Making Kitchen Knives – Part 14 – Straightening Curls

Last time I was working on this project, I had some very bad results from quench. This week I have finally managed to test one idea of correcting the problem and maybe prevent it from ever happening again in the future. And I am glad to say that it did work. Not perfectly, but the new process is definitively worth to use instead of the old one.

Here is first the comparison of the three worst blades before and after. As you can see, there are still some curls in there, but they are noticeably less pronounced and one blade is almost completely straight. They will still come smaller than intended out of the polishing process, I will still have to remove some material from the edge until I get to the straight part, but I estimate it to be about 1/2-1/3 of what it was before. On the worst blade, the curls went about 10-15 mm from the edge towards the spine, whilst now it is about 3-5 mm. That is a significant improvement, and I think that had the blades been quenched from a straight form, they would never have curled in the first place.

As I alluded to previously, the process that I wanted to use for correcting the blades is called plate-quench. It cannot be used for simple carbon steels. Only so-called deep hardening steels can be thus quenched, and N690 is such steel, according to some articles I found on the internet. Nevertheless, it is better to not have the internet at all than to believe everything you can read on it – the manufacturer recommends oil quenching.

So I have tested the process first on one blade that I accidentally broke when correcting an ever so slight banana-bend. When the broken blade hardened properly – which I have confirmed not only by scratching with my gauges, but also by breaking off a tiny piece of it – I went on with the curly ones. On one of these, I confirmed the hardening too by breaking off a tiny piece of the tip, with the remaining two I was satisfied with the scratch test only.

For the plate-quench are used two flat plates from either alluminium or copper. These two metals have very high heat conductivity and thus can cool down some steels fast enough for them to turn into martensite. Luckily I got quite a few nice slabs of alluminium on hand. And because I wanted to make the process a bit faster (despite not making time-measurements this time), I have made a simple prototype quench-jig.

It consists of two identical pieces of alluminium with a small hinge, and locking pliers. The hot blade went out of the forge between the plates with the edge towards the hinge. Then it was firmly clamped by the pliers to hold it straight. When it stopped glowing near the tang – indicating a temperature well bellow 600 °C – I dunked the whole thing in a bucket of cold water just to be sure. And just as last time, because it costs nothing, I have put the blades into a freezer straightway for a few hours before tempering them. None of the three blades cracked.

Not an actual quench, staged photo – sometimes I miss having third hand greatly. © Charly, all rights reserved. Click for full

It worked reasonably well and quick. I will definitively improve it and build a proper jig when the weather is nicer and I do not freeze my nuts off in my workshop. I will add a more stable hinge(s) and maybe even screw one of the plates to the pliers.

Another advantage of this process is no burnt oil gunk on the blade, no flames and no stinking oil fumes.

Poor Man’s Belt Grinder – Mark 3

My belt grinder has served me well, and for a hobbyist, it would be probably good enough. But since I am inching my way towards knife making not being just a hobby, I needed some significant improvement on it. And an opportunity luckily arose.

One of the good things about my previous employer was that there was an internal process for employees to get obsolete materials and equipment either cheaply or completely cost-free. I have used this opportunity quite often and got a lot out of it – I am well stocked in graphite and alluminium, I got precise analytic scales completely for free, and one of the last things I have managed to get was a variable frequency drive.

I was not able to haggle this one down to zero, it was a bit pricey even though used, and I also had to pay a bit to a professional electrician to connect it for me. I could get a new one for a bit cheaper if I capped it at the 1,5 kW that my motor has (this one can handle 5,5 kW) and took the cheapest one there is, but it was still a good deal even if it was not exactly a bargain.

And it works like a charm, even when I am not able to use anything more than the manual mode yet. Finally, I have the ability to change the speed of the motor as I need it, I can even reverse the rotation. I have tested it already and it is exactly what I hoped for-  finally I can work wood without burning it and I can sharpen tools and have a bit more time before the edge starts overheating.

I hope it continues to work well – I have great plans for the future. Multiple grinding wheels, a polishing attachment and, maybe, even a lathe attachment. The belt grinder shall not rest!

