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John, sorry to hear about your wrist. I hope you get well soon.

Thanks for the document, it is very clear and informative. I'm waiting for your video !

I suppose that with (jedi-)master-level skills it could be doable. But it's probably a very bad idea.

Diamond wheels do not like pressure so if you use only the shoulder you'll have to be extra extra light, as all the force of the blade will be focused there. Avoiding damage will be very difficult, though if you have just a couple blades it might no be such an issue.

Conversely, you'll be applying all the grinding effect on just the part that touches the shoulder of the wheel. So you'll have a lot of action just there. Grinding evenly to maintain the shape will be a real challenge.

And as will all stones you can't use the usual means (jig/bar) that allow for controlled angle grinding, which will not help.


Now about your brush cutter, I can't help but wonder : Are you 100% positive it is a recurve blade ? It looks to me like a straight blade but ground only in the tip area. You shouldn't have too much trouble grinding those on the Tormek, even freehand.

There are also few stones left unturned : compared to a few years ago, many improvements have been made.

Tormek now sells a FVB, the KS-123 solves the issues of the infamous AngleMaster when  sharpening knives, the pros and cons of each machine are well documented...

As for usage tips, any new Tormek user willing to lookup rich's Handbook or to spend some time searching the forum will find a trove of things to try to find their best match.

I guess we just have to wait for a new innovation by Tormek or the next controversial post to rekindle the fire of posting...

[...]

Hello, and welcome to the forum. I couldn't help but notice that 100% of your 2 first posts were resurrecting years-old posts to promote a commercial website. Not sure it's a good way to build up trust.

I just checked on the website of a french Tormek reseller, the SJs are 30% off. Which is about as high arebate as I've ever seen on anything Tormek.

Any idea why this would be ? Just a sales boost or are the SJs about to be replaced/discontinued ?

Hello,

I think the safest bet is to email support@tormek.se . You might also want to register your machine on the website even if it's way past the warranty period.

The impedance is a complex number, containing both a real part and an imaginary part. For an ideal capacitor, the impedance is purely imaginary, with no real part.

But for a real capacitor, there is a real part. Quoting from Wikipedia:

"The magnitude of the impedance |Z| acts just like resistance, giving the drop in voltage amplitude across an impedance Z for a given current I."

My calculation gives the magnitude of the impedance as about 210 ohms.

That's why I said "loosely" speaking. I'm ignoring the imaginary part, which is, as you say, responsible for the phase shift.

Agreed, *but* you based your calculation on the capacitance only, meaning you assume an ideal capacitor.

So you are not ignoring the imaginary part, you are dealing only with the imaginary part. The 210 ohms value you computed is a pure reactance, or said otherwise, no resistance at all.

To quote from the same wikipedia : "A pure reactance does not dissipate any power."

One note though, if you come over for dinner don't stick your hand in the knife drawer.

Do you mean you keep you ultra-sharp knives loose in a drawer   

So, loosely speaking, the capacitor offers a resistance to the flow of electricity of about 210 ohms.

The capacitor offers no resistance to the flow of electricity at all, it essentially alters its phase by 90 degrees (and multiplies it by a factor that depends on frequency). The resistance is the real part of the impedance and the impedance of a capacitor is purely imaginary : all the energy is conserved in an electrical form, none is lost to Joule effect.

It's not so much the spine thickness as it is the "thickness behind the edge".

Of course, knives with a thicker spine will - generally speaking - be thicker close to the edge. And if the knife is twice as wide close to the edge, the bevel will be twice as high.

This is not true with some japanese knives (honesukis for instance), that have a thick spine and a very thin edge.

Vadim was very clear when he stated the sharper a knife is to start, the longer it will remain sharp.  Depending on the use of course.
My target when I sharpen is 100.

I haven't read Vadim's book in a while but I think I remember him saying that initial sharpness was a lesser factor wrt edge retention than the bevel angle.

To add my $.02 to the answers to the initial question, my answer is "yes, probably". An easy way of knowing is to mark with a sharpie the place where you take you measurement on the BESS test medium. Then you can examine this area carefully with your microscope. If there was a burr, you'll see a dent on your edge.

Though I agree that sharpening with the Tormek (T3/4/7/8 SG2000, ...) requires training, patience, and skillbuilding, I think it's fair to say that you shouldn't need a non-included truing tool to be able to sharpen properly. And *if* the wheel is indeed out-of-square with the USB, then the blame falls squarely with Tormek.

That being said, that's a big "IF" : I don't think Tormek has begun shipping SG grindstones that are not square within acceptable tolerances. So the USB setup must be to blame, and though you might be able to true your SG-200, that won't work with, say, a DF-200.

So the way I see it : if the USB is indeed not reasonably parallel to the shaft, then I'd suggest dealing with Tormek support. But before that, I'd make sure to set it up using the recommended procedure where you press down on the threaded leg before tightening the corresponding knob, then the other one.

That doesn't mean that you won't eventually (or rather, soon) need a truing tool. But you shouldn't mess up your stone needlessly. And yes, the T-4/T-8 choice might actually be more real-estate-driven, rather than financially driven, all things considered.

[EDIT] The wheel being untrue when you checked it might be the result of your first sharpening sessions, where you might have applied pressure unevenly. A good way to check this would be to use a precisely machined square : if you see light shining through between the square and the top of the wheel when you lay one side of the square flat against the side of the wheel, then that's most probably the case. You could also check the trueness of your USB by tightening it as mentioned and using the side of the wheel as a reference for your square. [/EDIT]

Ken, the idea of the formula was to substantiate a reply to an objection regarding the choice of words of the OP.

I am no Richard Feynman, so I will not be able to be as clear as a professional teacher. Still, to make a long story short :

The concept of impedance is a generalization of the concept of resistance, i.e. the proportional relationship between current and tension. With a resistance, everything is simple : tension U is related to current I by the U=R.I relationship.

For a capacitor, U is related to the integral of the current over a period of time. But using mathematics in the complex world, integrating is "simply" dividing by j.w (assuming a sinusoidal current, and where j²=-1 and w or "omega"  is the pulsation of the current). So one can write U=Z.I with Z=1/jCw.

Conversely, for a solenoid, U=Z.I with Z=jLw.

Therefore, in electronics, impedance is a generic term covering at once R,L and C. And asking for the impedance of a capacitor is another way of asking for its capacitance. Pretty much in the same way that asking someone for their address will give you the name of their hometown, and a bit more.

As for E=m.c², if I may, there might be a slight twist in your VHS or your recollection of it. To apply E=mc² to your baseball, you would have to thoroughly disintegrate said baseball, and the energy released (in the form of massless photons) would be m.c², m being the rest mass of said baseball. If you could accelerate the ball to lightspeed, its mass would change and things get pretty messy from here. But e=mc² is always true, even for a baseball at rest. And you cannot accelerate it to c², which is not a speed.

Hope this helps,

Nick.

Impedance covering capacitance+inductance+resistance (Z=R+jLw+1/jCw), OP was correct...