I recently discovered something while laying out rafters with a framing square.I used my framing square to step rafters on a 9/12 pitch.These rafters also had a notch for a knee wall. We had already calculated the height and placement of the knee wall so that it would be in step with the rafters.When I pulled my raftters up, they didn’t fit exactly, they seemed to be about an inch to long.I checked my layout again with my dad’s framing square, and it seemed to be perfect.I had also marked my steps with a knife instead of a pencil to further insure accuracy. I decided to check my rafter length with a rafter table ( the kind that comes with a swanson speed square ), and sure enough, my rafters were about an inch too long. This baffled my dad , my brother, and myself. Usuallly the rafter table length will be within a quarter of an inch of the length when stepping them with a framing square. We tried stepping the rafter again, but this time used my brother’s square.This time, the length was within an eighth of an inch of the rafter table, and they fit perfectly.We checked my square and my dad’s against my brother’s and found that they were off. Each number was almost 1/32 of an inch longer than those of my brother’s square. This explained how our layout was an inch too long. My square is a Johnson brand, my dad’s is an Empire, and my brother’s is an old Stanley. They are all aluminum. I thought all framing squares were marked accurately, but I guess not. From now on I’ll check my square for accuracy .
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Brag on, Jay.
Does your framing square have little black diamonds on it in odd places? They are for a five in eight pitch roof.
Buy a Construction Master
If you know how to use a rafter table than why are stepping off? I think that's the least accurate way to do it. And IMHO it's alot slower.
Jon Blakemore
OMG, are public schools THAT BAD NOW. (sent my own kids elsewhere even 25 years ago, and glad of it)
9/12 slope, do it in your head unless you never learned that, 3/4/5 triangle, the hypotenuese . aka rafgter length, (dyd dey teech speling) is 15.
PS edit: apologies Jay, for the tone of the above since this was your first post, and welcome. For your interest, refer to some previous posts on peening squar3es to get them actually square. Myself, never have bought anything off the shelf but a starrett that was anywhere near square to start (should start more discussions<G>.
Quote of the day: Any chinese tool can be made square in 15 seconds (minutes?) with a file and ball peem hammer.
Edited 1/21/2004 12:10:54 AM ET by JUNKHOUND
Showoff....that's not a mistake, it's rustic
GREAT QUOTE LMFAO
I could be mistaken, but I don't think the problem with Jay's square is the squareness.
I read his post to mean that the markings on the square are not accurate (an inch is not an inch).
Rich Beckman
Another day, another tool.
Glad you mentioned that. That is what I was hearing as well.
Yes, Rich, that's exactly what i meant.
I'm not carpenter but I was on a job the first day the carpentry crew showed up. The straw boss was a friend, a very good carpenter from what I hear from others. Not that I could tell. First thing he did was compare everyone's tapes and squares. They took care to get everyone close.
He claims more fights start on jobs because the carpenters don't compare calibrate their tools. If one tape is an eighth too long and another an eighth too short the quarter inch difference can have both carpenters thinking the other is a moron. I suspect the same thing could be true with squares.
Getting everyone on the same scale seems like a good idea.
I try to do the same thing, hard to find the time when things are rushed, with meters and testers. Both for calibration and simple function. A tester that fails at the wrong time can get you killed.
That is one good story, bro. I'm gonna remember that one. Thanks.
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
I remember my papa teaching me that method of layout about forty years ago. Most of the time he used an old book by A.H.Reichers with lots of rafter tables. I prefer now to use the pythagorean theorum and a calculator with a square root button. Perhaps you know about the Heisenberg uncertainty principle. It was originally used to estimate the location of an electron in an atom. The practical application is that for every measurement there is a certain error. In your case you may be a sixteenth off for every time you step the square. The small errors all add up to one big error in the end. Find the length of the rafter using a calculator and just use the square to mark your cuts. The step method is very inaccurate no matter how good your square is.
Like when I had a guy layout a wall plate for trusses, he used a step it from a square method, I pulled my tape...wonder why the last trusses were skewed..he grew a pecil line each step..worse part he was the "elder" carpenter and should have told me to do the same or used a tape as well..
Did that elder carpenter date from back before plywood and drywall? I find things centered at 16 1/4" or 16 1/2" here and there. Back when they sheathed with solid sawn one by, it wasn't that important to get joists, studs, or rafters right on 16".
-- J.S.
As a matter of fact..yes he was from that era. And was from the 'boonies' in upstate Pa, where all the buildings in his area were built with whats on hand, usually local sawn, or recycled from the last house he built..that would explain it.
That's why I used the knife instead of a pencil, for accuaracy. The way my grandfather did it.
Jay -
Not being a carpenter doing framing and using the scales on my square for measurement, I've not noticed any difference between the two (squares) that I own. But I have found that of the 4 or 5 tape measures I have lying about in the shop, there indeed *are* differences. Found that out the hard way as well when using one for a while then another, my cabinet boxes were coming out not square and joints in face frames weren't aligning like they shoulda. Stretched out two tapes at a time to compare and there was indeed quite a difference over a given span.
Now only one tape is used for all critical measurements for any one piece that's being built. Better still, I just make a story pole using one tape and use the pole for everything from that point on. Doesn't help much with rafters, though! (grin)
From Beautiful Skagit Co. Wa.
Dennis
I know how it feels. For far too long I used a Stannley on square onich I had checked the angles for accuracy but not checked the rule. The angles were dead on but the rule was a hair over 1/16" short.