making a square end cut

ric1 · May 3, 2011

i have heard older fellows talk about making a square end on a board or whatever by using a method called 345 or something like that anyone know what i am talking about thanks.

Anonymous-0 · May 3, 2011

Make a triangle, that has a 3" leg, a 4" leg, and a 5" hypotenuse. That makes the 3-4" angle square (90 degrees).

tlak · May 3, 2011

If you measure down one side 3" and the other side of a corner 4" then the distance between those points should be 5". If not you rack the building till square, or if your cutting off boards just go get a speed square.

Gun guru · May 3, 2011

The 6-8-10 method also works. I use this for building decks.

senoj · May 3, 2011

Why not use a carpenters square or a T square?ggp

ric1 · May 3, 2011

just in case someday i dont have one

thurlow · May 3, 2011

Probably part of that pi are square or pi d thing (don't have a numerical keyboard (alt 227) on this computer.

Paul Janke · May 3, 2011

This is based on Pythagorian"s Theorem (sp?) where on a right triangle with sides A, B, & C, A squared plus B squared equals C squared. Squared means a number times itself. In the case of a 3,4,5 triangle, 3 times itself is 9, and 4 times itself is 16. 9 plus 16 is 25, and that is 5 times itself. Now are you thoroughly confused? If not, I could try to explain further until you are confused.

Jason the Red · May 3, 2011

Nice easy explanation. Also for larger areas any multiple of the numbers can be used, as long as the each number is multiplied by the same number( 6,8,10 or 12,16,20).

showcrop · May 3, 2011

It's for when you need to check the whole building as opposed to just a corner.

Goose · May 3, 2011

We called it "Pete's Theory". It was easier to write.

David G · May 3, 2011

It can be any multiple of 3x4x5.

johndeere720GA · May 3, 2011

The 3,4,5 or 6,8,10 ... also work in feet measurements not just inches. It would work in miles also but the string is way too long to keep it straight.

casenut1 · May 3, 2011

use the 6-8-10 to square the shingles up when putting on three tab shingles. to get the tabs to line up straight.

OldFarmTractor · May 3, 2011

In case you don't like 3:4:5, you can use....
3: 4 :5
5: 12 :13
8: 15 :17
7: 24 :25
9: 40 :41
11: 60 :61
12: 35 :37
13: 84 :85
15: 112 :113
16: 63 :65
17: 144 :145
19: 180 :181
20: 21 :29
20: 99 :101
21: 220 :221
24: 143 :145
28: 45 :53
28: 195 :197
32: 255 :257
33: 56 :65
36: 77 :85
39: 80 :89
44: 117 :125
48: 55 :73
51: 140 :149
52: 165 :173
57: 176 :185
60: 91 :109
60: 221 :229
65: 72 :97
84: 187 :205
85: 132 :157
88: 105 :137
95: 168 :193
96: 247 :265
104: 153 :185
105: 208 :233
115: 252 :277
119: 120 :169
120: 209 :241
133: 156 :205
140: 171 :221
160: 231 :281
161: 240 :289
204: 253 :325
wikipedia

JOHNNYfromMI · May 3, 2011

A sq + B sq = C sq

Ultradog MN · May 4, 2011

Yup, Good old Pythagorus. He's given me lots of help.
I use 3,4,5 or 6,8,10 all the time for setting tile in a room that is not square.

36 Coupe · May 4, 2011

Its useful for checking foundations and buildings.The steel square if a recent invention.Early squares were made of wood using 6 8 10.Early barns were built using a story pole to make measurements.You have to remember reading and writing skills were not widespread 200 years ago.

sws55 · May 4, 2011

There's a quick approximation for Pi also: 355 divided by 113. It's acurate to 7 decimal places. We used this on early calculators as slide rules were phasing out and only the really expensive calculators ($300 in 1973) had a Pi button. The tip to remember was: 113355 or one, one, three, three, five, five.

Anonymous-0 · May 4, 2011

Find yourself a framing square.
Use a tape measure across the diagonals or a steel rule.
For example measure from the 3 and 4 inch marks. If it does not equal 5 your framing square is out of square or your scale is off.

Brian G. NY · May 4, 2011

But.......I think only the 3:4:5 (or multiples of those numbers) will get the 90 deg
"square end cut" he"s looking for.

Mike (WA) · May 4, 2011

Thanks, OFT- I've committed all those combinations to memory, and have thrown away my T square. I had been hoping someone would show me an EASY way to get those square cuts, without having to lay a square across it and draw a line. What a bother!

I think I'm getting a headache. . .

The Dukester · May 4, 2011

In plain geometry a few years back (1949 to be exact) I learned; "In a right triangle, the square of the hypotenuse is equal to the sum of the squares of the two adjacent sides".

Anonymous-0 · May 4, 2011

Nope, not true. If you'd actually do the math in the formula mentioned by others here, you'd see that

making a square end cut

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