Tormek and Hollow Grind on Large Plane Blades

I broke down and bought a Tormek several years ago and like it a lot, but I still have problems with wide plane blades. The middle of the hollow grind tends to get concave or "lower" than the sides of the blade, so when I go to a stone for honing, a very noticeable portion of the hollow grind gets flattened on both ends of the blade before the middle of the blade gets honed. Once and a while I get it deads nuts on and my time on the stones is really quick, but I just put a hollow grind on my #7 blade last night and it ended up concave again. Does anyone have a method they use to minimize this.

PS: It's not the flatness of the water stones, but I do apply more pressure to the edges of the blade when on a water-stone. I don't think this pressure is the issue.

I've never once used a honing stone after the tormek. Just the leather wheel to buff out the edge. Gets things sharp enough for me.

I only use an 8000 grit shapton for removing the burr after the tormek. I use the finer tormek wheel (the one that is blue color), and just put a small secondary bevel on the primary bevel. Plenty sharp for me.

Then after repeated secondary bevels I'll go back to the coarser Tormek wheel and regrind the primary bevel.

For me the Tormek is very quick and works well.

Hello to the forum. I am new to the form but have lurked for years. I am a hobby woodworker, building 3-4 projects a year. Finally a Question I may be able to help with as I also have a Tormek and a #7 plane. When you use the Tormek jig and slide the blade left and right across the stone the center part of blade spends more time on the stone than the edges, thus removing more material, resulting in a concave grind. I apply more pressure to the edges of the blade with my fingers and move the blade as far as possible from side to side so the center part of blade is off the stone. I have had good results with this technique. A tip I have heard is to scribe a line with a felt tip pen and work to the line, but have not tried that.
Bill

While the center will probably grind down faster, once the jig hits the depth stops there should be no further center grinding allowing for the ends to 'catch up'.
Consistent pressure and movement should yield good results with this jig.
Since we are not robotic, little tweeks to our technique usually are needed anyway to get stuff to satisfaction.

There is no depth stop on the standard jig. Please elaborate.

Quote:

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Originally Posted by Tom Ewell

While the center will probably grind down faster, once the jig hits the depth stops there should be no further center grinding allowing for the ends to 'catch up'.
Consistent pressure and movement should yield good results with this jig.
Since we are not robotic, little tweeks to our technique usually are needed anyway to get stuff to satisfaction.

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Jim,
In reference to the planer blade jig, after setting the angle and parallelism of the grind, one uses the indexed height adjustment wheels to establish grinding depth.
As grinding progresses the angle of grind varies just a bit as the blade lowers down to preset depth. Once final depth is concluded the correct preset angle is achieved.

Check the blade edge quickly with a straight edge before you remove it from the tormek. You'll be able to tell easily if the sides are projecting ahead of the middle, and go back to the tormek grind quickly working those projecting parts off. IF there's a hollow on the iron, you'll be able to see it pretty easily with the straight edge.

This reference is for a planer blade jig, not the chisel/plane blade jig that comes with the unit.

Quote:

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Originally Posted by Tom Ewell

Jim,
In reference to the planer blade jig, after setting the angle and parallelism of the grind, one uses the indexed height adjustment wheels to establish grinding depth.
As grinding progresses the angle of grind varies just a bit as the blade lowers down to preset depth. Once final depth is concluded the correct preset angle is achieved.

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Well it seems that I misread the original post, I thought we were talking about planer blades and thusly the planer blade jig for the Tormek comes into play.
I now see that a wide plane blade is the actual topic, sorry for any mis info.

Before tackling #7 plane blades, I true the surface of my stone with the diamond tip truing tool, TT-50.

Use the Magic Marker trick that they describe in their handbook, and cover the entire bevel of the plane blade with black.
Check frequently to see that you are getting an even grind all the way across the blade. Apply more pressure, and spend more time on the areas that are lagging behind.

Look at the very tip of the edge with a light overhead, and look for reflections. Any flat surface here will reflect light back at you, and means you need to work on that area until you see no light reflected what-so-ever. You should be able to feel a 'Burr' right across the whole blade.

Check-out on YouTube "Rob Cosman sharpening", and you will see how he achieves a great edge on a plane blade, with a minimal amount of time and effort and abrasive.

I use Rob's method/David Charlesworth ruler trick , and only use my Tormek to regrind the bevel, after it get out of shape after a while. You will see that Rob really emphasizes the importance of having a truly flat surface on the stones, otherwise you will only get something that is approximately approaching sharp, but not true sharp. He also puts a slight camber into his blades to avoid 'plane tracks', which seems to be the opposite of what you are getting right now.

If you watch any of the Tormek videos on YouTub, you will see that they also have a square to check and see if the blade is set-up correctly in the jig. Something that seems to be a problem, especially in the older plane blade jig, so they came out with the new SE-76 jig to help make things better.

I would also watch how Rob Cosman sharpens chisels, using a florescent light to gauge a flat back.