My first Commission – Part 11 – Finished

I am done. It could be better and hopefully, in the future, I will be able to do better. And also be able to make better pictures.

The knife is balanced at the forefinger groove, blade length approx 110 mm, handle length approx 120 mm. N690 steel.

The knife in its simple leather sheath… © Charly, all rights reserved. Click for full size.

…and outside of it. © Charly, all rights reserved. Click for full size.

Blade detail. Etched are my initials and number 1 in Glagolitic script. The false edge is sharp, but not cutting sharp. © Charly, all rights reserved. Click for full size.

Handle from my late cherry tree, coated with hard, waterproof and scratch-resistant boat lacquer. Contrast washers jatoba, fittings stainless steel. © Charly, all rights reserved. Click for full size.

Today I finished taking pain medication for my hands. I will try and abstain from any strenuous work for one more week and we’ll see what happens next. The pain went almost, but never entirely, away. I am OK when I do nothing, but on Friday I wrote a short post on my Czech blog and my hands hurt afterward. The same goes for finishing the leather sheath – I had to swing a hammer a few times to mount the press studs and that caused some mild pain too, despite me being very careful and not needing to hit too hard. It worries me.

My first Commission – Part 10 – Starting the Sheath

First I must say that my writing will continue to be very, very sparse for about two weeks (again). I think I finally found out what is wrong with my hands. I had a pain in my metacarpal bones and joints ever since I worked a bit too much in a too short time. Sometimes it almost went away, but then it came back with a vengeance whenever I did some work. The orthopedist has made an x-ray and has ruled out arthritis, and I have not visited a doctor since because it got multiple times better to the point I thought I am OK.

I think I know what is wrong – I think I have started to develop stress fractures. Those are not visible on x-ray until they develop in a full-blown fracture.

And whenever they almost healed, I did something to aggravate them again. There is only one cure for that – several weeks of no-strain. And due to the nature of the injury, that also means no-excessive writing on PC, no grinding knives, no cutting or splitting wood, etc. I have tried consistently this last week to do that and today and yesterday I was again almost pain-free. But I think I need to keep it up for at least two more weeks for the bones to recover completely. If that does not help, then I am going to the doctor again to try and find out what the hell it is.

What I could safely do was to coat the knife handle with boat lacquer. And this weekend I started, carefully, working on the sheath.

First I have cut the two slabs for the sides and then two strips for the belly and the back. To get the strips to conform with the blade geometry I did not cut them curved but I formed them from a wet leather strip. When it dries, it holds form nicely and it saves material.

© Charly, all rights reserved. Click for full size.

The next step was to glue everything together with wood glue. In case you ever do this, beware. Wood glue on dry tanned leather works really, really fast. Not superglue-fast, but fast enough for you to want to be sure that when you press the parts together, they are in the correct position straight away. Wetting the leather beforehand might give me some time, but I did not want to do that because the clamps would leave impressions in it.

© Charly, all rights reserved. Click for full size.

I have let it dry for a few minutes, then I took off the clamps and I inscribed a line with a knife-tip for stitching and cut the opening for a belt. In case you are wondering why there are round punched holes at the end of the cuts – those are there to avoid stress concentration and thus to prevent the leather from tearing further when used.

© Charly, all rights reserved. Click for full size.

Now I leave it to completely dry until tomorrow evening. In the meantime, I am trying to figure out a way for making my maker’s mark on the leather. I could cut it, but that seems a bit inelegant.

My first Commission – Part 9 – Fitting, Signing, Assembling

© Charly, all rights reserved. Click for full size.

The HDD magnet proved to be very useful when polishing the bolster/handguard. It proved to be strong enough to hold it when grinding on the belt grinder, but also when polishing with the angle grinder. I did not intend to use the magnet in this way, but now I will because it has proven itself to be extremely useful for holding these tiny things steady. Shame that other metals that I am going to use for these things – aluminium and brass – are not magnetic.

