Trig Question

[jocat54]

I have a question for those of you who know trig.
When I use an online calculator for sine bar height for an angle of 20 degrees and a sine bar length of 2.5" I get an answer of 0.8551 inches---but when using windows scientific calaculator and using the formula, Tangent A x b, I get .9099255xxxxxxx. See highlighted below. What am I doing wrong?

 

[Bill Gruby]

If Angle A is 20*, its Tangent is .363970. That times "b" (2.5) is .909925.

"b" (2.5) / cotangent A (2.747477) is 909925

Your answer is .909925

I did it both by the book and tables and long hand.

"Billy G"

 

[Tony Wells]

Unless I am misunderstanding something about what you are asking, "c", the hypotenuse, is the 2.5000" constant for your sine bar, not the base of the triangle "b". As you elevate the sine bar, "c" stays the same and is used for calculations, whereas "b" will get shorter. So your gage block stack (typically used) would be sin20°*2.500

But it's been a long day and maybe I am misunderstanding something.

 

[Bill Gruby]

I gave him the right one of both his answers.
I agree the side "c" is the 2.5 side.
.342020 X 2.5 = 85505


"Billy G"

 

[Tony Wells]

Umm, but the gage block stack for a 2.500" sine bar at 20° would be 0.8551.

Side "b" is unknown at this point. The only constants are side "c" (2.5000) and the desired angle of 20°. Therefore you cannot use side "b" for your stack calculations.

 

[Bill Gruby]

look again LOL I was editing while you answered. You actually have 2 angles not one. The 90*. So you actually have all three angles. 90 + 20 + 70 = 180 LOL You are correct though, side "b" is of no concern here.

"Billy G"

 

[Tony Wells]

Correct, that 90° is assumed since we are dealing only with a right triangle. That's what makes everything else work.

 

[Bill Gruby]

I used to be much better at the math game but age has taken its toll on the gray matter.

"Billy G"

 

[Tony Wells]

That it does Bill.....that it does.

 

[rdean]

I never got very far doing trig so for me the easiest way to find the stack is use the Machinery Hand book.
Look up a 20 degree angle in the table and divide by 2 since the sign bar John is using is half as long as in the table.
1.71010 divided by 2 = 0.85505 rounded up to 0.8551.

I don't have to try and remember the formulas.

Now if I could just find my glasses.
Ray