Sharpness of a Cutter Edge

Most common is to eyeball it but you can use a small / cheap optical comparator - although you will have to know what your looking at..... and what geometry you need. Sharp is rarely the case for machining but it looks like you may be doing punch work. You may need to view a cross section on the comparator but scratching a nail sounds good!

http://www.m-osaka.com/en/exhibitors/212/

http://www.americanmachinetools.com/how_to_use_a_lathe.htm

http://en.wikipedia.org/wiki/Tool_bit

I recently read a book totally about sharpening and the author recommends using a cheap digital microscope (from a toyshop). I don't yet have one but will follow his advice.

Sorry, I can't remember the ISBN etc as I borrowed it from the local library.

Here's a web page that describes just such a setup using a $30 second-hand toy microscope for checking the sharpness of infill plane blades.

http://bladetest.infillplane.com/index.html

And here's a link to the home page.

http://bladetest.infillplane.com/index.html

Most articles on sharpening deal with woodworking tools, but it's important to keep machine tool cutters sharp as well. It saves a lot of grief.

Using a fingernail has always been a test of the 'fairness' or 'sharpness' of a punch edge. Using magnification devices is a newer method and probably more valid. The 'catch' is that there will need to be training in addition to the addition of the visual checking device. The punch design will need to be accounted for as well. Different materials hold edges differently and some actually need a small radius on the edge to operate efficiently while punching.

Sharpness of a cutting edge in a die can be determined to a certain degree with the described nail test, however during metal piercing (and many other operations) the keen-ness of the edge is just a portion of what needs to right to give a perfect cut with minimal burr and reasonable die-roll.

Many die applications have cutting edges which engage the material usually at 90 degrees and the rubbing effect on the punch may cause the front edge to be worn.

When the punch surface is re-ground or machined ie. sharpened the nail test may make a good impression, but the cut condition can still be poor as the cutting edge side may be worn, effectively draggin material creating a burr.

For metal cutters such as end mills this is different as there generally is much more than a 90 degrees in the form of a rake angle, in this case edge wear can affect the rake angle and change the chipping effect and in turn affect the finish. A nail test usually is adequate depending on the finishing surface finish requirements ie Ra, Rz Rmax etc.

A visual inspection with a low end tool makers pocket microscope, magnification lens or USB computer camera may be adequate when combined with the nail test for most cutting edge checking and cutting operations.

hi everyone..am back after a long break...now i need some comment on a more precise method of checking the angle of the cutter as i will be doing a research on it and also covering the red hardness...if anyone can contribute to this research they r most welcome..thks for your reply