[4]

Check My Math, Please (right triangle)

[3]
[10] Like what you see?
Click here to donate to this forum and upgrade your account!

TORQUIN

Active Member
Active Member
Joined
Mar 19, 2015
Messages
98
Likes
52
#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

H-M Supporter - Sustaining Member
H-M Supporter - Sustaining Member
Joined
Jul 2, 2014
Messages
5,201
Likes
5,566
#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

Active User
Non-Donating Member
Joined
Nov 24, 2014
Messages
533
Likes
349
#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.
 
Last edited:

682bear

H-M Supporter - Premium Member
H-M Supporter-Premium Member
Joined
Nov 28, 2016
Messages
202
Likes
348
#4
20180713_220629.jpg

If I'm reading the question correctly...

-Bear
 

tcarrington

Making miscellaneous parts for years now
H-M Supporter - Sustaining Member
Joined
Dec 27, 2013
Messages
43
Likes
42
#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

H-M Supporter - Premium Member
H-M Supporter-Premium Member
Joined
Nov 28, 2016
Messages
202
Likes
348
#6
39.266 degrees...

-Bear
 

TomS

Active User
H-M Supporter-Premium Member
Joined
May 20, 2013
Messages
1,687
Likes
658
#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

Administrator Trainee
Staff member
H-M Supporter - Sustaining Member
Joined
Jun 29, 2014
Messages
266
Likes
225
#8
Dial Drawing.png
 

Bob Korves

H-M Supporter - Sustaining Member
H-M Supporter - Sustaining Member
Joined
Jul 2, 2014
Messages
5,201
Likes
5,566
#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

Active Member
Active Member
Joined
Mar 19, 2015
Messages
98
Likes
52
#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

H-M Supporter - Sustaining Member
H-M Supporter - Sustaining Member
Joined
Dec 31, 2010
Messages
501
Likes
246
#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.
 
[6]
[5] [7]
Top