Heat damage to blades when grinding...

[David Weaver]

One problem is that we really only find out the capability of the various methods when we try them - despite many being pushed as universal sharpening solutions.

The focus here is to sort out a good grinding solution, but we're maybe going to have to agree to differ on that one. The thread follows directly from my experience in the past couple of months in setting up a bunch of chisels and BU planes - using what I happened to have available.

It's not even a subtle issue - it's that a method that shifts steel fast enough to be efficient on a job like re-angling the bevel on a heavy plane blade is far too aggressive for safe (for the tool) back flattening and bevel grinding on a chisel. Or vice versa - that a WorkSharp (bought to put flat bevels on Japanese chisels, and doing that and flattening backs on them very nicely) simply hasn't got the clout for jobs like the heavy reworking of a plane blade described. As it happens I got by on the plane blades using the adapted disc sander described before, but it produces a hell of a lot of heat and forced dropping back to the WorkSharp to finish stuff once the bevel started to significantly thin.

Presuming that it occupies the magic minimal heat/high metal removal rate space (something I'm happy to accept) I'd happily use a coarse white wheel or even CBN on a dry grinder - but neither does the flat bevels I'd prefer to stick with, there doesn't seem to be a variety in either case that uses the flat side of the wheel (please say otherwise if this isn't the case), and anyway I don't have a tool grinder.

I've got this far, and can continue with what I have since it's going to be mostly about relatively light duty re-grinding of bevels to eliminate the honing bevel from here on - but I'm left looking at what is an unsatisfactory mish mash of solutions. There has to be scope for a one size fits all flat grinding solution. e.g. a belt grinder with variable speed that at one end of the scale cuts at about the rate of the WorkSharp, but that at the other can shift a lot more metal and not cost an arm and a leg for consumables.

There's no fundamental issue in that there's something that I need to sharpen that I can't - but my instincts very much suggest that there has to be a single/one stop/much more elegant solution possible that would allow the offloading of all of the half and high risk solutions….

Ian, you're just incorrect in this case. it's that simple. The only comment I'd have is back flattening is not something that should be done with any power sharpening. It's subpar with a worksharp from what I've seen, very subpar from a makita grinder, and subpar from the side of a tormek stone (I have specific experience with the last two).

Fascination with flat bevels instead of hollow grinds is also a lack of experience. You can prefer flat bevels, but they offer no practical advantage over hollow grinds. The rest of the perceived problems with a method that works both fast and plenty fine are just that, perceived...and imagined. You need experience at this point, not more supposition. You're not going to get much agreement from people with the experience you're lacking because your conclusions are wrong. Not as a matter of opinion, either. They are incorrect because they are proven otherwise in practice.

[Bruce Mack]

David, could you talk about a basic set-up, recommending grinder size and make(s), wheels, tool rests and/or jigs, truing tools? I'm not sure I want or need to do this but do want to think about it. Thanks.

[David Weaver]

* Low speed 8" grinder or high speed 6" grinder. The make isn't that important, an import grinder is fine, just don't use the cheapest looking thing you can find because it'll have trash rests and a very low amp motor. $100 will get something 6" and import that's pretty good. i don't know what the price of the 8" slow speeds are, but they probably have wheels for turners on them instead of hand tol users, anyway.
* 46 grit wheels of moderate softness. Best I've seen so far are pink surface grinder wheels, but they are not cheap. it's nice to have one on one side and a harder wheel on the other for tool making or heavy grinding.
* dresser can be anything - I use the cheap T grinder that you can find on amazon. It strips the wheel of glazed abrasive fast
* need two piece rests. I use stock rests, nothing else. Everything else, actually, is a nuisance to me. When I had a cheap import grinder (I have a baldor now), it had two piece aluminum rests with detents. I ground the detents off so that it wouldn't settle in at specific angles and it was fine with the aluminum stock rests. I didn't really need to get a baldor, but I guess I was into treating myself, and at the time, baldors weren't that expensive (mine was about $270 or something as the 6" grinder with cast guards and cast two-piece rests. I think they want the moon for them now).

That's pretty much it. Keep the rests free of rust or anything sticky and keep the wheels dressed fresh. The remainder of the equation is just touch, and not that much of it is required. That and experience (and not that much of that is required, either.

[Bruce Mack]

Thanks David. I think I'll do it. Just had apparently successful back surgery so will wait until I get clearance for lifting, probably 3-6 months.

[ian maybury]

Think there's cross purposes involved here David, and it'd be a pity to end up arguing. I can assure you that a WorkSharp can do an excellent job of flattening chisel backs when correctly used. Anything that gives good control, removes material fast enough to be reasonable (multiples of the rate of removal by a 120grit waterstone), puts in minimum heat and creates a surface flat enough to subsequently clean up all over in a minute or two on a 1,000 grit waterstone can't be doing a bad job. It requires a fair degree of finesse in use, but if you too found yourself with little option but to work through a full set of chisels (bought some years previously, left untouched as a result of illness/other priorities and past being returned) with unexpectedly badly humped backs one after another you would likely find yourself quickly looking for a power assisted back flattening method too...

