Heat damage to blades when grinding...

[ian maybury]

Brian's thread on choice of chisels just set me thinking. I'd always thought it was just that I was using cheap chisels, but it starts to look like even good quality chisels sail pretty close to the wind so far as edge damage is concerned when working hardwoods. My white steels don't much like paring plywood for example. Which while it's known to be hard on edges you would imagine might not be that bad.

Guess I'm wondering if there's perhaps not more of us than realise it cooking the edge a little when sharpening, and consequently working almost all of the time with a less than optimum steel condition?

The reason for this suggestion is that when push comes to shove the action (both sharpening and cutting) really only happens at the last thou or two of the edge. It's got to be very hard for heat to conduct itself away from an edge that fine, and equally be very easy to in just this very localised strip get up to decent temperatures without causing noticeable bluing etc.

Many of us use e.g. our finger, or water boiling off to detect heat. Which by definition requires heating quite a large area, and implies that the actual edge may be getting a lot hotter. Even taking a lot of care like I did - on a Work Sharp running at 500rpm, and cooling in water after a few seconds of grinding - and not grinding right to the edge.

There's also the possibility that even if the heat treatment of steel was spot on that factory grinding (presumably liquid cooled?) might have messed it up a bit.

Wonder has anybody ever done the metallurgical analysis to determine what actually is going on, and determined just what is permissible and what is not? I'm not all that comfortable with most dry bevel grinding options for example - but maybe I'm being over cautious...

ian

[David Weaver]

It's pretty easy to determine practically if you're doing any damage of an appreciable amount. You can either get something like a tormek, or hand grind for a while with a norton crystolon.

I haven't seen any difference in edge holding between the first edge off of a grinder or a chisel that hasn't see the grinder for years.

I can literally put anything that I grind in my palm, though - the amount of grinding that occurs on a maintenance grind is very little and should never trouble an edge - even on a gray or brown stone (as long as said stone has been freshly dressed).

The fact that some things trouble edge is a combination of:
1) the act itself being beyond the strength of the edge (which is often a matter of a few degrees of extra bevel)
2) the act being carried out improperly, as in twisting or other than linear blows with a hammer

when you work something and you want to do something abusive while working, that's a good time to have high speed steel chisels.

Take a look under a loupe with bright light and see if you see light straw anywhere near the edge. If you don't, you've got no problems, though my practical test above is better - so long as the final bevel is equivalent on a chisel that sees a grinder and one that doesn't. that probably requires a honing guide.

Talk of burning edges has sold a lot of tormeks to beginners, but functionally, it's not a problem in the shop for anyone (or at least most) with a moderate amount of experience.

[bridger berdel]

The flip side of this question is to ask what is happening when I badly blue a chisel on the grinder, hone it anyway and see no difference in performance. Not that this happens much, but yes, it has happened.

[ian maybury]

That's a fair question too Bridger. Maybe the reality is just that chisels in general walk a fine line between edge failure and optimum performance.

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?

I have a Tormek too, and it works very well - but haven't so far got serious about finding a solution to the problem of how to accurately flatten/dress the sides of the stone (my chisels are sharpened single bevel - so i don't use the wheel in the normal format as i don't want hollow bevels) - and how to align tools. A horizontally mounted Tormek would be great, but then there's the issue of handling the water. Plus I like to be able to use a honing guide when forming the primary bevel as on the top surface of the WorkSharp. That's more or less Makita territory, but realistically I don't want to buy another grinder so it's probably down to finding a way to re-configure the Tormek.

Surprised that somebody hasn't done it already….

[Ron Brese]

It's usually recommended that when grinding a tool that's been previously honed that you don't grind all the way thru the edge and leave a small line of the polished edge unground. When you put this tool bevel back on the honing stones you work thru the polished edge that's left and pull a burr quite quickly. This of course serves a couple of purposes. It keeps you from cooking the fine edge and you also don't have to hone away the coarse grinding scratches. Using this method the edge just becomes more refined each time you work the iron.

Ron

[David Weaver]

Those side wheels on the tormek will get tired pretty quickly.

The reality with japanese chisels is that you should work with them until you are not getting any damage that can't be removed easily with a medium stone (like 1k type stone) and very quickly.

You can hollow grind them fine with the tormek, but it's unsightly.

You can hollow grind them on a dry grinder if you can keep them below about 125C but it's generally not needed, and anyone who will burn an O1 tool will burn white steel earlier, or at least draw out some of the temper.

I have dry ground white steel irons with the pink wheel with no issue and no noticeable loss of hardness, but I do that only when I get a used iron that is in serious disrepair (which includes things like having a big rounded bevel on the back).

