Many years ago, my brother in law, who was a mechanical engineer / toolmaker, gave me a bag of 'case hardening powder', which I still have. Does anyone know what exactly this stuff is (it's white, and if the police got hold of it, I'd probably be locked up whilst they determined just what it was ...) and how to use it ? I got to thinking about it today, when I was stoning the edge on a chisel ready for use tomorrow on a job. It occurred to me that once the original factory edge has gone from a wood chisel or plane blade or whatever, and you've resharpened it, it never seems to last as long again as it originally did. Is this because they harden the edge when it's made ? Is it appropriate, or even possible with home DIY facilities, to harden the edge once it's been restored ?
Chisel blades are made from carbon steel that is hardened by heating to cherry red heat and plunged into water, or oil to harden it. After this, the blade is heat treated again until it goes blue and cooled again. This makes the whole blade hard enough to take a good sharp endge. Where you might be failing is in not getting a good edge by not using a suitable sharpening stone and ending up with rough cutting edge that wears very quickly.
Moving on to the case hardening powder you have, this will consist of animal bones. The same carbon which was added to cutting blades when the steel was made. This carbon is distributed all the way through the steel, unlike case hardening that is only skin deep and is no use for hardening anything, unless it only requires a skin hardnes adding to it
The concept is to raise the steel to a certain temp at which it can absorb the carbon from the powder. This gives a low carbon steel a high carbon outer layer. The steel is then reheated and quenched to harden it. The inner core remains a low carbon softer steel. It is likely that a chisel is made from a high carbon steel so "carburizing" it with this powder would have no effect.
Which is the reason why it preferable to use a low speed wheel to sharpen a wood chisel or plane iron before honing it on an Arkansas stone or similar. Once overheated it is almost impossible for the average DIYer to restore the correct temper to the chisel/iron.
No idea. Never heard of the stuff - in white at least.
Kasenit is the usual case hardening powder. Greyish, maybe describable as light brown , and stored in tins because it doesn't enjoy moisture. It's very easy to use.
Cyanide hardening compounds are (IMHE) supplied in pellets, not as powders (or made up in solution) - again because of moisture. They're safe enough to handle (keep away from moisture and especially acids), but they are a hazard to work with. Like cyanide electroplating solutions, they're beyond most home workshops.
The only common white workshop powder I can think of would be silver- soldering or brazing fluxes - fluorides.
Case hardening is best used to make mild steel components more wear- resistant. It's a poor way to make cutting tools. It's also a poor steel metallurgically, and as good steels are cheap these days, you're better making tool edges from the good stuff directly.
The powder itself is a secret recipe that has changed in the last few years anyway. It's broadly a mix of a carbon donor (hoof and horn, but _not_ bone) and also a carbon dioxide donor (barium carbonate), possibly also a nitrogen donor, i.e. a cyanide.
If you have case-hardening powder, there are two ways to use it. The best way is to pack piece and powder into a sealed iron box, then roast the lot in an oven for some time. No-one does this. People who used to do it commercially, now use liquid baths instead. The workshop way is to heat up the workpiece to a dull red, then immerse it in the tin of powder and leave it to cool. Repeat for deeper diffusion. Avoid the fumes. Then harden and temper the workpiece as for a higher carbon steel.
sorry - not bone - Hoofs and Horns.Cyanide was used in my Toolroom - as a bath of molten cyanide salts. Provided a hard surface for gauging points , etc.. Not for cutting tools.
It's quite amusing reading some of the comments about secret recipes of potions and powders for case hardening, and for hardening and annealing/tempering metals. Whilst not being by any means an expert - big subject - I worked testing metals in a lab for a while, and actually had to measure thickness of the case hardening on mild steel strip: we cut the strip into randomly selected small sections, then encapsulated them in perspex cylinders with a nifty hot press (also handy for making souvenir coin etc key fobs) cut it in sections; polished to mirror finish; etch in conc HCl or similar, and then inspect under microscope and measure dark edge. Also had to try and measure hardness across the strips too - measuring the diagonals of a square produced by diamond with weights attached. Pain in the neck actually, and hard statistical work in the days when a calculator was a curiosity only affordable by devoted Sinclair fans... ah the little red lights... memories...
