Using 250mm stones on the T-3 / T-4

[RichColvin]

Dan @ Exact Blade has provided two great ideas on getting more life from your grindstone investment, and I've cataloged them on the Sharpening Handbook.  Here's a link to the page where it is documented :

http://www.sharpeninghandbook.info/Grindstones-StoneLife.html

What I find most exciting are the pictures he provided.  These show his use of old 250mm grindstones on his T-3, grindstones that no longer worked on the T-7 / T-8.


Now I just need to buy a used T-3 or T-4.  Maybe there is a guy nearby who has one in his basement, possibly gathering dust in a bowling ball bag....

Kind regards,
Rich

[cbwx34]

Dan @ Exact Blade has provided two great ideas on getting more life from your grindstone investment, and I've cataloged them on the Sharpening Handbook.  Here's a link to the page where it is documented :

http://www.sharpeninghandbook.info/Grindstones-StoneLife.html

What I find most exciting are the pictures he provided.  These show his use of old 250mm grindstones on his T-3, grindstones that no longer worked on the T-7 / T-8.


Now I just need to buy a used T-3 or T-4.  Maybe there is a guy nearby who has one in his basement, possibly gathering dust in a bowling ball bag....

Kind regards,
Rich

Glad he finally came around...


Comments on his YouTube video...



Picture and description are HERE

(Cool that now there's proof the T-4 may be up to the task).

[Pastor_Zatx]

As a person also looking into purchasing a T-4, I have to ask, why does the commentator say that the T-4 is fine for kitchen cutlery, but not bigger knives? Kitchen knives are three times the size of my folding knife collection. What knives are "larger" than kitchen knives other than a machete or something crazy?

[cbwx34]

As a person also looking into purchasing a T-4, I have to ask, why does the commentator say that the T-4 is fine for kitchen cutlery, but not bigger knives? Kitchen knives are three times the size of my folding knife collection. What knives are "larger" than kitchen knives other than a machete or something crazy?

I wondered the same thing myself. 

He actually says "heavy blades"... which makes me think "thick blades"... that maybe he's trying to thin down or something, and is adding more pressure to do it?  But even then, I'm not sure it matters... "adding pressure" doesn't necessarily translate to it "working faster".  Or maybe it's just the time spent thinning a heavy (thick) blade?  I can't think of another reason... "weight of the blade" shouldn't be an issue (within reason of course).

He's a member here... maybe he'll come along and explain... (I asked him in the video comments too).

[Ken S]

I have to disagree. First of all, I do not think the ideas are "great ideas". By the time a 250mm grindstone has worn below the 180mm diameter (not circumference) range, using it will create a substantial hollow grind on the tool being ground. I would expect a professional knife shop to switch a 250mm grinding wheel at or before 200mm to prevent the hollow grind from becoming excessive.

When I first got my T4, I put the six inch (150 mm) Norton 46 grit3X wheel from my dry grinder on the T4. It cut very well, but was too small to be practical. I made the next logical step and purchased an eight inch (200mm) 46 grit 3X for the T4. It works like a champ. I would rate it the best coarse wheel I have ever used on a Tormek, faster cutting than either the CBN or diamond wheels.

Relating to the T3 and T4, I love the T4. I would pass on the T3. The heat radiating zinc top on the T4 (later used on the T8) is a vast improvement over the T3. In my opinion, a new Bushcraft Edition T4 is the best deal going for a Tormek. In addition to the SG200 and SJ200, the T4 works with the Tormek DWF-200 600 grit and DWC-200 360 grit diamond wheels. For my money, Tormek's new diamond wheels have eliminated the need for the SB, not made in 200mm size. I also have an eight inch 180 grit CBN wheel which works very well wet or dry with the T4. I could also get an 80 grit CBN wheel. The T4 has quite a selection of useful grinding wheels.

I have not known of a case where someone purchased a T4 as a "starter Tormek" and actually " "upgraded" to a larger model. The fifty percent duty nonsense is not a real constraint in the real world.
If you calculate the Surface Feet per Minute with the T4 and T8, the higher RPM T4 motor cancels out the larger circumference.

I cannot speak from experience with a busy commercial professional sharpening business. If the truth is told, I doubt if even two percent of us will ever need that. I also doubt if many of the buyers of heavy duty large trucks really need them. A well equipped T4 is certainly up to the task for the great majority of us. It also has the benefit of being more easily portable.

A well worn Tormek wheel has already given full value. Buy a replacement wheel and be done with it!

Ken

[cbwx34]

I have to disagree. First of all, I do not think the ideas are "great ideas". By the time a 250mm grindstone has worn below the 180mm diameter (not circumference) range, using it will create a substantial hollow grind on the tool being ground. I would expect a professional knife shop to switch a 250mm grinding wheel at or before 200mm to prevent the hollow grind from becoming excessive.
...
A well worn Tormek wheel has already given full value. Buy a replacement wheel and be done with it!

On a knife?  I doubt that the hollow grind would be "substantial", or even noticeable.  The links in that, How Hollow is the Hollow Grind? thread should give a clue.  In fact there you just posted...

...
In my opinion, one can essentially ignore the hollow of a 250mm Tormek wheel. (By visual comparison, I also find little difference between the 200 and 250mm Tormek wheels.)
...

