Cutting jack rafters/pocket square?
pgproject
| Posted in Construction Techniques on
OK- I’m framing in a skylight. Need to add a new “jack” rafter. (If this is the correct term for a rafter that goes from the hip rafter to the eave).
My handy pocket square has all sorts of marks on it that are supposed to make this easy, but I’ll be damned if I can figure it out.
Can someone provide me w/ a quick lesson on how to calculate the angle and bevel for the hip cut?
Roof is 12/12.
Thanks a million in advance.
Bill
Replies
Think Hopalong Cassidy. Twin 45s. Both bevel and miter. I presumed a regular hip, that is, hipped pitch is 12:12, same as the common pitch.
I can't figure out what all those silly marks mean, either. I used my cell phone to figure yours.
On a regular hipped roof, the hip pitch will be x/17. If it's a 12/12 roof, it has a 12/17 hip pitch.
17 is a close approximation of the hypotenuse of a right triangle with legs of 12 and 12, the triangle you would see on a plan view of the top plate of the wall, the king rafter, and the hip rafter.zak
"When we build, let us think that we build forever. Let it not be for present delight nor for present use alone." --John Ruskin
"so it goes"
>>I presumed a regular hip, that is, hipped pitch is 12:12, same as the common pitch.<<Gene,A hip on a 12/12 pitch roof is not 12/12 the same as a common rafter, it's 12/17.Joe Carola
I didn't say "hip rafter," Joe. I said "hip," and meant the "hip roof plane." When the pitch of the hip end roof plane equals the pitch of the main roof (what I call "common") then the hip rafter is a regular one, on a 45 in plan view.
My cell phone calculated 16.968, not 17.
I like curved roof geometry the best, don't you? All these straight lines are getting boring. I was assistant super for the contractor that put the roof on this thing, many moons ago. Our curtainwall operation later put all the glass roof systems on air terminals like O'hare in Chicago. Nothing but curves! Gotta love 'em.
View Image
Gene,All I know is that the guy has a 12/12 pitch Hip Roof and he's talking about a "Jack Rafter" and the plumbcut is a 45° angle the same as the common rafters. If you want to call it a "Roof Plane" that's cool.>> My cell phone calculated 16.968, not 17. <<Your cell phone is wrong, it's 16.97056275" not 16.968 or 17".......;-)Curved is nice and I like anything with a challenge. The more complicated, the more fun!Joe Carola
Actually, it's 16.97056274847714 , but your number is close enough. <g>_______________________________________________________________
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Actually, it's 16.97056274847714 , but your number is close enough.
Shucks Heck, Gene's number is close enough (as long as the joint is sanded and filled) : - )
I'm sorry. I do rough framing (and it is really rough) to only TWO decimal inches of precision. ;-)
16.968 . . . 16.970 . . . they all are beginning to go fuzzy to these tired old bifocal-wearing eyes.
Oh.
I didn't realize this was paint-grade. I thought he was using prefinished jack rafter stock.
My bad.
Carry on. :~)_______________________________________________________________
tagline free since 2006
I gotta ask - Who did you call on your cell phone to get the answer? the voice at informationwouldn't give me anything but grief for asking her
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
LOL.
Wouldn't even give you the time of day, eh?
Do they even do that anymore?_______________________________________________________________
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Both roof slopes = 12/12, angle of intersection in plan view = 90°:
Mark your plumb line of 45° on the jack rafter, set the saw blade bevel at 45° and cut.
If for some reason the shallow faces of the rafter are plumb and the wide face is set in the plane of the roof: Mark the Jack Rafter Side Cut Angle = 35.26439° on the stick. Set the blade bevel on your Black & Decker to the Backing Angle = 30° and cut.
If you are cutting a really big rafter: Lay out the Jack Rafter Side Cut Angle = 35.26439° on the face set in the surface of the roof (and the parallel bottom shoulder of the Jack rafter) and 45° on the plumb faces. Whack it off as close as you can with a chain saw and finish with a planer.
All these layouts/cuts produce the same result.
Joe Bartok
Edited 10/11/2006 11:08 am ET by JoeBartok
My new Motorola Razor not only figures them, it cuts them.
Sounds like a tool you could shave with in the shower too!
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Technically you need to add two so you have double from wich to hang your headers from.
In practice, at least for old work, you probably need none and only need to head off the top and bottom of your rough opening then add trimmers from header to header for your rough opening width.
Eric
yourcontractor@aol.com
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If you're using a speed square, then you need to use the side that says Hip/Val instead of the Common side. The angle for a hip 12/12 is a 12/17 and the bevel is still a 45. It's tricky until you get it.
Dustin
>> If you're using a speed square, then you need to use the side that says Hip/Val instead of the Common side. The angle for a hip 12/12 is a 12/17 and the bevel is still a 45. It's tricky until you get it. <<Sarison,That's if he's cuttting the hip, he's not cutting the hip. He needs to mark the 12 on the common mark because he's cutting a jack rafter.Joe Carola
You don't need to use the hip/valley numbers unless you're cutting the plumb cut on a hip rafter, which you're not. You're cutting a plumb cut on a common rafter, even though it's intersecting the hip. So your plumb cut is 12/12, or 45º, with a 45º bevel (the angle of the hip rafter as viewed from above).
