Curved Platen V. Big Wheel

T

The Mighty Ginsu

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Aug 11, 2016
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Is there any reason to prefer a big contact wheel to a curved platen (or vice-versa)? Just wondering. Changing platens would be really convenient, and I could make them myself.
 
Platens run hotter and belts wear faster. A wheel also runs quieter.
 
That said, a 48" to 60" wheel needs a specially built grinder and will cost many thousand dollars. A 48" or 60" curved platen will cost about $50.

A large wheel is best made to run slow and wet.
 
It would definitely be more convenient to have a radiused platen rather than a 72" wheel (for example). A platen chiller would be your friend.

I agree that wheels are much quieter, smoother, and save on belt life.
 
Holy cow. When he said "large wheel" I though he meant maybe 14".

I have seen those absurdly large wheels in various videos. What are they used for?
 
I was asking because I'm not sure what I'm going to end up making, so I would rather not commit to a 14" or 8" wheel or whatever, prematurely. A curved platen, on the other hand, is cheap, and it would be possible to interchange them quickly.

I'm thinking it would be nice to start with kitchen knives, maybe 2" or so wide. I would love to make a nice cleaver 4" wide. But sooner or later, I'll want to make folding knives with blades no wider than one inch.
 
kuraki said:
Holy cow. When he said "large wheel" I though he meant maybe 14".

I have seen those absurdly large wheels in various videos. What are they used for?
Click to expand...

Large wheels are used here in Japan to grind blades very efficiently. They remove material quickly, and are water cooled, so you can grind continuously without needing to dip the blade. They are not necessarily for hollow grinding. Although they are used for grinding the shallow hollows (urasuki) on the back of chisel ground knives (such as yanagibas) the Japanese grind both flat and convex blades on them. For example, I know a maker who does very thin gyuto, which have a subtly convex geometry, and he grinds them entirely on wheels. However, he will transition to a horizontal stone to get dead flat surfaces (or to help even out the convex grind).

Having ground on these wheels, I can say they are absolutely amazing. Belt grinders may have them beat as far as versatility is concerned, but as far as efficiency, there's no contest. They grind fast, cool, and you can grind hundreds and hundreds of blades on one before you need to replace the wheel.
 
Yep highly efficient. Wish all grinders were designed and built this way.
A skilled bladesmith can grind a bevel in minutes with this rotating water stone and then just finish up on a 2x72

https://vimeo.com/181582297


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I grind all my blades on stone wheels and finish with buffing and scotch brite type wheels. The largest wheels I run are 16" and I have both stone and scotch brite in that size. I usually do hollow grinds but it is possible to get a very nearly flat or slightly convex grind on this kind of wheel.
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The wheels simulated in a curved platen are usually 36, 48, 60, and 72 inch wheels. The average maker will never have such wheels ... but can have a curved platen and get the sane hollow grind.

A kaiten toshi ( Japanese wet grinding wheel) is usually around 48" and the wheel costs thousands of dollars. It takes special training to dress these wheels right. The wheels used in Sheffield England were as large as 8 feet and were worked while laying down on a bench.

A curved platen and a platen chiller will allow a maker to do grinds that would be nearly impossible otherwise.

Tip:
A Breg Polar Care Cube chiller pack (used after joint surgery) is the perfect self contained cold water supply for a platen chiller.
 
I do mostly flat and convex grinds, but on occasion do a hollow grind. That said I still find used for my 8" contact wheel other than bevel grinding, it's very useful for certain profiling and handle shaping. When I do a hollow grind I normally use a 14" wheel. I'd love to get a 72" platen, but haven't had time to build one yet.
 
kuraki said:
Holy cow. When he said "large wheel" I though he meant maybe 14".

I have seen those absurdly large wheels in various videos. What are they used for?
Click to expand...

In a historical sense, those giant wheels were natural stone. As such any natural wheel cant run very fast.
A huge diameter can give decent SFM & associated grinding performance while running at a safe slow rpm.

Btw, despite relatively slow RPM, takes a lot of horsepower turning a huge wheel.
I would love to have one...
 
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making a curved platen it is not as easy as it could look like.
You will need tension on the belt and with a curved platen tha contact area is large, there is so much friction that if the motor won't stall a huge amount of heat is generated.
A platen chiller can be of great help as pointed out by Stacy
 
In workshop where I give engine crankshaft for rebuild .......They change grinding stone when they Dia. is worn to about 24 inches . They are three centimeters thick and i can bye that for 100 euro in several grain size ? Is not difficult to make a stand for that ...........
 
The Mighty Ginsu said:
I was asking because I'm not sure what I'm going to end up making, so I would rather not commit to a 14" or 8" wheel or whatever, prematurely. A curved platen, on the other hand, is cheap, and it would be possible to interchange them quickly.

I'm thinking it would be nice to start with kitchen knives, maybe 2" or so wide. I would love to make a nice cleaver 4" wide. But sooner or later, I'll want to make folding knives with blades no wider than one inch.
Click to expand...

You are kind of letting the "tail wag the dog" here. Figure out what you want to make first and get the equiptment for that. You can do a lot of different knives with a flat platen and a contact wheel, be it a 8"/10"/12"/14"etc. It seems you haven't made any knives yet? If this is the case I would suggest starting small. A 2" tall chef's knife is not an easy blade to learn on. A small drop point or something with a 3-4" blade is a great place to start so you can learn the basics. I only have a flat platen and an 8" wheel and have made anything from small skinning knives to large chefs knives. With that said I am wanting to get one of the curved platens so I can do taller hollow grinds.
 
Maybe I'm derailing a bit here but the large radius platen has intrigued me.

Chiller aside, what would be a good material for a large radius platen? Least amount of friction, greatest wear resistance? You're not going to find ceramic I'm guessing. UHMW is nice and slippery but I'm not sure it would hold up.

I don't hollow grind because I only have a 10" wheel and I don't like that radius on anything but the smallest knives and I don't care to invest in a larger wheel. But I could fab a chilled platen to any spec I'd like.

I really wish I had a way of putting rubber onto a wheel, it's the only thing preventing me from making contact wheels myself.
 
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