Anyhow, secret white powder you can all use next time to make a big hole in a wall and don't want to pay out for a drill you only use once? You have it by the kilo and it begins with S and ends in r. You got it. I'm surprised nobody has mentioned the trick for putting water pipes through walls: probably all spoiled rotten by power tools! Standard piece of iron water pipe - prob should wear mask as often lead lined: cut a jagged end of rough teeth on a length long enough to go through wall; blowlamp on end with said teeth till red hot - or hot as it gets before the gas runs out; dunk straight into pot of sugar, Lots of candyfloss smells and smoke and flames, so not to be done near your petrol cans or old newspapers! Actually any suitably coating carbon source will do, and old engine oil was also favoured by some, but sugar works fine and I generally have a pot of it in the garage for odd bits and pieces that want toughening. At a pinch you can even make your own springs...
I found that a dunk or two in the sugar bowl enabled me to bore through a cavity brick wall fairly neatly with the hammer and turn method similarly used with the old rawplug tools. Probably not quite as neat as modern drills, but such things were way beyond the pockets of mere mortals once upon a time, before those wonderful Chinese people caught the capitalist bug.
As for sharpening chisels and plane blades, it is quite hard to hold them at the 25 or 30 degrees positions by hand (and for drills very mindboggling, but you can get an eye for the angles in the end), but I have a very handy little clamp on a roller made by Eclipse, that you clamp your chisel or plane blade in; make sure the correct length is projecting for the angle in question, and then you roll it up and down your series of oil stones until all is razor sharp and satisfactory. Always start any job with sharpening the chisels and plane blades: satisfying and saves on lengthy once in a blue moon regrinds.
And while we are on blue. The hardness and temper of steels is of course ultimately dependent on their composition: some can be so hard it is difficult to find anything to cut them with once they have been heat treated (skilled metallurgists can get a good idea of the composition/hardness by looking at the colour of the sparks as they grind: not me). When grinding with a grindwheel always have a pot of water handy and keep dunking. For heftyish things like cold chisels dunk well before your fingers get hot or you will make the end so brittle it just snaps off when you hit the other end. With screwdrivers it's even more fussy as they heat up very quickly and are easily ruined, and will either snap as soon as you turn them, or twist like cheese (if it was only a cheap case hardened one). There are tables of temper colours for different purposes 'straw' coloured tending to be harder than 'blue' for example - but again varying with the metal. Straw just at the tip, for cold chisels, and grading into blue behind, to give a little bounce rather than snap...
Indeed, and I've learnt a lot - thanks all. The particular chisel in question was only a DIY shop 'cheapo'. I have sharpened it regularly, but only ever on a coarse / fine two sided oilstone, so not been overheated on a wheel. I wouldn't say that I am 'artisan skilled' at blade sharpening, but we were taught it at school in the woodworking classes many many moons ago, and I think that I am pretty fair at getting a good edge at about the right angle. My test for a good edge is to see if it will cut a piece of bent paper across its whole width. If it does, that seems to me to be a good enough edge for construction level woodworking. Cabinet making might be a different story, but this chisel is usually just used for things like lap joints on soft pine.
From what's been said, it is probably either just my imagination, or my lack of skill at precision sharpening, that makes it seem like the edge doesn't last as long as when it was new. I just assumed that being a cheapie, it was made from a low quality steel, and had just had its edge hardened originally, and that over time, I had stoned that away. I'll be doing a fair amount of chopping out with it today, so be interesting to see how it holds up.
If it's a real cheap cheapy it's entirely possible it was case hardened back where it was born in China. There is a shipment of nasty Chinese hack saw blades lurking in the small shops / boot fairs that cease cutting after the first few strokes as the case is very very thin!
I thought I was quite good at manually gauging blade angles until I got the sharpening guide. If they are still available they are well worth having. One thing they can help prevent is the end of the blade getting out of square, which is a pain in the neck in a plane blade, when you soon run out of adjustment on the side to side lever. You will almost always get a curve rather than a level angle with 'bare hand' honing too. Getting it back level and square again can be a long job, but if you always sharpen at the same set angle the problem is minimised (yes you can still press harder on one side than the other even with a honing guide). And, it is worth having a jig for drills too if you do a lot of drilling.
OK, here's the update. Chisel has performed absolutely fine all day, and edge still seems ok, despite there being a knot at just about every bloody place that I had to chop out, Why is knot wood in otherwise sos pine, so incredibly hard ?
That is a very good question. Thinking about it: the new trunk rings of the tree have to work their way out around the side branches; sort of making a sleeve around them and then needing to seal it all up with resin as they go. Interesting thought.
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