You're a better man than me though if you can get a WorkSharp to remove the large amounts of metal needed to reset the bevel angle on a thick BU plane iron within a reasonable period of time, and without requiring a second mortgage for consumables. Especially at UK £ to dollar prices. I wouldn't think of trying to use it to flatten the back of a plane iron unless it was very close already, it's just not big enough. Luckily the issue hasn't arisen given the excellent flatness and surface finish of Lee Valley BU plane blade backs.

For sure it's also possible to correctly grind a small tool on a high speed high heat inducing grinder - it's only a matter of reducing the pressure and contact time enough, and of achieving accurate alignment from first touch. It's clearly not the preferred option though, because it all becomes a very touchy operation - you wouldn't be using pink low heat low heat stones on your own grinder if it was.

It seems clear that what you describe is a proven high speed/low heat solution, but it's hollow grind.

You may well be correct that a hollow bevel is OK on japanese chisels (and it's clearly very convenient), but there's an awful lot of people out there that would (rightly or wrongly) beg to argue that it's not a good idea. I don't have a firm view on the matter. The decision to sharpen my set of chisels single bevel was entirely pragmatic. i.e. it was made on the basis that (as a person new to Japanese chisels) I wasn't if I could help it going to risk finding out the hard way that there is good reason for the caution about hollow grinding them.

I'm not keen on using all sorts of different bits of equipment if I can avoid it, hence this thread in the hope of flushing out some one stop flat bevel grinding solutions (a variable speed belt sounding very promising because it should be able to handle the more delicate tasks done by the WorkSharp, and also the faster metal removal with low heat build up that's useful for working heavy blades) - but don't mistake my floating a question based on a line of thought for dogmatism or some sort of fascination.

It may or may not prove a good option in practice, but it seems worth a look before discarding the possibility. One option should it prove impractical would be to trial a few chisels with a hollow grind and see how that goes...

[Reinis Kanders]

I use worksharp with foot pedal and 100 grit diamond plate and it works pretty well for flattening backs of the blades, but I only flatten first inch or so. Seems to work, same for chisels, but there I flatten a bit more than inch. Everyhing seems to be sharp enough. I mostly work with soft HD pine, fir, cedar or soft maple because that is all I have around here within a 45 min drive.
Diamond plate also dissipates heat better and I vacuum off swarf from it while flattening.

[Chris Parks]

I have a question for Derek, is the linisher you are using high or low speed?

[David Weaver]

Think there's cross purposes involved here David, and it'd be a pity to end up arguing. I can assure you that a WorkSharp can do an excellent job of flattening chisel backs when correctly used. Anything that gives good control, removes material fast enough to be reasonable (multiples of the rate of removal by a 120grit waterstone), puts in minimum heat and creates a surface flat enough to subsequently clean up all over in a minute or two on a 1,000 grit waterstone can't be doing a bad job. It requires a fair degree of finesse in use, but if you too found yourself with little option but to work through a full set of chisels (bought some years previously, left untouched as a result of illness/other priorities and past being returned) with unexpectedly badly humped backs one after another you would likely find yourself quickly looking for a power assisted back flattening method too...

You're a better man than me though if you can get a WorkSharp to remove the large amounts of metal needed to reset the bevel angle on a thick BU plane iron within a reasonable period of time, and without requiring a second mortgage for consumables. Especially at UK £ to dollar prices. I wouldn't think of trying to use it to flatten the back of a plane iron unless it was very close already, it's just not big enough. Luckily the issue hasn't arisen given the excellent flatness and surface finish of Lee Valley BU plane blade backs.

For sure it's also possible to correctly grind a small tool on a high speed high heat inducing grinder - it's only a matter of reducing the pressure and contact time enough, and of achieving accurate alignment from first touch. It's clearly not the preferred option though, because it all becomes a very touchy operation - you wouldn't be using pink low heat low heat stones on your own grinder if it was.

It seems clear that what you describe is a proven high speed/low heat solution, but it's hollow grind.

You may well be correct that a hollow bevel is OK on japanese chisels (and it's clearly very convenient), but there's an awful lot of people out there that would (rightly or wrongly) beg to argue that it's not a good idea. I don't have a firm view on the matter. The decision to sharpen my set of chisels single bevel was entirely pragmatic. i.e. it was made on the basis that (as a person new to Japanese chisels) I wasn't if I could help it going to risk finding out the hard way that there is good reason for the caution about hollow grinding them.

I'm not keen on using all sorts of different bits of equipment if I can avoid it, hence this thread in the hope of flushing out some one stop flat bevel grinding solutions (a variable speed belt sounding very promising because it should be able to handle the more delicate tasks done by the WorkSharp, and also the faster metal removal with low heat build up that's useful for working heavy blades) - but don't mistake my floating a question based on a line of thought for dogmatism or some sort of fascination.

It may or may not prove a good option in practice, but it seems worth a look before discarding the possibility. One option should it prove impractical would be to trial a few chisels with a hollow grind and see how that goes...

