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The rise divided by the run represents the tangent of the angle (from horizontal). So you need the arctangent of 2/12, or 0.16666.. My trusty HP calculator says that this angle is 9.46 degrees.
What's d'matter, you don't read 4-figured tables anymore?
Does anybody have one of those around?
My CRC book is back in the spare room, under a quarter-inch of dust.
If ignorance is bliss why aren't more people
happy?
Put your speed square on a board pivot the square to 2/12 pitch on the common side look at the degrees on the end of the square in line with the 2/12 pitch.
In this order using your scientific calculator 2 divided by 12 inv tan
If you memorize that, it will always give you the degrees. If you use a speed square, just take those degrees and subtract from 90
Subtracting it from 90 will give you the degrees for birdsmouth cuts and seat cuts in blind valleys and cut for the ridge board.
9 1/2 degrees is the headcut for the rafters at the ridge and 80 1/2 degrees is for the birdsmouth, seat, and ridge.
All my work is trusses so I frame blind valleys this is how I figure them.
Don't use calculators very often except to cipher up someones bill.
If this is wrong please set me straight. It seems to work fine for me, caveman style.
I thought it was like you wrote until I read a FHB article in the Roofs book a few years ago.
The seatcut is technically the 9° and the plumb is 90-9
Your speed square measures from 90 and that is why this is the case. Your saw also bevels from 90, not 0. It can be confusing sometimes.
I think I understand what you are saying, as usual I'm putting everything on the wrong side of the |x|. Thanks
Heck brownbagg, you mean to tell me you build things with pitches other than 12/12? That's about all I've used for the last year or so. I was beginning to think it was some sort of mandate or something.
If I would ever need one again, I would pull out my Const. Mstr. Calc. enter the number for rise and "12" for the run and just hit pitch. Or you can just enter the rise and hit pitch twice. I keep a copy of roof framers bible handy in truck somewhere also.
k
If I would ever need one again, I would pull out my Const. Mstr. Calc. enter the number for rise and "12" for the run and just hit pitch. Or you can just enter the rise and hit pitch twice. I keep a copy of roof framers bible handy in truck somewhere also.
k, I see the advantage of building everything in 12/12, you know the angle is going to be 45 without fussing with the above. BB is just trying make things complicated. :)
Yea, and no fussing with a framing square. Just lay that ole 12" Speedsquare on the piece tight and mark the diagonal. That's as easy as it gets. To bad moving around on the roof with those cuts ain't that easy and gettin harder all the time!
k
Thats really the only thing they are good for. The only problem then is that they are too small.
blue
Heck Blue, I would vote for my calculator bein smaller. Mine takes up plenty of room as it is. I use mine for tons of calculations on the jobsite every day. It's one of my most useful tools as my mind ain't as sharp as it used to be.
k
Kcoyner, I use a calculator onsite too for lots of things. Calculating degrees isn't one of them though. I can honestly say that I've never calculated a degree in my entire career.
blue
I calculate degrees on every house because about 50% or more of the roofs we frame (90% of the houses we build are stick framed) are irregular and it's easier to deal with degrees than roof pitch.
Also, if you proficient with a CM, then a framing square isn't worth using.
Real men use wormdrives :-)
Also, if you proficient with a CM, then a framing square isn't worth using.
Please post pictures of you using that CM to mark the level cut on your next 4/12 rafter! I hope your using 2x12 rafters...
What does your CM have...some special extension piece, or do you just make the small mark, then slide the cm halfway over and line up the line and mark, then repeat that till you have the entire level line marked out?
You ought to try a framing square....
blue
Also, if you proficient with a CM, then a framing square isn't worth using.
Please post pictures of you using that CM to mark the level cut on your next 4/12 rafter! I hope your using 2x12 rafters...
What does your CM have...some special extension piece, or do you just make the small mark, then slide the cm halfway over and line up the line and mark, then repeat that till you have the entire level line marked out?
You ought to try a framing square....
blue
Blue Blue Blue Blue Blue you're being glib
Why would I use the framing or rafter square? Please explain to me why I should do that. I don't often do this, but I'm going to do it now Ready?
I can calculate, cut and stack a roof (regular, irregular, polygon) faster than you can calculate, cut and stack a roof any day of the week.
Is that because I'm more intelligent than you? Absolutely not. It's because the CM is a great tool to calc roofs with.
Fact of the matter is, the rafter square was a perfect tool in its day, and it still is, but it is NOT as productive as a CM for calculating a roof. I use a 12" speed square to mark my rafters. Working in degrees is easier to understand, explain and teach.
Oic, you use a CM AND a speed square.
