15-2018), NortonDommi (06-18-2018), philipUsesWood&Brass (06-15-2018), Seedtick (06-15-2018)

3. Thanks, great use of tools we have.

My Scales are either Imperial fractions & Decimal units, OR Imperial & Metric Units.

Unfortunately for us, any company that would (DOES ?) provide similar scales for a Combination Square would Charge BEYOND what the Average "Joe in his Shop" could afford!

I have Two 6" scales, An Antique, butusable Starret, I bought 15 years ago for \$30.00. And a PEC Nitride Coated Imperial/Metric, that I bought last year, for . . . . . . . . . . . . . . . . \$30.00.

I just stare at the Starret, I USE my PEC, Precision Equipment Corporation is my "I can Afford" tool source.

Great Concept though, thanks.

philip
from the Great Pacific NorthWET.

4. Marv
I have been running a few ideas through my head and maybe you and I could come up with a practical solution. Shoot me a email and I'll tell you my ideas.

nel2lar AT Yahoo DOT com

Remove the caps and replace with proper signs

Nelson

5. Thanks mklotz! We've added your Improvised Tangent Bar to our Measuring and Marking category,

Doug

7. Marv, you can get a metric square for cheap, probably not the quality you want, but.....
https://www.aliexpress.com/item/New-...ceBeautifyAB=0

\$4.25 shipped to the USA.

8. Marv's idea using a depth mic gives a bit more precision quite easily. Many thanks, Marv

9. ## The Following User Says Thank You to Saltfever For This Useful Post:

saintrain (07-01-2018)

Doug

11. ## The Following User Says Thank You to rossbotics For This Useful Post:

philipUsesWood&Brass (06-19-2018)

12. Originally Posted by rossbotics

Doug

That will work.

I suspect that we never see designs like that in production because the motion of the plate is non-linear relative to the handwheel calibration. That means a table would have to be used to determine the handwheel setting required for a particular angle.

Still, it has the advantage of being self-contained, not requiring a set of gauge blocks, so easier to store and carry.

13. Doug
There you go. Now all you need to do is go to the machinist book and see how much you need to raise it to a required angle with out gage blocks. I knew you was up to the challenge.
Very nice now to make one.
Thank you
Nelson

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