Calculating a radius

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Forum topic by Robert posted 08-08-2020 10:32 AM 306 views 2 times favorited 5 replies Add to Favorites Watch
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3950 posts in 2334 days

08-08-2020 10:32 AM

If you have a portion of an arc and the distance between the ends (chord), does anyone know how to calculate the radius?

What I am doing is trying to duplicate a bow front table curve without a a bunch of trial and error using a circle cutting jig.

-- Everything is a prototype thats why its one of a kind!!

5 replies so far

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#1 posted 08-08-2020 10:57 AM

Radius from Arc is basic geometry; look up ‘Intersecting Chord Theorem’.

Here is cliff notes version:

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-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

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Fred Hargis

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#2 posted 08-08-2020 10:59 AM

There are on line calculators, but you also need the height of the chord.

-- Our village hasn't lost it's idiot, he was elected to congress.

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#3 posted 08-08-2020 11:01 AM

Section 3 in the link below has a formula a for calculating radius from chord and sagitta.

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#4 posted 08-08-2020 12:23 PM


-- Everything is a prototype thats why its one of a kind!!

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#5 posted 08-08-2020 03:01 PM

You can also do it if you only know the length of the chord. Use the calculator in this link. Enter your measurement for the length of the chord for side A and B and the calculator will calculate side C. One half of side C is the radius for the circle. If A is 10 , B will also be 10 and C will be 14.142. divide that by 2 and the radius is 7.071

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