# Roundover Bit Size



## garryjc (Sep 11, 2004)

I have found several roundover bits of various sizes. I am not clear how to determine the size of the roundover. I know I can simply use a bit on results, but it would be nice to know the size for future jobs.


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## John Smith_ (Jan 10, 2020)

draw some circles with a protractor - the diameter of the circle will coincide with the router bit size.
I have a big one that is 1-1/8" Radius all the way down to 1/8" Radius.


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## mgmine (Jan 16, 2012)

The size doesn't matter as much as what you want the edge to look like. If you want a completely rounded-edged then the chart that John posted will be your best guide. But keep in mind that the thickness of the wood plays a factor. I find it best to just run a sample piece and adjust the bit to where it looks best.


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## Barry747 (Jun 16, 2011)

John's post is excellent. A round bit is 1/4 of a circle and it's identified by the radius. So, a 1" diameter circle has a radius of 1/2". The corresponding roundover bit is a 1/2" roundover bit. 

If you're into math, you can find the radius by measuring the chord (shown in John's second picture) and the height of the arc (that would be the distance between the rule and the top of the arc in John's picture) and then use those measurements in a formula like the one found here: Circle - Radius from chord length and arc height You can change your units of measure too. 

Hope this helps.


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## Nate2016 (Jul 11, 2016)

The easiest way that I have come up with to come up with the radius of an existing bit is to measure the overall diameter of the bit, subtract the diameter of the bearing, take what is left over and divide it by 2. That is the radius.


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## Barry747 (Jun 16, 2011)

Actually, it just occured to me that there is a very easy way to determine the size, only takes a few seconds and doesn't involve much math. Order something similiar to this https://www.amazon.com/Pickett-CHA1...29469065&sprefix=circle+templa,aps,226&sr=8-5 I have a smaller one that I use to draw arcs for rounded ends on small table tops. Just move the bit from circle to circle until you find the one that fits. Then divide the circle size by 2 and that's the radius of your roundover bit. Easy.


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## papasombre (Sep 22, 2011)

John Smith_ said:


> draw some circles with a protractor - the diameter of the circle will coincide with the router bit size.
> I have a big one that is 1-1/8" Radius all the way down to 1/8" Radius.
> View attachment 399310
> 
> ...


Coincidences do exist.
Yesterday a neighbor came to me asking for a piece of molding with a round-over edge and I needed to take the measurement to know if I have the proper router bit to make the piece.
John's reply came timely.


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## Bemgolf (Aug 24, 2021)

John Smith_ said:


> draw some circles with a protractor - the diameter of the circle will coincide with the router bit size.
> I have a big one that is 1-1/8" Radius all the way down to 1/8" Radius.
> View attachment 399310
> 
> ...


 Just wanted to reach out and say I loved the image showing what the cut woudl look like. I am new to this forum and appreciate all the astude people on here.


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