Old framer trick to square two perpendicular lines.

[The Tool Tyrant]

Ya, so I AM an old (retired) framer but I still remember neat little tricks. While reading another thread requesting help with figuring out a hypotenuse, it made me think of the old 3-4-5 (hypotenuse being 5) trick.

Problem: You need to frame a wall square with another wall, you have no calculator and you're clueless with trigonometry or you just want to show someone how 'cool' you are.

Solution: Mark a point (we'll call "A") anywhere along a given line (or wall), on the same line or wall measure and place another mark (we'll call "B") 3' from the first mark ("A") next, have someone (preferably a well endowed female) hold the 'dumb' end of your tape measure at point "B". Next hold a pencil (carpenter pencil prefered) at the 5' mark on your tape measure and draw an arc where you guess a line square with point "A" would cross. Next, once again have your 'helper' hold the dumb end of your tape at point "A", then holding your pencil at the 4' mark on your tape, draw an arc that crosses over your first arc. Where the two arc lines cross, (we'll call "C"). Now, snap a line from point "A" through point "C". Now you have two perfectly perpendicular lines. Collect your trophy and move along.

Same thing except different steps...if you wanted to check two existing walls to see if they're perpendicular, measure out from 3' on wall "A" from where the walls intersect, place a mark on the wall. Next, measure out 4' on wall "B" and place a mark, the diagonal distance between the two mark should be 5'...exactly.

Note: you can use multiples of 3-4-5 (6-8-10...9-12-15...12-16-20 etc) for greater accuracy on longer runs.

This could have all been easily illustrated with a few simple lines and numerals, but I'm old and clueless

 

[ford fanatic]

I was a framer years ago...used this a lot building pre fab walls when our jig was broken.

 

[Tejay]

Years ago in high school I thought who cares about some freak named Pythagoras. Then down the road I was using it nearly every day WTF

 

[LXCam]

Tis good advice and been using that method for years. Another method that many aren't aware of is using arc's. The actually measurement doesn't mean anything as long as they have sufficient space on one plane on both sides of the intersecting plane.

Lets see if I can explain this without loosing everyone. A picture would be better, but ain't gonna happen.

You have a straight line with points A, B and C spaced equally apart. B is the intersecting point of your perpendicular line. Using the arc method you use the distance between A and C. Use A as your base point and draw the arc above B, then using C as your base point draw the intersecting arc (well call that D) above B and you'll have a perfect 90.

If you need a 45 use the distance between B and C. Using C as your base point draw your arc at appx 45 degrees to B. Then use D and do the same and your intersecting point will be 45 degree's to B.

Anyhow for guys that don't this stuff these are good lessons to remember.

 

[darwyn]

For reference, this method was used by the ancient Egyptians. The Greeks called them "rope stretchers" because they used knotted ropes for their measuring devices.

 

[LXCam]

I got another one that many have no clue how to do. How you you plumb a tall pole that is tampered. Being an electrician I've installed countless 40, 60 and 100ft poles that were a tamper design and not square. So just tossing a level on the side of them doesn't work. And unless you have and know how to use a transit this is the simplest method.

Use a 6-7ft length of string and a plumb bob or even a heavy nut. Hold the string as high as you can in front of you and site the pole against the string at two point 90 degrees to the orientation of the pole. If you have a good eye this is just as accurate as other means.

K, I'm all out of stupid useless cheap advice.

 

[LXCam]

For reference, this method was used by the ancient Egyptians. The Greeks called them "rope stretchers" because they used knotted ropes for their measuring devices.

Ya, will this is all I got to say

حصلت على حبل مع عقدة تعادل في ذلك الحق هنا.

 

[ambenz]

How about a video to explain the concept!

<iframe width="560" height="315" src="//www.youtube.com/embed/69cslx6ER7k" frameborder="0" allowfullscreen></iframe>

 

[The Tool Tyrant]

K, I'm all out of stupid useless cheap advice.

They're only "stupid" and "useless"...until you need them!

 

[p_mori7]

have someone (preferably a well endowed female)...

Yes.

 

[oldmxracer]

I am 64 and used the 3-4-5 method many times in My life !

An old timer or two taught some things many years ago !

