Possible to repair SJ-250 Japanese Waterstone ?

[Nico]

Did something boneheaded the other day and accidentally damaged my Japanese Waterstone.

It'd been a while, and I'd forgotten that you're supposed to use this stone edge-trailing. I was polishing the blade into the wheel and the inevitable happened: as I lifted the blade off the stone, the edge caught the wheel and dug into it, creating a small gouge.

I am hoping (praying) that this can be repaired somehow, maybe with something like the TT-50 Truing Tool?

Any advice greatly appreciated.

[tgbto]

First of all this can - and will - be fixed with the truing tool.

I'd suggest you use diamond plates or the Tormek stone grading tool on the fine side to smooth the edges of the broken area.

Also, I think the conventional wisdom for using the TT-50 with the japanese stone is to always contact the edge of the stone with the diamond tip going inward, and not outward. In other words you true from the outside to a bit past halfway, then lift the truing tool by rotating it slightly around the USB axis, then proceed from the other side. That avoids small chips along the edges.

Back to the source of your woes, sharpeing edge trailing sure avoids that kind of issues. Still, I only use the SJ stone edge-leading (as I find it makes honing much faster) : you just have to make sure you apply constant pressure with your hand on the jig toward the USB, even when lifting the blade. This is true whatever the stone used, and it gets more important when the sharpening angle increases.

Cheers,

Nick.

[Nico]

Thanks a ton for that advice.
I will give it a go... and let you know how it went.

Nico

[Nico]

To the community: Pontus from Tormek support has also responded to my request for help and offered this instructional video:

https://youtu.be/_9izVW7g6uo?t=591

The video confirms tgbto's comment about always truing from the edges to the center of the stone with the TT-50.

Thanks to all,
Nico

[smcinco]

Oh yes, I've seen way worse (saying for a friend).  Truing tool is your friend.

[Ken S]

There is an old saying that what something does to you, it can also do for you. Superabrasive wheels (diamond and CBN) are promoted because they do not wear down in diameter. While this is convenient for consistent setup, it also means that any damage to the single layer of abrasive can ruin the wheel. The "old reliable" SG (and SB and SJ) wheels can still function after a lot of surface damage.

Ken

[Nico]

Thanks guys for all the feedback. Haven't repaired the wheel yet, but will get to it in the next few days.

I had assumed that from now on I'd have to be measuring the diameter of that wheel each time I grind (polish) a new angle.

As we say in Japan, "shoga nai".

Nico

[RichColvin]

Nico, when I true my SJ grindstone using the TT-50, I have learned to advance it VERY SLOWLY across the surface.  The slower you move the TT-50's head across the SJ grindstone, the smoother the remaining surface will be.  That makes the next step easier.


Rick Kruger made some upgrades to his TT-50, making it automated.  He was able to set the speed very slow.  I seem to remember that he would complete a pass in 10 minutes or so.  And that the resulting surface was quite smooth.

[Nico]

Hi everyone.

I did the deed this evening and got the stone surface back to almost new. Albeit with new dimensions: Ø248.2mm. I guess I am going to need to use calculators in the future to get accurate angles...

I did go very slowly back and forth so got a very smooth and even result.

However! That TT-50 does have a learning curve! In particular, I noticed something unusual happening each time I approached the edge of the stone and had to stop to move the TT-50 tip to the outside of the stone to complete the pass coming inwards again. What I found was, even though I took extreme care not to move the USB adjustment nut as I loosened the clamp screws to raise and lower it, when it came down again it was not at the same height as it was before. Most times it was a bit lower which meant when I started my finishing pass (from the opposed side of the stone inwards), the amount of material removed was greater.

However, by doing several passes at the same height, I ended up getting a smooth and level result.

When I investigated this phenomenon in more detail I found the cause was due to the fact there is only 1 adjustment ring nut on the USB. And even if it does not change position, when you loosen the 2 clamping screws, there is a tiny amount of play in the USB (between the USB leg that has the lock ring vs. the leg that is free). This results in the TT-50 cutting bit ending up in a slightly higher or lower position when you re-clamp. Because you are coming in again from the outside of the wheel, it's hard to get this exactly right with the pass you made from the opposite side to get a perfectly even result. I tried to re-clamp as consistently as possible but was surprised how hard it was to get it perfect.

Anyway, you can overcome this by doing several passes with the USB ring nut at the same setting until you hear no more material is being removed any more from either direction. Then you can adjust down a tiny bit for the next level.

