Pot-stirring regarding grinders and burning tools..

[D_W]

I think I've probably bought more grinders and grinding methods than most people (not sure if anyone on here has played with more sharpening stones, either). My contention in the past (reminded by a recent thread on here about dry grinders) was that a dressed wheel of the coarsest grit you can find (and not a friable one flinging bits everywhere) was satisfactory for everything with the possible exception of carbide and high vanadium turning tools.

This past year, I bought two 1320 watt 8" grinders. They are scary powerful, and I'm glad that I didn't buy a 10/12 or 14 inch grinder as wheel failure on anything bigger must be a richter scale event.

At any rate, they are full speed grinders because I wanted to use them to grind annealed steel and shape metal, and two of them because one has a belt grinder attachment and a wheel, and one has a cutoff wheel to go with the grinding wheel.

Short story long....I also have a 6" baldor grinder with a very worn in 80 grit CBN wheel. You can burn something on CBN if you get in a hurry, especially if the wheel is as well used as mine.

To test my theory of coarseness rather than grade of wheel or hardness being the best idea for fast bevel honing, I dressed the A24 wheel on my 8" full speed grinder and just reset the bevel on three used japanese chisels. The A24 wheel will grind faster with less heat than my 80 grit cbn wheel at a much lower speed. With a light touch, it doesn't obliterate the edge of the tool with coarse scratches, and it burns only if you intentionally force it to burn something. Time to reset a bevel on each japanese chisel (these chisels were out of square or had very steep bevels on them) was about one minute with no overheating.

This is interesting to me for one specific reason - probably the best platform for grinding a hollow (and not to the edge) is any grinder (cheapest 6" with a two part rest or an add on rest is fine, along with the very cheap coarse wheels). It's cheap, and the more expensive stuff doesn't measure up. The only platform that I can think of that grinds cooler is expensive coarse belts on the belt grinder.

A hard wheel (cheap) on a grinder just needs dressing a little bit more often, but while I've worn my CBN wheel into slowness, the T-shaped diamond truing tool that I bought almost 15 years ago appears to be unaffected.

 

[Ttrees]

Hello David, regarding refreshing bevels
How far up the primary bevel do you grind to with your setup..
Do you work the last, say 3/4 to 1/2 a millimeter of the primary on a lap,
leaving just a line of the honed steel?
Do you leave a different amount regarding steel composition?

I recently watched Cosman grind a thick iron, Not sure what type of steel it was,
possibly the IBC or the wood river,
but he was grinding the iron with a lot of pressure with a CBN wheel,
I cannot find the particular video it was in yet, but was seriously impressed with the CBN wheel.

Now I've not ground such a thick iron before, but fairly sure I would blue the edge on my Stanley/Record plane iron's with the wheels that came with the new grinder with half that pressure.

Still way too frugal, not use my cheap wheels up though, and likewise to buy a dressing tool, which might be a good idea.
Having to get bit of steel to dress them is a pain, if I want to sharpen drill bits, or want a sharp corner on something, etc
so was thinking it might not be such a bad idea to have two wheels for the primary.
A cheap one of some description, and a CBN for close to the edge (only when they become wayy cheaper)

Although I think you said before that, the softer part of the laminated steel pulls diamonds out of the nickel, so that would mean a few tools wouldn't be suited, and those laminated irons seems to be the worst offenders for bluing for me.

I don't know why I've blued some irons before, using a consistent approach each time, nice hefty tool rest and water nearby.
It could be that my stone was glazed, I was thinking temperature of the workshop could make a difference?
Could just be my imagination , but seems like every time I burn something the workshop is cold, less than 10 degrees C, and rarely in the summer months..

I would be happy to use a lap for the last bit of the primary,
but there's a lawnmower in the way where the lap used to go ATM...
so I'm considering making something for the lap that would hold down abrasive paper properly taught, instead of having to use an adhesive or adhesive backed fancy paper.
That way I wouldn't have to have a designated place for the lap, so I could do away with having to clamp blocks down each end.
Not really thought about it yet, but I might do soon enough.

