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Check My Math, Please (right triangle)

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TORQUIN

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#1
On a lathe project I want to cut and angle from 1.100" dia to 2.735" dia, over a 1" distance. I need to know the angle to set the compound to. The way I calculated this is to create an imaginary triangle between the 2.735" and 1.1" diameters, across the 1" distance. This led me to first subtract the small diameter from the equation because it it outside of the imaginary triangle.
2.735 = 1.100 = 2.635"
Now I plugged in the values to a triangle calculator at https://www.calculator.net/triangle-calculator.html.
It gave me 31.451 and 58.549° . I have set the compound to either of those angles but it is not meeting those two diameters over a 1" distance. Not sure what I am doing wrong.
Part is 2" long, and I am trying to have a single angle going from 2.735" to 1.100" in the middle 1" of the part, having .5" of 2.735 dia and .5" of 1.1" dia on either end. This is for a hand knob. The large end of the angle is at the correct location, linearly, and the small end is 1.100", for .5" in length. The black line is the 2" mark, from the end.
A pic of the part, currently.
2018-07-13 21.31.16s.jpg

Thanks,
Chris
 

Bob Korves

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#2
Your first mistake is in your first subtraction. The answer should be 1.635. Try again with that number and see what you get...
 

extropic

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#3
You have made an error in your definition of the problem. Probably didn't consider that you should use 1/2 the difference of the diameters (use the change in radius, not diameter).
Regardless, I think the angles you want are 39.266° from larger diameter to smaller and/or 50.734° from smaller to larger.
 
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682bear

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#4
20180713_220629.jpg

If I'm reading the question correctly...

-Bear
 

tcarrington

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#5
the compound setting should be based on difference in radius, not diameter.
I think you will get 39.3 / 50.7 for your compound.
you need a 0.818 inch change in 1.000 inches.

edit - we posted at about the same time
 

682bear

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#6
39.266 degrees...

-Bear
 

TomS

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#7
On a lathe project I want to cut and angle from 1.100" dia to 2.735" dia, over a 1" distance. I need to know the angle to set the compound to. The way I calculated this is to create an imaginary triangle between the 2.735" and 1.1" diameters, across the 1" distance. This led me to first subtract the small diameter from the equation because it it outside of the imaginary triangle.
2.735 = 1.100 = 2.635"
Now I plugged in the values to a triangle calculator at https://www.calculator.net/triangle-calculator.html.
It gave me 31.451 and 58.549° . I have set the compound to either of those angles but it is not meeting those two diameters over a 1" distance. Not sure what I am doing wrong.
Part is 2" long, and I am trying to have a single angle going from 2.735" to 1.100" in the middle 1" of the part, having .5" of 2.735 dia and .5" of 1.1" dia on either end. This is for a hand knob. The large end of the angle is at the correct location, linearly, and the small end is 1.100", for .5" in length. The black line is the 2" mark, from the end.
A pic of the part, currently.
View attachment 271893

Thanks,
Chris
Page 674 of Machinery's Handbook 30th edition gives you the formulas you need to compute the angle. Hope this helps.
 

vtcnc

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#8
Dial Drawing.png
 

Bob Korves

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#9
Be careful that the scale you are reading on the cross slide is giving you the angle you want. It is very easy to set up for the wrong portion of the quadrant. This is a VERY common mistake.
 

TORQUIN

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#10
Sorry, I put in the calculated larger dimension wrong. It should have been 1.635. That's what I used for the calcs. My problem was the use of diameter, not radius, for the calcs. After adjustment of the compound, it looked much better, and the second one looked perfect.
Thanks to all for the check and info.

2018-07-14 07.28.25s.jpg

2018-07-14 08.11.32s.jpg

Thanks,
Chris
 

rock_breaker

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#11
Sorry, I put in the calculated larger dimension wrong. It should have been 1.635. That's what I used for the calcs. My problem was the use of diameter, not radius, for the calcs. After adjustment of the compound, it looked much better, and the second one looked perfect.
Thanks to all for the check and info.

View attachment 271932

View attachment 271933

Thanks,
Chris
It helps us to see if we are as smart as the average bear.
 
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