The next thing I have done after the bolster was fitted was to make the handle. That did not go too well as you may remember. The first piece of wood had cracks, on the second piece of wood I messed up the drilling and the third time was the charm. It is a nice piece of wood and looks great when the grip is fully shaped, but I do wish that I have managed to get the grain alignment a bit better. But grain alignment is not something that anyone else fusses about that much, so I should not fuss about it either. Here you can see the grip roughly cut and shaped on the belt sander.

© Charly, all rights reserved. Click for full size.

After the grip was shaped, I have also glued to ti the end cap/pommel thingie and I have decided to sign the blade before assembly.  For that, I have tried a new thing, which unfortunately completely and utterly failed.

I have bought photosensitive lack that is used for etching PCB boards. The idea is, you spray-paint your metal surface, you print your design, you put your design on the surface and use UV light to quickly deteriorate the paint on illuminated areas. Then you wash out the deteriorated paint with a 1% solution of NaOH and voila – you can etch.

The paint did not deteriorate under UV lamp as advertised and the NaOH solution did not wash it out of the illuminated areas. I have followed every step of the instructions, multiple times, and it just did not work. So I tried to increase the NaOH solution concentration – and it washed off all of the paint. So until and unless someone shows this particular product to me to work, I am considering it an unfortunate waste of money.

I do not want to make my signatures too big, and I want to number the blades from now on, and the wax is not very conducive to tiny fine details. So I had to revert back to how I did things in the past, with slight improvements. I have covered the blade with plastic adhesive tape. But this time I have used double-sided tape on the parts where the signature and numbering were due to go, and then I glued to it one print of the now useless stencils for the failed photo etching. Then I cut out the letters with shaving razor and a pointy scalpel blade.

Because I did not want to damage this blade, I have first tested this new technique on the failed machete (that fail has proven quite useful, I have hardened piece of steel for experimenting).

© Charly, all rights reserved. Click for full size.

Etching in a cup with solution works, but it takes a lot of space and a lot of solution to immerse the whole blade. So I have built myself a new thingie that allows me to perform etches with very little solution.

I took a piece of graphite and ground it flat to about 20x30x5 mm. On top, I glued a piece of wood and covered it all with excess epoxy glue to protect it against moisture. The next day I drilled a 6,5 mm hole into the wood down to the graphite. Lastly, I took a piece of 8 mm brass pipe, cut M8 thread in the hole and on the pipe, and I screwed the pipe into the hole so far that it has a solid connection with the graphite.

For the etching itself, I have simply put a piece of felt soaked in diluted FeCl3 solution on top of the design, between the blade and the new graphite electrode. Anode (+) on the tang, cathode (-) on the brass pipe and after five minutes the job was done. The etchings are clean and nice looking.

© Charly, all rights reserved. Click for full size.

 

© Charly, all rights reserved. Click for full size.

Just like last time, I have no pictures of the assembly. Imagine me slathering epoxy mixed with wood dust all over the tang, hammering the handle onto it and then peening the end of the tang whilst being in a constant state of panic that something goes wrong. Nothing went wrong, although I am not happy with how the peen turned out. But the customer did accept in advance that peened tangs can be a bit unseemly. Even unhardened stainless steel does not like to be peened and tends to crack around the edges. And I did not dare to try and weld soft steel stud at the end of the tang, this steel allegedly does not weld well. But maybe I will try something different for the second blade. This one is unfortunately stuck with this, although it might get a bit better with some more polishing.

 

So the knife is now more or less finished and functional. The last thing to do is to clean and polish the wood to about 300 grit and then impregnate it with boat lack.

© Charly, all rights reserved. Click for full size.

My first Commission – Part 8 – Bugger

I thought I will finish shaping the handle today. Instead, I have to start all over again – the piece of cherrywood that I used had some deep cracks (they were not on the outside) that got too wide and too visible in addition to two unseemly knots. The knots themselves could be seen as a part of the wood, but the cracks kill it definitively.

I have just spent some 2 hours shaping a piece of firewood.

My first Commission – Part 7 – Sharp!

