I want to be able to calculate the length and cutting angles of a diagonal brace. The door has a frame constructed of 5 members top bottom left right and a diagonal brace (see image) I know the width and height of the door and I know the frame timber thickness. Is there a formula for cutting length and angle of cuts
Joinery problem
- Thread starter mjwsparky
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Formula? Sure, but it would be only for this design unless it included ALL possible changes to future designs.
1) Are you SURE you want it diagonal sharp corners to rectangular sharp corners? Not everyone really does after looking at it.
2) The difficulty is the nominal width of the diagonal member. It is NOT parallel to the top or to the bottom. It's that angle you're looking for.
After that, it's a little geometry. How close have you gotten?
Frankly, I might just stick a board on there and mark it. If the rectangular frame is open in the center, that should be trivial.
1) Are you SURE you want it diagonal sharp corners to rectangular sharp corners? Not everyone really does after looking at it.
2) The difficulty is the nominal width of the diagonal member. It is NOT parallel to the top or to the bottom. It's that angle you're looking for.
After that, it's a little geometry. How close have you gotten?
Frankly, I might just stick a board on there and mark it. If the rectangular frame is open in the center, that should be trivial.
Dr.Peterson
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To clarify, I believe this is the figure:
You know w, h, and t, and want to find x, y, and angle IGK.
You can use similar triangles to solve. The resulting formula will not be pretty. And as suggested, laying it out and marking a line may be more accurate, in some sense.
You know w, h, and t, and want to find x, y, and angle IGK.
You can use similar triangles to solve. The resulting formula will not be pretty. And as suggested, laying it out and marking a line may be more accurate, in some sense.
Cubist
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It's a week and a half with no response from the OP. Here's the answer that I obtained in the hope that some joiners may find it useful if they should come across this page. Please check that your marking out looks reasonable before actually cutting. Refer to @Dr.Peterson 's diagram above for h,w (inside frame measurements) and t for thickness.
Let [math]q = h^2-t^2[/math]
Let [math]p = \frac{wh-t\sqrt{w^2+q}}{q}[/math]
Then...
[math]y = h\sqrt{p^2+1}[/math]
[math]KG = tp[/math]
Armed with the lengths y and KG, and a set square, no angles are necessary to mark out the brace. Not a pretty calculation!
Let [math]q = h^2-t^2[/math]
Let [math]p = \frac{wh-t\sqrt{w^2+q}}{q}[/math]
Then...
[math]y = h\sqrt{p^2+1}[/math]
[math]KG = tp[/math]
Armed with the lengths y and KG, and a set square, no angles are necessary to mark out the brace. Not a pretty calculation!