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How do you cut a circle in half.

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Forum topic by wseand posted 06-23-2017 08:46 PM 831 views 0 times favorited 22 replies Add to Favorites Watch
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wseand

2796 posts in 2882 days


06-23-2017 08:46 PM

Topic tags/keywords: question circles

Ok here we go. I need to cut a large fan shroud as close to in half as I can. Making two projects out of it, a entertainment center and wine rack. The shroud is 50” ID and 58” OD, it has an arc to it that is about 8” in depth. I have a few ideas but looking for any ideas. Some reason I just can’t get it into my pea brain of how to do this. Sent pic to help.

Any ideas would be great.
Thanks,
Bill.


22 replies so far

View Smitty_Cabinetshop's profile

Smitty_Cabinetshop

14857 posts in 2458 days


#1 posted 06-23-2017 08:52 PM

Grab a stick, any kind of long straight edge, scrap, whatever, and place one end on the inside edge of the rim. Stand up the straight edge and slide it back and forth along the upper edge of the rim, looking for the longest run that registers. When you find it, hold it steady and mark the location of the straight edge on the rim, top and bottom. That’s half.

Unless I really don’t understand what you’re trying to do, that’s how I’d proceed.

-- Don't anthropomorphize your handplanes. They hate it when you do that. -- OldTools Archive --

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DS

2824 posts in 2260 days


#2 posted 06-23-2017 08:53 PM

Bill, it seems that your work piece is already marked at the quadrant points with holes drilled for brackets.

Lay this flat on your work bench, use a small square from the bench and eyeball and mark a line through the holes.

Then pick your tool of choice – maybe a hacksaw, or a grinding disc and don’t stray too far from the lines.

Good Luck

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

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firefighterontheside

16963 posts in 1696 days


#3 posted 06-23-2017 08:55 PM

Measure the circumference. Divide it by two. You can use just a piece of string or such.

-- Bill M. "People change, walnut doesn't" by Gene.

View waho6o9's profile

waho6o9

8036 posts in 2417 days


#4 posted 06-23-2017 08:56 PM

It seems to me there’s 4 holes on the top ( 2 where the L brackets are still attached to ) and those

should be 4 quarters, so the reference points would be at 12 and 6 o’clock .

Scribe a line and jigsaw it with a metal blade. Or put a metal cutting blade on a skill saw and have

at it.

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GR8HUNTER

2968 posts in 552 days


#5 posted 06-23-2017 08:57 PM

take the 50inches so take 50×3.14 ”= 157 divide that into 2 = 78.5so just mark anywhere measure around it 78 1/2 inches will be half :<))

https://images.search.yahoo.com/search/images;_ylt=AwrBT8wPf01ZerUAsxJXNyoA;_ylu=X3oDMTByMjB0aG5zBGNvbG8DYmYxBHBvcwMxBHZ0aWQDBHNlYwNzYw--?p=diameter+of+a+circle&fr=yfp-t-s

-- Tony Reinholds,Pa. REMEMBER TO ALWAYS HAVE FUN

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Loren

9639 posts in 3488 days


#6 posted 06-23-2017 09:03 PM

I would stretch a piece of string around the top
rim and mark it with a sharpie to indicate the
end. String does stretch a bit. Stretch it out
on the ground and mark the center. Then
put it back around the rim and mark those
two points with chalk or tape or a scratch.

That marks the one rim. To accurately mark the
larger rim, put it flat on concrete surface and
drop a plumb line from each mark on the inside
and mark the concrete. Put the string under
carefully and stretch it between the two marks
from under the larger rim. You’ll need a helper.
When both marks are bisected by the string,
mark where the string exits the larger rim.

Then do your best to connect the two marks
on each rim.

I think this is a pretty exact and sort of pita way
of doing it, but if you really want it as close
as possible to evenly divided, I think it’s a
good bet.

###

All that said, you can easily tape a piece of string
to any point on the rim and stretch it across
and eyeball it. The longest spanning point
is the exact bisection and I think you’ll actually
be surprised at how accurate your eye is.

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papadan

3584 posts in 3208 days


#7 posted 06-23-2017 09:10 PM

”How do you cut a circle in half. ” With a circumference, silly boy! ;-)

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jbay

1861 posts in 739 days


#8 posted 06-23-2017 09:17 PM

For entertainment value….
Dunk it down 25” (29” if you use the big side) in the swimming pool and mark the wet line…..

-- If anyone would like to see my Portfolio, PM me and I would be glad to send you the link.

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papadan

3584 posts in 3208 days


#9 posted 06-23-2017 09:21 PM

I like this one!


For entertainment value….
Dunk it down 25” (29” if you use the big side) in the swimming pool and mark the wet line…..

- jbay


View wseand's profile

wseand

2796 posts in 2882 days


#10 posted 06-23-2017 09:31 PM



For entertainment value….
Dunk it down 25” (29” if you use the big side) in the swimming pool and mark the wet line…..

- jbay

Jbay will this pool work. Only one I have.

View wseand's profile

wseand

2796 posts in 2882 days


#11 posted 06-23-2017 09:45 PM

Gentlemen. Thanks for ideas. I’ve been remolding a friends house lately and just didn’t have enough brain cells for this.

Papadan,
Do they sell circumference at Harbor Freight?

Loren,
I was thinking of something along those lines. I just didn’t know how to find that center mark. Great idea with the sting and plumb Bob.

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jbay

1861 posts in 739 days


#12 posted 06-23-2017 09:48 PM

You could cut a piece of wood 29” (or 25” depending on the side you want to mark)
stand them both against a wall and mark both sides along the top of the wood

-- If anyone would like to see my Portfolio, PM me and I would be glad to send you the link.

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MrUnix

6017 posts in 2039 days


#13 posted 06-23-2017 09:50 PM

Easiest method has already been described a couple of times. And it’s even easier if you just use a tape measure instead of a string or piece of wood. Pick a point, any point, and measure from there to the other side. Wherever the longest measurement is obtained is dead center. Circles have magic properties :)

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

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jbay

1861 posts in 739 days


#14 posted 06-23-2017 10:48 PM



Easiest method has already been described a couple of times.

Cheers,
Brad

- MrUnix

No method is realized until at least 8 people say the same thing. :)

-- If anyone would like to see my Portfolio, PM me and I would be glad to send you the link.

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BenDupre

531 posts in 328 days


#15 posted 06-23-2017 11:26 PM

Use an angle grinder

-- The problem with communication is the illusion that it has occurred. – George Bernard Shaw

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