Anyone have a SG250 stone with about 200 mm left?

[jeffs55]

We had a long discussion about this same thing years ago as I was poopooing the use of the T3 now the T4. One of my arguments being that the stone on the then T3 was already used up. The first moderator of the forum and importer of the Tormek system, Jeff Farris said on the forum that he retired stones at 200mm. Yet the T3 is born that way. Turns out the limiting factor was the ability of the T7/T8 nee Supergrind stone to reach the water trough. At 200mm it was about at its limit to remain wet. No one was actually concerned with the concavity caused by the smaller stone. But as noted above there is an increase in hollow ness. Is that a word? Once again, it was I that expressed concern about this as I considered it a serious weakening of the edge due to less meat behind the edge because of the greater hollowness. I was pretty much poopooed away yet again on my thinking. I am still of the opinion that a flat grind is the best grind for a knife blade or any other blade.

[cbwx34]

We had a long discussion about this same thing years ago as I was poopooing the use of the T3 now the T4. One of my arguments being that the stone on the then T3 was already used up. The first moderator of the forum and importer of the Tormek system, Jeff Farris said on the forum that he retired stones at 200mm. Yet the T3 is born that way. Turns out the limiting factor was the ability of the T7/T8 nee Supergrind stone to reach the water trough. At 200mm it was about at its limit to remain wet. No one was actually concerned with the concavity caused by the smaller stone. But as noted above there is an increase in hollow ness. Is that a word? Once again, it was I that expressed concern about this as I considered it a serious weakening of the edge due to less meat behind the edge because of the greater hollowness. I was pretty much poopooed away yet again on my thinking. I am still of the opinion that a flat grind is the best grind for a knife blade or any other blade.

I'm guessing this is the thread you're referring to?

https://forum.tormek.com/index.php?topic=2413.0

Jan's pictures are gone, but I think it's the same ones in this thread...

https://forum.tormek.com/index.php?topic=3428


At any rate, it would seem to me that it would be easy enough to test...   (maybe?)   

But, I don't think one is "best"... depends on what you're doing.

Lately, I've been doing the main grind on a T-4 (EDC knives mostly)... then finishing on a diamond stone (just enough to clean up the edge).  Not sure if it's best... but it's working well for me!

[Ken S]

What do we know? And, what do we not know? We know that an SG-250 worn to 200mm will fit on the T4, including the water trough.
In fact, a 250mm full size SG-250, or any 250mm Tormek grinding wheel, will fit if the water trough is removed. I know this for two reasons: I swapped wheels, and, I measured the part of the shafts which hold the grinding wheel on my T8 and T4. Both models measured identically. Although the 250mm wheels have a 50mm thickness and the 200mm wheels are 40mm thick, the 250mm wheels are indented more, making them interchangeable.

What do don't know, or at least I don't know, is if the extra weight of the thicker wheel would overtax the lower wattage motor of the T4.

Jeff, at the risk of sounding like an Originalist, when Jeff Farris made that statement, "the Tormek" in the US (where Jeff Farris was the Tormek agent and demonstrator) was the 250mm Super Grind 2000 or T7. In my 2009 handbook, the SuperGrind 1200 was not available in 120volt 60 Hz for US use. I believe he was thinking only in terms of the 250mm models. (Incidentally, the water trough on the T8 is designed to function with smaller wheels.)
We disagree as friends.

John,
I think you are probably better off with your replacement SG-200. That's more of a gut feeling than a well reasoned, documented position.

Ken

[jeffs55]

I'm guessing this is the thread you're referring to?

https://forum.tormek.com/index.php?topic=2413.0

Bingo.

[ega]

jeffs55:
If "hollowness" doesn't ring true, try concavity.
AFAIK, the only merit of a hollow ground bevel on, say, a chisel or plane iron is that hand whetting becomes easier.
Ice skate blades are probably another matter.

[Ken S]

In 1972, I bought a garden variety dry grinder for the time, a six inch, 3450 RPM Sears Craftsman. Most of us were using six inch grinders back then. Many of us were still using oilstones. Flat grind sharpening would have been a very labor intensive project. Two contact point hollow grinding made a lot of sense. Yes, Ega, as you note, the advantage of hollow grinding was in labor saving.

I can spot a hollow ground blade from a six inch grinder. I have difficulty seeing the difference between blades ground with a T4 and a T8, even using a straightedge. I have compared chisels sharpened with both sizes. In my opinion, with either a 200mm or a 250mm diameter grinding wheel, the hollow ground effect is more theoretical than practical.

Ken

[BeSharp]

I have acquired a SG200 wheel. I am no longer in need if a wheel for my T4.

Thank you,
John

I have a 200mm SB silicone blackstone wheel for sale, but I never contacted you as I'm in Canada, and shipping across the border is just crazy right now. I just received a 12 lb (5 kg) shipment from a US sharpening supplies dealer. The expedited shipping (by air) was $90 CAD and it still took 14 days.

[Ken S]

I have had several small orders recently shipped from overseas. Shipping costs are crazy. I think the prudent thing now is to hold off if possible.

Ken

[jvh]

Hello,

why guess what is difference between flat and hollow grind on different wheel diameters when calculation is available nearly one year? I thought that it is resolved...

Differences for small thicknesses of blades (typically ca. 1 mm at the edge heel) are negligible, for thicker blades (eg. chisels) there are higher deviations but I didn't observe any difference between flat and hollow grind in real life.
For me, there is only limitation for Scandi grind which should be flat according to purists. Practically I didn't see/feel difference between flat grind and grind made on T-8 eg. on carving knife Morakniv 106.

Example below is double bevel grind with blade thickness 10 mm (= single bevel grind with blade thickness 5 mm), grinding angle 25°, wheels dia 200 mm and 250 mm.

jvh

[jeffs55]

 $90 CAD

What's that, about $15 USD? LOL

[BeSharp]

It was $67.22 USD.

[John S]

BeSharp,  Thank you for the thoughts. 

I wonder why shipping costs has skyrocketed? Can't be fuel prices.  I have to assume opportunistic price gouging.  Freight Boats and planes cost the same to sail and fly.

John

[BeSharp]

That's what it costs for US Postal Service Expedited Air to Canada. Apparently many retailers are refusing to ship by ground as it will be even slower due to the increased volume. Many Canadians, including myself,  used to pop across the border to pick up as many American retailers offer free US shipping. Due to COVID, we can't do that anymore.

[jasonstone20]

I am also in the market for a Japanese Waterstone, if anyone has another SG250 that is worn down to 200mm, please contact me: jasonstone20@yahoo.com