Tom

 

[D_W]

As far as the CBN wheels go, when I got mine, it ground so cool that the only way you could burn an iron on it unintentionally was leaving a corner on the center of the wheel and dragging the iron across. They slow down over time and mine (80 grit) is fairly fine cutting. It's the bees knees for refreshing the hollow of japanese razors where slow and fine is what you want, but it's about a fifth of the cutting speed and 3 times the heat that it was when new.

No clue how fast they wear for a person not making tools, but I do the annealed metal work with a traditional wheel to save the CBN wheel (traditional wheels are faster on unhardened metal, though - it's very hard metal that slows them down or glazes them.

I'd expected CBN wheels would drop in price as imports became directly available, but the wheel that I have (from wood turners wonders in the US, almost certainly made in china, but well made) with a radius on each corner is still the same price as when I got mine (and now taxes are assessed here on internet purchases, whereas a tabular end of year amount was allowed in my state if you didn't track individual purchases - it was pennies on the dollar given my hobbies vs. paying at the point of sale).

i'd expect someone just refreshing bevels may have the same wear level that I have after a couple of decades, but the initial really smart fast work that cosman shows will be gone for most people in a small fraction of that.

CBN really shines on turning tools and carbide, though.

re: how close to the edge? as close as I can get to it when I grind to extend the time between grinding. the first edge after honing is generally a fraction of a MM. I've never noticed durability issues unless a really coarse abrasive gets all the way to the edge and does damage below the level of the scratches. That's usually gone in one or two hones, but not very desirable if you hone only 3 or 4 before regrinding.

 

[Ttrees]

Thanks David,
So you're saying you don't use a lap for finishing off the grinding,
regardless of what composition the chisel/plane iron is made from?

Do you always try and get the primary that far, aiming for a fraction of a mm
of secondary bevel left, or might a laminated iron have a slighter larger secondary, after the first hone,
seeing as it is easier to work with using said hone.
Do you go straight to the washita on your plane irons, (if you don't have your buffing wheel at hand)

Cheers
Tom

 

[D_W]

Thanks David,
So you're saying you don't use a lap for finishing off the grinding,
regardless of what composition the chisel/plane iron is made from?

That's right. Everything is ground near the edge, including newly reset japanese chisels (they shouldn't need power grinding after that, but it doesn't hurt them).
My plane lapping sheet will do primary grind just fine, but it also generates a lot of heat if you use pressure. You can burn your fingers if you work too briskly (high speed and pressure), and make sparks if you try.

Do you always try and get the primary that far, aiming for a fraction of a mm

Yes, as close as I can get to the edge. If I completely remove the edge, that's OK. If the complete removal were to go heavily into the edge, that's where trouble occurs, but I don't think anyone does that. No difference between laminated, hard, soft, etc.

Do you go straight to the washita on your plane irons, (if you don't have your buffing wheel at hand)

Yes, unless it's not out on the bench. I don't use V11 much, but that's the only thing I can think of where the washita kind of poops out. I no longer have any A2 irons or tools except for a spokeshave, but A-2 doesn't tolerate washitas very well, anyway. It's the only steel I've used that gets bits pulled out of the metal by the washita (SGPS does, also, but nobody would ever use that in woodworking tools). I'm sure more of the exotic knife steels with big carbides would do the same (or reasonably sure).

When I make tools or do heavy restoration, it's not uncommon for the first edge or two to be full hardness but kind of chippy, but the bevel grind on those is often done with a heavy hand. I'd imagine even in annealed steel, harsh grinding can leave some cracks below the surface of the abrasions. (seeing this effect more drastically is pretty easy - cut nails with a plane iron or knife and things will look good once you hone out the damage, but then the edge above where the original damage was will also fail right after it looks great).

