alternative use of old grinding wheels

[Ken S]

We have a couple of issues here, and some confusion from the handbook. Page 155 of the latest edition of the handbook under Lifetime of the Stone states" "We recommend that the stone is changed before it wears down too much. You should not allow it to be less than approx. 180mm (7") in diameter in order to ensure a satisfactory grinding performance. The smaller T3 stone should not be less than 150mm (6")."

Elsewhere in the handbook, I believe there is a different recommendation for minimum size to be 200mm (8"). This is also the recommendation cited by Jeff55 as stated by Jeff Farris.

Unfortunately, neither the handbook nor Jeff Farris stated the reasons for this limit. I believe they have more to do with difficulty keeping the wheel wet than in having more hollow grind. The hollow grind issue is easily resolved by adding three degrees to the bevel angle.

There may be potential tool clearance constraints with smaller diameter grinding wheels. I am not sure of this.

Rich,

I believe your difficulty is from the surface of your grinding wheel, not its diameter. I have frequently referred to the grinding wheel as consumable, but lasting a long time, like brake discs on a car. Some tools will wear the wheel more quickly, just like driving in the mountains will cause more wear on the brakes than driving on flat roads. Gouges localize the wear on the grinding wheel. Therefore, the wheel needs to be trued more often. It will wear more quickly. It is the nature of the tool.

With your T200, have you upgraded to the new model (TT-50) of the truing tool and the micro adjust version of the universal support? I realize you prefer to be turning rather than sharpening and truing your wheel. However, you cannot expect top performance from your tools unless your grinding wheel is true. The key is early and frequent light truing.  the upgraded jigs and accessories really do make this easier to do.

I do not see Tormek ever making a T47. There are too many good business reasons against it. However, you could have one made by a local machine shop. (We have not yet resolved whether or not the T7 shaft will work with the T4.) If it is not compatible, all you would need to do is take your T4 shaft to a local machine shop and ask them to make one with ten millimeters more on the wet wheel end. You could reduce your cost by having them make it with non stainless steel and reverting to the old right hand thread on the wet end. Bring your wallet, this may cost almost as much as the T4. You would need to modify the water tray as well.

I do not think this is practical. As I stated earlier, I believe your best course of action is to procure a TT-50, micro adjust universal support, and a new SG-250. These should cost between $350 and $400. As an alternative, you might consider selling your T2000 and putting the proceeds toward a new T7. I believe that would cost less than $350.

Ken

[Herman Trivilino]

Another option would be devising a way to trim the width of those old SG-250 grindstones down to 200 mm so they will fit on the T4.

I understand the "need" to find a use for things like those old worn grindstones that seem to have a lot of value left in them. It reminds me of a lesson I learned the hard way. One of my hobbies is speaker building. I had a pair of KLH-22A speakers that I had bought used when I was in college. Over the years I had ruined them by playing them too loudly and replacing blown drivers with whatever I could find to fit. That is a sure-fire way to produce a crappy sounding speaker because the crossover circuitry is designed to match, among other things, the electronic characteristics of the drivers.

In recent years I was finally learning the right way to approach issues like these, and I wanted to preserve those old KLH cabinets and restore the them to their former glory. It turns out that such a thing costs much more money than it's worth because everything would need to be redesigned from the bottom up around the cabinets themselves. So in the end I salvaged any parts I could from them and set them out by the curb for trash collection. The terminal plates with the KLH logo, along with the inductors from the crossover circuit, survive in a well-designed pair of speakers that now grace my classroom. They make great conversation pieces and they sound awesome.

[Ken S]

Good thoughts, Herman. We do not stop learning when we reach adulthood. Your speakers remind me of my nice, very flat combination oilstone. I inherited it from my grandfather who probably bought it eighty years ago. It may well have been worn hollow when he bought it. I spent the effort to restore the old oilstone partly as a way to honor my grandfather, just like Jan did with his grandfather's mortise chisel.

In my case, the cost included essentially ruined a two hundred dollar diamond flat plate. My grandfather, a practical, thrifty man, would have questioned the wisdom of my efforts.

Ken

[jeffs55]

If I could buy a reasonably priced T47, and use stones that are otherwise useless (I.e., <200mm), this seems like a good idea.   
It is more profitable to sell you the stone rather than a way to use a depleted stone. It is always about the money. On the other hand, if a business is not profitable it ceases being a business and becomes a government welfare agency.

[Ken S]

Close, but not quite.

