Math Guru Needed

[bugstruck]

Rox, Just read your Bio and checked out your website. Now who's impressed?? /forums/images/graemlins/cool.gif /forums/images/graemlins/grin.gif Looks like some high quality products your producing over there. I should know the symbol for Francs and Euros but don't. As I recall France converted to the Euro, correct? So I guess I know the Euro symbol now?

Anyhow, it's a pleasure to make your aquaitance. Guess we need tractors everywhere, certainly including Olive farms.

Are you allowed to ship your products to the US for sale? I would assume the Governments get their nose in that.

EDIT Probably should have PM'd you this as I'm woefully far off subject, so I'll beg the others my indulgence.

 

[Mayhem]

Thank You for the replies.
I've been looking into a pole barn 30x50 and have looked at the
http://socketsystems.com/ page.
17.4 ft long 6x6 wood be costly if you built it with their system, not to mention the price of all the hardware. Its starting to look like trusses are cheaper in this aplication. Too bad, I liked the high inside ceiling design.
/forums/images/graemlins/confused.gif

 

[bugstruck]

You could scissor truss it for some more interior volume.

 

[turnkey4099]

Excellent post. I screwed up the last time I framed a roof. Made my pattern rafter, cut all 30 of them, got ridge and rafters up the first day. Walked around the next mornign with a cup of plasma and saw that I had reversed the square for the tail cut. Had to correct it working from a ladder. Not fun. Fortunately I only lost a small bit of the overhang that had no effect on anything.

Harry K

 

[bugstruck]

Turnkey, I've been on that ladder as a Carpenter Apprentice sawing rafter tails that a Carpenter Foreman had miscalculated the overhang distance on, even though the angles were right. So even the so called pros can make a mistake. I recall having to trim a few of my own too, that came up a little long (fortunately) on a bastard hip. That's not an expletive deletive, it's carpenter speak for "a roof hip (hip roof of course) with different slopes converging".

So, I wouldn't have anything but good to say about someone who took the risk and challenge head-on, built it themselves, and learned something. I'm glad you did it! Had you not made a few mistakes somewhere in that process, that would have been, well... just surprising. So your a risk taker.... of sorts, eh? /forums/images/graemlins/wink.gif

 

[gotrocks]

You seem to have your answer, but here is a drawing of you project.

I still don't know how to show picture in this "screen" so ck attachment.

 

[trlong]

Bird,

Yep. Sure is one of t he handiest formulas I've ever used. Never did think I'd use it much, at home, 'til I started building decks and sheds myself. Also, the other really handy formula to remember (same formula, just specific application) is the: 3x4x5 triangle. Always gives a nice right angle when carefully measured out. Don't care if 3x4x5mm, ft., furlongs... still pretty handy.

Eddie,

Depending on where in NY, snow load is a real issue. Myself, I like 12/12 pitch (but not fun for trying to walk on). Least I'd go (up here in snow country) is 10/12, atleast without standing seam to get it the snow off. Lots of folks have to use "snow rakes" or get up and shovel off low pitch roofs by mid January.

Tom

 

[gotrocks]

Hi Bird and all you other "math teachuns" /forums/images/graemlins/grin.gif
Did any of you hear about the old farmer that saved & sacraficed to send his boy to college?
When he came home his Pa asked him what he had learned.
He said "well Pa I know the area of a circle is Pi R square.
Well Pa hit the roof, he said
"any fool knows pie are round, cornbread are square" /forums/images/graemlins/tongue.gif

Please pass the syrup /forums/images/graemlins/smile.gif

 

[SCB]

The formula that bird mentions is the pythagorion(sp) theorum. It works with any numbers. A squared plus b squared equals c squared. I had to use it recently when measuring distance of my septic from my well. Problem was, a straight line measurement went right through my garage. using the theorum, it was an easy calculation.

 

[bugstruck]

It's the most used goemetric formula in all the building industries field services. Virtually all in this discussion know this, but I'll throw this out for others who may not want to run the math but have a need to use it in some practial, simple way. You can take the the 3-4-5 rule mentioned above and multiply or divide those numbers to square any 90 degree corner. So it can be a 6-8-10 or a 15-20-25, etc. depending on the scale of the layout and the accuracy required.

Another rule is that if your doing hip and/or valley stick-built roofs, with the same slopes converging on a given hip or valley, the rafter cuts are a 17 instead of a 12. So a 7/12 slope hip roof will have a 7/17 cut (7/16.97 as I recall is the real #) at the hip intersection, no matter the pitch. So a 5/12 roof gets a 5/17 hip angle cut. But you still need to use a square table to read the sidecut angle (bevel). Or you need to calculate it. Easier to just read the table on the framing square. Assuming you bought a professional one with the tables and not the stupid stuff many now have engraved. The speed squares also gives you the hip and valley sidecut angles. Keep in mind the bottom (wall) cut and top (ridge cut) is still a conventional 7/12 in this example.

Another trick to get rafter lengths in the field, if you don't have calculator handy and no deck or flat surface to mock-up the layout, is to walk the rafter length off with a framing square. You can do it right on the sawhorses. And you can start at the ridge or the wall and work either way. Not quite as fine for accuracy but usually within 1/8" for total length in the right hands. A 12" speed square will do it too. Simply make the ridge cut plumb mark, then mark where the 12" point of the square is aligned with the bottom of the rafter (assuming your laying out using the bottom edge as is usually the case). Slide the square away from the ridge and place the rise # (call it a 7) on the previous 12" mark you just made. Then mark the 12" again at the rafter bottom edge. You just walked off 2 linear feet on the true horizontal. Do it 15 times and you walk off 15'. Need 4" more? Just keep the square aligned on the 15th mark position and mark 16" on the long leg. That gets you to 15'-4" of span. So you don't need the pythagorean theorum to determine the rafter length. Another way is to use the rafter tables. They give you the slope angle for any given even inch pitch over one foot of span. Read that number and multiply it by the feet of run (span or horizontal distance). That's what they mean by rise and run. Run being the span distance from the ridge to the wall (outside) bearing point.

Are we bored yet? I am. If I were really teaching it I'd pull out something like you see here: Rafter link
Once you get this down your a bonafide roof Carpenter. Still not a Carpenter though.