expanded TT-50 thoughts

[Ken S]

I have posted before about my preferred TT-50 technique. I learned this by "resharpening" a turning skew. I set the jig according to the booklet recommendations and soon realized that the skew did not fit the standard specs. Instead of just resetting the skew to match the existing specs, I decided to regrind it to the Tormek jig specs. Bad move. It created a lot of time consuming work. The one bright spot was that I became fluent with my TT-50. I should have just shifted the skew gradually, correcting it over several sharpenings.

This experience helped me develop my mental bar graph of using the TT-50. Imagine a bar graph where the horizontal axis represents use time of the tool. The vertical axis represents the cutting efficiency (sharpness) of the tool. The tool begins with 0 time and 100% cutting efficiency. As the tool is used,  the cutting efficiency gradually decreases. Eventually, the TT-50 is used to restore the stone to 100% efficiency. Combining all the points lets us arrive at an average cutting efficiency.

If the TT-50 is used more often, the average cutting efficiency is improved. This principle is shown in the online class on Pressure. Done frequently, only a very light cut is needed, perhaps only half a number on the micro adjust. Wear on the grinding wheel in minisculs. For heavier or prolonged use, efficiency can be improved by leaving the TT-50 preset in a second support bar.

Here is a link to the Pressure online class. There is much good information in it.

https://www.youtube.com/live/7laP_ysnMwo?si=FzjiYp79vs5zLKfS

Ken

[tgbto]

I'm not sure the truing tool restores the "cutting efficiency" of the stone. It's not as if the SG won't sharpen anymore if not trued for a long time. It will probably not sharpen squarely, and might create low spots on knives or planer blades and such.

The stone is more aggressive after the truing tool is used because of the temporary low grit, but that will quickly settle back to the standard average SG-250 grit. The truing tool ensures the surface of the wheel is parallel to the usb, with a constant diameter.

Sharpening technique, as well as the kind of tool getting sharpened, will have an impact on how the stone wears down, and how its geometry is impacted in the process. It will therefore require more or less frequent truing, but not because the abrasives cut less efficiently.

So I don't think it's a matter of what the average cutting efficiency is, but rather how close the wheel is to its optimal shape. Too high a pressure will exacerbate high spots and low spots, narrow tools will quickly create ridges on the stone. The sharpeners' skill (in keeping pressure optimal, using the full width of the stone, keeping tools square with the wheel, etc.) will increase the time in between two truing sessions.

Also, careful use of a diamond plate in the SE jig will keep the stone parallel to the USB for longer periods, and skill or the use of two USBs will reduce the risk of low spots.
In my experience, the use of the grading tool degrades the shape of the wheel quickly, requiring much more frequent truing. This is because it is very hard to keep it parallel to the USB (after all, why would your hands be parallel to the USB ?), and it is used roughly at constant pressure, which will tend to dig into the already low spots.

When I sharpen knives only and use diamond plates once in a while to temporarily change the grit of the SG, I barely feel the need to true at all. This increases the lifetime of the SG in the long run.

[Ken S]

TGB,

Your points are well taken. It may surprise you; however, I agree with you. In my own sharpening, I use a set of three DMT diamond cards. Each is epoxied onto a piece of steel 2" x 8" x 1/16". This was a piece of 2' steel from my local hardware store cut into thirds. These are placed into older square edge jig (s).

I fully credit Wootz for conceiving the idea o using diamond plates to keep grinding wheels true and graded. I consider my minor modification a small improvement. Wootz' premature passing was tragic in many ways. Who knows what concepts Wootz would have developed with a longer life.
believe both truing and grading are developing concepts. I do not believe either Wootz' concept or my modification will prove to be the end all.

I often do not know the experience level of the members involved. Some members, like you, are obviously more skilled than the majority of the membership. I suspect most members are still using the stone grader, many using it very infrequently. For some, I believe these suggestions might be a step up in their technique. I encourage more advanced posts like yours. It will help us all grow.

Ken

[Herman Trivilino]

I'm not sure the truing tool restores the "cutting efficiency" of the stone.

I guess it depends on what you mean by efficiency. A freshly-trued stone definitely cuts steel more aggressively. I wouldn't sharpen a good knife on a freshly-trued stone. It removes too much steel from the knife blade. I would find my dullest chisel, lawn mower blade, or other tool to sharpen on a freshly-trued stone. In fact, I often keep a dull tool handy to be sharpened immediately after truing.

Ken is absolutely right about truing often and lightly. Not only will it give you better results, it's more economical. Because an out-of-round grindstone will very quickly get more and more out of round as you use it and you will have to remove a lot of material to get it round again. A grindstone will last longer if you keep it from getting out of round by truing it often.

It's kinda like brake pads and rotors. Putting new pads on a rotor with a rough surface will make the pads wear faster. It's more economical to machine the rotors when replacing the pads.