[Bruce Mack]

I am reluctant to get a grinder to prep my irons for waterstones. #1 reason is cowardice--I expect my learning curve would result in trashing a few favorite blades, even starting with a sacrificial iron from, say, a Home Depot loser. #2 is the expense of a new shop machine with its necessary berthing on a table/bench that is already crowded,
Like Ian, I use a Shapton 120, but chiefly to flatten the bevel using the side sharpening technique to take the belly out after "excessive" rounding from my freehand sharpening. This works well and fast. For my LV low angle bevel up smoother I have several blades, 25 and 38 degrees, so don't see a need for further angle adjustments as would be facilitated with a grinder. My Precious is the LN 4 1/2 bevel down with 45 degree frog. With cap iron set close it seems to handle all domestic woods I use. No back bevel for that baby.
Just an amateur's view.

[ian maybury]

Thanks Ron, David. My view is strictly amateur too Bruce. I'm very much at the getting to know you stage with both the waterstones and white steel chisels, and have just come off a major back flattening and bevel setting exercise which has probably coloured my perceptions on how long it all can take a bit. I also ended up having to reset the bevel angle on three very thick 50 deg Lee Valley O1 and A2 BU planes irons bought some years ago before the realisation had dawned that the 25deg does most jobs, and that steeper cutting angles and cambers are best put on over that in the form of a micro bevel. This turned out to be very hard work indeed, even using an 80grit sanding disc for heavy metal removal - although it was entirely down to my making bad buying choices. The quality of the LV BU blades is actually incredibly good.

I'm relatively well aware of the practice of not grinding back through the bevel when re-honing Ron - although i had no choice but to do so given the pretty haphazard (too shallow) bevel angles on some of the chisels to be brought back to 30deg. Against that I took a lot of care on the WorkSharp as above - what most would regard as OTT.

I guess the question about heat damage was intended more to explore the question of whether or not in situations like this (since so many report fairly rapid edge degradation, even on good chisels) it's posible that we unwittingly disturb the heat treatment in a micro zone right at the edge when shaping the bevel - even using what are normally regarded as conservative and acceptable methods such as those you describe David. Or that (as seems well accepted) the makers sometimes do when grinding - it's not unusual to hear reports of this.

Either way as both yoursef and Ron suggested earlier the proof on that particular one will likely emerge with successive re-honings.

On grinding solutions David. It sounds like your experience (and the common wisdom) is that it's possible to use any of the above methods provided care is taken and the edge is not cooked - with the underlying point being that now that the tools are set up grinding will be a very rare requirement anyway. That said i guess i'd have been dead pleased if somebody had piped up to say 'use an xyz stone, that's really quick' - that there is a wet manual (safe) option about that cut fast enough to be an alternative when there's a lot of metal to come off...

I did fine with the 80grit sanding disc on the wide and thick plane blades - switching back to the WorkSharp once the edge started to thin a bit to head off the risk of overheating. Very easy to overdo it though - as Bruce dry power grinding makes me nervous. Seems like it's just another skill to be refined for use when appropriate. The Tormek likewise works as a route, but is surpisingly slow. Ditto the 120 grit Shapton. When blade thickness and width (volume of metal to be removed) come into play there doesn't really seem to be a one size fits all solution except perhaps a surface or similar toolroom wet grinder...….

[Kees Heiden]

It's probably inevitable that you overheat a narrow part of the edge on the grinder. All those sparks indicate pretty high temperatures. But that's one reason why we continue on a whetstone. You remove that overheated layer quick enough. I don't find that I loose hardness, not even in the white steel Japanese chisels.

[Jim Matthews]

I use the Knife grinding set from Lee Valley, with the 1" belt running vertically.

It's only needed on the most badly damaged blades.
I keep a coffee can of water to dunk the blade,
every few passes.

Haven't taken the temper off any steel, yet.

Start with a medium grit belt, or charged leather belt
if you're concerned about overdoing things.

FYI - It's the means by which I reliably camber plane irons, too.

[David Weaver]

I have never used the worksharp, so I don't know what it does to burn things. The two fastest burns I have ever seen, or three, I guess are:
1) high speed belt grinder with a hard platen - you will get extreme heat at the contact point if you use any pressure on anything but fresh abrasive. Instant blue
2) disc sander (seemed like a good idea, but probably the hard platen thing again)
3) a fine grit wheel on a bench grinder

As far as changing a bevel from 50 to 25 degrees, that's a lot of work no matter how you do it. The fastest thing I can think of with low heat is a cheap belt sander with really coarse grit - no super tight belt over a hard steel platen. But once you do that grind once, you never do it again. A coarse wheel on a bench grinder is a better compromise.

