How do I find this arch!?

[bob]

The simplest way, as previously noted, is to trace it.

Assuming that it is a chord of an actual circle and the dimensions of that chord is known, then you might either use a 3 point circle constructor, as in Flexi, or visit...

http://http://www.1728.org/circpart.htm

...and work a little fundamental trigonometry.

 

[TyrantDesigner]

Like others have said, trace it with a paper pattern, make a template from plywood, make sure the template works in the spot, design for those specifications, route out with the template in material of choice, apply graphics and graphical elements as needed.

 

[Alti-Plotter]

All of these calculations are worthless if the person building the arch just eyeballed it.

The absolute best, no-worries and only way to fit an existing arch is to go and get a template of it.

+1

 

[showcase 66]

If it is a perfect radius for the arc. With your dimensions. the radius would be 150.2778 inches. In a perfect world this would work for you. In real world, I would make a template. In reality the calculation is not that hard but in the grand scheme of things making a template would be best.

 

[Techman]

calculus derivative. The area under a cruve. As the slices get closer to infinity the accuracy increases.
Length of x length of y derive the area. = arch.

Then make the template anyway because this is not a perfect world.

 

[James Burke]

AutoCAD 3 point arc. Basically, the distance between the two points and the height of the chord is all that is needed.


JB

 

[Pat Whatley]

Let Rick do it. It's a variation of a circle....that's his job.

 

[studio 440]

this http://www.mathopenref.com/arcradius.html

 

[Mike Paul]

Ladder in the truck and make a template.

If you wing it... bring the belt sander.

 

[Pixels Are Bad Mmmkay?]

Is the photo already skewed to some degree? The photo doesn't look like it's taken that far out of perspective. I would just create a Photoshop image that is sized to your height and width dimensions (or down-scaled equivalent) and use the skew, perspective, and scale tools to get it to proper size and perspective, since it really doesn't seem that far off to begin with. Then I would trace the sucker with Corel. I'm all for that approach. Anything else seems either too time consuming and troublesome at this point, or too risky.

 

[oldgoatroper]

Is the photo already skewed to some degree? The photo doesn't look like it's taken that far out of perspective. I would just create a Photoshop image that is sized to your height and width dimensions (or down-scaled equivalent) and use the skew, perspective, and scale tools to get it to proper size and perspective, since it really doesn't seem that far off to begin with. Then I would trace the sucker with Corel. I'm all for that approach. Anything else seems either too time consuming and troublesome at this point, or too risky.

The only thing at this point that isn't risky, is to make a template from the arch.

 

[MikePro]

return trip? hogwash. gas and time is money, and you'll stress yourself out for no good reason. trust in your initial survey skills.

a square-on photograph and a few measurements to aid in scaling is all i'd need.
after that, illustrator is your friend. I'm pretty sure I could get a dead-on fit but i'd still subtract an inch or two to aid in ease-of-install and it would cover my butt if i was just a little bit off during the survey/fabrication.

 

[FS-Keith]

Like others are saying I would just make a template. But i would be willing to bet that shape is very precise. It was probable cut out on a hot knife cnc, that's all foam there under the dryvit

 

[phototec]

I am working on a sign for a building that was just renovated. They built this arch area for the sign into the front, and I'm just wanting to make sure that I'm thinking right so I don't have to redo this and be out lots of time and money.

I took the length of the two sides to the bottom of the arches, then I took the middle of the arch, and used the pen tool to connect the dots. Is it that simple? In my head there should be more to it, but I don't know what it would be. I'm going back to all of this geometry stuff in my head, but just not 100% the right way to confirm my arch is right. Can anyone help me to make sure, judging by these measurement?

Using your photo and dimensions, I created a full size drawing in Adobe Illustrator using the CADtools plpug-in for scale and dimensions, enlarged you photo for size verification (had to rotate it slightly to the left), then made the drawing on a separate layer over the photo. According to my drawing and calculations, the arch radius is 150 inches.

CADtools is the BEST plug-in ever created for Illustrator, I can't live without it.

https://www.hotdoor.com/cadtools

 

[Keith Rae]

Template it, if your arch is not the same as theirs it will look like crap. The lighting for the sign needs to be addressed there is more light shining on the outside of the frame than inside that will lite up their sign, that will cause huge shadows along the signs edge.

 

[TheSnowman]

They already said that they hated the lights. That's just random lights the construction guys put in I assume. So those will be changed after we do this. What a mess it all is. I think Phototec hit it on the head...but just for peace of mind, I'm having my installer go build a template today. It's supposed to be decent weather, so hopefully he won't have any wind whipping through the street throwing his cardboard around.

 

[Border]

Let Rick do it. It's a variation of a circle....that's his job.

Best advice yet. Sub it to the Master.

 

[Billct2]

Another possibilty is to make it undersized and add a trim around the edge afterwards.
The "foam" moldings bend easy.

 

[Bobby H]

There is zero substitute for measuring the actual opening.

The best thing to do, as a couple of others have stated, is measuring all the aspects of the opening (not just a couple of measurements and eye-balling the rest I've gotten that nonsense from a couple former co-workers).

Measure the width of the opening.
Measure the tallest point of the arch to the base of the opening.
Measure the height of the left and right ends of the opening.
Get height measurements at several points in between using even increments.
You'll get a pretty accurate V.O. measurement from this, especially if the builder used an even curve radius to develop the arch.

I strongly discourage the practice of scaling measurements from photographs alone. Distortion brought on through the effects of perspective, shooting angle and optical issues in the camera lens (barrel & pincushion distortion) make a photograph only close to scale and never truly accurate. You need accurate measurements of the visible opening.

 

[Suz]

I'd make a template of it too, as others have suggested. When I pattern airplanes I am often told the plane is symmetrical (except for a few smaller details which might include vents, antennas, exhaust on cowling, etc...

Still, I pattern both sides for a good fit. I find center and run a tape line all the way down. Using either thick kraft paper, or stable clear plastic, I pattern one side, then flip it over at tape line center. This tells the story of it's symmetry.

Good Luck! Let us know how it worked out.