Radiius of router bits

[Jerry Bittner]

Okay, I've got a few roundover bits. Question is how to determine the radius since they do not have any markings.
That is, for any individual bit.

[Ben Davis]

you should be able to match some of them to core box bits if you know their size. One should fit with the other pretty well matched. I dunno of the top of my head about the off sizes though.

[Richard Bazemore]

Drill Bits

[glenn bradley]

Richard's got it.

[Peter Quinn]

Ruler by eyeball? Works for me. Or test cuts, ruler by eyeball?

[Tom Veatch]

Don't standard roundover/beading bits usually increase in discrete increments? Like by 16ths from 1/16 up to 3/8 and by eights from there? That's course enough for ruler and eyeball to do it for me.

[Steve Clardy]

I use 1/8 through 1/4 often enough I can usually just eyeball them.
But if I have a brain fart, I just use a tape and eyeball across the width of the opening on one side.

[Charles McCracken]

Jerry,

For most roundover bits you can measure the diameter of the bit, subtract the diameter of the bearing and divide by two to get the radius.

[Lee Schierer]

Gently lay the cutting edge on a 6" scale and read the difference between the marks on the bottom corner near the bearing to the upper corner. Whatever you read on the scale is the radius. I use a scale with 1/32" markings as most round over bits only jump by 16ths.

[Cliff Rohrabacher]

J&L 500 to 1 optical comparator
Or just grab a measuring stick. It'll be the fractional size that your tape measure says it is - unless it's metric.
If it is metric throw it away because all metrics are inherently dangerous.

[Will Blick]

they actually make set of guides, to read round over radius...

I think woodworkers supply sold them.... pretty handy, as you can also read the radius of finished edge as well..... they measure inside and outside radius...