This doesn't hold true if you've got an irregular hip roof- two different common rafter pitches meeting at the hip.
zak
"When we build, let us think that we build forever. Let it not be for present delight nor for present use alone." --John Ruskin
"so it goes"
You don't need to use the hip/valley numbers unless you're cutting the plumb cut on a hip rafter, which you're not. You're cutting a plumb cut on a common rafter, even though it's intersecting the hip. So your plumb cut is 12/12, or 45º, with a 45º bevel (the angle of the hip rafter as viewed from above).
This doesn't hold true if you've got an irregular hip roof- two different common rafter pitches meeting at the hip.
ditto Zak's comment, and I am sure later in this thread that Framer has the same or similar comment.
I'm not sure what a pocket square is but it sounds the same as a speed square.
Triangle shaped with hip-valley, common, and degree scales.
Pivot square until it lines up with 12 on the common scale. Set saw to a
45 bevel and cut.
Pivot the speedsquare until it hits 12 on the common side. Or don’t even bother with any numbers at all, just mark the 45° side of the speedsquare and be done with it. It’s a 12/12 pitch roof so that’s the same thing and it’s faster and easier.
Bill,
Here's a little sketch. Hope it helps.
joe, that needs to be posted as a Jpg or as a GIF for most people to be able to open it
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Here we go my friend.Joe Carola
I knew we could count on you for a good sketch, but you are moving up in the world with sketchup. Getting better and better. Having fun?
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
>> I knew we could count on you for a good sketch, but you are moving up in the world with sketchup. Getting better and better. Having fun? <<Piffin,I think it's great. I want to use it more.I didn't know that everyone couldn't see it. From now on I will save everything under jpg. Thanks again.Joe Carola
Hey, all, THANKS!It's a jack rafter (going from the Hip rafter to the plate)both planes of the hip are 12-12 (actually more like 11.x - 12 - the roof angle is about 44 degrees instead of 45)the plumb cut is 46 degrees.I ended up using a sliding bevel gauge to get the bevel. It ends up being way beyond the 45 my Skill 77 will cut, so I just marked the bevel real well and 'freehanded' the bevel cut- worked great. I just checked it with my 'speed square' (thanks for the correction), and it lines up on the 12 hip/valley mark as suggested. Is there some better way to cut this sharp a bevel?worked great, thanks for all your help- this forum is the greatest.Bill
Try cutting your rafter on a 45 bevel and your 46 plumbcut. Then check the bevel with your bevel gauge. It will read steeper than 45 because it is a compound cut. When your board is plumb and your gauge is level, sight down and it will be a 45.
how is 46° way beyond 45°??????If it really requires 46° on one side of the hip, the hip is off and the other jack on the opposite side is 44°
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
>> It's a jack rafter (going from the Hip rafter to the plate)both planes of the hip are 12-12 (actually more like 11.x - 12 - the roof angle is about 44 degrees instead of 45)the plumb cut is 46 degrees.I ended up using a sliding bevel gauge to get the bevel. It ends up being way beyond the 45 my Skill 77 will cut, so I just marked the bevel real well and 'freehanded' the bevel cut- worked great. I just checked it with my 'speed square' (thanks for the correction), and it lines up on the 12 hip/valley mark as suggested. Is there some better way to cut this sharp a bevel? <<Bill,
What was the pitch of the roof? Your pitch sounds like is was an 11.5/12.You mark your plumbcut at 11.5/12 and then set the saw at 45° no matter what the pitch is. If you had to use a bevel gauge to get the angle for the saw setting that was way beyond 45°, then your hip isn't running at 45° and is maybe running at 67.5.Is this for an Octagon roof or a 45° bay roof?There should be no other reason to cut greater than a 45° saw setting for the jack rafter unless the hip is running greater than 45°.
Joe Carola
He's probably referring to the reading he gets on the rafter after the bevel is made. If you cut a 12/12 rafter on a 45 bevel, then put your square on top of the rafter so you can read the degrees of the bevel, because its a compound cut it will appear more than 45. Kind of like the old way to cut ratfers on the top with a handsaw. The mark you would make wouldn't be 45 degrees, it would be some trig. calcutlation related to the width of the board and the angle of the cut.JK
>> He's probably referring to the reading he gets on the rafter after the bevel is made.If you cut a 12/12 rafter on a 45 bevel, then put your square on top of the rafter so you can read the degrees of the bevel, because its a compound cut it will appear more than 45. Kind of like the old way to cut ratfers on the top with a handsaw. The mark you would make wouldn't be 45 degrees, it would be some trig. calcutlation related to the width of the board and the angle of the cut. <<John,I know they read different if you do that and they read different for every pitch.If that’s what he did and his hip is running at 45°, then he wasted a whole lot of time cutting with a handsaw for no reason when he could've just cut the jack plumnbcuts with a circular saw set at 45°.