.... where you can't tell the difference in 50mm... but another 20mm wear it becomes "substantial" or"excessive"?  Maybe on something with a wider bevel... chisel comes to mind for some reaaon.   By your description here... a T-4 wheel would need replacing with very little wear.

Whether it's worth it or not is dependant on the circumstances, but getting an additional 10mm out of a stone (removing a 180mm from a T-8 and putting it on a T-4 for another 10mm or so)... would get a bit more $$ out of the stone.  From what I saw in the Exact Blade video... he has quite a few stones, so could be a decent savings.

I think "full value" is determined by the owner... which makes the ideas worth posting... just like any other, it may work for some, not others.

[GKC]

I can see two different concepts here.  CB is noting that there is a smaller difference between a 200m and a 180mm wheel than between a 250mm and a 200mm wheel, which Ken has found irrelevant, whereas (in this post) Ken is not talking about the difference but the point at which the diameter of the wheel results in a hollow grind that is "too hollow"; that is, the apex might not be sufficiently supported by the metal behind it.    The ultimate question is the radius of concavity at which a hollow grind results in insufficient support behind the apex.

And yet, as with CB, I don't understand Ken's concern with using a 180mm wheel on a T8, or moving it over to a T4, if a somewhat worn 200mm wheel (at 180mm) is fine on a T4. The point could be important to those choosing between a T8 and a T4, because the wheels on the latter might not be able to provide as much service before the degree of hollow grind becomes too great.  Maybe Ken can elaborate.

Gord

[Ken S]

I would like to back up to the start of this topic and get all of the facts straight.

The handbook states the recommended minimum size of the grinding wheels as 180mm for SG-250 and 150mm for the SG-200. Whether or not we choose to follow these numbers as gospel, they present a proven starting reference.

I'm sure the use of the word"circumference" for "diameter" is just a slip of the tongue and not a big deal. We all know that the diameter of a circle is the length of a straight line through the circle and that the circumference is determined by multiplying the diameter times pi.

Rich, would you please correct the handbook to read the correct width of the SG-200. It is 40mm, not 45mm.

The cost per millimeter figure for grinding wheel wear is only part of the story. For a professional sharpener, to be fair, the figures should include the number of tools (knives) sharpened and the revenue received. These numbers are strictly by guess: If you sharpen knives at a farmers market twenty Saturday mornings; one hundred knives a session @ five dollars a knife; and your grinding wheel lasts the season with normal wear:
$500 x 20 sessions = $10,000. I don't think that's a bad business return for a $174 grinding wheel.

Enough words for one reply (rare for me    

Ken

[RichColvin]

Rich, would you please correct the handbook to read the correct width of the SG-200. It is 40mm, not 45mm.

Ken,

Corrected that mistake already.  Thanks for catching it though. 

I also added :

Ken Schroeder advises against acquiring a T-3 or T-4 simply for this purpose. His reasoning is that the cost of the T-4 or T-3 is high enough that it is more cost effective to just buy new grindstones. But, he does admit that if you have a smaller machine (or want one for portability reasons), this may be a good option.

Kind regards,
Rich

Oh, and by the way, I raised my water trough by putting a piece of wood below it.  I am seeing how much more I can get from the grindstone!

[Ken S]

Rich,

I know your intentions are good, and I appreciate the easy access you have already provided to my article on the kenjig. However, I do not wish to be quoted on this topic. Would you please remove the two quotes attributed to me on this subject from your handbook?

Please let me preview and authorize anything in the future attributed to me.

Thanks.

Ken

[cbwx34]

To be fair, it's basically what you said in the earlier thread.

No comment on the "hollow grind" statements you made earlier? 

I'm not sure your math would hold up... for example, you may charge $5 a knife, but you don't make $5 a knife.

Oh well, moving on...

Rich, how about this for a quick truing tip?  https://youtu.be/qSRhdG4YcgE ?   

[RichColvin]

CB,

There is NO way I am linking to that video !  Setting aside the safety problems, it really looks like something which started with, "hey, hold my beer ...".


Ken,

I've removed your name from the topic on my site.  I apologize :  I had no intent to offend.  And, given that this thread seems to have gone that route, I would appreciate it being locked for further comments or additions.  This forum is very useful for sharing of ideas, and I'd like it to stay that way.

Kindest regards,
Rich

[cbwx34]

CB,

There is NO way I am linking to that video !  Setting aside the safety problems, it really looks like something which started with, "hey, hold my beer ...".

Haha... I know.... just thought I'd lighten the mood.

[Ken S]

Rich,

As always, all is good with us.

CB,

My math was based on seven extensive studies. Just kidding, of course. I have never been nor will I ever become the forum mathematician. My figures were guesses, however, I would expect a professional sharpener to make considerable revenue from a grinding wheel.

I don't understand all the subtleties of hollow grinding. It does seem that if he had wanted to, Torgny Jansson could have designed a much less expensive grinder using smaller wheels if he had wanted to do so. That makes me think a large diameter wheel was fundemental in the design. My 1972 vintage six inch dry grinder was typical of that era. As long as the grinding wheel is kept wet, there are many tools which do not require clearance..

I will be interested to read Tormek's new hollow grinding thoughts now that they offer flat grinding with the new diamond wheels.

Ken

[Elden]

Interesting video. Recommended for anyone? No. Chance of something bad happening? Yes, but if done with proper care....... He turned way out of round grinding wheel to acceptable, ready to be trued wheel in a fraction of the normal time.