SB-250 Blackstone

[ionut]

A friend of mine asked me to sharpen a couple of sets of 12" planer knives. The first set was done on the original Tormek stone and the condition of the blades was very bad, after a couple of sharpening session done by a professional company not only the amount of steel removed was huge, but the angles were not consistent anymore and the blades were looking like coming from different machines. So the first set was done on the original stone and given the condition of the blades and the thickness it took me longer than I expected and it ate a fair amount of the stone so I decided to get the black stone which was on my list for a pretty long time.
The second set of blades was even worse than first one, one of the blades was all wavy on the top of all other defects. I trued the stone immediately after installation, the stone was parallel with the universal support as it came but it was a bit out of round. After 1/12th of the depth cut the stone was perfect for starting grinding. After setting up the planner jig I have finished both blades in a third of the time compared with the first set on the original stone and the through didn't have much of the stone in it but the magnet had a bubble of steel on it the size of half of a gold ball.
After that I've tried it on some carbon steel chisel from the same source and in very bad shape as well. The story is completely different, as expected the grinding action on high carbon steel is less efficient than the original stone, in fact is less efficient than my Japanese 800 stone, but the black stone was meant for HSS and special steel alloys so I didn't expect to be fast. In my case the grinding action on high carbon steel of the black stone was comparable with the original stone when graded to 1000. it acted more like a glazed stone. It looks like the scratch pattern as it comes after truing is finer than the scratch pattern of the original stone in the same condition.
It can be efficiently graded but this stone will wear the coarse side of the stone grader as well.
I have removed lots of steel on those two planner blades to bring them in perfect condition and the wear characteristics of the stone are excellent, as well as the speed so if you have to sharpen HSS planer or jointer knives  or other HSS blades I think it is a smart investment, it will work much better and you will keep the original stone for much longer.

Ionut

[Robbo]

It has been my finding that the black wheel does wear better than the sg250 however it does tend to glaze and you have to use the fine side of the grading stone in order for it to cut.

I sharpen HSS and some tungsten turning tools mainly.

[Ken S]

Interesting post, guys.  Two thoughts come to mind:

1) Why do so many people (dare I say "we") wait until once sharp edges are not dull but blunt?  I wonder what the last hundred feet of boards run through that planer look like?

2) I believe clever people will soon be sharpening things like lathe bits on the Tormek with good success.  Would the original Tormek users have envisioned the efficient way turning tools are now sharpened on the Tormek or that drill bits can now be sharpened easily and well?

When switching wheels, is it necessary to retrue the stone each time?

Ken

[ionut]

Robbo - I believe the glazing is caused by the stronger bond on the black stone which I would expect to happen. On softer stones glazing happens slower as particles are dislodged easier allowing fresh ones to take the action but that wears the stone faster. For the planner blades I've done yesterday I didn't use the grader and even though the stone felt glazed it didn't seem to lose the effectiveness on HSS. I tried the grader when I played with the HCS chisels but as expected that didn't change the results much.

Ken - I believe is pretty easy to get there when you don't have means for sharpening, like my friend, and rely on professional sharpening. My only concern is the fact that the so called professional sharpeners didn't really care about the blades, they've cut a lot of material and didn't bother to put the same angle on the blades. The wood probably looks pretty bad with blades in that condition and there will be lots of hand planning left to be done but I believe the machine is the one that has more to "suffer" with such dull blades.
Truing is only required when the stone is not true, if truing would be required when changing the stone that would be bad, it would mean that something is not mechanically consistent on the machine. I always true a stone when is new as I didn't find any of them being true out of the box but the truing is minimal.

Ionut

[Ken S]

Good point, Ionut.  Often the most difficult part of a task is finding someone capable of doing it and motivated to do it well. Your friend is fortunate. Life is a continuing education.

Ken

[Robbo]

Robbo - I believe the glazing is caused by the stronger bond on the black stone which I would expect to happen.

I totally agree Ionut, it was put up as something to be wary of when sharpening HSS turning tools in rapid succession.

You don't notice that glazing is taking place until the tool is blunt.

Ken, I sharpen a few of my metal lathe tips on the Tormek. Generally just for a final cut, I then replace the tip for the next job.

[Ken S]

Robbo, a good use for the Tormek.  The real strength in the design favors sharpening over shaping.

Ken