Now I get it.
blue
Blue,Who are you kidding? You know you use a speedsquare because it's right here. Remember this thread?.......;-)http://forums.taunton.com/tp-breaktime/messages?msg=49588.51Joe Carola
olle: I haven't read much in the way of books on this topic nor have time to browse the internet, but I'm curious. When you say "systems of math" ... did the framer's guilds incorporate trigonometry in their methods? Tables of logarithms and trig functions have been extant for a few hundred years but I always assumed the average tradesman of bygone days wouldn't have had access to an education of this nature and would have relied solely on geometry, ratio and proportion.
BTW, we use the pitch system up here in the north country too. Worse yet, a couple of months ago someone showed me a new framing square he had purchased marked Imperial inches on one side, decimal inches on the other. What are the chances of making a mistake with something like that?
Joe Bartok
Edited 2/17/2006 10:59 am ET by JoeBartok
Joe yes the french and the german Guild system did and does teach trig as well as geometry. They also have a an excellent drawing system . Hence the title master. Check out the compagon web site . it is abit cluncky if you use goggles translator but some interesting stuff if you read french. I also have a mertic framing square which I have lent to a window maker that lives nearby and sends windows to Canada , and europe. The one you describe sounds interesting . I collect squares I will have to find that one
Here is the correct spelling Compagnon du devoir
Edited 2/17/2006 4:02 pm ET by olle
Interesting, I always wondered if trig was used. The French in the Compagnon links is a bit tough to follow.
I found these pictures while Googling. Pretty wicked joinery! Especially those spirals following a cone - where you start figuring that?
http://72.14.207.104/search?q=cache:6PwhDV-9g5IJ:tfguild.org/news/newsfrance2003.html+Compagnon+timber+framing&hl=en&gl=ca&ct=clnk&cd=1
Joe Bartok
Edited 2/17/2006 4:25 pm ET by JoeBartok
Joe I have been amazed for years. Those pics are just the begining . After the apprentiship , then the journey and then the masterpiece. There is a musem in Paris that has a collection of Compagnon master works, and there will be a display in Charleston this year sometime. Keep looking for more things , the timber framers guild may have more stuff
I visit the Timber Framer's Guild site now and again and they do have some pretty neat stuff. Actually I registered on the forum years ago but never participated and have forgotten my password. There isn't really anything in their forum which interests me anyway. I like to work with the technical and theoretical aspects of framing and joinery, to really understand mechanics and the math. There are rarely any posts on such topics in log building or timber framing forums, in fact are actually more questions and answers of this nature here and at JLC. I guess timber framers already know the hows and whys of joinery and that's why there are few questions.Joe Bartok
Joe The timbers framers guild magazine "Timber Framing " Has one of the best articles explaining the math and the geometry I think that has been written in years . It is dericeted to timber framing but the math and the info still applies the articles start in issue # 70 and finish with # 71 and # 73 well written and excellent drawings.
I don't understand this from Joe Bartok: "someone showed me a new framing square he had purchased marked Imperial inches on one side, decimal inches on the other. What are the chances of making a mistake with something like that?"
Manufacturers have included tenths and twelfth scales (as well as eighths and sixteenths) on steel squares since the mid 1800s. Many also included a hundreths of an inch juxtaposed to sixteenth of an inch scale. Today, these squares are still widely distributed by major tool makers. If you go to Stanley and other tool sites, the manufacturers usually call these squares "Rafter Squares". They call steel squares without these differing scales and without the rafter and octagon tables "Carpenter Squares." I grew up using what is specified as a "rafter square." These were and still are the standard 16 by 24-in. square on jobsites. Most of the carpenters I've known call all 16 by 24 -in. squares "framing squares".
I'm not a framer or a carpenter so I'm not that familiar with the different variations on the tools of the trade.Joe Bartok
Your right Mudslinger. I started with a "professional" rafter square manufactured by Stanly in the 70's. Sometime in the 80's they started selling a flimsy aluminum "homeowner's square". I was delighted to see that it was all 1/8th scale on all the legs, both front and back. I wasn't just delighted, I was thrilled! I've never went back to that other square and I still have it (my first square). I just moved it this morning in the garage!
Those different scales drove me to drinking!
blue
I've heard of it all now JOE! There aint no way in heLL that I'd have a square like that onsite. I won't even use a framing square that isn't uniform on all legs. Those twelf scales and tenth scales used to drive me bananas.
blue
If one scale was metric the difference would be obvious, but this was the first time I had ever seen a square with two different Imperial divisions. The person I was helping made two mistakes within the first hour. I felt like doing him a favor and stepping on the damned thing by "accident" when he wasn't looking ...Joe Bartok
I forgot about THAT speedsquare Joe!
Now, I gotta go dig through my tools to find it.
