alternative use of old grinding wheels

[Elden]

http://forum.tormek.com/index.php?topic=2413.msg12059#msg12059

   Thank you, Herman, I am amending the term "angle" to "edge".  That was my meaning, but I used the improper word.

   After giving my other statement ("Simply decrease the angle to get rid of the excess metal.") more thought, I want to clarify what I mean. Lower the micro adjust on the US bar so that the heel of the tool will be reduced, forming a double bevel. It would not need to be reduced much, only enough to remove the extra metal left. This would result in a tool with a primary and secondary bevel, having the Tormek ground look.

   Personally, I don't think it will really matter that much.

   Jan, how many degrees difference will there be at the heel of a 6.35 mm thick tool, ground at 25°, using a 250mm diameter versus a 175mm diameter grinding wheel?

[Jan]

   Jan, how many degrees difference will there be at the heel of a 6.35 mm thick tool, ground at 25°, using a 250mm diameter versus a 175mm diameter grinding wheel?

Assuming a 6.35 mm thick chisel, ground at 25º we will get following figures:
a)   for 250 mm grindstone the heel angle is 31.2º and hollow size is 0.18 mm,
b)   for 175 mm grindstone the heel angle is 33.5º and hollow size is 0.24 mm.

So, the difference between the heel angles is slightly more than 2 degrees.

From the practical point of view the heel angle of a tool has nearly no effect on its performance, only the edge angle is important.   

Jan

P.S.: The drawing shows the situation for 250 mm grindstone diameter.
Hatch shows the extra metal on the heel, which would be removed when grinding flat.

[Ken S]

Why not just set the jig for twenty eight degrees?

Regarding using six inch grinders, in my late dry grinder days, I used a Norton white wheel in my six inch grinder. The white wheel was more friable than the traditional gray wheels. Worn grains crumbled off more easily than with gray wheels. If I had not purchased my Tormek, my six inch white wheel would be a less than five inch wheel. Of course, I did the final sharpening with  bench stones back then.

Ken

[Jan]

For your 5" grindstone diameter the hollow will increase to 0.31 mm which is not dramatic, but the heel angle will be more than 36° and similarly will increase the extra metal on the heel.
However, in my opinion,  still fully functional chisel shape. 

Jan

[Ken S]

By the time the wheel is ground down to five inches, hopefully, a Tormek has appeared. Ken

[Jan]

The heel angle itself is not very important for tool performance, but it brings important lesson for freehand sharpeners.

When the edge would meet the grindstone at the heel level of the chisel (see the drawing in reply #31), than we would ground an edge angle 31.2° (using 250 mm stone) instead of the desired 25°.

In other words, when by freehand sharpening we drop the level on which the edge meets the stone by some 6 mm, we will increase the edge angle by 6.2°.

For 175 mm grindstone diameter this error will increase to 8.5°. And that's too much, that's not acceptable. 

Jan

[Herman Trivilino]

So what is the issue?  The length or the diameter or both?

The issue is the diameter. Ken, will the T7 mainshaft fit in the T4? I realize the lengths don't match, but if the diameters do it can be done. Then you just attach an old 200 mm diameter grindstone from a T7 and see if the wider T7 trough will fit on the T4. It would be a good use for an old trough that got replaced with upgrade. And then ... wait for it ... Bob's your uncle!

[Herman Trivilino]

Why not just set the jig for twenty eight degrees?

Because you want the edge angle to be 25°?

[Ken S]

Herman,

The shafts of the T4 and T7 look almost identical. The problem is the part of the shaft inside the housing is slightly shorter with the T4. (The part of the shaft which holds the grinding wheel is also 10mm shorter.) Nice idea; it just doesn't work. And, I doubt it is cost effective. IMHO, the most cost effective solution is just to purchase a new grinding wheel. Keep the old one for the odd rough job.

The reason I suggested setting the jig for twenty eight degrees is to compensate for the approximately three degree hollow grind with the smaller diameter wheel.

As a side thought, using twenty five degrees for chisels is really a compromise. For delicate paring operations, an angle approaching twenty or fifteen degrees works better. For heavier work, or with A2 steel, thirty degrees works better.

Ken

[Herman Trivilino]

As a side thought, using twenty five degrees for chisels is really a compromise. For delicate paring operations, an angle approaching twenty or fifteen degrees works better. For heavier work, or with A2 steel, thirty degrees works better.

The hardness of the wood makes a difference, too. As you know, I am not the most delicate of carpenters. Nothing fancy for me. If the wood is too hard I respond by hitting the chisel harder with my mallet. That will quickly chip the edge of a chisel in which case I simply add a micro bevel at a larger angle.

[grepper]

"Nothing fancy for me. If the wood is too hard I respond by hitting the chisel harder with my mallet"

[Ken S]

As Theodore Roosevelt said, "Speak softly and carry a big mallet." 

Herman, I did not fully answer your question. Both the T4 and T7 shafts have the same diameter and threads. The lengths are slightly different, and the T4 has a cross pin. The T4 uses a standard nut on the leather honing wheel end and a plastic knob on the grinding wheel end. Both seem adequate.

Ken

[Smitth8273]

As per the Tormek instruction book I always replace my sg-250 wheel when the stone gets to about 200mm. Over the years I have accumulated a lot of stones in this category.
Occasionally, I will fit one on my Tormek to sharpen a large cleaver or double axe. Other than that I have not found any other suitable use for them. Considering the cost of these wheels I was hoping to hear some ideas of how to use them beyond the Tormek recommended wheel life. Thanks for your input.

I use wheels down to a smaller diameter. If you have a lot of 200mm wheels I would but them from you!

Let me know.

[Ken S]

One of my favorite quotes is by Mark Twain, "Man is the only animal with the one true religion, all seven of them."

The handbook also talks about replacing the stone when it reaches 180mm. I believe the real problem is keeping the stone wet. I would recommend replacing the grinding wheel while it still has useful life and reserving the worn stone for work which is less critical.

Ken

[Ken S]

I have noticed worn Tormek grinding wheels listed on ebay. Most are under eight inches (200mm). The latest price is $35 US. I think the most practical use of worn grinding wheels, if not as table weights, is to sell them and put the proceeds toward a new wheel.

Ken