I'm not defending the worksharp, I think it was popular for reasons that I don't know, and for a while it was really popular. I'm describing a dry grinder as the only power sharpening tool anyone needs to have in a shop to work quickly and without damaged tools.

A couple of other items:
* Japanese tools shouldn't need a grinder at all, they are designed to be honed on the full flat bevel with very soft metal backing the iron. I haven't had to grind a tool that's in use in several years (in terms of japanese tools) and have only ground an inexpensive jack plane and some used or cheap irons that have showed up far out of shape. The plane that I have set up like a jack does get ground with a dry grinder from time to time with no ill effect.
* backs on all tools should be lapped by hand - it needs to be done only once, and it's best if it's finished on whatever will be used to polish the wear off of the back of an iron. If someone uses a worksharp from A to Z every time they hone, then it may be appropriate for flattening backs because there will be no stone for it to disagree with.

The case that there is no damage to blades off of a dry grinder with an experienced user is not dogmatism. The opposite is nearly true. For years we heard about dry grinders burning edges and hollow grinds being weak, and things didn't change until there was a magazine article about using a dry grinder. As far as the hollow goes, there still seems to be people believing that there may be some weakness from a hollow off of a 6" in diameter wheel, and that's not the case. I challenged the entire forum over a period of years to show damage on any edge that was suspected to be due to a hollow grind on any common grinder in use and there has never been any.

I used to trouble over the same thing and try to set my edges so that the lowest tangent off of the hollow would be as great as what I would've had for a flat bevel, but all of that stuff is such a waste of time.

[Derek Cohen]

Hi Chris, by linisher I assume you mean the belt sander. It is such a basic machine that would not give it a more prestigious name!



The first machine I purchased was a cheap sander for wood and intended solely as a grinder for blades. I could not justify spending more on a linisher for metal. It developed electrical problems and the store took it back and I spent a little for a better model. This has 1 hp and runs at 1400 rpm.

Again, it was erely intended to grind metal. The graphite plattern was removed to work on the flat cast iron. The belts used ranged from 40 grit upward. It worked very well as a grinder: relatively cool - much more so than a dry grinder wheel - and the jig I built was accurate enough for repeating a bevel angle. I still have it, but now it is mainly used for the disk sander. I stopped using it when I started freehanding blades more regularly and discovered that a hollow grind was easier to use in this regard.

Regards from Perth

Derek

[Chris Fournier]

Those sparks indicate heat being REMOVED from the blade. It's the heat that remains that is the issue

Someone has actually learned about sharpening, but likely not from a woodworking forum! Sparks can fly and you can still touch the cutting surface when all is right.

Get the right bond, frialbility, and 46 to 60 grit will serve you well forever on WWg tools. No need to ramp things up to anything fancier unless you are sharpening HSS all the time. Even then CBN is not a must, nor is diamond. I have CBN in my machine shop for use on carbide, all HSS for th elathe and mill gets the AO cup.

Folks over complicate and invest in sharpening processes all the time. KISS and trust the time honoured methods, you'll be just fine and missing out on nothing from a practical standpoint. Bragging rights? You may be second in line.

[Chris Fournier]

Ian, you're way over thinking this, there is no point where you'll have any practical problem with a dry grinder unless all get and swarf must be captured.

You don't need to hone off any appreciable amount with the stones, either. I don't, and I grind right to the edge and did when I used a cheap gray wheel. It just needs to be coarse and dressed. I don't even keep water at my grinder.

I have been waiting for this for some time David! The pot calling the kettle black. Over thinking is stock in trade around here if you know what I mean, and "practical problem" had me bent over gasping for breath between peals of laughter. Thank you for the comic relief, contextual of course. Nonetheless you are absolutely correct, there is "overthinking" afoot, it thrills me that you recognize this!

[David Weaver]

Reggie Jackson strikes again!!!..."pselling" error and all.

[Chris Fournier]

Reggie Jackson strikes again!!!..."pselling" error and all.

It was a pie cooling on the window sill David, too good to pass up. "Reggie Jackson" was a nice touch! I had to Wiki him to get the full meaning.

All future pies will stay on the sill. Chris.

[Noah Wagener]

[QUOTE=ian maybury;2324887

It's early days for me on the white steel chisels David, so it's not a case of having a firm view. A coarse stone that will hand regrind bevels fairly quickly sounds like a good test. Perhaps it's because so far i've mostly been forming/re-angling bevels, but even the Shapton 120 seems a little slow though. Wonder if a coarse Crystolon would do any better?[/QUOTE]

I happened across an Australian forum where Stu Tierney wrote that a Sigma 120 is about as fast as a powered grinder. I do not know if your Shapton is a glass stone but he also wrote that that stone (the 120) is rubbish. i would think Crystolon stones need to be very friable as they are silicon carbide. The sigma apparently does not wear yet maintains speed.

[Noah Wagener]

I wish i would have read this thread a few days ago. I bought an 80 grit grade k stone and it is not much better than the gray wheel. Despite the claims that i will never blue a tool; on thin bevels it gets hot in seconds and the grinder is only foot powered. It is a neat feeling how the hollow ground bevel registers on the stone though.