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Grinding New Bevels

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This is probably well-trodden ground but I’m hopeful that someone will have gone through this before and can help.

 

I have a nice set of oil stones that I use for ordinary sharpening and they work great.  But I still struggle when I get my hands on an old plane or chisel and have to regrind the bevel or just grind nicks out. 

 

I have a bench grinder that came with the typical gray wheels.  These things are super slow and I’ve seen many people in magazines using the white and blue-green grinding wheels but I can never find those.  I’ve looked in my local Woodcraft and a couple of tool places but they don’t have the Norton brand.  I am unfamiliar with the other brands and so don’t know if they cut as fast or not. 

 

Once long ago, I stumbled across a 3x6” DMT diamond plate for cheap ($35).  It is a steel plate marked “Dia-Sharp Coarse” on the side.  This cut really fast for awhile.  After a long session of trying to flatten the back of a plane iron, it seemed to slow its cutting speed dramatically.  I did clean it more than once with water but that didn’t speed up the cutting at all.  The surface left behind on the plane iron was very shiny so it made me wonder if I had somehow worn the abrasive out.  I read somewhere on this forum that diamond plates have this plateau; as if they begin life more coarse than the rating suggests and you soon wear them down to that.  I don’t know but I do know that the one I have is no good for basic regrinding of anything.

 

So here’s my questions:

 

  1. Do diamond plates have this “plateau” effect or did I possibly just get a bad one?
  2. Given that I only want to use my bench grinder for coarse regrinding of a new bevel, which grits of grinding wheels should I buy?  I’m assuming I can find them online at multiple places so I just need to choose some grits.
  3. What’s the difference between the white wheels and the blue ones?

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You want the blue one, which runs cooler so you don't burn up the steel.

 

This is what I have and it works well.  You still have to take your time or you will burn up your steel.   

 

The white might work as well, but I don't have experience with it.

 

You can get them on Amazon.  

 

Josh

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For roughing in the bevel on a chisel, I like the cheap diamond plates from HF. 3 grits for $10, and they seem to work quite well. A bit small for most plane irons, but will do in a pinch.

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There are probably people who grind more plane irons than we do in our shop but not many. We make the irons for all the planes we produce and always have. We've recently made some changes in our grinding set-up and let me show you what we have and explain why.

 

First here are our grinders:

 

ng1grinders.jpg

 

A Jet belt/6"grinder combination, a Palmgren 6" high speed grinder, a Baldor 6" high speed grinder, and a Jet square wheel grinder. All but the Baldor have modified or shop-made tool rests. Grinding is a rough shaping operation so we use coarse wheels. All wheels are chosen for their width and, where we have a choice, their coarseness. The grinding wheels increase in width from left to right and are 1/8", 3/16", 1/4", 1/2" and 3/4". The 1/2" and 3/4" wheels are 24 grit grey wheels, just standard ones. We've tried the white wheels and the new blue "cool" wheels but think they're a waste of money. 24 grit wheels grind cooler and faster. It hard to beat a well dressed coarse wheel for grinding cool or grinding quickly. The only wheel with a flat or square dressed face is the 3/4" and the rest are dressed with a curved face. The diameter arc is about equal to the width of the wheel and these are used for molding planes. Here are some of the new old stock gumming wheels we recently bought.

 

ng2gumming.jpg

 

These 3/16" and 1'4" wheels are new old stock saw gumming wheels. I really like them but wish they were more flat. They're out of flat enough that dressing and balancing them takes a bit of effort.

 

The 1/8" wheel is a chain saw sharpening wheel that's coarse enough to remove metal quickly and with minimum heat.

 

ng3eighth.jpg

 

Above is the 1/8" wheel and below is a two piece tool rest made for the square wheel grinder. One can tilt the platen of the grinder to grind bevels but dust collection is difficult when doing this. We use both the square rest and the shop-made one. Change over is just a matter of loosening a single cap screw, changing rests and tightening the cap screw again.

 

ng4rest.jpg

 

There was a question about diamond stones and there have been issues with some Cubic Boron Nitride (CBN) grinding wheels reported lately. I wasn't surprised by the problems people reported with  their electro-plated CBN grinding wheels. We have an oscillating diamond grinder in our metal shop and I learned an expensive lesson with it. I put a new wheel on it and wore all the nickel plating and diamonds off the wheel in about an hour's steady use grinding O-1 tool steel. The wheels run $160 or so. I was sure the wheel was flawed and called a the manufacturer's tech department. The tech rep explained the soft nickel matrix is designed to wear away slowly and expose fresh abrasive when grinding materials that generate a powdered swarf. This would include things like carbides, glass, stone, or ceramics. Steel generates a swarf made up of very small shavings. These shavings come off very close to the wheel, close enough they have enough beam strength to cut into the matrix and actually cut it away which releases the diamonds. We do use diamond stones but only to dress our oil stones, we don't use them on tool steel.

 

ng5diamond.jpg

 

Our diamond grinder that operates just rotating or with rotation and a side-to-side oscillation. Below is one of the brazed carbide tool bits we grind for use in our metal shop. This one has been sharpened a few times and the way the steel body has been kept ground back to avoid diamond wheel wear is visible.

 

ng6bit.jpg

 

For refining molding plane irons we use flex shaft grinders and have multiple hand pieces to make changing points easier and faster.

