How to convert an inch dimension to arc minutes for precise measurement?

  • Thread starter Thread starter SevenToFive
  • Start date Start date
  • Tags Tags
    Arc
AI Thread Summary
To convert an inch dimension to arc minutes, the discussion focuses on calculating the allowed movement of 1/8 inch on a 3-foot diameter roll. The circumference is calculated as approximately 113.1 inches, leading to a fraction of a revolution of 904.8 required to move 1/8 inch. This results in an allowed rotation of about 23.87 arc minutes. A quick estimate using the navigational offset rule suggests that 1/8 inch on an 18-inch radius equates to approximately 25 arc minutes. The calculations confirm that both methods yield similar results, emphasizing the importance of precise measurement in engineering contexts.
SevenToFive
Messages
56
Reaction score
3
How can l convert an inch dimension to arc minutes? We have a customer who requires a 3 foot diameter roll not move more than an 1/8 inch. I need to convert the 1/8 inch to arc minutes to compare to the backlash in our gearing.

Any help is greatly appreciated.
 
Engineering news on Phys.org
SevenToFive said:
How can l convert an inch dimension to arc minutes? We have a customer who requires a 3 foot diameter roll not move more than an 1/8 inch. I need to convert the 1/8 inch to arc minutes to compare to the backlash in our gearing.

Any help is greatly appreciated.
1/8" is a fraction of the circumference and arc min is the associated angle.
 
18" is radius and the angle is [1/(8*18)] rad = [{(180*60)/(8*18)}/π] arc min = 75/π = 23.87 arc min
 
Last edited:
  • Like
Likes SevenToFive
I get a different answer, by a factor of π.
D =36"
Allowed Move = 1/8" = 0.125"
Circumference = π⋅D = 113.1"
Circum/Allowed Move = 113.1/0.125 = 904.8 (the fraction of a revolution req'd to move 1/8")
Allowed Rotation = 360°/904.8 = 0.3979° = 23.87 arc min
 
  • Like
Likes SevenToFive
Tom.G said:
I get a different answer, by a factor of π.
D =36"
Allowed Move = 1/8" = 0.125"
Circumference = π⋅D = 113.1"
Circum/Allowed Move = 113.1/0.125 = 904.8 (the fraction of a revolution req'd to move 1/8")
Allowed Rotation = 360°/904.8 = 0.3979° = 23.87 arc min
I am sorry I had committed a calculation mistake,now I also get the same answer.
 
  • Like
Likes russ_watters, Baluncore, SevenToFive and 1 other person
For small angles, a quick estimate can use the navigational offset rule of “1 in 60, per degree”.
So 1/8” on a radius of 18” = 1 in ( 18 * 8 ) = 1 in 144.
Apply the 1 in 60 rule, then multiply degrees by 60, to get ( 60 * 60 / 144 ) = 25 arc min.

The 1 in 60 navigation rule comes from 1 radian ≈ 57.29578 degrees.
Mathematically we have ( 60' * 57.29578° / 144 ) = 23.8732 arc min.
 
  • Like
Likes SevenToFive
Thanks everyone for the replies. Greatly appreciated.
 
  • Like
Likes Tom.G

Similar threads

Replies
18
Views
8K
Replies
2
Views
2K
Replies
1
Views
2K
Replies
2
Views
2K
Replies
2
Views
2K
Replies
24
Views
8K
Replies
8
Views
2K
Back
Top