Hell isn’t forever after all. Today I have finished both blades and for the second one, I opted for a satin finish. Not because it is easier – it is not – but because I wanted to see the difference and decide what I like more for the future. Well, I am still undecided, but I can see the difference. And so can you, although it was not easy to think of a way to photograph this.

© Charly, all rights reserved. Click for full size.

The satin finish was made by me not going to the finest buffing compound. Instead of that, I went for a fine abrasive pad right after the medium buffing compound and I dragged it along the blade a few (hundred) times. And I probably will do some more.

After the blades were finished, I have decided to sharpen them. I probably will sharpen blades before assembly for several reasons. Firstly I like making apple seed (convex) edges, that give the blade look as if it does not have a secondary bevel at all. For that, I might need to re-buff the blade a bit, and that can only be done before the handle gets in the way. Secondly, should I scratch the blade by accident during the sharpening, it is easier to re-polish it before assembly. So whilst I do not necessarily sharpen the knives to shaving sharp at this stage, I do sharpen them to some 90%.

This steel (N690) should not be sharpened at an angle steeper than 15°, steeper than that and the fine edge allegedly tends to break off. I have no reason to doubt this since the blades are hard as hell. This time I have a way to get a really nice and consistent angle – I could use my magnetic jig. So I did. The N690 is steel with so-called “secondary hardening”, so it is basically nearly impossible to overheat and destroy the edge during sharpening. Nevertheless, I took care to take my time and not overheat it, it does not pay to get into bad habits.

© Charly, all rights reserved. Click for full size.

You may see that there is no platen behind the belt, so I am using a slack-belt setup here. That means the secondary bevel will be concave and the cutting edge itself will be sharpened in fact at an angle a bit higher than 15°, which is ideal for a hunting/camping knife of this type.  Convex grinds are very durable – the knife that I have made for my mother needs sharpening only about two-three times a year despite being used and abused daily.

Speaking of that, when I was at it I also sharpened all her kitchen knives. Those took just one-two very quick passes on the slackbelt and then a few passes on my stropping wheel (made according to Walter Sorrell’s video)

© Charly, all rights reserved. Click for full size.

Your eyes do not deceive you, that grinder with the stropping wheel is back-to-front.  For stropping, the wheel must rotate in the direction of the edge, not against it, because it is softer than the blade and if you try stropping against the edge, the blade will bite into the fast-spinning wheel and dire consequences will follow. Having the grinder backward allows me to work on the upper side of the wheel, so should it grab the knife and throw it, it will hit the wall and not my leg or the concrete ground. I find it also a lot easier to strop the blades that way.

The stropping wheel gets the knives to scary-sharp in mere seconds. I am using the coarse stropping compound, in my opinion, it makes a better edge than the fine ones.

Now the blades are polished, nearly completely sharp and wrapped in masking tape. It took me three times more time than I think it should and about 30% more than I thought it will. But now the most time-consuming and nerve-wracking part is hopefully behind me and next steps will be free of trials and tribulations. Or at least with significantly shorter ones.

My first Commission – Part 6 – Halfway Through Hell

© Charly, all rights reserved. Click for full size.

This weekend I only could work for about 4 hours on this project, but I have finally managed to finish one blade.

I am not happy with it. Like, at all. I could have done a better job, and I have done a better job in the past. I just could not get into the thing at all. I kept making mistakes, and whilst to make a mistake on belt grinder takes a split of a second, correcting it can take hours. After 400 grit I went to hand-sanding. It is more strain on the fingers than the belt grinder, but a lot less space for a mess-up. And therefore I was, paradoxically, suddenly a lot faster. I might switch to hand sanding on the other blade sooner.

After 1000 grit I went for buffing wheels. Buffing a blade like this is not optimal and if I did not mess up the grind on belt grinder so often as I did, I would not go for it and I would polish it up to 7000 grit sandpaper. However buffing has one advantage, besides being fast – it hides and smoothens slight imperfections on the bevels by ever so slightly rounding up the ridges. Which is also the reason why I normally would not go for buffing for a blade like this.

