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

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

1. ### dirtydeedsNew 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. ### Â­New 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. ### Â­New 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. ### ChekhovMember

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. ### dirtydeedsNew 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. ### Â­New Member

Did you look at THIS

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

7. ### Â­New Member

> mr verycleaverman

just in case pythagoras was wrong wrong ive looked at

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

What! Look again. Look again! :^O

8. ### dirtydeedsNew 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. ### dirtydeedsNew 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. ### Â­New 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. ### dirtydeedsNew 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. ### Â­New 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. ### dirtydeedsNew 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. ### dirtydeedsNew 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. ### dirtydeedsNew Member

ill correct my wording, run not span

im to bed

19. ### dirtydeedsNew 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. ### TrogNew 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