Quick Tip: Measure diameter of a circle

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Blog entry by bigfoot11 posted 01-23-2016 04:45 AM 863 reads 0 times favorited 4 comments Add to Favorites Watch

I’m in the process of making a small dust separator to work with my CNC and needed to make very tight fitting lid for a 5 gallon bucket. After fiddling for a few minutes and getting ten different measurements, it donned on me to take advantage of a flat table and some squares.

It’s so stupid simple, I can’t believe I’ve never seen it done this way before.

4 comments so far

View kiefer's profile


4873 posts in 2087 days

#1 posted 01-23-2016 04:57 AM

I have used this idea for years and it’s nothing new just a large caliper made with two framing squares

-- Kiefer

View bigfoot11's profile


80 posts in 1102 days

#2 posted 01-23-2016 05:06 AM

I was going to make a wooden clamp like yours but it made no sense just another thing to store.

The speed square makes it trivial to get it dead perpendicular.

View OldGuysRule's profile


130 posts in 393 days

#3 posted 01-23-2016 07:56 AM

I’ve used that method for years, only I hold them in a square and close it in until both read the same. Say like I did when measuring the lid for my dust collector. Which I don’t have a picture of me doing it. So that doesn’t help much. LOL

-- Rod P.........OLD GUY......Learning new things!

View jbay's profile


700 posts in 319 days

#4 posted 01-23-2016 02:48 PM

If you don’t have any squares handy.
Place a mark on the edge of the bucket and line it up with a mark on a flat board.
Roll the bucket one revolution and put another mark on the board. Measure the distance between the 2 marks and divide by Pi. (3.141)

-- Many times my “MO” involves Judging others, playing God, acting as LJs law enforcement, and never admitting any of my ideas could possibly wrong or anyone else's idea could possibly be correct.--

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