This is the blade that goes to the customer. Next weekend I will hopefully finish the second one and then I can start on the accessories.

But after I am done with currently started projects, I will definitively make a batch of these. It is a complicated shape, and thus an excellent exercise.

 

My first Commission – Part 5 – Hell is Forever

Shiny already, but still not even remotely enough. © Charly, all rights reserved. Click for full size.

Wheef. Making a commission when I still have to spend forty hours a week at my daily job is not something I would recommend. I could find this weekend seven more hours for grinding and polishing, and I am currently at Trizact A65 (the equivalent of grit P320), but not finished.

The right blade in the picture is finished on this side with this grit, on the left blade the false edge and the flat are finished, but the bevel is still only at P240. And to make my life easier when picking up the blades next weekend (or perhaps some evening during the week, but most probably not – it is not a good idea to try polishing when tired and sleepy), I have marked each surface that is not finished yet.

Chasing scratches is a nightmare. Partly it is my (lack of) skill. Partly it is the tool – I had to repair and improve some parts of my belt-grinder because the belts were not tracking properly and wobbled from side-to-side. That means I have welded on a threaded nut for the screw that adjusts the tracking wheel and I have given a little twist to the spring that provides tension to the belt. The twist helps to keep the arm with the tracking wheel steady, it tended to bend and thus was not stable.

Also, the whole machine vibrated too much – I had to remove the clamps that were holding it to the table, because they got in the way, but now it has wandered around. I put a few bricks in it for weight and that seems to have helped a bit, but possibly not enough. I suspect I will have to bolt it down, something that I do not like to do in case I will make changes to the workshop.

But as they say, it is not about the tools, it is about the hands.

And regarding my hands, things do not look so good in the long term. For the last eight weeks, I had persistent pain in the first joint of my both index fingers, so I finally went to an orthopedist. On an X-ray he found nothing, which is good – I probably just strained the ligaments in the spring and those take a long time to heal. I do not have arthritis. Yet. But he also has told me that because my mother was heavily hit by arthritis in her fifties, to the point that she had to get two artificial joints in her thumbs, the odds are that I will get the same. And there is nothing I can do about it, except making it worse. Works he particularly discouraged me from doing were works including hammering and working in a wet environment with vibrating machinery. Hand-forging is probably out of the question for me completely and for grinding I will have to develop and put to use quite a few helping jigs to reduce the strain put on my fingers.

My first Commission – Part 4 – Welcome to Knifemaker’s Hell

I really wish my first customer has chosen a knife with simpler geometry. For future projects of this kind, I will have to make some more attachments for my belt grinder, because it is woefully inadequate for the concave false edge. I messed that up several times already and quite a few times I got frightened that I will have to start all over again. Whether I manage to correct the slight flaws that are in there remains to be seen, my guess would be no. It will cut alright, but it won’t be perfect no matter what I do. Grrr.

This weekend I have spent with grinding as much time as I could – approx 4 hours each day. More is not possible, at least not for me. Grinding on belt grinder is for me very mentally tiring, because I have to concentrate a lot more than I had to when grinding manually. Because whilst grinding on the belt grinder is quicker, it is also possible to make mistakes quicker.

At this point, I should be finished with polishing, but I am unfortunately not even halfway through. Mainly I have myself to blame for this. If you remember, when writing about the kitchen knives I mentioned that after the first grind with the magnetic jig I went back to freehand in order to be able to alternate the angle of attack to get a flatter and more even grind. Well, I forgot to do that with these two knives and I ground them both up to 120 grit ceramic belt on the jig. The result was ever so slightly wavy grind that I had to correct now that the blades are hardened. So I had to start all over at 40 grit and work my way up, sweating profusely whenever my hand slipped slightly. But at least one thing is clear now – whatever misgivings I had about the blades being perhaps not hardened properly, I do not have them anymore. They are extremely hard and tough to grind, which is why it took me so long to get to 150 grit today, which is the point at which I had to call it quits.

