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Calculation / Formula for cathedral or arched cabinet doors

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Noel

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Anybody help me on this one? Danny Proulx uses one but I can't really get on with it and I can't find any other ones.

TIA.
 

Noel

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deserter":1okw3o64 said:
Is it the radius of the part circle your trying to work out?


~Nil carborundum illegitemi~
In essence yes, the arc and chord etc. Various sizes of cathedral doors to make so need something so that they they all blend in. They have to match various sizes of existing doors. I may be able to borrow a door if I need to.
 

9fingers

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Noel,
Assuming the curved edge is part of a circle (it need not be - could be an ellipse or an arbitrary oval)
If you have the length of the chord 2L and the distance D between the chord and the circumference of the circle, then the radius of the circle is given by:-


R=(L^2 +D^2) /2D

hth

Bob
 

Noel

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9fingers":1ztwyiuw said:
Noel,
Assuming the curved edge is part of a circle (it need not be - could be an ellipse or an arbitrary oval)
If you have the length of the chord 2L and the distance D between the chord and the circumference of the circle, then the radius of the circle is given by:-


R=(L^2 +D^2) /2D

hth

Bob
Thankyou Bob, good on yer.
 

CHJ

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Noel, if you need to match the form of existing doors with the uncertainty of how the curves were constructed, would it not be better to scribe a pattern from an existing door or it's frame and use that to scale up or down by fixed amounts , rather than bothering with calculations that may or may not be the same as used for the original.
 

Noel

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CHJ":2m7grtym said:
Noel, if you need to match the form of existing doors with the uncertainty of how the curves were constructed, would it not be better to scribe a pattern from an existing door or it's frame and use that to scale up or down by fixed amounts , rather than bothering with calculations that may or may not be the same as used for the original.
That's something I hadn't considered Chas and it seems obvious. As long as all the different doors look in proportion I'd be happy. I do have a tendency to over complicate matters.
 

CHJ

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I'm one for rarely bothering about finite dimensions, as long as components fit or match each other and tend to work with rods rather than rules when working with existing structures or components.
Last time I had to do similar I just marked up a series of contours on a sheet of hardboard at the steps required using dividers and used it as a full sized template, starting with the biggest and trimming it down in stages to the smallest.

(A technique borrowed from garment pattern grading where numerous production patterns are cut from a common design sheet.)
 

9fingers

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Looking here http://en.wikipedia.org/wiki/Gothic_arc ... _character, it seems that a common form of arch is the equilateral one.

Here the radius of each curve equals the width of the opening and the centre of the curve is at the top of each vertical element of the opening.

It might be worth check to see if your pattern complies with this principle and if so scaling other sizes becomes a doddle. Also any trim or moulding radii are readily derived form the basic door.

Bob
 

CHJ

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That makes a lot of sense, using a pair of dividers to scribe the arcs from a simple reference point would be the obvious for the timeframe. The ones I had to copy (screen details not doors) were somewhat more pointed with a radius greater than the width.
 

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