Saturday, February 16, 2013

WorldSkills dévers de pas & trait carré

To compete in the World Skills International Competition for carpentry you must have a complete understanding of the roof framing geometry of dévers de pas & trait carré.

dévers de pas  = DP line
trait carré  = TC line or TP line

Google's translations of anything with the words dévers de pas or trait carré still sucks.

Google translations from this PDF file are just terrible.

Valley Rafter Edge Bevel Angle

Original French Text:

L’angle formé par la ligne partant du sommet pour joindre le dévers de pas à sa rencontre
avec l’axe du faîtage en plan donne l’angle de coupe sur la face déversée. La mise en herse de la
hauteur 12 à la rencontre de l’axe du faîtage donne l’angle et la longueur sur la face déversée
recevant les empannons.

Google English translation:

The angle formed by the line from the top to reach the slopes of not meeting its
with the axis of the ridge in plan is the cutting angle on the face spilled. The implementation of the harrow
height 12 to meet the ridge axis gives the angle and length of the face spilled
Jack rafter receiving.

dévers de pas --> slopes of not

dévers de pas  should translate to:
dévers de pas --> the angle of the projection line 

dévers de pas --> The slope of a piece of wood is warping or sloping.

dévers  --> cant ... tilt
dévers  --> cant .. this is not plumb.

definition of 1798 French Academy dictionary
Cant, is also a noun. "We must mark the timber along its slope,"that is to say, according to its slope or warping.

 trait carré  -->should translate to:
 trait carré  -->  a line that cuts another line at right angles or a perpendicular line.

Tim Moore's blog on Stereotomy
The art of representing objects in section, elevation and plan in order to cut them out. - Louis Mazerolle

Tim's drawing's on this page are a good start on understanding the DP & TC lines.

or Chis Halls blog for those of you that are very advanced in the theory of timber framing by Louis Mazerolle.

Here are a couple of examples of the timbers/rafters rotated into the roof surface plane that use the DP line to find the slope angle of the rafter and the tilt of the rafter. 

Real world examples of rotated valleys

Roof rafter support post and rafters forming a maze of  angles.

Valley rafter rotated into the roof surface plane, long before we were born.

Some more models of the rotated valleys.

Valley rafter rotated perpendicular to roof surface. The jack rafter side cuts have a zero degree miter angle.

Rotated valleys on an polygonal plan with a sloping ridge and prow rafters on the end of the gable roof.

Close up of the valley's foot print and the jack rafters  running at different  directions. One set of jack rafters running  perpendicular to the ridge and the other set running perpendicular to the gutter line.

dévers de pas

To simplify the DP line geometry I'm using a square rectangle plan with an equal pitched roof slope in this example. The valley rafters that are rotated into the roof surface plane are crossing each other. 

Equal Pitched Roof Slope
8:12 = 33.69007

Develop the hip rafter right triangle BGH. The rise of the roof is 8". Draw GH 8" in length and perpendicular to line BG. Then draw line HB, that represents the true length of the hip rafter.

Next draw the line LD perpendicular to line AB that intersects line BG at D. Then draw the line DF perpendicular to line BG. Line DK is equal in length to DF and is perpendicular to line LD. Draw the line LK. Next draw a line that is perpendicular to line LK.Continue line LD to intersect the line KM . The line KM is the TC line. From E, draw a line to M. The line EM is the DP line, that will establish the rafter's miter and bevel angle.

The line TC is always perpendicular to the roof surface. Laying a framing square on the roof surface from point L thru point D will locate the point M. 

In this next drawing the point P is the intersection of line BG and EM. From point P draw a line to F. Transfer the lines between point F,P,E and D to the side of the drawing to establish the miter angle of the rafter that's rotated into the roof surface plane. We need to establish the point Q and V for the miter angle.

Draw the line DF' perpendicular to line ED. Next strike an arc from center point D the length of DF' . Then draw the line DF. Draw the line PF.   Strike an arc from center point P the length of PF. Strike an arc from center point E the length of EF'. Where the two arcs intersect , point Q, draw the line QP and EQ. Draw another perpendicular line to EQ that intersects at point P. This will form the line VP. The angle VPQ is the miter angle of the valley rafter rotated into the roof surface plane.

This next drawing shows how to develop the bevel angle of the valley rafter rotated into the roof surface plane. The bevel angle is 2 * the Jack Rafter Side cut Angle.

The geometry shown on this page can be used to develop the dévers de pas,  DP line, for any roof eave angle, like an pentagon (108°), hexagon (120°), octagon (135°) etc... , when the valley rafters are rotated into the roof surface plane.

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