Stone grader sp-650 makes no difference on SB-250 wheel

[jekoors]

I am using a t7 with the SB-250 wheel.
I am trying to shape a 1" Crown powder metal flat skew with a straight (not radius) edge.  I am changing the edge angle from 45 degrees to 30 degrees.  I am sharpening from the vertical mount to increase the grinding pressure.  This is probably a worse case scenario with size of the chisel and the amount of steel I need to remove.

The grinding progress becomes slower as I get closer to the final bevel angle (at 220 grit).  You would expect this as more of the bevel is pressing against the stone and therefore more steel needs to be removed.   As I'm nearing the end of the grinding process, say 5% of the bevel left to grind, progress is minimal if anything.  The only way I can make any progress in grinding the rest of the edge is to true the stone with the tt-50 truing tool (which gives me a fairly course surface on the wheel).  After a few minutes of grinding, I'm making no progress again.  Dressing with the coarse side of the stone grader makes no difference.  I had to true the wheel 6 times just to reshape on side of the chisel.
The stone grader seems to be glazed (much smoother than the original surface) on both sides.  It's relatively new, but I'm told the "glazing" is to be expected and it does not impact the performance of the stone grader.  Is this limited grinding performance to be expected?  I'll be eating through my wheel pretty quickly with the truing tool at this rate. 

Any help would be appreciated.

[Stickan]

Hi, Use the edge on the stonegrader , it works well. Also use it a bit more often, then it should be better.

[Rob]

Hi there and welcome

Firstly, the reshaping of large area High speed steel tools is not what the Tormek does well (as you rightly allude to).  This is really the job of a faster, typical dry bench grinder.  As you've also discovered, the wheel glazes quickly and needs "de-glazing" to restore the cutting action.  The diamond tool is excellent at doing this but time consuming and reduces wheel diameter fast.  At over £100 for a new wheel that's bad!

Theoretically the stone grader should do its job to bring back the wheel. It can work better than you've described but the advice is to do it:

1) Often &
2) Really lean on it....to the point where it almost stops the wheel from turning.

That will get you so far.  Buying a cheap (mine cost £8) T-bar diamond dressing tool will really speed things up as it brings back the cutting action very fast (at the expense of wheel diameter though).

Personally, I gave up expecting the T7 to cope with major steel removal some time ago.  Oddly enough skew chisels are the worse in my experience.  My solution was to get a BGM-100 and mount that against my dry grinder so I can re-use the investment in the jigs.  Now I SHAPE with that setup and SHARPEN with the Tormek.  The Tormek is great for putting a fast efficient edge on turning tools and close to useless in shaping them if you want to move some distance from the factory grind (which lets face it....you do).

Bottom line...it can be done but its laborious, time consuming and "wheel, eatingly" expensive (if that's a word).  Given you're nearly there now I wouldn't bother going to all this trouble, just lean on the stone grader, but for the future.....a dry grinder or sanding abrasive belt approach is far better for shaping.

[Herman Trivilino]

That's all good advise.  Here's a drawing of what Stickan was describing.



Another option you might want to consider is the SB-250 grindstone.

http://tormek.com/international/en/accessories/grindstones/sb-250-tormek-blackstone-silicon/

[Rob]

I think he is using the silicon wheel Herman (at least he says so in his post).  And bear in mind my experience with both planer blades and skew chisels is also with the silicon wheel.  So despite its manufacture aimed at HSS tools it still is a nightmare to shape rather than sharpen.  One off is fine....multiple times, its a real drag.

[Herman Trivilino]

Oh, yeah.  I missed that.