I like the idea of automating the feed screw of the TT-50! I had exactly the same idea as I was doing it manually. I have a few spare stepper motors... perfect application for one!

[tgbto]

Hey,

Glad it worked for you. The japanese stone has a tendency to wear down quite quickly anyway, be it by truing, heavy cleaning or sheer use.

Maybe using a counter-nut (is that even the right word) against the first you can avoid the issue you mentioned with the height changing ever so slightly each time ?

[Ken S]

I must be missing something. I true my SG, SB, and SJ wheels with straight, side to side traversing passes. I take very small bites, usually no more than half a microadjust number, and very slowly, usually around two minutes across.
I have occasionally used deeper cuts and faster passes. I confess that I enjoy the slower pace of seeing the wheel gradually become more true with each pass. I have become a believer in the value of frequent, light truing. It helps clear my mind knowing that my wheel is true; it lessens the number of unknown sharpening gremlins.

As for a wheel with 248.2 mm diameter, I am not worried. I recall a forum discussion with our late member Jan. Jan was an engineering professor. He was one of the shining stars of our forum. He was very intelligent, highly educated, and still retained his practical passion for sharpening. I have always used Dutchman's (Ton Nillesen) grinding tables which use 10mm changes in wheel diameter. They are precise enough for my needs.
Jan favored using changes for every five mm changes in diameter. Jan was practical as well as highly technical. In my opinion, if five mm changes provided adequate precision for Jan, that was more that sufficiently precise for me. We are not mating knives. If two knives are both very sharp, in my opinion, minute differences in bevel angles are insignificant.

Please let me be clear. I am not disputing the value of our various computer programs. They all have their uses. However, computers are capable of far more precision than is usually required. No carpenter uses a micrometer to frame a house. Machinists regular work to standards of tolerance. Machining parts beyond normal specified tolerances adds cost and no practical value. I would suggest the same applies to knife sharpening.

Ken

[Nico]

The suggestion for a lock nut on the USB adjusting ring is good to stop you accidentally moving it, but it won't completely remove the slight amount of play when the USB is un-clamped. It's because the other leg is free to travel minutely. If the other leg also had an adjusting ring, then I think the play would be eliminated. Anyway, we are only talking about a slight amount of play, the only reason I noticed it is that when coming in from the opposite side of the wheel back to the center, the 2 cuts don't match up. If, when you lifted the USB to reposition the TT-50, it came back down at exactly the same height, this phenomenon wouldn't happen. Anyway, not a big issue, just something to be aware of.

Thanks Ken for your input. It's good to know that for most sharpening applications rounding the wheel diameter to the nearest 10mm will give an acceptable result!

[Ken S]

Tormek's suggestion of lifting the support bar and moving the TT-50 diamond to be able to travel inward is fairly new. The SJ was introduced around 2009, several years before the lifting suggestion.

I suspect the lift was started because of chipping complaints from users who set the TT-50 to cut too deeply. (Who wants to take "forever" to true a grinding wheel?) By making very shallow cuts and not needing to lift the support bar, there is no problem with misalignment. True your grinding wheels frequently and lightly. A light pass or two does not take forever.

Ken

[SergeiDubovsky]

I did a similar repair not so long ago. Additionally, ran a diamond plate in the SE-77 over the stone surface. I didn't go slow with TT-50, so it was bit rough.
I did Grit 80, followed by 400, 1000 and 2000. The result was pretty much the same as I remember it was out of the box.

[Nico]

Tormek's suggestion of lifting the support bar and moving the TT-50 diamond to be able to travel inward is fairly new. [...] I suspect the lift was started because of chipping complaints from users who set the TT-50 to cut too deeply. [...] By making very shallow cuts and not needing to lift the support bar, there is no problem with misalignment. [...]

This is interesting. So I followed the recommendation in the Tormek TT-50 tutorial video and lowered the USB height by exactly 1 numeral on the adjustment ring each time. Being the curious type, I did want to see what would happen if you run the diamond tip off the edge of the stone (instead of lifting and repositioning). With the cut being set to 1 numeral, I experienced quite noticeable chipping of the stone's edge as the tip ran off it, even though I was going extremely slowly. To your comment, Ken, I guess that means the cut wasn't shallow enough so next time I will move the adjustment ring by maybe half a numeral and see if this eliminates the edge chipping.