Far as the side of the tormek wheel (maybe I said this or maybe I missed it earlier), they go to sleep pretty quickly, and if you try to put a diamond hone against the side of the wheel it will just eat the hone (i've tried it). You'd probably have to take the tormek wheel off and rub it on a sheet that was covered with loose abrasive that is very coarse. Like 40 or 60 grit silicon carbide.

The alternative is to hold something like this against the wheel, but it would take a while to do the whole wheel:

http://www.amazon.com/POWERTEC-71003...iamond+dresser

(I've been using a dresser of that style for 6 or 7 years now on the bench grinder, and I was sure that it wouldn't last very long, but it's held up well and I'm still using the same one, and I used it on the tormek a little bit, too, though it's a bit coarse for that).

Ian - the comment about just having experience is correct. I think you'll (if you want to grind with a bench grinder) gravitate toward a coarse wheel that is either soft or that is hard but that is dressed often, and you won't even see temper colors near the edge of anything, let alone blue. You won't be able to do this correcting a bevel, but in my opinion, maintenance grinding on anything results in a tool that you can put into your palm after you grind it if the wheel is coarse enough and dressed well enough.

[ian maybury]

Sounds like the potential micro burning issue is a dead duck anyway - if only because it's easy to hone away as you guys say.

I can agree about the fast burning scenarios - but despite this as above did fine on the early stages of heavy metal removal re-angling the bevels on the plane blades on a sanding disc on 80 grit AlOx. It'd burn the edge or a corner in a moment once it starts to thin down towards the edge though. Keeping the entire area of the bevel in contact at all times is important too to stop burning - i used a honing guide off a DIY perimter table. I did one on a Bosch variable speed belt sander with 80g AlOx - the 200m/min variablke speed gives good control, but it needs the right platen and flush jointed belts. I also hollow ground a plane iron on the Tormek, and then flattened the bevel on the WorkSharp - works OK too, but slower.

I managed to demolish a diamond plate trying to dress the Tormek wheel too. Tormek do a carborundum dressing stone too which might work. Or maybe set up their screw fed point diamond in an appropriate way. I haven't done anything about trialling a set up to use the side of the wheel as a primary flat bevel grinder because it's a bit slow and apart from the water didn't seem to bring a lot to the party.

The Worksharp (working with a honing guide off the accessory top surface/table) actually does a very decent job. A slowish surface speed (around 500ft/min) means it doesn't heat all that much if the abrasive is kept fresh (you would have to be heavy handed to do harm), and the level of aggression is about right for chisels. It's very slow to remove significant amounts of metal from a plane blade though. The self adhesive abrasive discs get very expensive over here, and diamond discs while cooler are probably not a great deal more cost effective as they don't last as I had hoped. (on heavier jobs like plane blades anyway)

The one size fits all primary bevel grinding solution (capable of forming a plane bevel as well as doing maintenance grinding right down to small chisels) remains elusive it seems, especially when the preference for a flat bevel is factored in…. (low speed bench grinders with soft wheels sound like a candidate if a hollow grind is OK)

[lowell holmes]

I have a variable speed bench grinder, but seldom use it.

If I need to re-grind a chisel, I will put it in a honing guide and turn a belt sander upside down in a bench vise, and then grind it on the belt.

Afterwards, it will be honed in 3 grades of diamond hones. After stropping on mdf charged with green honing compound, the bevel is mirror finish.

This is the only time I use honing guides.

[David Weaver]

The one size fits all primary bevel grinding solution (capable of forming a plane bevel as well as doing maintenance grinding down to small chisels) remains elusive it seems, especially when the preference for a flat bevel is factored in…. (low speed bench grinders with soft wheels sound like a candidate if a hollow grind is OK)

Use of a bench grinder with coarse wheels satisfies everything except the flat grind. There is no real advantage of such a flat grind, though, and with the smallest of chisels (less than 1/4" and even those), it may make just as much sense to hone those without grinding.

A knife grinder/belt grinder would also work instead of a bench grinder if you want a flat bevel and are willing to keep a coarse abrasive belt on it and learn where you can finesse it to avoid burning.

[ian maybury]

That's the way my train of thought is headed too - but so far I'd rather stick with the flat bevels. Already have a variable speed Bosch belt sander which doesn't get a lot of use on other stuff.

Sounds like the trick may be to get it set up properly - to organise some fixtures etc.

The Tormek is 10 years old but not much used. (i always did the planer thicknesser knives on it - but until the waterstones hand sharpened hand tools on diamond plates) It'd be nice to sell it, but I have most of the fixtures which can be adapted to other devices and no doubt no sooner than it would be gone some need or other would arise….

Thanks again David/guys, it's always great to be able to bounce stuff around. It's always tempting to think that El Dorado in whatever field is just around the corner, to question the status quo...

ian