 

[Inspector]

I don't have the expertise you guys do but I have always found that a dressed wheel cuts cooler. To that end I frequently dress the wheels but I don't use the commercially available diamond dressers like D_W uses, as cheap as they are. I use a segment from a concrete/road saw blade. I asked nicely of a crew and was given a few blades, which is enough for many lifetimes of myself and friends. Cut the blade up with a cutoff wheel in an angle grinder, plasma cutter would be quicker, and dress the edges, then it is ready to impale in a quick handle. Ignore the little corner of granite countertop in the picture. Missed it when I cropped. There is about an 1/8th of an inch /3mm of diamond matrix on the edge of the blade. That segment is 8" / 200mm long so there are a lot in a blade.

Pete

 

[Ttrees]

That sounds interesting Inspector...
Do you use that for dressing the cheap grinder wheels or do you use if for the friable white or pink wheels?
Only remembered that I bought a set of these not so long ago for the wee angle grinder,
only costing a fiver for the box (Lidl), and wouldn't even need to cut them up.

Been looking for something cheap that would dress the wheels for a good while.
I will defiantly be trying this out
Thanks

Tom

 

[D_W]

That sounds interesting Inspector...
Do you use that for dressing the cheap grinder wheels or do you use if for the friable white or pink wheels?
Only remembered that I bought a set of these not so long ago for the wee angle grinder,
only costing a fiver for the box (Lidl), and wouldn't even need to cut them up.

Been looking for something cheap that would dress the wheels for a good while.
I will defiantly be trying this out
Thanks

Tom

View attachment 100783

The T shaped diamond tool direct from china is about $6US including shipping (partially due to our subsidizing of small items shipped from china). I don't know if it's quite as cheap in the UK, but it should be close.

Any soft annealed steel will strip the top layer of abrasive off of most wheels, too. Grinding tools annealed will create visible wear on my wheels. It's the hardened steel that doesn't allow the particles to dig in deeply enough to get pulled off.

The piece of material above also looks like a good idea.

Those T-shaped tools on ebay look like junk, but the one that I have was about $11 and it could grind several wheels down to the arbor before it would stop working. Even the 24 grit wheels don't beat it up.

 

[Inspector]

I have only used it on bench grinder wheels of all colours. I don't see why they wouldn't work on a disc grinder wheel but the wear on the dresser might be uneven but for the price so what. They would also work on grinding points, like Dremel and die grinders. As for the colour of the wheels it doesn't matter and industry use aluminium oxide wheels that are grey and are thee same as the white, pink or blue ones for the most part. Even the cheap wheels for breaking edges for welding cut better when dressed.

Pete

 

[D_W]

I'd imagine most of the difference is in the binder until you get to things like seeded gel wheels (but I doubt more than a few people use those - they're expensive and shed particles). I"ve had pink, white, gray and brown al-ox. It seems obvious to me that the white wheels are just white alundum. Not sure what makes the colors what they are in other wheels, but dressing a wheel is the equalizer in terms of making a hard wheel cut cool like a more friable wheel.

The virtue of the gray type wheel I'm thinking of (it has no ID On it telling its hardness, just "A4024" on the back) is that it's $27 for an 8x1 wheel and $16 or $17 for 6x3/4 inch. My cbn wheel was $125 ($150 now), a pink wheel that I had was $42, and I think seeded gel wheels are around $60 for a 6 inch type. All work fine, but the 24 grit gray wheel can double for grinding annealed steel and tool making.

I'm not likely to buy a CBN wheel for the larger full speed grinders, though they're not much more expensive - mostly because the point of both of those grinders for me is tool making either heavy wheel grinding or belt grinding. But it would be interesting to see how it would work full speed.

The general advice that I got when I started woodworking was that 8" full speed grinders would burn tools, but I didn't find that either with the stock wheel (36 grit, and harder, but fine when dressed) or the replacement that I put on it.

The white wheels here are generally for turning tools and make a lot of heat due to their smaller grit size in general (and they can glaze just refreshing one tool or sharpening one turning tool), but nobody with HSS turning tools is going to care much about heat, esp. since the exotic turning tools like 10V and high cobalt steels are even more heat resistant than the standard stuff.