Blimey the hardest job I've done so far...

Discussion in 'Carpenters' Talk' started by alwaysworking, Jul 31, 2007.

  1. dirtydeeds

    dirtydeeds New Member

    get a rafter cut a 70 degree plumbcut and raise it till its vertical (against the vertical edge of a ridge)

    mr very clever man

    IT GIVES YOU A ROOF WITH 70 DEGREE PITCH

    it does not give you a 20 degree pitch roof as you claim



    you are wrong
    pythagoras was correct, thousands of years ago
     
  2. ­

    ­ New Member

    Pythagoras has nothing to do with this. He calculated the relationship between the proportions of a right angle triangle.

    We're discussing the angles.

    The pitch is the angle the roof has to the horizon.

    So a 20 degree pitch slopes up at 20 degrees from the ground.

    The plumb cut is where this rafter meets a vertical face (say a ridge board).

    In this example it is 70 degrees. That's why it's called a PLUMB cut. It is plumb/vertical.

    Keep asking the questions and I'll help you out for as long as I feel you're able to cope.
     
  3. ­

    ­ New Member

    > get a rafter cut a 70 degree plumbcut and raise it
    till its vertical (against the vertical edge of a
    ridge)



    IT GIVES YOU A ROOF WITH 70 DEGREE PITCH

    it does not give you a 20 degree pitch roof as you
    claim


    Blimey, you really don't understand roof framing do you! :^O

    Why would you cut a 70 degree angle (the ridge cut) and then raise it until it's vertical? It's the ridge cut not the seat cut.

    Sheeeeeeesh!
     
  4. Chekhov

    Chekhov Member

    Call me stupid if you like but a "plumb cut" is a "plumb cut" regardless of the pitch isn't it? I know I'm a bit thick but the pitch is irrelevant to the "plumb cut" isn't it? The pitch can be anything but the "plumb cut" is always ....well plumb!
     
  5. dirtydeeds

    dirtydeeds New Member

    mr verycleaverman

    just in case pythagoras was wrong wrong ive looked at your diagram

    you have DRAWN a 20 degree plumb cut, BUT youve labeled it wrong
     
  6. ­

    ­ New Member

    Did you look at THIS

    If you still don't get it I give up with you.
     
  7. ­

    ­ New Member

    > mr verycleaverman

    just in case pythagoras was wrong wrong ive looked at
    your diagram

    you have DRAWN a 20 degree plumb cut, BUT youve
    labeled it wrong


    What! Look again. Look again! :^O
     
  8. dirtydeeds

    dirtydeeds New Member

    mr very clever man

    you are an armchair diyer.

    i can frame a roof and carpenters have been doing it for centuries before me

    the plumb cut on a rafter is the same angle as the pitch

    do remember equal and opposite angles from school or are you still trying to proove pythagoras wrong
     
  9. dirtydeeds

    dirtydeeds New Member

    mr diyer

    rafters are cut on the ground where they are laid horizontally crown upwards.

    take a speed square scribe a line 20 degrees from the crown and cut the rafter. raise the rafter into position (so the cut is now vertical)

    it gives you a 20 degree pitch

    draw it out

    then come and tell me that carpenters have been doing it wrong for centuries
     
  10. ­

    ­ New Member

    > Call me stupid if you like but a "plumb cut" is a
    "plumb cut" regardless of the pitch isn't it? I know
    I'm a bit thick but the pitch is irrelevant to the
    "plumb cut" isn't it? The pitch can be anything but
    the "plumb cut" is always ....well plumb!


    Indeed the plumb cut is always plumb but when pitching a roof you have to cut the timbers to suit the roof angle. So for a 20 degree pitch roof you would mark the top of the rafter with a 70 degree bevel (and cut along this line). This would give the top cut of the rafter a plumb cut when the rafter is pitched at 20 degrees.
     
