Rotary Platen Question

Outdoor Gear Dad

Outdoor Gear Dad

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Jun 1, 2019
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I have had a rotary platen for awhile, but am just now committing to actually learning to use it. This may be a stupid question but is there a rule of thumb on which portion of the slack to use and when? for clarification, the platen rotates so you have different levels of slack...Small, medium and large lets say.

Do you use one for larger blades and one for smaller?
 
I don't have one either but I would imagine it simply depends on how much convex you want on any given blade.
 
Yeah it’s just a matter of how much convexity you want with the small section being least convex. You can probably also adjust the belt tension to make all lengths less or more convex. No rule of thumb just whatever grind you’d like based on intended use.
 
I'm interested in hearing any tips too. I just got one and haven't used it much yet. My biggest hope for it was achieving better belt finishes so I don't have to hand sand every single knife. All I've really done with it so far is throw a belt on it and refinish a couple of shop knives I had laying around. It does seem like I got a nicer surface finish without any facets with much more ease than I would have trying to use the flat platen. I was searching youtube last night for rotary platen tips and didn't come up with anything.
 
The long section is very useful for handle shaping.
 
When I had one several years ago from KMG, I found that the backing belt would cup slightly if you weren't careful and could quickly put a groove in the blade at the edge of the belt. I sold my KMG to Matt Parkinson and he used it on his 2nd episode of Forged in Fire and put a small groove in his blade due to it. I tried to angle the blade off to one side to prevent cupping when I was grinding on it. Working harder from one side seemed to reduce the cupping issue for some reason? The amount of convexing depends on what you want to do with the blade. For handle shaping, it worked really well, too! It just takes practice and experience to use the rotary platen effectively.
 
I use mine for shaping handles where the guard meets the handle. The handle material is softer than the guard material so with a regular slack belt the handle material wears away faster and leaves a "dip" where the handle meets the guard.
With the rotary platen this is not a problem.
 
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