When to use which stone?

[Hatchcanyon]

After working with the inherited T-7 for 4 month and beeing very impressed what can be done with it there is a question for which I do not have a conclusive answer.

The machine - previously not very often used, more or less new - came with the SG stone. Some time later I complemented it with the SJ stone for better edges. But this was not the ultimative setup for the HSS turning tools my wife uses. To grind these tools more effective we bought the SB stone.

My observation within the last weeks is that I do not use the SG stone anymore. Even if it is said grinding standard tools as plane irons or chisels is not faster on the SB than on the SG I have some doubt about this statement. At last it feels faster on the SB. Another point is that one do not need to change the stones except for the SJ.

Now I wonder if there is any technical argument for using the SG on any grind task? (Ok, it is a bit cheaper.)

Rolf

[Ken S]

Rolf,

You ask an interesting question. Before November of 2008, the answer was easy. The SG was the only grinding wheel actively produced by Tormek.

You have used the SJ and SB more skillfully than many of the members. In my opinion, these less than optimal results are mostly the product of Tormek's training program. The main thrust of Tormek, the handbook, has changed very little since originally being written by Torgny Jansson. This is not just a criticism. The technique is still very solid. The handbook was written for the SG. The SJ and SB are barely mentioned. I think this oversight is unfortunate, as I believe both of these wheels have generally untapped potential.

My initial tests with the SB were disappointing. It did not remove as much high speed sreel from a metal lathe bit as the SG removed. I found this puzzling and held off making conclusions. The SB requires a different grinding technique than the SG. Tormek presently only offers a hint about this, not good instruction.

I am finally having better results with the SB, although the SG remains my go to for my carbon steel woodworking tools. This may be for technical reasons, or it may be from habit. I believe it warrants further testing.

Ken

[wootz]

I also noticed that though SB wheel is intended for HSS steels, carbon and stainless steels are indeed ground faster on SB than SG, however, when it comes to sharpening high Vanadium steels, SG works noticeably better.

SB as silicon carbide is best for grinding HSS steels, while SG as aluminium oxide is best for Vanadium-rich steels.
For example, Crucible recommendation to use SG for grinding their Vanadium CPM steels: "SG type alumina wheels or CBN wheels are recommended for best performance with CPM steels" (see the Machining and Grinding section there).

Other than these two extremes, either can be used, but...
IMO SB cannot be graded as fine as SG, and SB cuts definitely more aggressively, and for this reason I often prefer SB to SG for profiling the edge, but in fine sharpening rather switch to SG.

Considering all said, and that now you have both SB and SG stones, why not have SB always coarse, and SG always graded fine - this will work for the majority of steels.
This two-stone set up has obvious advantage over re-grading the same stone for every blade.

With time, you  may meet other types of steel that SG grinds better than SB, some sort of high carbon steel was mentioned on this forum before. Just when you see that your SB struggles with a particular blade, try switching to SG. That happened to me when I tried sharpening S-110V, VANCRON-40 and VANADIS-10 blades on SB, and switching to SG resolved the pain.

[Ken S]

Well done, Wootz!

You may have uncovered the magic bypass for frequent regrading we have been seeking. I like the idea of using both the SG and SB, utilizing the best areas of each.

Keep us posted!

Ken

[Herman Trivilino]

I've never used any grindstone other than the SG, but I understand that the SB is more difficult to prepare in the fine 1000-grit state than the SG. This is an issue when sharpening knives or chisels, for example.

[Ken S]

The person who has kept my faith alive with the SB is Steve Bottorff. If it works well for Steve, I have faith that it will work well for me. I have been getting better results with it since adapting a lighter touch, and better results with the horizontal position (grinding wheel moving away from the edge). Using the SG technique of really leaning into the wheel produced poor results for me.

Steve allows his SB to find its natural grit, as opposed to using the stone grader. I have had good success with the stone grader and the SG. My experiences with the SB and the stone grader have not been so positive. I like Wootz' idea of using the SB coarse and the SG graded fine.

I have experienced the SB cutting very well. I have not been able to do this consistently. I am working on my technique and remain confident for the long run.

I believe the key to success with knives, especially with the SB, is developing a light touch.

Ken

[Hatchcanyon]

Wootz,

yes there were a situation, where the SB did not work very well. This was on an old HSS blade where the SG did remove material so slow that it was useless. This failure of the SG was the reason for buying the SB. Until now I do not know why the SB clogged? May be it was new? After letting it dry and a preparation run it was up again and did not cause trouble since then. (I've worked the same iron again.)

The problem is there are virtually hundreds (thousands?)  of different alloys on the market. Trial and error is often needed.

Working my wifes turning tools - HSS only - needs the SB and she likes an edge finer than the one you get from a coarse graded SB. Due to the fact that the tools do not need to be regrinded, only shapening, I normally use the SB set to fine but set it to coarse for the chisels and plane irons I use. Haven't measured it but switching may need a little longer time than for the SG.

Often I polish the tools using the SJ and there is no large difference in removing grind marks from a fine set SG or a fine set SB. Maybe the coarse grind marks are more different.

One thing I learned is don't push the tool too hard on the SB as you would on a SG. Using less force seems to speed up the action - bit this is not a measured fact, it is a feeling.

Yesterday I reshaped some chisels I had used for dovetail cutting.  After setting the machine to the right angle grindig with the SB needed a very short time for each tool, maybe less than five seconds. Next time I'll try to measure.

The sound is more aggressive, the feeling  too and maybe the user is more impressed. All together makes easily up for a pretty prejudice - maybe, maybe not!

Rolf