# Im trying to find the angles for a jack rafter?



## mpooley (21 May 2008)

Please please i need help!!

Im trying to find the angles for a jack rafter?

have been trying to get this right all day.

rafters are for a posh conservatory so need to be perfect.

how do you do it?

is there any simple rule that i can follow ?

when i work it out using sketchup i get a compound angle of 34 degrees by 60 degrees but when i cut it - it s miles out!

I do this very rarely and usually its going to be covered up in a roof so i can get it "good enuff"

ive looked at the calculators on the net but they baffle me 
 

conservatory roof is at 34 deg
house roof approx 45 deg


help


mike


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## skipdiver (21 May 2008)

The edge bevel should be 40 and the other bevel should be whatever your common rafter is.So 34 if that is what the roof is.


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## mpooley (21 May 2008)

skipdiver":1flbfgp4 said:


> The edge bevel should be 40 and the other bevel should be whatever your common rafter is.So 34 if that is what the roof is.



ta 
so is the edge bevel always 40?

oh and what is the edge bevel lol  

when i place the rafter on the mitre saw what angles should i use?

sorry to sound so thick but well i am thick  

mike


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## skipdiver (22 May 2008)

Sorry Mike but i just gave a quick answer to your query before heading off to my brothers house to watch the cup final.The edge cut is only 40 in this instance(actually it's 39.7)and changes with the roof pitch.This only applies to the hip jacks and not the valley ones which change with the angle of roof you are cutting into.It's very difficult to explain but basically set the saw to 34 degrees to mitre cut and 40 degrees to bevel cut.And dont forget that the cuts are handed.

Try a site called blocklayer.com,type in the info and it will give you the angles.


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## plug (22 May 2008)

Mark the plumb cut on a piece of timber, set your circular saw to 45 degrees and cut along the line, the angle of the cut on the edge of the timber is then correct (called the Top Edge Cut). This is the quickest way to find the angle.


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## skipdiver (22 May 2008)

The edge cuts are only 45 degrees up to a fifteen degree roof pitch and after that they gradually decrease.The correct edge cut for a 34 degree roof is 40.


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## skipdiver (22 May 2008)

Just had a thought.Is the said conservatory an Edwardian or Victorian?That is to say is it square or segmental?Tell me what you are trying to achieve and i will see if i can help.


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## mpooley (22 May 2008)

skipdiver":3h0bjjqz said:


> Just had a thought.Is the said conservatory an Edwardian or Victorian?That is to say is it square or segmental?Tell me what you are trying to achieve and i will see if i can help.



well its neither :? 

Its a post and beam oak conservatory the roof is doug fir
and it joins into main single story kitchen of house at a right angle.

so have two valleys on where the 45deg kitchen meets the 34deg conservatory.
there is no ridge as such as the usual way (so ive been told ) with this type of roof is a bridle joint.
the rafter spacing is 740mm so there is only the one valley jack. (each side of course :lol: )

I've got the roof framers bible but cant make head nor tail of it (pathetic i know)  

I just have a complete brain blockage when it comes to compound angles

is that enough info?

thanks


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## mpooley (22 May 2008)

Oh ive just measured the angle at which the valley rafter is rising it is approx 30degs
and to keep the topsides level for glazing the sides of the valley eg top corner down to ground as it were (im good at this techinacl jargon arent i ?) is approx 75 degs :lol: 

i dont know if that helps but i thought id let you know 

8):lol:


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## Andy Pullen (22 May 2008)

You are vague but I assume you are trying to cut the common rafters into a valley or a hip, and not cut the actual hip itself. 
Whenever you are cutting rafters into a hip or valley you are trying to disect a 90' angle and so the angle is half this, ie 45', that is the theory but in practice it can vary by a couple of degrees because of discrepancies elsewhere. That is the top cut and the side cut is just the same as your common rafters.

HTH
Andy


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