Any tests for carbide sharpness?

[Stephen Cherry]

Recently I bought a bunch of used shaper cutters, router bits, etc. Some are in much better shape than others. Is there any quick test for sharpness of carbide other than a test drive? With hand tools, I usually try to shave some hair off my arms (not enough left on my head to make a good test). I know that carbide will never really get that sharp, but is there a similar quick test to see if a sharpening is due?

Thanks
Steve

[Andrew Hughes]

I use a magnifine glass to look at the tips and edge. Andrew

[Mel Fulks]

You might find a magnifying glass of some help . A number of times I have examined by eye and picked the duller of a couple of choices, and had to swap. Any thing in a set (cabinet door sets, dados,etc) be sure to get the whole set sharpened at one time even if some have not been used .When I decide something is too dull I put it in a special place so that it won't fool me again.Make sure employees do that,too

[Sam Babbage]

I use the thumbnail test as a quick and dirty method, I find it difficult to explain the sensation, but if you take a known sharp bit and gently draw your thumbnail over the edge at about 90 degrees you will get a smooth scraping sensation, a blunt bit will give different sensations, depending on how blunt. As I said, it's rather difficult to describe, your best bet is to learn with a few bits of known sharpness, ie: freshly sharp, usably sharp and blunt as hell.

[Myk Rian]

Light reflection on the edge.
If you get it, dull.
If not, sharp.
Finger nail test also works.

[Tom Walz]

The scientific test is usually a measurement of the edge radius.

You can get carbide sharp enough to shave with depending on the grade. However it is rarely a good idea.

How sharp do you want them? An edge that is too sharp is much more likely to chip or spall.

There is a difference between a dull edge and an edge with land (flat or hone). Cal an edge that is super sharp a 10. Then call an edge with a light hone a 9. In many cases that 10 edge will dull down to a three while the honed 9 edge is still at a 6 or 7.

[Mel Fulks]

All good methods. It's just harder to tell with carbide than steel.Fortunately if all shop personal puts anything dull in the to be sharpened place;it's not a problem. When you're USING a cutter you know if it is sharp. Sometimes I just have to test used stuff on the machine.