Ceramic / Glass platen backing rotary platen?

C_Claycomb

C_Claycomb

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Dec 11, 2000
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The Reeder grinder has features on their rotary platen to allow for a rigid backing platen to be fitted to back the rubber belt. They sell a hardened 440C platen for this, but it is quite expensive for someone who is only a hobby maker. I am thinking about making a pyroceram faced platen, maybe on an aluminum backing for heat dissipation and was wondering if this might be a bad idea? I have made a couple of rigid ceramic platens for my Coote with JB Weld and a screwed on step, and was thinking of something similar, just much shorter.

What do folk think?

I don't have an easy set up for heat treating platen size material, so hard steel is a lot more difficult to arrange than the ceramic, which I already have.

I know Moen Works do a very fancy rotary platen with backing and cooler, but haven't seen much else mentioned.
This video shows how Reeder set theirs up. 11:20 I haven't got a good bracket yet, so still very much at drawing board stage.

Thanks

Chris
 
Making a hardened platen is waaay easier than making even a basic knife. It's just two tapped holes on some 2 inch wide stock and then fully harden it. It's a sacrificial component, so I don't see much use in over thinking it. The biggest problem is that it gets hot, really hot. I don't think I would even try to use it without a platen chiller. I used components from Nathan and got the idea form Matthew Gregory:


oc18YW7.jpg
 
You do need a platen chiller if you're going to do much grinding on a platen backed radial platen.

We do this in production and it works very well.

I do like a hardened platen but if you're not keen on heat treat I have found that an aluminum bronze (wear plate and bearing material) works for this application without heat treat. We have a couple like this with thousands of knives on them, it works.


We make really good platen chillers but we're out of stock. However there are a number of knock-offs out there now and I'm sure they work fine. Or make your own, even if it's not perfect you need something or you will have a major heat problem with extended grinding.


Be aware the belt will be pretty loud at first until it breaks in but it eventually quiets down and is pretty quiet. I've found that not all belts are the same. I like a cheap belt for this application because they're less reinforced and softer and create a smoother grind. I think that Gates makes a good cheap belt.
 
Hi guys,
Thanks for posting. I am not sure if we are talking about the same thing though. I am talking about a rotary platen, but the examples you both given are radial platens.

As for making a hardened steel platen, that isn't on the table right now. I don't have a heat treat system set up. 🙁 I like the idea of bronze, but sourcing that type was a pita the last time I looked. I have a piece of the ceramic of the right size, so that would be my first choice.

Still interested in hearing thoughts from folk who have backed rotary platens or used one.
 
Look in the picture I posted. It is a rotary platen with a flat backing. In the video Greg has a backed rotary platen with a radiused platen. There is a J-groove rubber belt that rides between the flat platen and the abrasive belt. I think the ceramic could work, but you'll definitely want a shelf. I feel like it would generate a lot of static electricity (two non-conductive materials rubbing each other at high speed). And again, heat will be an issue. I forgot to turn the water pump one time and I could smell burning rubber within a minute. The platen was steaming hot when I spritzed it with water.
 
Doesn't putting a flat platen behind behind a rotary platen's belt defeat the purpose of making a convex grind?
 
It's more like a soft platen, or a leather platen. It minimizes the belt bump you get when the seam runs over the hard platen.
 
SirSpice said:
Look in the picture I posted. It is a rotary platen with a flat backing. In the video Greg has a backed rotary platen with a radiused platen. There is a J-groove rubber belt that rides between the flat platen and the abrasive belt. I think the ceramic could work, but you'll definitely want a shelf. I feel like it would generate a lot of static electricity (two non-conductive materials rubbing each other at high speed). And again, heat will be an issue. I forgot to turn the water pump one time and I could smell burning rubber within a minute. The platen was steaming hot when I spritzed it with water.
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Don't I feel an idiot! One day maybe I will learn not to post so late at night when my observation skills are low!
Sorry, and thank you.

The rotary platen I have has room for only a 4.25 inch backer, not much room for a chiller I think. What you say about heat might just put an end to the idea for me. I am not yet ready to set up water pumps and pipes. I was also worried about static, but was willing to try it and see if it was a problem.

I wonder how the guys at Reeder manage since they make and use a backer without a chiller. Maybe their set up doesn't have the backer pressed against the rubber as firmly as the longer designs?

The reason that I am looking at this is that I like flattish grinds with convex edges and thought it would be nice to be able to use a fine finishing belt to hit the flats then roll the edge without changing the tool.

Thanks again SirSpice, and Nathan!

Chris
 
I like Greg's engineering and products, but I can't see why you would put a hard backing plate behind a rotary platen. It seems like it would eat up the rubber rotary belt fast. Rubber creates a lot of friction ... that is why they make tires from it. mI would be curious to hear from someone who has run one of those for a while.
 
