Reviving a T-7

[Rob]

just as a tip....when you come to grinding those chipped bevels...make sure the stone is as rough as possible because they will take a long time to remove.  Keep MASSIVE downward pressure with your fingers, far more than you think is reasonable, it wont hurt the machine.  Keep regrading the stone with the rough side of the grader, and I mean every minute or so because it will glaze quickly and stop cutting with that huge surface area of bevel to remove.  Ensure you mount the chisel on the top support bar so you're sharpening with the wheel coming towards you rather than the lower position.  The upper position is a more aggressive cut which you'll want for dinged bevels.

Once you get them sharp, a tickle to bring the edge back wont be such a drama but removing dings means removing a lot of steel and that takes a long time on the Tormek if its not cutting optimally.

Bottom line....keep the stone cutting by keeping it graded rough, frequently.

[Timberwright]

Thanks for the great post, Rob.

As I understand it, the black stone (SB-250)  is harder than the grey stone (SG-250).  Bearing in mind that I've never used either type
of cutter, please excuse the "new guy's" question: Do you think that the black stone would give better service as a "repair" stone?
In other words, do you think that the black stone would be more effective in reviving the chipped chisels I previously described?

Here's to learning something new every day.

Cheers

[Rob]

don't give posting "new guy" questions a second thought.....we all started the day we bought a Tormek didn't we :-)

Your question about the blackstone is a good one and I'm not 100% certain this is the right answer but here goes the theory, I'll then add my own personal experience given I have both stones.

The theory is that because the blackstone is a harder ceramic and capable of cutting High speed steel (harder then your carbon steel framing chisels) then it "should" cut your carbon steel more aggressively than the grey one might.  Thus we can deduce it would be a better choice for dinged tools because it will remove steel faster. 

My practical, real life experience isn't quite as clear cut as that.  Here's my take:

I had the regular grey stone for about 5 years and did all my bench tools with it plus knives and indeed anything else that needed sharpening (lawn mowers, secateurs etc).  About 3 years ago I got back into wood turning and bought the Tormek turners jig kit to help handle the complex profiles of the likes of bowl gouges and skew chisels etc...all of which are tricky to sharpen to say the least.

Add to that the fact that turning tools get hot due to the friction with the fast spinning wood.....so the solution to that difficult environment is make them out of high speed steel because it holds an edge longer and can withstand higher temperatures without its temper being drawn.

I bought the blackstone as a dutiful customer does.....because its designed for HSS right?

Now in practice, I found that the grey stone is not good at sharpening HSS because its just too soft, although it can do it, slowly.  The blackstone can certainly do it.  But when I use it on my standard plane irons and bench chisels I cant honestly say I notice much difference from the grey stone??

So, I'm a bit confused about that.  The blackstone should in theory work faster "downstream" and the grey stone shouldn't work at all going "upstream".  In reality I find very little if any noticeable difference downstream with the SB but the SG does struggle with HSS.

To add to the conundrum, I also bought the planar jig and found that rather slow.  Bottom line is that hard metals with big surface areas like wide chisels and planar knives don't give up their steel to the Tormek easily.  Bench plane irons are a doddle because the surface area (less steel) of the bevel is small.  Your narrow chisels will be a doddle for the same reason but once you get to an inch and above and especially if they're dinged (you need to remove a lot of steel) its harder work.  The problem is the ceramic stone glazes over quickly and needs the surface regrading (roughing up) to keep it cutting.

I'd be interested to hear any other perspectives on the real life experience performance of the SB.

Bear one thing in mind...you're unlikely to do any harm whichever stone you try out because they do last a long time so just "have at it" and post away as you bump into problems and we'll abuse you whenever we get chance :-)

[Herman Trivilino]

Once we have the funding for it, I will place my order for the missing Tormek accessories, which includes the upgraded EzyLock Main Shaft, and install and/or use them.  After that, I will install the original SG-250 stone and practice with it on some old chisels that were taken out of service due to severe chipping.  Assuming that we eventually get positive results, I'll give the SB-250 a try.

You have the SE-76 Square Edge jig and a new SB-250 grindstone. I recommend you go ahead and get some practice on those old chisels while you wait to order the truing tool, stone grader, and honing compound. The Tormek is not a fussy piece of equipment, it's a work horse designed to grind steel in a precise way. Just remove the parts of those old chisels that make them dull and they'll be sharp. You're timber framing, not carving piano legs. If you don't get them as sharp as needed, go ahead and finish the job with your usual sharpening methods. The Tormek will have removed the lion's share of steel needed to reshape the tool and get the nicks out.

You may find that you don't need the new main shaft.

[Rob]

I would tentatively agree with Herman that practice is of course a good thing but beware setting out grinding wide bevels with no ability to get the stone cutting again once it glazes!  Without the grader and/or the diamond truing tool you'll get frustrated very quickly at the stones inability to cut and that will put you off using the tool.  You'll wind up unfairly judging it based on its performance when glazed.  As I've already said, my experience of its performance when glazed is not good.  You really do need to keep roughing it with the stone grader or better yet, true with the diamond jig as that give the roughest (most cutting) surface possible.

[Ken S]

I ran a test with the SG and SB wheels. I placed identical 3/8" (10mm) square metal lathe cutting bits in the SE-76 and ground for a timed five minutes. These bits are at least HSS. To my surprise, the SG removed noticeably more steel. I trued the SB wheel and ran the test again with the same disappointing results.

I used a lot of pressure for these tests. The handbook states that the SB will cut even with very light pressure. I may have been using too much pressure for the stone to cut well. It may also have glazed and needed to be graded during the five minute period. I do not consider my initial test results conclusive.

Incidentally, the SG wheel with the T4 removed the same amount of metal during the test as the T7 SG.

Ken

[Rob]

Well that just doesn't make any sense???  Metal lathe cutting bits would be tungsten carbide I would imagine which makes even less sense in that they're even harder than HSS.

I just don't understand that at all?

[Herman Trivilino]

Ken, try a light pass with the truing tool over the SB grindstone. I suspect it's clogged.

[Ken S]

Rob,

Inserts for cutting tools are usually tungsten carbide. Bits which don't use inserts are usually HSS or related alloys. (Just like carbon steel can be sharpened more keenly than HSS, HSS can be sharpened more keenly than carbide. The edge just doesn't last as long (by a wide margin).

I agree that my results are puzzling. I would have expected the SB tool to remove more HSS. That's why I am keeping the jury out until I investigate "operator error" on my part.

Ken