Another round of "what the heck is this?"

[VelocityDuck]

Length is just under 6". The rods/cylinders are about 5/8".

PXL_20230520_125740030.jpg (648.24 KiB) Viewed 1598 times

PXL_20230520_125720366.jpg (687.82 KiB) Viewed 1598 times

[rmac]

Finally, one I recognize! It's an old rusty sine bar.

[Lew Hartswick]

I suspect it's "Exactly" 5.000 inches between centers of the "rounds".
...lew...

[RONALD]

Here you go! Buy new!

https://www.mscdirect.com/browse/tn?msc ... 20Keywords

[VelocityDuck]

Well I'll be.

I thought about a sine bar, but I thought those had the cylinder only on one end. (I'm learning)

Oh well, now I got another tool that I'll never use.

[liveaboard]

I recognized it as a sine bar; but maybe someone could explain what a sine bar is used for?
Because I don't have a clue.

[Charles T. McCullough]

I recognized it as a sine bar; but maybe someone could explain what a sine bar is used for?
Because I don't have a clue.

rmac (above) has a link to a Wikipedia article that explains it. It is used to determine an angle, because the bar itself is considered the Hypotenuse of a right triangle and the height that one end of the bar is raised is the height of a right-triangle. With those two numbers you divide to get the Sine of the angle at the other end.

[Harold_V]

While it's true that a sine bar can be used to determine an angle, it is generally used to SET an angle with a high level of precision. It is for that reason that the distance between the two rolls is critical. Even if it isn't precisely 5" (or 10"), so long as the exact distance is known the height of the required stack for any given angle can still be determined using trigonometry.

Tria=three and gonia=corner ----- it's all Greek to me.

H

[VelocityDuck]

I recognized it as a sine bar; but maybe someone could explain what a sine bar is used for?
Because I don't have a clue.

I found a This Old Tony video that is informative (and as usual, humorous)
https://www.youtube.com/watch?v=PO-Ab7YfBzY

[liveaboard]

Now I know.
Thanks guys.

[Charles T. McCullough]

While it's true that a sine bar can be used to determine an angle, it is generally used to SET an angle with a high level of precision. It is for that reason that the distance between the two rolls is critical. Even if it isn't precisely 5" (or 10"), so long as the exact distance is known the height of the required stack for any given angle can still be determined using trigonometry.

Tria=three and gonia=corner ----- it's all Greek to me.

H

hee hee... I used the word "determine" to mean inclusive of "Set" and "Measure", but I guess my vocabulary missed.

As to "high level of precision"... I always feel like my precision is improved when I get math involved, but then the origin of the numbers in the math have to be more precise than the end result or the end result just looks precise because my calculator has 10 digits in the display. How accurate is the length of the sine bar? It can vary a measurable amount depending on temperature (and how many times I have dropped it). How accurate is whatever I used to raise one end of the sine bar? How clean are the surfaces the ends of the sine bar are resting on (this includes the surfaces of the cylinders on the ends of the sine bar and the surfaces of what ever is raising the one end and what it all is resting on)? And how accurately measured was whatever was used to raise the sine bar? And in a ham-handed idiot like me, how accurate did I use the el-cheap-o devices used to make the measurements?

The old, "Calculate it on an electronic calculator, measure it with a wood ruler, mark it with chalk and cut it with a torch, and I need new bifocals, precision!?

[mklotz]

The error in the angle set with the sine bar is a function of two other errors - the error in the sine bar length and the error in the stack height.

The equation that describes the sine bar is:

sinA = H/L

where:

A = desired angle
H = stack height
L = sine bar length (distance between roll centers)

Usually, the sine bar length is well known and its contribution to the angle error can, to first order, be ignored. The important error is then the error in the stack height.

With a little bit of calculus we can differentiate the sine bar equation and obtain the equation that relates the height error to the resulting angle error:

dA = dH/(LcosA)

where:

dA = error in angle in radians
dH = error in stack height

(To convert dA to degrees, multiply by 180/pi = 57.296...)