 

ng7flex.jpg

 

Another grinding process is lapping freshly heat treated irons flat. The irons do distort slightly in heat treating. We use a Lap-Sharp lapping machine for this. I wouldn't recommend trying to sharpen a tool on it though. This has a relatively slow rpm, is used with a rust resisting coolant, and a foot control. It saves a lot of wear-and-tear on our hands.

 

ng8lap.jpg

 

Below is my honing area. There are only two of us in the shop and Don has his own honing area. We both do pretty much the same thing though. It's just that it's not uncommon for both of us to be honing tools at the same time. Our oil stones are frequently dressed with coarse diamond stones.

 

ng9hone.jpg

 

I hope this may answer some questions. I've been doing this for 19 years and have learned a few things.

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Wow lwllms.  That may be the best response I've ever seen in an online forum.  Thanks very much. 

 

I wish I was old enough to retire - I'd come over there and apprentice just to learn some of that deep knowledge.

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There was a question about diamond stones and there have been issues with some Cubic Boron Nitride (CBN) grinding wheels reported lately. I wasn't surprised by the problems people reported with  their electro-plated CBN grinding wheels. We have an oscillating diamond grinder in our metal shop and I learned an expensive lesson with it. I put a new wheel on it and wore all the nickel plating and diamonds off the wheel in about an hour's steady use grinding O-1 tool steel. The wheels run $160 or so. I was sure the wheel was flawed and called a the manufacturer's tech department. The tech rep explained the soft nickel matrix is designed to wear away slowly and expose fresh abrasive when grinding materials that generate a powdered swarf. This would include things like carbides, glass, stone, or ceramics.

 

Hi Larry

 

That's not the way I understand it.

 

Firstly, diamond is not recommended for carbon steel as the graphite in diamond is absorbed by the iron in the steel. This causes the diamond to wear at an astonishing rate. I would imagine that the diamond wore first on your wheels and, once that was gone, the nickel electroplating went.

 

I was the one to raise the alarm about the CBN wheels. They are amazing for lathe tools, which are often HSS, however the newer stye wheels with a radius at the sides are prone to a camber along the flat area. I suspect that this is caused by the machining of the radius (lifting the steel). The straight wheels are likely to be more reliably flat.

 

It strikes me that there are two methods of grinding: either have a thinner wheel with a convex face, along the lines outlined by Joel Moskowitz in his FWW articles several years ago. This would be the preference for someone freehanding the blade on a flat rest. I have done this for years. 

 

The other method relies on a perfectly flat wheel since a blade is moved across it parallel to the face, and this is the method used by the Tormek. I set up a CBN wheel to duplicate this, and it worked extremely well for time with the radius wheel. However it was a fluke as the wheel was dished and I must have got lucky with the set up ... until the rest moved. Then it no longer worked. The wheel was replaced by a straight wheel, carefully set up with the Tormek tool rest, and it is doing its job again. Frankly, I would be happy to freehand on one of these wheels if I could get a convex one. They are really excellent, and you should look into one - cool running and extremely long lasting. Nothing like diamond at all.

 

Regards from Perth

 

Derek

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Hi Derek,

 

I'm aware of the claims of many knife makers about diamonds being absorbed by steel. It's a myth.

 

It's true that carbon can flow in solid steel but the steel has to be at or above critical temperature for that to happen. One can also cause diamonds to change to graphite but it requires high temperatures and an inert atmosphere. Diamonds are pure carbon and they either have a diamond's crystalline structure or they don't. Synthetic diamonds often have traces of impurities but they can't be part graphite. Being pure carbon, diamonds burn like coal and have an ignition point of about 1330° F. The critical temperature of high carbon steels is around 1450° F. Before the carbon from a diamond could possibly be absorbed by the steel, the diamond would burn up. Diamonds are as good at conducting heat as they are hard, you're not going to insulate them. I don't remember the exact temperature at which diamonds can convert to graphite but it's above the ignition point. Fortunately we have a normal amount of oxygen in our shop's air so it's irrelevant to me. The only thing produced when pure carbon burns is carbon-dioxide so it probably appears to knife makers that the diamonds disappear when high speed grinding with diamonds.

 

It's the system of mounting diamonds and their ignition temperature that makes them unsuitable for grinding steel, especially high speed grinding. Our diamond grinder runs at 480 rpm and the diamond wheel is lubricated with WD-40 which has a lower ignition point than the diamonds. The diamonds on my wheel went away because the nickel matrix that held them in place went away.

 

CBN requires the same mounting systems as diamonds. Most of the CBN wheel sites I've seen say the wheels are intended for carbide or high speed steel turning tools. Given high speed steel's spark pattern when grinding I would guess it generates a fine granular swarf when ground. When I turn aluminum on the metal lathe I sharpen high speed tool bits on our diamond  grinder and haven't noticed wear of the electroplating. I keep checking it though.

 

BTW, our thin wheels with convex faces facilitate grinding concave curved profiles in molding plane irons. I also don't care to put as wheel as heavy as yours on one of our grinders, the weren't designed for it. One of the things one runs into when grinding as much as we do is the need to keep an eye on the temperature of a grinder's motor. When a grinder motor gets so hot we can't keep a hand on it we shut it down and work on other stuff for a while.

 

One other thing. I hope no one looks at my earlier post and starts looking at a Palmgren grinder to buy. They are a decent grinder if modified but dangerous if not. The inside and outside wheel mounting flanges aren't the same diameter and are different enough I wouldn't use one of these without turning new outside flanges for it. This is a violation of every set of grinder safety rules I know of. If you don't have a way to get some new 2 3/8" flanges made, don't buy this grinder.

 

 

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