Try s2-32 hard felt from Mcmaster Carr. It has a little give to it, but makes for a nice belt finish. I use that and a F3 felt piece for my convex grinding/finishing. F5 was just too soft for grinding. Leather will also work to soften the belt splice bump.
 
I've made a rotary platen with exactly what you've asked about: an aluminum platen with a ceramic glass liner. It works just fine. You want the face of your glass to be flush or just very slightly proud of the wheels so that there's not a lot of extra tension of the belt against the glass. You'll also want to keep your speed on the lower end.
Yes, the belt will wear, and things do get warm, but I haven't had any major issues and I'm still on my first micro v-belt with plenty of life left. Now, I don't use this all day, every day, but I think I've used it enough to know that it works. You'll hear a little bit of belt squeak at first, but once it breaks in, it does get better. Sometimes I'll put a little bit of spray lube on the back of my rubber belt, but I don't find it strictly necessary.

As for whether this defeats the point of a rotary platen, it's not exactly for the same use as a rotary platen. It's basically accomplishing the same thing as the Moen platen by eliminating belt bump and giving a softer backing.
 
Stacy E. Apelt - Bladesmith said:
I like Greg's engineering and products, but I can't see why you would put a hard backing plate behind a rotary platen. It seems like it would eat up the rubber rotary belt fast. Rubber creates a lot of friction ... that is why they make tires from it. mI would be curious to hear from someone who has run one of those for a while.
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I have run them for a long time. We use them in production, it's Mark's primary grinding tool. We've been using them for years. It does eventually wear out a belt and a platen but I don't think a hobbyist would ever wear one out. We get hundreds of hours before needing any re-work. I think that Mark probably has 2,000 hours on one by now and I think he's on his second platen and third belt in three or four years. A regular flat platen wears out faster.

I got a regular rotary platen years ago and no matter how firm I set it, it had too much give. You couldn't get work done. It was too convex. The grinds were a mess. You still get a convex grind even with a hard backing, it's just less convex. And you can bear down hard enough to fracture the grinding grit to keep it sharp and cutting. And you don't have to use a FLAT flat platen, I use shaped platens. It is efficient, it gives good control and a nice finish and it practically eliminates splice bump.
 
Nathan the Machinist said:
I have run them for a long time. We use them in production, it's Mark's primary grinding tool. We've been using them for years. It does eventually wear out a belt and a platen but I don't think a hobbyist would ever wear one out. We get hundreds of hours before needing any re-work. I think that Mark probably has 2,000 hours on one by now and I think he's on his second platen and third belt in three or four years. A regular flat platen wears out faster.

I got a regular rotary platen years ago and no matter how firm I set it, it had too much give. You couldn't get work done. It was too convex. The grinds were a mess. You still get a convex grind even with a hard backing, it's just less convex. And you can bear down hard enough to fracture the grinding grit to keep it sharp and cutting. And you don't have to use a FLAT flat platen, I use shaped platens. It is efficient, it gives good control and a nice finish and it practically eliminates splice bump.
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That is wild! I never would'a thunk it.
 
Stacy E. Apelt - Bladesmith said:
I like Greg's engineering and products, but I can't see why you would put a hard backing plate behind a rotary platen. It seems like it would eat up the rubber rotary belt fast. Rubber creates a lot of friction ... that is why they make tires from it. mI would be curious to hear from someone who has run one of those for a while.
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I was thinking exactly the same thing...
 
It does squeal like a pig for a day or two before it breaks in but it eventually settles in and gets quiet and wears pretty well.

7AFXAIu.jpg


^that one has seen thousands of knives run across it without much trouble
 
In a completely unrelated search, I found this thread from 2018. I post the links because the older thread is really good on finishing, and seeing it being discussed with enthusiasm three years ago makes me feel a little less stupid for asking the question here....I even don't feel too bad about missing it in my search for rotary platen posts, it isn't an obvious find.

Acceptable finish

So I am working on yet another 270 mm AEB-L suji. What I have been doing with these lately is grinding them down pretty thin and then working my way up to 65 µm gator belts. I then scrub them down with 320 grit EDM stones with occasional trips back to the 65 µm built to get rid of some of the...
www.bladeforums.com www.bladeforums.com
Stacy E. Apelt - Bladesmith said:
I grind to 220 and then use a Scotch Brite belt.

kuraki said:
.... So 2 things made a belt finish possible for me. One is the rotary platen with a glass platen behind the longest length. ....
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What a great idea!!!
I never thought of this solution, but always felt it was a shame you couldn't use the long space for true flat grinds. I think I will be out in the shop this weekend with a piece of heavy aluminum angle stock and measure for a piece of pyroceram.

Now, if you can find a way to make the bearings in the rotary platen last longer, you will be a true genius;)
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I wonder is it possible splice bump to be eliminated in a simpler way ? What if we glue something behind belt in same thickness as splice material ?
 
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