How to calculate - Woodworking Talk - Woodworkers Forum
 4Likes
  • 2 Post By GeorgeC
  • 1 Post By wretched64
  • 1 Post By GeorgeC
 
Thread Tools Display Modes
post #1 of 16 Old 06-19-2019, 02:57 PM Thread Starter
Member
 
Join Date: Oct 2017
Posts: 75
View wretched64's Photo Album My Photos
How to calculate

How do I calculate this length. These boards meet at center top 45ed together and then extend down to wall where it meets them at a 45. Width needs be 84. How do I find out using math how long to make the pieces

Sent from my SM-G965U using Tapatalk
wretched64 is offline  
Sponsored Links
Advertisement
 
post #2 of 16 Old 06-19-2019, 03:28 PM
Senior Member
 
Join Date: Jul 2008
Location: Florida Panhandle
Posts: 11,596
View GeorgeC's Photo Album My Photos
You need to draw that triangle a little more accurately. What I think you are depicting is an isosceles triangle. That is a triangle having 2 equal legs. That would be the legs going from the top to the wall.


In a triangle all angles must add to 180 degrees. In this case you have a right triangle at the top so this is a right isosceles triangle. The ratio of the legs in a right isosceles triangle is 1:1:square root of 2. You have specified that 84 is the length of the side that has the ratio of the square root of 2.
therefore your other 2 sides are 84 divided by 1.414 = 59.41 inches.


George
TimPa and Tool Agnostic like this.
GeorgeC is offline  
The Following 2 Users Say Thank You to GeorgeC For This Useful Post:
Onefreetexan (06-19-2019), wretched64 (06-19-2019)
post #3 of 16 Old 06-19-2019, 04:25 PM Thread Starter
Member
 
Join Date: Oct 2017
Posts: 75
View wretched64's Photo Album My Photos
Quote:
Originally Posted by GeorgeC View Post
You need to draw that triangle a little more accurately. What I think you are depicting is an isosceles triangle. That is a triangle having 2 equal legs. That would be the legs going from the top to the wall.


In a triangle all angles must add to 180 degrees. In this case you have a right triangle at the top so this is a right isosceles triangle. The ratio of the legs in a right isosceles triangle is 1:1:square root of 2. You have specified that 84 is the length of the side that has the ratio of the square root of 2.
therefore your other 2 sides are 84 divided by 1.414 = 59.41 inches.


George
Yeah I just hand drew it. We dont make things perfect here until they are built. Lol. Thanks

Sent from my SM-G965U using Tapatalk
Tony B likes this.
wretched64 is offline  
Sponsored Links
Advertisement
 
post #4 of 16 Old 06-19-2019, 10:41 PM
Moderator
 
Steve Neul's Avatar
 
Join Date: Sep 2011
Posts: 25,771
View Steve Neul's Photo Album My Photos
The top angle, is it a 45 degree angle or two miters making it a 90 degree angle?
Steve Neul is online now  
post #5 of 16 Old 06-20-2019, 06:29 AM
Senior Member
 
Join Date: Jul 2008
Location: Florida Panhandle
Posts: 11,596
View GeorgeC's Photo Album My Photos
I read it as 2 45's.



Hard to tell several areas, that is why I suggested more accurate drawing.


George
wretched64 likes this.
GeorgeC is offline  
post #6 of 16 Old 06-20-2019, 06:31 AM
Senior Member
 
Join Date: Jul 2008
Location: Florida Panhandle
Posts: 11,596
View GeorgeC's Photo Album My Photos
Quote:
Originally Posted by wretched64 View Post
Yeah I just hand drew it. We dont make things perfect here until they are built. Lol. Thanks

Sent from my SM-G965U using Tapatalk

If you want good answers, you must at least make them good enough so that responders can tell what it is that you intend to build.


George
GeorgeC is offline  
post #7 of 16 Old 06-20-2019, 06:42 AM Thread Starter
Member
 
Join Date: Oct 2017
Posts: 75
View wretched64's Photo Album My Photos
Quote:
Originally Posted by GeorgeC View Post
If you want good answers, you must at least make them good enough so that responders can tell what it is that you intend to build.


