SJ250 Question

[darita]

Thanks all for the replies.  Since the edge will be refined whether edge leading or trailing, I'll play it safe and go edge trailing to prevent damage to the very delicate SJ.  I know how the SJ absorbs water like a sponge and gets extremely soft after doing so. 

The SJ is not particularly delicate.  Rather, it can chip easily. 

Also, the SJ does not absorb water "like a sponge". In fact, I find that it absorbs it very little water.

Finally, I've not experienced it becoming spongy. But, I only leave the SJ grindstone in water during the time I'm using it.  Once I'm done, I remove the water from the stone. 

Maybe "like a sponge" was a bit dramatic.  How do you true your SJ?

[Ken S]

The traditional Tormek technique as laid out in the handbook was based around using the SG-250. Even though the SB and SJ wheels were introduced more than ten years ago, they shared only a paragraph in the handbook.

Over the years, I have noticed a lot of what I call high speed dry grinding and bench stone thinking trying to be applied to Tormek thinking with mixed success. I would include trying to apply SG thinking to the SJ (and SB) with these not always successful crossovers. The SG, SB, and SJ wheels are all useful tools for their intended purposes. Each has pros and cons. I believe it is a mistake to try to use the same technique with all three of them.

Ken

[darita]

OK...this is weird.  I trued the SJ with my TT-50, then graded the surface with a 400g flat diamond stone.  The wheel wasn't truly true, however can someone explain this result after using the SJ on two chisels?  I used it after a 1200grit wheel.  Has anyone else had this happen?

[TireguyfromMA]

Hmmm...just guessing, but that looks like a constant oscillation pattern that might be related to  manufacturing?  Did you notice any oscillation while truing with the TT-50? It would be interesting to run a dial indicator over that stone while rotating it by hand on the motor shaft. I would send those photos to TORMEK product support to hear if they have a good explanation.

[darita]

Hmmm...just guessing, but that looks like a constant oscillation pattern that might be related to  manufacturing?  Did you notice any oscillation while truing with the TT-50? It would be interesting to run a dial indicator over that stone while rotating it by hand on the motor shaft. I would send those photos to TORMEK product support to hear if they have a good explanation.

I did notice some vibration, but not enough to be of concern at the time.  Using the TT-50, I didn't notice any vibration other than that created by grinding.  I think I will email support on this.

[tgbto]

Interesting, could you give the reading taken with a tape measure in between two stripes on the wheel ?
A 50hz phenomenon with a 248mm (trued) wheel would give 1.5 cm.
I don't have the inner diameter of the drive wheel in mind, but it could also be something that happens with every revolution of the drive shaft, it can be easily computed.
I wouldn't rule out that it has something to to with your grading. First off, 400g seems quite coarse to me, that's something I would use for grading my SG, not my SG. Vadim used to recommend 1000g for the SJ. That being said, it's like the stone has been smoothed out by something wobbly...

[darita]

Interesting, could you give the reading taken with a tape measure in between two stripes on the wheel ?
A 50hz phenomenon with a 248mm (trued) wheel would give 1.5 cm.
I don't have the inner diameter of the drive wheel in mind, but it could also be something that happens with every revolution of the drive shaft, it can be easily computed.
I wouldn't rule out that it has something to to with your grading. First off, 400g seems quite coarse to me, that's something I would use for grading my SG, not my SG. Vadim used to recommend 1000g for the SJ. That being said, it's like the stone has been smoothed out by something wobbly...

Best I can do is, it's about 8mm peak to peak on average on the second photo.  Also, on that photo, I did try 1k diamond. I did send a note with photos to Tormek Support.  One thing...after using the TT-50, the surface was higher on the inner surface than the outer.  I noticed that when I mounted the 400g diamond in the SE-77 to smooth the surface.

[darita]

I've got a thick, heavy, 160g flattening diamond plate.  Can I simply rest that against the USB to grade the surface of the SJ?  Seems like that is doing the same thing as the SE-77, just eliminating the middle man.

[3D Anvil]

I don't see why you couldn't use the USB as a rest for stone grading, provided the plate is stiff.  But I think 160 grit is way too course for the SJ stone.

[darita]

I don't see why you couldn't use the USB as a rest for stone grading, provided the plate is stiff.  But I think 160 grit is way too course for the SJ stone.

Yes it may be, however I wanted to try it since I use that same diamond plate to flatten all of my other water stones and ceramic stones.