moving to the stone grader

[Ken S]

This topic is an expansion of my TT-50 topic. The same concept of average cutting efficiency can be applied to the stonegrader. It works in both keeping the stone coarse and fine. Again, I recommend watching the Pressure online class linked here:

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

Ken

[tgbto]

As mentioned in the TT-50 topic, I believe the stone grader actually brings the stone out-of-true faster (which then requires truing). So it seems to me its effect is somehow contrary to the truing tool (except in its ability to coarsen the grit, albeit very temporarily).

I highly recommend using the truing tool with care, and diamond plates to adjust the grit of the SG stone, as mentioned in numerous topics on this forum and as demonstrated by the late Wootz on YouTube here and here.

[Herman Trivilino]

As mentioned in the TT-50 topic, I believe the stone grader actually brings the stone out-of-true faster (which then requires truing).

Hmmm... I wonder what leads you to this belief?

It's quite possible that you're right. It could also be true that the act of sharpening brings the stone out of true. Certainly something must be causing it to happen, since we know for sure that it does get out of true.

Again, I go to my automotive disc brake analogy. Just as the brake pads, and to a lesser extent the rotors, are designed to wear, so is the grindstone. Using it makes it wear. Things like using the stone grader, using the truing tool, or even the very act of sharpening a tool itself, will make the make the grindstone wear faster, so will driving your automobile make the brake pads and rotors wear faster.

This is part of the design of these things. It's how they function. It costs money to operate these devices because of this wear.

[tgbto]

As mentioned in the TT-50 topic, I believe the stone grader actually brings the stone out-of-true faster (which then requires truing).

Hmmm... I wonder what leads you to this belief?

Well, the "short" answer is : the stone grader has no reason to be held parallel to the USB. And there is no reason for the pressure applied by any hand to be equal to whatever is required to keep the stone true (or bring it closer to true) at any moment in time.

To elaborate a bit, having a human press down on the stone grader with the wheel turning is inherently an **instable** process, as whatever defects will be amplified instead of smoothed:
If the wheel has a low spot, the tool will follow the shape of the wheel and the pressure will increase when the surface of the wheel starts to rise right after the low spot. Conversely, the pressure will drop slightly shortly after the beginning of the low spot and shortly after the end of the low spot. The result will be to dig a bit into the stone at the lowest point, and grind a bit less around the high spots.

The delay in response between the cause and the effect is a perfect way to create oscillations (so called Pilot induced oscillations are an endless source of ... "interesting" situations in aviation or otherwise). Mixing oscillations and instability will not result in a nice result.

The fact that the tool is held by both hands compounds the previous phenomena by introducing variations not only along the circumference of the wheel but also between the internal and external shoulders of the wheel surface at any given point along its circumference.

This is not unique to the stone grader : if used in an uncontrolled fashion, the diamond plates may also create such undesirable effects, although holding them in the SE jig reduces the sideways variations. For a process to bring the stone closer to true (or at least no farther), you have to dampen the oscillations and bring the result closer to whatever "true" means, in this case : any point of the surface of the stone is at the same distance from the USB. The TT tool is well suited for that, the more recent version being less prone to oscillations.

I often use a diamond plate with the far end resting over a second USB, so I can both control the height precisely and grind the high spots first. Whatever flex remains in the setup (or non-parallelism between both USBs) is still a source of out-of-trueness, but it is still better overall.

Oh, and I agree 100% that sharpening brings the stone out-of-true. It does so because the edges being ground are never parallel to the USB, and they are often narrower than the wheel. I'm sure every Tormek user notices some slight variation of the noise or the water flow, that gets repeated with every turn of the wheel. That's a sure sign we're creating low spots.
Still, the steel edges are usually softer than the stone - for obvious reasons - whereas the stone grader is harder. So the latter is very good at rounding out the shoulders of the wheel, but also at bringing it out of true.