George
Thought I explained the concept good enough. O well

Sent from my SM-G965U using Tapatalk
wretched64 is offline  
post #8 of 16 Old 06-20-2019, 06:43 AM Thread Starter
Member
 
Join Date: Oct 2017
Posts: 75
View wretched64's Photo Album My Photos
Quote:
Originally Posted by Steve Neul View Post
The top angle, is it a 45 degree angle or two miters making it a 90 degree angle?
2 45 angles making a 90

Sent from my SM-G965U using Tapatalk
wretched64 is offline  
post #9 of 16 Old 06-20-2019, 07:30 AM
Member
 
Join Date: Sep 2018
Location: Adirondacks
Posts: 46
View Frost's Photo Album My Photos
https://www.spikevm.com/calculators/...ter-length.php

Is this a shed roof? No matter as the calculations would be the same. Your drawing shows a 45 degree angle , which is a 12/12 pitch. Enter half of 7' (84") into the equation as the width and there you go.

Google how to calculate common rafter lengths and it will be clear. You might also read up on using a framing square as you can use it to step off lengths and then add any overhangs if you want and its just good to know how to use one.. They were the original calculators.

Or, you could just draw it out on a piece of plywood if you have one.
Frost is offline  
post #10 of 16 Old 06-20-2019, 07:55 AM Thread Starter
Member
 
Join Date: Oct 2017
Posts: 75
View wretched64's Photo Album My Photos
Quote:
Originally Posted by Frost View Post
https://www.spikevm.com/calculators/...ter-length.php



Is this a shed roof? No matter as the calculations would be the same. Your drawing shows a 45 degree angle , which is a 12/12 pitch. Enter half of 7' (84") into the equation as the width and there you go.



Google how to calculate common rafter lengths and it will be clear. You might also read up on using a framing square as you can use it to step off lengths and then add any overhangs if you want and its just good to know how to use one.. They were the original calculators.



Or, you could just draw it out on a piece of plywood if you have one.
It's my starting point for a slat wall I start with those 2 pieces and work around then.

Sent from my SM-G965U using Tapatalk
wretched64 is offline  
post #11 of 16 Old 06-20-2019, 07:56 AM Thread Starter
Member
 
Join Date: Oct 2017
Posts: 75
View wretched64's Photo Album My Photos
And 59.41 was exactly the length need for Long to short with 84 being the hard measurement. Tha is for help

Sent from my SM-G965U using Tapatalk
wretched64 is offline  
post #12 of 16 Old 06-20-2019, 08:24 AM
Moderator
 
Steve Neul's Avatar
 
Join Date: Sep 2011
Posts: 25,771
View Steve Neul's Photo Album My Photos
The 59.41 sounds right. I drew it to scale and came up with 59".
Steve Neul is online now  
post #13 of 16 Old 06-20-2019, 08:58 AM
Senior Member
 
Join Date: Aug 2017
Posts: 1,557
View Tool Agnostic's Photo Album My Photos
I used the Pythagorean Theorem and got the same answer: 59.4 inches. Because of the way the angles are cut, the inside length and outside length are the same.

Side length = sqrt((84^2)/2) = 59.4
Tool Agnostic is online now  
post #14 of 16 Old 06-20-2019, 09:09 PM
Senior Member
 
Tony B's Avatar
 
Join Date: Jul 2008
Location: Dickinson, Tx. / Denison, TX
Posts: 3,090
View Tony B's Photo Album My Photos
Quote:
Originally Posted by wretched64 View Post
Yeah I just hand drew it. We dont make things perfect here until they are built. Lol. Thanks

Sent from my SM-G965U using Tapatalk
Right On!

Tony B



Retired woodworker, amongst other things, Sold full time cruising boat and now full time cruising in RV. Currently in Denison, Tx
Tony B is online now  
post #15 of 16 Old 06-21-2019, 01:45 PM
Senior Member
 
Join Date: Jan 2010
Location: NW Pa
Posts: 2,815
View TimPa's Photo Album My Photos
Quote:
Originally Posted by GeorgeC View Post
You need to draw that triangle a little more accurately. What I think you are depicting is an isosceles triangle. That is a triangle having 2 equal legs. That would be the legs going from the top to the wall.


In a triangle all angles must add to 180 degrees. In this case you have a right triangle at the top so this is a right isosceles triangle. The ratio of the legs in a right isosceles triangle is 1:1:square root of 2. You have specified that 84 is the length of the side that has the ratio of the square root of 2.
therefore your other 2 sides are 84 divided by 1.414 = 59.41 inches.


George
yeah, George nailed it!
TimPa is offline  
post #16 of 16 Old 06-22-2019, 10:27 PM Thread Starter
Member
 
Join Date: Oct 2017
Posts: 75
View wretched64's Photo Album My Photos
Wall up and letters attached

Sent from my SM-G965U using Tapatalk
wretched64 is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Woodworking Talk - Woodworkers Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome