Simulating Large Diameter Wheels?

[Aiden CC]

I've started to become interested in single bevel Japanese knives, and earlier today I tried out forging an usuba. The forging went alright, but I had a lot of trouble grinding the subtle hollow on the left side of the blade. On relatively narrow blades in the past I've used my 12" contact wheel and held the blade at an angle to get an effectively larger radius, however, on this blade, which is about 1.8" wide, for whatever reason that approach was giving a slightly convex surface. I was able to get a functional surface by starting a hollow in the middle and "rocking" it to the edges, however the finish from that isn't as consistent as I would like, with dips from the corners of the wheel. Does anyone have experience doing a grind like this/have any ideas on how to get better results?

 

Thanks!

[Dan Hertzson]

I used a 12" wheel, but my blade wasn't nearly that wide.  You might want to look at water cooled large radius plattens.

[Randy Griffin]

I would like to see some of your work when you get this sorted out. I'm a fan of the single bevel knives. Amazing how sharp they can get.

I also think a large radius platten would be best.

[Aiden CC]

2 hours ago, Dan Hertzson said:

I used a 12" wheel, but my blade wasn't nearly that wide.  You might want to look at water cooled large radius plattens.

That makes sense. I have a Grizzly 2x72 and a lot of what I’ve seen is for the 3 wheel style grinders but I could probably whip something up (though maybe not the cooling part). My platen already has a radius from wear though it’s probably something like 5ft; just enough that it won’t grind straight lines. 
 

1 hour ago, Randy Griffin said:

I would like to see some of your work when you get this sorted out. I'm a fan of the single bevel knives. Amazing how sharp they can get.

I also think a large radius platten would be best.

I have one blade that I’ll probably just finish functionally though not aesthetically, will probably do a show and tell thread, but can put some pictures here too. 

[Brian Dougherty]

Does anyone make and sell the radiused platens anymore?  All the ones I have heard about came from Nathan the Machinist, but it doesn't look like he still makes them.

[Dan Hertzson]

Also note that in the sushi knife class I took the instructor "precurved" the concave side of the blade mechanically before grinding.  In that case we were using single side laminated steel (HC on the concave cutting side and mild on the beveled side).  He did the curving cold, after forging and annealing, using large radius clapper dies and a big, slow power hammer.  When I tried to emulate this at home I used a swage block and large radius top fuller to achieve a similar effect.  Not sure if this is a good idea for non-laminated steel, and the blanks are certainly prone to warping in final heat treat (and expected to do same apparently - I think Murray Carter discusses addressing this in his book).

 

I think you can make a simple one yourself, that isn't water cooled.  I suspect that a mister system would work to keep the belt cool enough, or possibly in combination with a graphite pad behind the belt as well to reduce friction.

[Randy Griffin]

What is the purpose of the hollow grind on the backside of the blade? Urasuki is it called?

[Joël Mercier]

Ease of sharpening and perhaps better food release.. 

[Aiden CC]

8 hours ago, Dan Hertzson said:

Also note that in the sushi knife class I took the instructor "precurved" the concave side of the blade mechanically before grinding.  In that case we were using single side laminated steel (HC on the concave cutting side and mild on the beveled side).  He did the curving cold, after forging and annealing, using large radius clapper dies and a big, slow power hammer.  When I tried to emulate this at home I used a swage block and large radius top fuller to achieve a similar effect.  Not sure if this is a good idea for non-laminated steel, and the blanks are certainly prone to warping in final heat treat (and expected to do same apparently - I think Murray Carter discusses addressing this in his book).

 

I think you can make a simple one yourself, that isn't water cooled.  I suspect that a mister system would work to keep the belt cool enough, or possibly in combination with a graphite pad behind the belt as well to reduce friction.

I forged a deba today and forged in a bit of concavity and it worked fairly well. The spine was a bit thick to work cold, so I did it hot. I was able to use the top of my platen to make a hollow, I may clean it up by hand later. Both blades I’ve forged are laminated, the usuba warped, but the deba came out pretty straight, probably since it’s so thick. 
 

I won’t have much time for knives for a while, but it may be worth making a curved platen in the future. 

[Joël Mercier]

I believe the reason why the concave side has to be mechanically done is because the high carbon part(traditionally 30% of the thickness), if was ground in, would run too thin as the edge wears out.

 

That leads to the other advantage of this type of blade. The edge and bevel keep the same geometry through the whole life of the knife. When the primary edge(secondary bevel) becomes too thick, they run the secondary edge (primary bevel) on the waterstone until the primary edge isn't visible anymore. Then they do a new tiny primary edge. So the secondary edge will run up the blade as it wears out. 

[Aiden CC]

Its very hard to catch on a photo, but using the worn out part at the top of my platen I was able to get a serviceable hollow. It’s a bit ugly, and not the same thickness all the way around (being wider at the spine than the edge, for example), but for a personal knife, it’s ok. 

[Cason Hicks]

Bill Behnke makes a 36" radius platen http://www.billbehnkeknives.com/available_items.html 

[Dan P.]

I had a 36"(ish) radius platen that I made myself. It got the workpiece very hot. I found it difficult to manage heat with already HT'd knives.

[Alan Longmire]

That's why the ones Nathan the Machinist used to sell were water-cooled.  Internally.  Probably why he stopped, they were expensive to buy and I imagine quite a pain to make for the low demand.

[John N]

I use a chunk from the outer race of a big (very big) roller bearing. It is simulating a 600mm diameter wheel. 

 

As it is from a bearing, it is pot hard, that helps with it not wearing prematurely. As it is a substantial lump of steel it gets warm, but not concerningly hot - Its best not to have the belt too tight though!

 

I grind with the belt 'running away' from me in this configuration, so all the crap is flying away from me!

 

[Joël Mercier]

1 hour ago, John N said:

I use a chunk from the outer race of a big (very big) roller bearing. It is simulating a 600mm diameter wheel. 

That's simply genius! Thanks for sharing John!

[Aiden CC]

5 hours ago, John N said:

I use a chunk from the outer race of a big (very big) roller bearing. It is simulating a 600mm diameter wheel. 

 

As it is from a bearing, it is pot hard, that helps with it not wearing prematurely. As it is a substantial lump of steel it gets warm, but not concerningly hot - Its best not to have the belt too tight though!

 

I grind with the belt 'running away' from me in this configuration, so all the crap is flying away from me!

 

I might have to try and find something like that! Though I imagine it might be difficult. 

[John N]

I have got lots of the bearing left, but postage would be killer ! -

 

By just using a small 4" chord of the bearing it keeps the frictional area down (reducing the heat build up)

[Gerhard Gerber]

13 hours ago, John N said:

I use a chunk from the outer race of a big (very big) roller bearing. It is simulating a 600mm diameter wheel. 

 

I have 2 of those, from a Caterpillar, you're giving me ideas!

[Aiden CC]

6 hours ago, John N said:

I have got lots of the bearing left, but postage would be killer ! -

 

By just using a small 4" chord of the bearing it keeps the frictional area down (reducing the heat build up)

I would imagine! Do you have an idea what it came from originally?

[John N]

1 hour ago, Aiden CC said:

I would imagine! Do you have an idea what it came from originally?

 

yes, it was a double spherical roller bearing from a clutch on a 2500 ton Massey we rebuilt. I rebuild forging machinery so end up with all kinds of interesting odds and ends!

[Aiden CC]

22 hours ago, John N said:

yes, it was a double spherical roller bearing from a clutch on a 2500 ton Massey we rebuilt. I rebuild forging machinery so end up with all kinds of interesting odds and ends!

I'll keep my eyes open for parts like that, though I may end up taking the principle (thick piece of steel, large radius, short arc length) and try to cook something up myself. Might be too out there, but it seems like laying a bunch of weld beads on one side of a piece of steel would warp it into a circular arc while also adding mass. I might be able to do some math and see if that is feasible. Milling might be an option, but would turn this into a very time intensive project and I already have a lot of machining to do in the next few months for another project.

[Brian Dougherty]

I have the means to get some water cooled radius platens made.  It would be expensive, but not terribly difficult to have the parts machined and heat treated.

 

I'm not interested in doing this for money, but if there isn't a commercial option out there, and people want to talk about getting a batch made, we could work through what it would actually cost.

 

I have less than zero interest in doing this if someone else already sells them, but that doesn't seem to be the case.  

[John N]

If I was going to make something commercially (which I have zero interest in doing!) I would make what I have pictured above, (works perfectly), but possibly add a hole through the platten that an airline could be connected to, a few PSI would 'float' the belt off the platen a few thou when grinding pressure was not applied to it. It would be a much simpler solution than water cooling.

 

I can grind 1/2 a dozen knives one after another on the one I have pictured without heat issues, so it might be a waste of time (gimmick)

Edited January 23, 2020 by John N

[John N]

8 hours ago, Aiden CC said:

I'll keep my eyes open for parts like that, though I may end up taking the principle (thick piece of steel, large radius, short arc length) and try to cook something up myself. Might be too out there, but it seems like laying a bunch of weld beads on one side of a piece of steel would warp it into a circular arc while also adding mass. I might be able to do some math and see if that is feasible. Milling might be an option, but would turn this into a very time intensive project and I already have a lot of machining to do in the next few months for another project.

 

Its such a shallow arc you could freehand it on a piece of steel, on a slack belt, 'good enough'