I actually did find one that I kept. I used it up north when I was cutting and marking tiles. The tile job was done on the diagonal and I found it useful for marking the lines on the tile with the sharpie. I've never used it for anything else and it's still up north. I did try to mark a rafter with it but it is not a very useful tool in that regard unless you're only marking plumb cuts on small stock.
I'm glad you guys love them. They just don't do anything for me.
blue
If regual CM calculators are too small for you, they do make desktop versions. They have bigger buttons and a bigger display, for guys with big fingers and bad eyesight.(-:http://www.calculated.com/prd16/Construction+Master+Pro-Desktop+.html
Q: Why do gorillas have big nostrils?
A: Big fingers.
Yeah, what is it with 12/12's now. I'm the same way. The only time I get relief is when I have and 8/12 and 12/12 Bastard Roof. Yeah that's relief for you! Whats the point in a 2/12 anyway?
12 in 12 is 45 degrees.
1/12 of 45 is 3.75.
Multiply everything else by this (i.e., 2 in 12 = 7.5 degrees, 3 in 12 = 11.25 degrees, etc.)
Angle = arctan (rise ÷ run)
For 2/12, arctan (2 ÷ 12) = 9.462322°
Joe Bartok
Edited 2/14/2006 10:28 am ET by JoeBartok
You're right. My bad.
Draftguy,Using your logic a 24/12 roof would be plumb. Obviously it isn't because the curve is asymptotic.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
You are correct, sir. Was checking what I'd written and had to run out to a meeting when I posted it. Wrong logic.Does this mean a 120 in 12 roof pitch will not be vertical? :)
Does this mean a 120 in 12 roof pitch will not be vertical?
120 (or any number) in 0 would be vertical
"he...never charged nothing for his preaching, and it was worth it, too" - Mark Twain
Well, it seems as all the mathematicians have had their say....now I'll tell you what I was taught.
In the olden days, we framed all roofs of 4/12 and maybe a 5/12. A steep roof was a 6/12.
Our "rule of thumb" for determining degrees was the pitch x 4 + 2. That normally worked fine for the lower pitches that we used since we were only cutting cheek cuts and things of that nature.
When we started doing steeper roofs, this rule of thumb failed. If you do the math, a 12/12 would be 48 + 2= 50degrees. We all know that's not right.
Instead of using the thumb rules, I started marking the actual layout on the edge of the rafter and lining up my saw to hit the lines exact. That solution is still the one I use today when I'm hacking up odd roofs like a 7.5 / 12 roof. When I frame on a regular basis, I simply remember all the normal roofs, just like I automatically can remember all the unit lengths and sums of the two legs.
blue
Why not just use yuour Swanson Speed square, Blue?;)
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Why not just use yuour Swanson Speed square, Blue?
Umm, maybe becauase I might not have one...
I did find one a couple years ago and again tried to figure out what it was good for. It is great for marking 45's on 2x4's and 2x6's. So, I could carry that "special" tool for marking 12/12 rafters, but alas I don't keep specialty tools. I leave them in the stores that sell them!
Real men use framing squares.
blue
I hope you don't mind me pulling on your leg a bit. I use a framing square for framing too, but I have a large size speed square and it seems like the most common use I make of it is to calculate angles in degrees after a layout, so I can set a bevel on my circ saw.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
The large speed squares are great for scribing lines, too.
"Citius, Altius, Fortius"
or scraping ice off lumber
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Saw guide.
Door stop.
One way boomerang.
"Citius, Altius, Fortius"
I am going to be alittle crazy now . But the USA is the only Country that uses roof pitches, such as 4/12 ,or 12/12 . Most countries use degrees. this much more user friendly and if you are taught the math much more versatile. We have been dumbed down since the invention of the framing square and even more since the invention of the speed square. The good roof guys here can figure anything out using the math or developed drawing. The real key is to be able to see the geometry in you head and transfer the marks to the lumber. I love the math but still believe in being able to draw it as well. These systems of the math and drawing were the heart of the old guilds in europe.
"Not to confuse the issue with facts" - where have I heard that before?
If I recall the NC General Contractors studying I did the pitch is not what I always thought it was.
Apparently, technically, the angle of one side of a roof off the horizontal plane is the "SLOPE". Technicaly the pitch is the combination of the two opposing slopes.
So Ime thinks you could have a 6:12 slope on both sides of the roof, or a 3:12 one side and a 9:12 on t'other side - and both would have a 12:12 pitch. Either that or the Pinot Noir is kicking in.
Let's not confuse the issue with facts!
Techincally speaking, your correct. Pracitcally speaking, the kind we do on the jobsite, you are geekish.
In my 30 some years or construction, I've never heard anyone refer to an 8/12 as a "one third pitch". If they did, I'd probably ask them what book they've been reading!
blue