  11. dirtydeeds

    dirtydeeds New Member

    ps and tell me that the last 35 degree pitch roof i framed with 35 degree plumb cuts hasnt been condemmed by

    the architect
    the builder
    the contractor
    the building control officer
    the next door neighbour
    and children in the street

    for having a 55 degree pitch
     
  12. ­

    ­ New Member

    > mr diyer

    rafters are cut on the ground where they are laid
    horizontally crown upwards.

    take a speed square scribe a line 20 degrees from the
    crown and cut the rafter. raise the rafter into
    position (so the cut is now vertical)

    it gives you a 20 degree pitch

    draw it out

    then come and tell me that carpenters have been doing
    it wrong for centuries



    What's with the insults? Diy'er? I've been pitching hand cut roofs for over 25 years and have trained dozens of chippies we've had on our gangs.

    Lighten up mate. We're having a discussion. If you want a 'forum fight' the go elsewhere.

    Ok, I'll try and explain again.

    You have a length of 6"x2" laid on the ground as your rafter. The roof pitch is to be 20 degrees.

    Let's mark up this rafter with the lines to cut.

    First the top cut/plumb cut/ridge cut, where the rafter will meet the ridge. For this you would set a bevel to 70 degrees and mark this cut.

    You then need length of rafter (calculated by run x ready reckoner measurement for the given pitch).

    The length of rafter is measured fro the top of the ridge and again this is marked with your 70 degree bevel. This is the line of the back of the plate.

    You can now do one of two things to get the birdsmouth:
    1) Take a square off this plumb cut.
    or
    2) Take a 20 degree bevel and mark along the seat cut.


    You now have the ridge cut marked and the birdsmouth marked.

    These can now be cut.
     
  13. dirtydeeds

    dirtydeeds New Member

    come on mr verycleverman

    your getting it wrong because you are drawing a rafter as a single line, it isnt its 150mm wide (or whatever the design calls for)
     
  14. dirtydeeds

    dirtydeeds New Member

    ok, lets deal with the plumb cut, the birdsmouth deals with itself and its position is 1/cos pitch x span (adjusted for ridge thickness)

    so ive got my rafter on the ground set a bevel of 20 from the crown (towards the toe of the rafter)

    raise it to the ridge, i have a 20 degree pitch roof

    ive even drawn it on autocad but dont know how to post it here
     
  15. dirtydeeds

    dirtydeeds New Member

    ill correct my wording, run not span
     
  16. dirtydeeds

    dirtydeeds New Member

    im to bed
     
  17. ­

    ­ New Member

  18. dirtydeeds

    dirtydeeds New Member

    ill reply later i have a days work ahead of me
     
  19. dirtydeeds

    dirtydeeds New Member

    different sides of the same coin

    the angle to me is 20 degrees clockwise from a line perpendicular to the rafter ie off a vertical cut

    to vcm the angle is 70 degrees anticlockwise from the crown of the rafter away from the toe

    we end up with the same result

    i like my vision because you CAN make a cut along my reference line and get two pieces of timber

    i dont like vcms vision because you cant cut along his reference line, you are effectivly cutting thin air and you dont get two pieces of timber




    personally i dont care for bevels on roofing work, you need a second tool to set the bevel to the required angle

    and it is too easy to knock a bevel slightly out, if you know youve done it ok........... BUT you have to reset the bevel again. using the second tool

    if you dont know youve knocked the bevel you dont know until the rafter doesnt fit, if youve done the job right and cut ALL the rafters first, none of your rafters will fit
     
  20. Trog

    Trog New Member

    All I know is if I'm going to mark out a rafter for a 20 degree pitch there's no way i'd set my bevel at 70 degrees to mark the plumb cut. That is one steep angle (seat cut, yes)I'd be setting my bevel at 20 degrees or whatever the pitch is. So I'm with dirtydeeds on this one, nothing personal ecm and like you I've been pitching roofs for 25 years.

    Regards
     

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