I disassembled my T4 and T7. The shaft from the T4 is slightly shorter than the T7 shaft. They do not interchange.

Going by the 170mm minimum diameter for the SG-250, by that point there is very little flat area remaining on the side of the wheel. As long as the water trough can be shimmed up enough to keep the wheel wet, the wheel should continue to be usable, although the hollow grind will be increasingly more pronounced.

I have not worn down a wheel that much. However, when my wheel gets down to the 220 to210mm range, I will start watching for a sale at my local dealer. I believe purchasing a replacement wheel when it is discounted is the most cost effective way to get the most value from a wheel. I realize many of us do not have the luxury of a local dealer.

As for a Tormek 47, it is definitely a pleasant luxury having two Tormeks. The jigs and accossories are inter hangeable between the two models. Whether it is logical to have one or two Tormeks depends on the intended use. I would have  one up and running before even thinking of adding a second unit.

Should one opt for having two Tormeks, again, I would let the work be the deciding factor as to which model(s) to choose.

Ken

[Herman Trivilino]

I disassembled my T4 and T7. The shaft from the T4 is slightly shorter than the T7 shaft. They do not interchange.

The lengths should differ by 10 mm (the difference between the widths of the 50 mm and 40 mm grindstones).

I thought the issue, though, was the diameters of the main shafts. If they match then it seems a T7 main shaft could be inserted in a T4 so an old 50 mm wide grindstone from a T7 could be mounted on a T4. Then you'd have to see of you could somehow mount a T7 water trough on a T4.

[grepper]

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

[jeffs55]

 As long as the water trough can be shimmed up enough to keep the wheel wet, the wheel should continue to be usable, although the hollow grind will be increasingly more pronounced.

After the comma (,) says it all. The hollow grind becoming more pronounced is the reason for the size limit on the wheel, as I have tried repeatedly to make clear. At some point, you are just not going to have a usable edge. Of course you could literally be splitting hairs and use the stone but then, all you are doing is splitting hairs and of what use is that except in a demonstration of sharpness achievablilty. Splitting hairs is fine for demo purposes but show me where that edge can be sustained long enough in the real world to be of any use.

[Ken S]

Jeff,

I agree with you about the hollow grind becoming increasingly intrusive with smaller diameter. I remember the quote from Jeff Farris. However, I do think it is unfortunate that Jeff did not include the reasons behind his statement.

Hollow grinding for cabinetmaking tools has been a long standing accepted and advocated practice. I do not recall anyone claiming it was superior to or equal to flat grinding, just that it is quicker and requires less work. The 1909 vintage Bedrock planes I pyrchased from the original owner came with a hollow ground edge. Most grinders, especially in home shops, used six inch wheels. The combination of hollow grinding and micro bevels (narrow secondary bevels which do the actual cutting) has been standard practice. Granted, this is a practical expedient.

Ken

[Elden]

   So let me think out loud. If the edge becomes stronger and greater as shown in the following thread, a smaller grinding wheel will lead to an increase of the amount of metal behind the edge. Simply decrease the angle to get rid of the excess metal.

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

[Jan]

Good thought, Elden. I fully agree with you. 

Jan

[Ken S]

One of the things which fascinates me with the Tormek is its versatility. In the case of chisels (and plane blades), the Tormek can easily be set to the standard twenty five degree bevel setting and essentially left there. It's a "no brainer" way to get consistently sharp edges with the same bevel angle. You can also custom fine tune with complete control. The choice is yours.

Ken

[Herman Trivilino]

The hollow grind becoming more pronounced is the reason for the size limit on the wheel, as I have tried repeatedly to make clear.

But the T4 comes with a 200 mm diameter grindstone. So if that diameter grindstone is good enough on a T4 then it's good enough on a T7.

[Herman Trivilino]

If the angle becomes stronger and greater as shown in the following thread, a smaller grinding wheel will lead to an increase of the amount of metal behind the edge.

The angle stays the same, the tool gets stronger because of the extra metal on the heel. And that extra metal might get in the way when doing certain types of work such as carving. You could remove it with a grinder. That's not an elegant solution, but it's the one I'd go for in a pinch.

[grepper]

"But the T4 comes with a 200 mm diameter grindstone. So if that diameter grindstone is good enough on a T4 then it's good enough on a T7."

And, even a 200 mm wheel is almost 2" larger than your basic 6" bench grinder that a lot of folks use to sharpen stuff.