Any interest in a run of concave platens for convex grinds?

Nathan the Machinist

Nathan the Machinist

KnifeMaker / Machinist / Evil Genius
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A gentleman who has acquired a fair bit of my work in the past has requested a concave platen. I'm in the middle of a run of flat platens right now and I am going to make a special for him while I'm setup. While I'm at it I could do others. I don't want to make a bunch of these if there is no interest, so the purpose of this thread is to gauge interest in a concave platen.

I'm thinking it would be something like a 24" radius (48" dia) hollow on one side, a flat area in the middle then a 36" radius (72" dia) on the other side, so the platen would look a bit like a really wide stretched out W when viewed from the side.

I'm going to make one. I'm wondering if anyone else might be interested in one while I'm at it.


This is not a sale thread, I'm judging interest to reduce my risk of making grinder attachment that no one wants.

Thanks,
Nathan
 
Dumb question of the day. Is this a tried and true method of convenxing? I imagine that you must go with a very shallow depression so that you are able to push the belt to the back but I just can't picture the belt "hugging" the the curve the entire way without pulling a hard angle at the top. Did I make sense? Still on the fence but if you could still flat grind on it and it had one of your radiused top edges I would probably jump on.
 
strider214 said:
Dumb question of the day. Is this a tried and true method of convenxing? I imagine that you must go with a very shallow depression so that you are able to push the belt to the back but I just can't picture the belt "hugging" the the curve the entire way without pulling a hard angle at the top. Did I make sense? Still on the fence but if you could still flat grind on it and it had one of your radiused top edges I would probably jump on.
Click to expand...

He tells me he already does it this way.

It would be a shallow depression, it wouldn't go from the top to the bottom the length of the platen, it would be a couple zones that are hollowed out.
 
Basically, what you are talking about is a mini slack belt platen. I wouldn't want one.

For one reason, it would require every blade to have the same degree of curvature, which would be hard to do. Also, I can't imaging being able to keep a hard contact within a dedicated concave surface without over-grinding either the spine or the edge, or both. No matter what you do, the belt will be applying more force there......you can make a belt curve around a convex surface and it will conform, but you can't make a belt under tension curve to fit a concave surface.

I find the rotary platen from Beaumont does this task perfectly. You have a choice of four amounts of cushioned concave curvature, with the ability to adjust the firmness..
 
The only arguement in favor of doing it in steel as opposed to rubber would be that the rotary platen is better than a slack belt for convexing but still not ideal. You can still get too much convex if you try to do a full height grind. With that said, i don't see that I need one of these platens and you know that I will buy darn near anything, Nathan. :D.
Dan Pierson said:
I agree with Stacy. I can't see how this would be as good as my rotary platen.
Click to expand...
 
Yeah, I think I would be out too for the reasons mentioned above. Of course I might change my opinion if I ever get to see it in action.
 
Your comments make sense to me. Thank you everybody for your input. I'll make the one for this fellow and perhaps one more for me to play around with and stop there, at least for now.

Thanks, :thumbup:
Nathan
 
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