Hollow grinding and a Tormek question

[Zeddedhed]

I've read somewhere (I think on Dieter Schmid's website) that irons for wooden planes shouldn't have a hollow grind.
Does anyone know if this really makes any difference to the performance of the iron?

Also, when I grind on my Tormek I find it hard to get the grind square to the iron. I've tried all sorts of things, checking that the iron is perfectly square in the jig etc. The only variable I can see is that the main support bar seems not to have a definitive registration point. With the main nut tightened it's still possible to raise or lower the extreme end of the bar. Does anyone else experience this?

 

[Random Orbital Bob]

the trick I've always used is to use a square to mark the reverse of the edge with a perpendicular line (right close to the tip where you can eyeball it as you grind) and then apply appropriate finger pressure on either side of the iron as you pass it left to right (assuming you're grinding topside ie towards the edge).

This advice is what Tormek recommend as well. In other words, though the jigs get (the SE76 square edge jig) get you 90% of the way there, there is still an important element of operator steering to get it just right.

There is a little bit of play in the support bar as you move further away from its fixings bracket, another reason you need to exercise operator control. You'd be surprised how much more metal you can grind off by simply giving a leaning bias to one side or the other depending on where the excess metal is.

 

[deema]

Have to say I may be lucky but never had the problem with the Tomak. I believe if memory serves the recommendation is to keep the part being sharpened still on the stone, I don't I move it across the stone from from one extreme with the blade just on the stone to the other. I find that this stops uneven wear and I seem to always end up with a perfectly square grind. The only other thing I do is check with a square that the tool is perpendicular to the jig. The face of the jig that is used to register chisels and plane irons is not that square on my jig.

A hollow grind just makes it quicker and easier to sharpen the secondary bevel when it needs touching up, less metal in contact with the stone. In actual fact if you don't add a secondary bevel what ever angle you set the tool at on the Toamak the actual angle ground is a lot shallower and the blade won't initially stay sharp as long.

 

[AndyT]

Haven't you read any sharpening threads on here? :wink:

Putting aside the strength of their opinions there do seem to be plenty of successful woodworkers who either avoid hollow grinding as the work of the devil or embrace it as the One True Way.

So take your pick!

 

[Zeddedhed]

Andy,
to be honest every fibre of my being cries out "'tis against God and Nature" when i see a hollow ground plane iron or chisel.

And then, when I need to re-establish a primary bevel on a badly dinged blade or a boot fair find my Tormek looks oh so inviting (compared to my paving stone grade diamond stone).

I guess I'll have to try and be a bit less emotional about it and a bit more rational!!