Improvised tangent bar

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Jun 15, 2018, 11:33 AM
mklotz

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)

https://s3-us-west-1.amazonaws.com/f...e/113221-1.jpg

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.
Jun 15, 2018, 05:33 PM
philipUsesWood&Brass

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.
Jun 15, 2018, 08:07 PM
ncollar

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
Jun 16, 2018, 05:42 AM
DIYer


Thanks mklotz! We've added your Improvised Tangent Bar to our Measuring and Marking category,
as well as to your builder page: mklotz's Homemade Tools. Your receipt:

<div id="blocks"> <div class="block b1 pngfix"> <div class="bimg"> <div> <a href="http://www.homemadetools.net/homemade-improvised-tangent-bar"> <img src="/uploads/214992/homemade-improvised-tangent-bar.jpeg"/> </a> </div> </div> <div class="head pngfix"></div> <div class="left pngfix"></div> <div class="right pngfix"></div> <div class="blockover b1 pngfix"> <div class="title"> <a href="http://www.homemadetools.net/homemade-improvised-tangent-bar">Improvised Tangent Bar</a> <span> by <a href="http://www.homemadetools.net/builder/mklotz">mklotz</a></span> </div> <div class="tags">tags: <a href='http://www.homemadetools.net/tag/measurement'>measurement</a> </div> </div> </div> </div>
Jun 18, 2018, 01:27 AM
rossbotics

I'll have to think about this one Marv, gotta couple ideas swimming around up there

Doug
Jun 18, 2018, 05:52 PM
metric_taper

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.
Jun 18, 2018, 05:59 PM
Saltfever

2 Attachment(s)

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

Attachment 24429 Attachment 24430
Jun 19, 2018, 05:59 AM
rossbotics

1 Attachment(s)

What do you think about this ? Just a basic design, nothing scientific

Doug

Attachment 24431
Jun 19, 2018, 09:03 AM
mklotz

Quote:

Originally Posted by rossbotics

What do you think about this ? Just a basic design, nothing scientific

Doug

Attachment 24431

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.
Jun 19, 2018, 10:58 AM
ncollar

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
Jun 19, 2018, 11:31 PM
rossbotics

I agree on the mechanical movement and what you say about a table, I thought maybe you might be up for a challenge like myself, if someone doesn't need that high end precision then this design would work for that, there is another way to elevate the upper bar but you couldn't raise it only about 20° not 44°, this is the only way I see to accomplish such movement (mechanically)

I'll make a deal with you, I'll give you the measurements of the 3 points of my triangle, you then in return tell me what the T.P.I. are on the screw I'll be making, figure it to where one revolution on the dial would be equal to say .250" - .500" rise on the upper bar ? doesn't matter there to much, just as long as it's nothing oddball, I can change the three measurements on triangle to whatever anytime.

I think you and I could come up with something that would be satisfactory for your home shop machinist,

Doug
Jun 20, 2018, 09:52 AM
mklotz

1 Attachment(s)

Well, I worked out the geometrical relationship for what you pictured. In a word, it's not pretty. I knew the relation of angle to screw movement would be nonlinear but it's even worse than I thought.

The attached diagram shows the relevant equations that relate the angle of the upper plate, 'z', to the location of the pivot on the moving nut, 'x'.

At the risk of insulting your intelligence, I'll point out that mathematics always works with angles in radian measure, so the pi/2 is the equivalent of 90 degrees.

Attachment 24452
Jun 20, 2018, 04:17 PM
philipUsesWood&Brass

I know this is a little off tangent (attempt of Pun) but I saw this while shopping for "V" Blocks and Bought one:

Now, To have energy to SPARE for hobby time!!!!

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

philip The Pacific NorthWET is dry!
Jun 20, 2018, 04:54 PM
mklotz

Quote:

Originally Posted by philipUsesWood&Brass

I know this is a little off tangent (attempt of Pun) but I saw this while shopping for "V" Blocks and Bought one:

Now, To have energy to SPARE for hobby time!!!!

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

philip The Pacific NorthWET is dry!

I've got one. Save your money.

The scale is too tiny to read easily and the vernier is a joke. It works OK as an adjustable holder if you have precision angle blocks or a sine bar with which to set it. (Of course, if you have those you don't need it.) The adjustment locking screw is on the bottom - a master stroke of bad design.

Too small to serve as a boat anchor, it's only real utility is as a paper weight.
Jun 21, 2018, 12:45 AM
rossbotics

Quote:

Originally Posted by philipUsesWood&Brass

I know this is a little off tangent (attempt of Pun) but I saw this while shopping for "V" Blocks and Bought one:

Now, To have energy to SPARE for hobby time!!!!

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

philip The Pacific NorthWET is dry!

Don't waist your money
Jun 21, 2018, 01:08 AM
rossbotics

The math will never work out just right to use with a calibrated handwheel , got on cad this morning, no way, to many variables, waisted time, oh well Marv we tried, looked good anyway LOL

Doug
Jun 22, 2018, 10:57 AM
mklotz

Searching "tangent bar" on Google Images led to this device...

VERTEX Micrometric Tangent Bar & Angle Gauge Block Set - Secure Tooling Sdn Bhd

which is emphatically NOT a tangent bar. Rather, it's a limited range sine bar with the conventional gauge block stack replaced by a calibrated screw. Now, you can get away with this as long as the angle is very small. When sin(A) is small, it's true that:

sin(A) ~= A

(angles expressed in radians). In another thread...

http://www.homemadetools.net/forum/g...3620#post78402

I showed this chart...

angle = 1 deg: sine = 0.017452, radians = 0.017453, error = 0.005077 %
angle = 2 deg: sine = 0.034899, radians = 0.034907, error = 0.020311 %
angle = 3 deg: sine = 0.052336, radians = 0.052360, error = 0.045707 %
angle = 4 deg: sine = 0.069756, radians = 0.069813, error = 0.081278 %
angle = 5 deg: sine = 0.087156, radians = 0.087266, error = 0.127037 %
angle = 6 deg: sine = 0.104528, radians = 0.104720, error = 0.183005 %
angle = 7 deg: sine = 0.121869, radians = 0.122173, error = 0.249205 %
angle = 8 deg: sine = 0.139173, radians = 0.139626, error = 0.325666 %
angle = 9 deg: sine = 0.156434, radians = 0.157080, error = 0.412420 %
angle = 10 deg: sine = 0.173648, radians = 0.174533, error = 0.509506 %

Because of the very linear relationship, especially in the range of 0 to 5 degrees, a calibrated screw as pictured in the earlier reference is possible. But it's still a sine bar, not a tangent bar.

The simplest conception of a tangent bar would look roughly like a sine bar. The gauge block stack would be replaced with a bar of fixed height, "Y". A screw would allow this bar to be slid back and forth beneath the bar holding the work such that the distance of the bar from the pivot, "X", could be adjusted. Then the bar angle could be found from:

tan(A) = Y / X

Of course, the dial on the screw could not be easily calibrated because of the very non-linear form of the tangent function. This explains why one never sees commercial versions of such a device.
Jun 22, 2018, 11:04 AM
rossbotics

This is exactly why I said we could not use a graduated dial, oh well off to something beter