 

[manwithtools]

Also known as Pythagorean's theorem, A squared plus B squared = C squared. This is the math everyone needs to know at a minimum.

 

[383]

Remember the number 1.414. If your sides are equal length, multiply the side length by 1.414 to get the diagonal measurement. Example: 48" on each side, 48x1.414=67.872; round numbers 67 7/8".

 

[mitusa]

We always squared our buildings by measuring diagonally from one corner of the building to the other.

The building corners are A, B, C and D going clockwise.

The distance from A to C should equal the distance from B to D. If it does, the building is square. If not move one of the corners to make it square.

We used this to build the forms or to drill the holes for pole buildings.

 

[PCustoms]

This came up at work the other day, used to be an interview question for incoming maintenance and engineering techs.

They stopped using it when the engineers weren't able to answer it, or so I was told.

I just used it this afternoon to square up some walls I'm building in the basement, 1st wall is parallel to the floor joist above and everything is squared off that using 3-4-5 rule. 2nd wall even ended up pretty parallel the to the concrete which was a welcome suprise

 

[olytdi]

This is an "old" trick? ****! I thought everyone knew this! Learned it in high school.

Maybe they don't teach things like this anymore...

 

[Sawdustmaker]

This came up at work the other day, used to be an interview question for incoming maintenance and engineering techs.

They stopped using it when the engineers weren't able to answer it, or so I was told.

I just used it this afternoon to square up some walls I'm building in the basement, 1st wall is parallel to the floor joist above and everything is squared off that using 3-4-5 rule. 2nd wall even ended up pretty parallel the to the concrete which was a welcome suprise

I believe this. Taught mathematics in high school for 22 years and college for 23 years. The 3-4-5 trick has many variations and is the easiest to use. There is also the 5-12-13, 8-15-17 and so on. The combos are many. They are called Pythagorean Triples and are characterized by the fact that the sum of the first two squared equal the third squared, which is always a perfect square. Perfect square is a number whose square root is a whole number. So for 8-15-17 you get 64+225=289. 289 is 17 squared. A combo like 7-10-?? won't work. 49+100=149 149 is not a perfect square.
3-4-5 is the most useful (DUH!).

OK, you guys asleep yet?

 

[Sawdustmaker]

This is an "old" trick? ****! I thought everyone knew this! Learned it in high school.

Maybe they don't teach things like this anymore...

BTW We do teach it, today's students don't give a c&%$!

 

[rslaback]

Don't forget you have other options as well:

5-12-13
7-24-25
8-15-17

and naturally all the multiples as well.

 

[383]

We always squared our buildings by measuring diagonally from one corner of the building to the other.

The building corners are A, B, C and D going clockwise.

The distance from A to C should equal the distance from B to D. If it does, the building is square. If not move one of the corners to make it square.

We used this to build the forms or to drill the holes for pole buildings.

I'm laying of a 63'x624' poultry house next week, can I borrow your 700' tape??? Just kidding, I'll use a 50 yr old David White transit to square it up.

We usually go corner to corner as well, if the building is less than 100' long, but sometimes there are obstructions in the way, so we need to have other tricks up our sleeve.

 

[kwoswalt99]

I can make a right angle with a chalk line and pencil.

 

[Sawdustmaker]

We always squared our buildings by measuring diagonally from one corner of the building to the other.

The building corners are A, B, C and D going clockwise.

The distance from A to C should equal the distance from B to D. If it does, the building is square. If not move one of the corners to make it square.

We used this to build the forms or to drill the holes for pole buildings.

Use of the geometry theorem:

If the diagonals of a parallelogram are equal, then the parallelogram is a rectangle (4 right angles).

 

[MushCreek]

Assuming that the building is actually a parallelogram. That's a big assumption the way some contractors operate.

 

[BFBOB]

We always squared our buildings by measuring diagonally from one corner of the building to the other.

The building corners are A, B, C and D going clockwise.

The distance from A to C should equal the distance from B to D. If it does, the building is square. If not move one of the corners to make it square.

We used this to build the forms or to drill the holes for pole buildings.

Yes, IF AND ONLY IF opposite walls are of equal length. You skip that step, and all bets are off.
And just to make it interesting, it also only works if the four corners are coplanar. (in other words, the floor must be flat.)