Joe Carola
OK- so you mean I just could have cut the 44 degree plum cut with the saw set to 45 degrees? It makes sense, as the hip rafter is 45 degrees to the sidewall plate...my head is starting to hurt...Bill
>> OK- so you mean I just could have cut the 44 degree plum cut with the saw set to 45 degrees? It makes sense, as the hip rafter is 45 degrees to the sidewall plate...my head is starting to hurt... <<BillYes!Not trying to sound like a wise guy, but everyone told you to set the saw at 45° to cut the plumbcut.You cut all these with a handsaw using your bevel gauge to mark the top and bottom of the plumbcut? OOOOHHHHHFFFFFAAAA!Just busting your chops a little. Your forearm must look like Popeye's now................;-)
Joe Carola
No, only cut 2 2x6s, pulled back the guard on the Skil 77, did it by eye!Glad to provide some amusement.BIll
Bill,Tomorrow, go and scribe a plumbcut and set the saw at 45° and cut it and you'll see how it works.What did you cut the Hip plumbcut bevel at?Joe Carola
Framer- I'm gonna go test it right now.Here's how I did it- first, I cut the 46 degree plumbcut with the saw set at 90. Then, I just drew the bevel on the edges of the 2x6 using the sliding bevel gauge. Like you said, when viewed from straight on, this bevel appears to be way greater than 45, so I connected the line on the back of the board, then cut it 'freehand' with the 77. (don't try this at home-board was clamped securely!) Now that I think about it, I did end up holding the saw at an angle suspiciously close to 45 degrees!!To be perfectly honest, I was impatient, and didn't wait to go online and read the answers to my post, since I had "figured out' how to do it all by myself (see how great that worked!)Maybe if they didn't put all them dang numbers on the speed square, I would have just trusted my instincts and cut it with a 45 bevel.Anyway, I did get 'em cut fairly easily, except for the loss of hair from excessive head scratching (like I have any anyway!).Live and learn. At least I didn't sever a digit (or 3).BillEdited 10/12/2006 9:10 pm ET by PGproject
Edited 10/12/2006 9:13 pm ET by PGproject
>> Here's how I did it- first, I cut the 46 degree plumbcut with the saw set at 90. Then, I just drew the bevel on the edges of the 2x6 using the sliding bevel gauge <<Bill,Scribe your 46° plumbcut and don't waste your time cutting it with the saw at 90°. Just mark the plumbcut and set the saw at 45° at make your cut.Joe Carola
Joe- yes, I know now. I did it that way so I could hold the saw at the angle to 'freecut' the bevel, wich is obviously unnecessary if just cutting with the saw set to 45.OK everyone, stop laughing now and remember stupid stuff you did before you knew better. This is the first dumb thing I've done this year. Damn, almost made it to Halloween!Bill
>> OK everyone, stop laughing now and remember stupid stuff you did before you knew better. This is the first dumb thing I've done this year. Damn, almost made it to Halloween! <<Bill,No one's laughing at all and it's not a dumb thing you did. There's even guys that frame for a living and think that the saw setting is different for every pitch and don't realize that it's not and the saw is set at 45° with a hip running at 45° no matter what the pitch is.Joe Carola
thanks
I'm still trying to figure out how he cut it "freehand" I'd really like to see a video of that. I lost a bet a long time ago about this topic, over beers after work. I was swearing up and down a 45 bevel is a 45 bevel, boy was I wrong.JK
John,He probably put the bevel gauge at the ridge lying on top of the king common and got the angle that way and thought that the saw should've been set to that angle. A lot of people think that for some reason the saw setting changes with each pitch change because they don't realize that the saw setting always is set to the angle the hip runs at in plan view. For all 45° hips the saw setting is always 45° no matter what the pitch is.People get confused with the "Side Cut” numbers on the framing square and don't realize there's no need for the sidecut table unless they want to cut with a handsaw for some crazy reason or a big timber they want to cut that d they don't have a saw big enough for.
Joe Carola
Thanks, Piffin.
I gave up trying ot open it. Guess I am not only framing disabled, but computer disabled too!
not problem at your end. He drew that in the new Google sketch-up program, so it had been saved by default as a sketchup file, which can only be opened by that program at this time. But Sketchup allowed him to do a file/save as/ *.Jpg type of file so he could present it for all the world to see.
He just forgot the first time to save it as a Jpg for us.
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Google Sketchup is a free download and will open any .skp file. Google has another free download, and it is the Sketchup Viewer. It too will open a model file with the .skp extension.
With the viewer, you can manipulate the file and use the page controls. You cannot modifiy the file. But the viewer would allow you to see the file as a presentation slide show, with the model morphing and turning on screen.
You and Mike Smith can probably do this with your expensive packages, but I can do an animated paged show that shows a client the project coming together from excavation, through sitework and structural, and then on through finish. And I can send it to them as a Sketchup file, with them using just the viewer to see things.
I did not realize they had a viewer out already, but I anticipated that when I said something along the lines of not everyone...at this time"Like most new PCs come with a PDF reader now, but there was a time recently when the browsers did not include them and you had to do a download, I expect that in a year or two, either most PCs will have this viewer built in or most image programs will include the format in their abilities at least so far as reading it.I can remeber only 2-3 years ago emailing clients a PDF presentation and having them reply, "I can't open it" Groan!!!
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