3 types of flat platens, radius platens, platen chillers for KMG

Nathan the Machinist

Nathan the Machinist

KnifeMaker / Machinist / Evil Genius
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Knifemaker / Craftsman / Service Provider
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There are a lot of different items in this thread. Please read the descriptions below and follow the ordering instructions to make sure you get what you need. Please also read the tips and instructions below so you understand how these are best used.

To start with we have radius platens. These are made of A2 and hardened to HRC63-64. There are three sizes that simulate large wheels, 36", 48" and 72". They're $110 each.

If you buy a radius platen you're probably going to want a water cooled platen chiller because they get hot.

We also have flat platens with end radius, large and small. They're made of 1/2" A2 hardened to HRC 63-64. "Small" has an end radius of 1/8" on one end and 1/4" on the other end. "Large" has an end radius of 1/4" on one end and 1/2" on the other end. These can be used for lengthwise grinding with the top wheel removed. The mounting holes are blind to prevent a witness mark from showing in your work. They're $90 each.

If you're going to grind with the top wheel removed it will get hot and you will need a platen chiller.

We also have plain D2 flat platens. They're made of 3/8" PFG D2 and heat treated in a way to maximize abrasion resistance. If all you're planning on doing is old fashioned flat grinding this is the platen for you. They're $90 each.

Most people don't need a platen chiller for regular flat grinding, though many people do benefit from one.

And last we have aluminum water cooled platen chillers for $60 each.

Flat rate shipping in the USA is $5.







These items are made to fit the KMG standard, which is 2X8 with 1/4-20 mounting holes that are 6 3/4" center to center. Some people have adapted these to other grinders.

I will give a description of the items in separate posts below to keep this first post short and sweet.





If these platens will fit your grinder and you would like to buy one of these, I need you to please follow these instructions to help me keep up with everything (otherwise folks will fall through the cracks).

1: State your claim in this thread.

2: send me an email (not a private message) carothersknives at gmail dought com

The email should include what you are buying, your BladeForums handle (i.e.: "Nathan the Machinist"), your actual name, your shipping address and your paypal email address.

I will send a PayPal invoice to that email.

3. Pay the paypal invoice. Once it is paid, I will ship your order to the name and address you gave in your order email.

If you don't want to use paypal, we can arrange to send a check.

I don't imagine there will be shortages this time, but if there are, it will be based upon first come first serve who posts in this thread. I have to do it this way to keep things sane.
 
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Radius platens simulate large wheels. They're called a "radius platen" because they're machined with a radius. The size number references the size wheel they simulate. So a 36" radius platen actualy has an 18" radius. It simulates a 36" diameter wheel.

radius_platen.jpg~original


There are ten 36" platens, ten 48" and five 72".

Personally I like the 36" the best. 48" is the most popular. 72" is too subtle to really notice with your eyes and is mostly used by folks making certain kinds of kitchen knives.

In using the radius platens I have found the effect is subtle, but noticeable. It isn't a flat grind, but it isn't really a hollow grind. I believe this is a historically accurate grind for blades ground in yesteryear on really big stones. I see this being a cool grind for blades made in an older style, and blades like kitchen knives where you would want a full height grind on a tall thin blade.

36_hollow.jpg~original



The A2 is quality steel from Latrobe, heat treated at Peter's Heat Treat with cryo and is harder than a woodpecker's lips. But it can still wear out quickly if exposed to certain grinding conditions that cause grinding grit to accumulate on the inside of your belt and cut the platen. Some belts have dry lubricants, coolant and other "aids" that work great on a contact wheel but can cause black gunk buildup on the inside of the belt that can then cut the platen, particularly when they get hot or damp. If you're getting black buildup on your platen beware of cutting grooves.

Unlike a flat platen that you can re flatten, a worn out radius platen is toast. You can extend the life of your platen by not using it to rough or profile. If you establish your grind on a regular flat platen or wheel and if you'll avoid cutting it with grinding grit your radius platen will develop a mirror finish and can grind hundreds of knives over its life before developing troublesome wear.

You will probably want a platen chiller if you're using a radius platen, particularly the 36" and 48".
 
There are 10 "small radius" flat platens and 10 "large radius" flat platens. The small radius is 1/8" and 1/4". The large radius is 1/4" and 1/2". I use 1/2" the most because it gives a nice gradual plunge that looks good and is strong.

These are 1/2" thick with blind mounting holes to prevent witness marks from showing in your work.



I think that grinding lengthwise along a platen is an under utilized technique.


81_zps4b566cf4.jpg~original


I like finish grinding this way, I get smoother geometry with fewer flaws. If you sight down a blade ground the conventional way you can usually see flaws in the way light is reflected as you move the blade around. For me, ground lengthwise gets much closer to flawless and a more even scratch pattern.

You can call it good at that point or use it as a head start on hand sanding.

This is a belt finish:

2.jpg~original



Grinding lengthwise generally involves removing the top roller from your platen attachment and draping the belt directly over the top of a shaped platen. I lean the platen back and run the grinder forward. Some people run it tip first and/or in reverse because there is less risk of slipping up and messing up your plunge but I learned to do it this way because I was concerned about catching the tip and getting hurt.

Running the belt directly over the platen generates a lot of heat. This increases your need to lift and dunk, and it gets hot enough to burn your belt. You need some way of cooling your platen. I suggest you make or buy a water cooled platen chiller.

The platen will wear. I only use it for finish grinding and I use it at low speed. There are some belts that build up sticky residue on the belt and platen that become loaded with grit and will eat up a platen. A damp belt can do this pretty bad. You should grind totally wet or totally dry to avoid problems and be on the look out for trouble.

Lengthwise grinding avoids the hot spots that bias the edges of a platen or wheel and allow a smoother more perfect geometry and the ability to have extremely clean plunges. In many cases it also eliminates the need to hand sand.

