How true is true

[Fineline]

To gauge whether the stone is parallel with the usb, I bring the usb very close to the stone, leaving about 0.5mm gap (guess) so that I can see a thin line of light.
I then rotated the stone and eyeball the gap and I can see more or less it is parallel. However, I noticed that as I manually rotated the stone, I can see a very small variation in the width of the gap, even though after I have done the truing with the TT50. In the manual, it says radial runout is +/- 0.2mm. However, since the weight of the stone is always resting on the shaft, should we see any runout at all after truing?. Put in another way, if I bring the usb very close to the stone, when I rotate 1 full turn, I should not expect any contact between stone and usb. By very close, I mean keep making the gap smaller and smaller until the first contact takes place when I rotate.
What's your experience on this? (I don't have a dial indicator )
If you leave a tiny gap between stone and usb, do you think the gap should remain constant after truing?
Thanks.

[Stickan]

Hi,
The stone should run true radially (up and down) within +-0.2mm ( Total 0.4 mm) as said in our handbook page 154.

Stig

[Ken S]

For many years I have had a hobby fascination with machine shop technology and precision measurement. In precision measurement, the goal is to be "within tolerance". More demanding tasks require more precise tolerances. Engineers must insure that a product maintains a balance between being within tolerance and within reasonable cost parameters.

Having the ability to measure precisely has dramatically improved the quality of our lives. With mass produced interchangeable parts, the average person can now have items far superior to what would have been affordable to only the very rich at one time.

Even the finest laboratory grade granite inspection plates are not exactly flat. Within tolerance for laboratoy equipment is often measured in less the ten thousandths or millionths of an inch. Precision surface grinding equipment can generally produce tolerances in the ten thousandths of an inch range when used by very skilled craftsmen. The Tormek could be manufactured to much more precise stands, but why? How many Tormek owners would willing to pay ten or twenty thousand dollars and serve a multiyear apprenticeship for sharpening operations which were traditionally done by hand, often by the shop apprentices?

When we check the squareness of our chisel edges with an engineer's square, we are producing sharp edges with our Tormeks far beyond those required for our work. I suspect most bench stones do not approach the +or - .2mm Tormek standard. Even handcut dovetails and mortice and tenons do not require that precision. Beyond a certain point, we are working to massage our egos.

Ken

[Herman Trivilino]

Even the finest laboratory grade granite inspection plates are not exactly flat.

As everyone knows, there is no such thing as exactly flat. The closest I know of is something called "optically flat". Lenses and mirrors used in equipment requiring the highest of precision will make use of optically flat surfaces. Optically flat simply means within one wavelength of light. The shortest light waves we can see have a wavelength of about 400 nanometers, so the variation in flatness cannot exceed, or in most cases even come close to, this amount.

On the other hand, acoustically flat would allow for variations on the order of 2 centimeters, since that's the wavelength of the shortest sound waves we can hear.

Note that a length of one centimeter is the same as a length of 10 million nanometers!

[Ken S]

Interesting, Herman. I would like to suggest that the content matters. No one measures the edge of a chisel in nanometers.

Ken

[jeffs55]

Gentlemen, I would suggest that sharp is when the tool will shave hair by its own weight being dragged across your hairy part. In other words, the sharpened object is PLACED, not held in one hand and dragged across the "hairy" appendage. If the weight of the sharpened object is sufficient to cut, literally hairs, while being dragged across the "hairy" object; then it is as sharp as necessary. NO, not as sharp as "necessary" but actually sharp. I can do this with knives of a certain weight. Give me a break, they do have to possess at least some mass for gravity to assist.

[tdacon]

I test the sharpness of my chisels the same way I test my katanas: I hold the tool in one hand with the edge facing upwards, and then toss a piece of extremely fine silk cloth into the air, letting it land upon the sharpened edge. The tool is sufficiently sharpened if the silk falls away from the edge, cleanly split into two pieces.

Tom