 

[darwyn]

Ya, will this is all I got to say

حصلت على حبل مع عقدة تعادل في ذلك الحق هنا.

Lol, hieroglyphs!

 

[EdT]

I have used he 3-4-5 and its derivatives many times and, of course, it works fine. For smaller areas when setting walls sometimes a sheet of plywood makes a pretty good square. Another good number to remember is that 1 degree is .017" in an inch or approximately .2" in a foot or 1" in 5 feet. So, if you're off one degree in a thirty foot wall you're 6" off. A degree is bigger than most people imagine.

 

[Tim Kennedy]

Isn't it : A squared + B squared = square root of c ?

 

[kwoswalt99]

Isn't it : A squared + B squared = square root of c ?

4(1/2)ab+c^2=(a+b)^2
2ab+c^2=a^2+2ab+b^2
a^2+b^2=c^2

 

[manwithtools]

Isn't it : A squared + B squared = square root of c ?

No...

 

[manwithtools]

4(1/2)ab+c^2=(a+b)^2
2ab+c^2=a^2+2ab+b^2
a^2+b^2=c^2

What language is that?

 

[kwoswalt99]

What language is that?

Algebra.

 

[LXCam]

Isn't it : A squared + B squared = square root of c ?

Nope. That equals C squared. It is the square root of C that is the hypotenuse. Damn key board doesn't have that sign to show you. But if you take the value of C squared then hit the symbol that looks like a check mark with a horizontal line added to the top extending to the right then hit equals on your calculator will give you the length.

 

[MBfreak]

Thanks for the " coplanar " heads up.
And to you lost souls who keep whining about " todays students are not yak, yak, yak ".
I think you guys are way out of line.
Todays young engineers that I meet at work as MSc, BSc and the occasional PHd in electrical engineering knows loads of more math than my generation ( graduates of the mid sixties ) did back then.

That greek who is hailed as the "inventor" of the 90 degree triangle algebra was many hundred years behind Babylonians, Persians and even thousands of Indians and Chinese.
The greek input to ancient culture is often subtractive . The hooligan idiot " Alexander The Great" burned down a city in Persia while drunk / on drugs. Irreplaceable.

Best regards

Ola

 

[bobmulry]

How about..................

SOH CAH TOA

 

[LXCam]

How about..................

SOH CAH TOA

If a guy can't remember 3,4,5 and simple derivatives of it and 1,2,3 for mixing concrete then how the heck is he gonna remember changlish??






And cause I'm sure it'll get asked. 1 scoop cement, 2 scoops sand and 3 scoops rock.

 

[dave*99]

Susie could tell oscar had a heap of apples

S=O/H

C=A/H

T=O/A

 

[kwoswalt99]

Susie could tell oscar had a heap of apples

S=O/H

C=A/H

T=O/A

Some old hippie caught another hippie trippin' on acid.

 

[Doug B]

Ya, so I AM an old (retired) framer but I still remember neat little tricks. While reading another thread requesting help with figuring out a hypotenuse, it made me think of the old 3-4-5 (hypotenuse being 5) trick....
Note: you can use multiples of 3-4-5 (6-8-10...9-12-15...12-16-20 etc) ...

I seem to recall a few years ago on this forum, a guy was building a shed and was trying to square up the floor frame. Several guys explained the 3-4-5 deal to him, and off he went to square it up. A day or 2 later he came back on, confused and frustrated, saying his floor system was visibly way out of square. Turns out he was trying to do a 4-5-6 triangle...

 

[greasyfingers01]

Some old hippie caught another hippie trippin' on acid.

Single over head
Cams are hot
Towing on asphalt

I came up with this one in school. Easier for me to remember

Sent from my SM-N910V using Tapatalk

 

[The Tool Tyrant]

If a guy can't remember 3,4,5 and simple derivatives of it and 1,2,3 for mixing concrete then how the heck is he gonna remember changlish??

Exactly my point of starting this thread! I guess 'KISS' is not spoken here.






And cause I'm sure it'll get asked. 1 scoop cement, 2 scoops sand and 3 scoops rock.

Is that a cookie recipe?