For the final finish pass I like to double up two belts so it has a bit of give. This will give you the smoothest most even finish. A clean 120 grit grind doesn't look rough and a clean 320 grit looks slick as hell.

I like the yellow Klingspor 312 J flex belts. Other belts I've tried tend to gouge and gall when a bit of grit pulls free. It goes without saying, use fresh belts.

In order to run two belts at the same time you're going to need to stretch a belt. Take a new belt and put it on the grinder under high tension and run it and get it soaking wet. Once it runs a little while it will stretch so you'll need to stop and pull your attachment out and run the tension up again. At this point it is stretched. You'll want to go ahead and rub the grit off the belt splice at this point to prevent splice bump from showing up in your finish. I use an old file. You can then take another belt like it that hasn't been stretched to run inside of it and they'll run together that way.

Like any new grinding technique there is a learning curve with lengthwise grinding, particularity if you're grinding like I do with the grinder running forward and tip down, standing to the side so you don't stand in line with a potential launch. You're probably going to slip and ruin a plunge before you get a feel for it.

You want to present the blade to the belt slightly edge first and out towards the belly. Roll it in, then roll it up. The mechanics are similar to regular grinding as you angle the blade out as you approach the tip. You'll want to stay away from the round over on the platen unless you're grinding your plunge. When you do grind your plunge you'll want a firm grip on things and press it in deliberately. Then roll the blade out towards the tip in one smooth deliberate motion hitting the entire length of the blade for an even finish.

It isn't rocket science folks. It wasn't hard for me to learn to do and I think it is a very cool technique.

I hope this is helpful.






The A2 is quality steel from Latrobe, heat treated at Peter's Heat Treat with cryo and is harder than a woodpecker's lips. But it can still wear out quickly if exposed to certain grinding conditions that cause grinding grit to accumulate on the inside of your belt and cut the platen. Some belts have dry lubricants, coolant and other "aids" that work great on a contact wheel but can cause black gunk buildup on the inside of the belt that can then cut the platen, particularly when they get hot or damp. If you're getting black buildup on your platen beware of cutting grooves.

This is a high quality precision tool. Avoid wailing on it such as rough profiling etc and it will develop a mirror finish and can grind hundreds of knives over its life before developing troublesome wear. I lap my out flat every 50-150 knives and have never actually worn one out.



If you just want a regular flat platen for regular flat grinding, I recommend the D2 platen. It costs the same and will wear longer. It's 3/8" thick with through tapped holes like the OEM.
 
The water cooled platen chiller is a very useful gizmo. You just about need one if you're grinding with a belt warped around a formed platen, but even folks doing regular flat grinding have found these to be very useful. I've gotten a lot of great feedback about these and I use mine all the time and wouldn't want to be without it. Grinding against a cool platen is a good thing.

chill1.jpg


These have an internal meandering water path circuit where you can pump, siphon or otherwise flow water to control the temperature of your platen. I use ice water and get mine cold.

chill2.jpg


The mating surface is precision machined flat and the back of my steel platens are also precision machined flat so you can simply bolt these up and get fairly decent heat transfer. For better heat transfer or to use a platen I didn't manufacture you can use a little thermal grease during assembly to get really good heat transfer.

chill4.jpg


The chiller is sealed with a buna N o-ring that is rated to 250 F. The o-ring is compatible with water, antifreeze and most oils. It is not particularly compatible with acetone, so if you're planning to flow subzero acetone through it for use as frozen quench plates - you probably shouldn't. The assembly can be opened to remove clogs or replace the o-ring if necessary. If opened, you should use a little smear of grease to lubricate the o-ring upon reassembly.

The pipe thread is a standard 1/4 NPT. You are responsible for hooking up your own coolant supply. I recommend swivel push-to-connect fittings and 1/4" or 3/8" plastic tubing, though rubber hose and hose barbs work too. I'm using a dinky little centrifugal pump here and a bucket of water. The meandering coolant path in the platen chiller induces a lot of turbulence in the water flow which helps you get good heat extraction without needing a lot of water flow. An aquarium pump is adequate. Or you might opt to hook up to your regular water supply and simply dump the water (though you'll go to hell for wasting water). Just remember you don't need huge flow or pressure here. Keep up with your tubing to keep it out of the grinder wheels and mechanism using zip ties or similar.


Put ice in your bucket for a cold platen. This can reduce your need to lift while grinding, particularly when using formed platens that can get extremely hot.
 
Nathan, you mention: "72" is too subtle to really notice with your eyes and is mostly used by folks making certain kinds of kitchen knives."
Just curious. What kind of kitchen knives?

Anyway I'll take a 36" radius platen a small end radius platen and a chiller.
Thanks!
 
rcetroy said:
Nathan, you mention: "72" is too subtle to really notice with your eyes and is mostly used by folks making certain kinds of kitchen knives."
Just curious. What kind of kitchen knives?

Anyway I'll take a 36" radius platen a small end radius platen and a chiller.
Thanks!
Click to expand...

Here's a nice Yanagi-ba: http://www.bladeforums.com/forums/showthread.php/1220957-dragons-breath-Yanagi-ba

Single bevel Japanese knives have a shallow hollow on the back so when they're laid flat you can sharpen them (or remove a wire edge) you're not honing the entire surface.

They're also used on thin knives and cleavers for vegetables and fish.
 
Ooh I've been waiting for these to come back, i missed the radiused flat platens last time. Already have a cooler, and one of the first 48" you made, wanted to add a flat but you were all out.

I'd like one of the large radiused flat platens =)

Email incomming.
 
Nathan,
I would also like a flat platen with a large end radius and a platen chiller. Email inbound.
 
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