trig

Discussion in 'Carpenters' Talk' started by yozman, Mar 26, 2005.

  1. dirtydeeds

    dirtydeeds New Member

    serious question andy, are you (were you) sponsered by dewalt when you were on tv (bad spelling again)
     
  2. limestone cowboy

    limestone cowboy New Member

    Calm down DD, it's only a forum. I've checked your calculations and they are spot on.

    Yoz, 18.78 (call it 19) degrees is a low pitch. Out of interest, what roofing material are you using?
     
  3. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Whoops dirtydeeds. You're wrong again. Sorry.

    The part I am questioning(I might not have made it clear)
    was the part where the thickness of the plate made a difference.
    If the 1000mm height of the ridge is measured from the top of the plate, the ridge will be 1000mm above the top of the plate, even if the plate was 10m high. The ridge would be 11m high. And the angle would be exactly the same. There's my question.

    However, I don't know if the measurement is taken from the top of the plate, so if it isn't that invalidates my question, and everything is back hunkydory. Are you with me ?

    Handyandy - really
     
  4. dirtydeeds

    dirtydeeds New Member

    sorry all. was away doing important things on festool, back with you in a minute
     
  5. Dewy

    Dewy New Member

    Too remember simple trig:-

    Some People Have
    Curly Black Hair
    Too Plastered Back

    S=P/H
    C=B/H
    T=P/B

    where:-
    S=Sine
    C=Cosine
    T=Tangent
    P=Perpendicular
    B=Base
    H=Hypotenuse.
     
  6. dirtydeeds

    dirtydeeds New Member

    andy, i think we have an understanding at last. im just going to ponder on your question a little longer. but you are right about the starting level (10m) being irrelevant

    PS im always wrong, clare says so, so it must be true
     
  7. dirtydeeds

    dirtydeeds New Member

    dewy, the one i was taught was

    SOH
    CAH
    TOA

    sine=opp/adj
    cos=adj/hyp
    tan=opp/adj
     
  8. dirtydeeds

    dirtydeeds New Member

    ps dewy

    my hair was black and curly and sometimes im plastered
     
  9. bathstyle

    bathstyle Active Member

    Was taught the SOH CAH TOA thing too!
    We were told it was an old Indian prayer or something!
    Amazing what you remember from school :)
     
  10. limestone cowboy

    limestone cowboy New Member

    We were taught:

    Silly Old Horses
    Clumsy And Heavy
    Trod On Albert

    Nonsense, but it works.
     
  11. NOGGIN

    NOGGIN New Member

    Jeese,

    what cufuffle! I was impressed with your calcs DD, I don't pretend to have that much skill at maths but I don't doubt you. I can at least agree with your calcs for the length from plum cut to plum cut.

    Yozman, If you don't have a chopshaw with angles marked out or carry some sort of protractor around with you try this.

    Simply draw (set out) the roof to scale (a piece of ply,or plasterboard will do) I suggest a scale of 1/3.

    Draw a right angled triangle with a rise of 333.33 (the rise 1000 / 3) and a span of 746.66 (the span 2290 minus 50 for ridge /3).

    Draw a line from the top of the rise to the outside of the span and you have you angles and lengths all nicely displayed in front of you at 1 third scale.

    you can set up your sliding bevel for the plumb and seat cuts, measure the length for the rafter (this you need to multiply by three).

    No rocket science required.
     
  12. Dewy

    Dewy New Member

    The mathematics teacher I had taught us that so we would never forget it.
    For him trig was a matter of life or death for many.
    He was a Lancaster bomber navigator so his trig kept the crew on course and was needed to get to the correct target.
    He is one of the few teachers I can remember because of his love of maths and the way he taught it.
     
  13. dirtydeeds

    dirtydeeds New Member

    andy, the thickness of the plate makes no difference in the same way as the staring height (10m) makes no difference.

    (not teaching ducks) but to raise a roof we need only 3 things, the span (which HAS to be measured on site because brickies cant build buildings square or vertical [despite protestations]) the thickness of the ridge and the pitch (given by the architect/engineer)

    becasue we were both being agumentative (this post is however NOT however a love in) the point i was deliberatly making was that if you cut the rafter the wrong length you end up with a pitch that is NOT the correct angle required by the architect/engineer. result the angles are wrong.

    hope this explanation isnt clear as mud
     
  14. dirtydeeds

    dirtydeeds New Member

    limestone, PML, but, when i stopped found it was the same thing

    I WILL get back to redoing the calcs, but its too much fun and nobody i know can pitch a roof in the dark
     
  15. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    andy, the thickness of the plate makes no difference
    in the same way as the staring height (10m) makes no
    difference.

    (not teaching ducks) but to raise a roof we need only
    3 things, the span (which HAS to be measured on site
    because brickies cant build buildings square or
    vertical [despite protestations]) the thickness of
    the ridge and the pitch (given by the
    architect/engineer)

    becasue we were both being agumentative (this post is
    however NOT however a love in) the point i was
    deliberatly making was that if you cut the rafter the
    wrong length you end up with a pitch that is NOT the
    correct angle required by the architect/engineer.
    result the angles are wrong.

    hope this explanation isnt clear as mud

    Backtracking, beep beep beep :)
    Yes your explanation wasn't as clear as mud, thankyou

    Handyandy - really
     
  16. dirtydeeds

    dirtydeeds New Member

    dewy, i wish i had had a maths teacher with that much love of his job. the guy made it sound as if learning maths was a interesting relevant AND of life or death. (it clearly was)
     
  17. dirtydeeds

    dirtydeeds New Member

    andy

    OUCH i thought it made perfect sense.
     
  18. dirtydeeds

    dirtydeeds New Member

    OUCH. OUCH. OUCH

    that was painful, i just read your post (properly) again
     
  19. NOGGIN

    NOGGIN New Member

    Andy clearly doesn't realise that the difference between the inside and outside of the wallplate changes the length of the span thus the angles of the pitch, plumb cut, seat cut and length of the rafter.

    I refer to my earlier post, I would do this, cut a patten and offer it up to check all was well before using it to mark out the other rafters.

    PS I wish we could have had a decent maths teacher at school, ours was a lifeless bully who would hold anyone up for public humiliation for any mistake, but never give an explanation for where you went wrong.
     
  20. dirtydeeds

    dirtydeeds New Member

    noggin, STRICTLY speaking as long as you adapt the maths and layout to suit, wether (cant spell it to save my life) you measure the run to the outer edge or inner edge of the plate it doesnt matter. some people do the internal face BUT most do the external face of the plate because you can hook your tape on it
     

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