Still a long way to go. © Charly, all rights reserved. Click for full size.

I estimate I will need about ten more hours overall, on and off the belt grinder, before I can call these two blades finished. That means at least one more weekend. At least. It also means more than double the time that I think it should have taken me. When I am done with this and with the kitchen knives, I will probably make a batch of these blades as an exercise, I must get the muscle memory and experience and know-how to do a proper job in a reasonable time, I cannot dick around with one blade for months on end anymore.

Making Kitchen Knives – Part 13 – Headscratching Curls

These are the three blades that were quenched by using protective stainless steel foil. The function of the foil is to prevent decarburization during the extremely high temperature at which this steel needs to be held at for prolonged time in order to get all carbides into solution.

My initial thoughts were that the blades warped because they are ground too thin. Well, that is not true. Today I have measured the thickness and they are indeed way thinner than I should have made them – all are just 0,35-0,45 mm thick at the cutting edge – but three of the remaining blades are even thinner, three are in the same range and only four are thicker. And of those thinner or just as thin as these, one has very, very slight bend towards the tip that should be possible to correct, and the rest is straight.

So the blade thickness is not the cause. I cannot imagine what else could it be, I do not believe that the foil could have such impact, not to mention that these blades were pulled out of the foil prior to quenching.

My second guess would be decarburization, maybe the experimental protective coating did not work as well as it should and the steel has lost some of its carbon, making it less prone to warping in the quench. But it should also leave it much softer post quench, and I just do not see that.

I have tried my hardness assessing gauges on bought kitchen knife – that big fat stainless steel overpriced junk to be precise – and I got the same result as for the softest one of these – that is, approx 52 HRC.

This means that the blades where my 62 gauge does not scratch are definitively the hardest blades and harder than the store-bought one. And the 62 gauge scratches all these three, but it does not scratch 3 of those where I used the experimental protective coating. And to add to the confusion, one of those three hardest ones is also one of the thinnest. This to me rules out decarburization as the deciding factor for the warping, although it might have caused the high variation in hardness.

I do not believe it is due to my grinding skill, because that should distribute the warping randomly and not only on the three blades that were quenched with foil.

Currently, I am just scratching my head. Any opinion is welcome.

My next step can be either to make these blades circa 5 mm narrower by grinding away the curly parts or trying to re-harden them with the protective coating and maeybe even trying plate-quenching instead of oil. I have never done plate quenching, maybe this could be a good opportunity to try it out…

My first Commission – Part 3 – Quality Control

I took both blades to work and measured the hardness on the tang and near the spine. On one blade I have measured 52 HRC, which is actually good and is the value that I was aiming for this area. The second blade however only measured 47 which gave me a pause, because it just did not feel right (it is still perfectly OK value for the spine though). Scratching with an ordinary file has shown that both blades are softer at the spine than at the cutting edge, which is too desired and that it came out that way straight out of tempering means that I do not need to temper the spine extra with a propane torch, which was my original plan.

The “better” blade looks now like this.

Tempered blade © Charly, all rights reserved. Click for full size.

You can see the scratches from further testing at home, where I have indeed established that both blades are approximately identical – both hardened through, but harder at the edge, both probably 52 HRC and more. So how came about the difference in measurement? I got an idea how that could happen and it turned out to be correct – the blade with lower measured value is ever so slightly bent, it is not visible with the bare eye, only when I put a straightedge alongside it and looked against the light. And I have measured it on the convex side, which means it was behaving a bit like a spring thus lowering the measured value. That is the reason why these measurements are supposed to be done on clean and flat-ground things with parallel surfaces.

And how did I establish, that both blades are nearly identical? With these.

Gages for estimating hardness. © Charly, all rights reserved. Click for full size.

I have made these miniature chisels in the winter and I measured them at work. I used nearly the same process as when McGyvering the precursors for these last year. Then it got put on hold until yesterday and today when I finally got to etching their HRC hardness onto the blades and inserting them in handles.

They are not perfect, for some reason the hardness can wary within one blade so the higher one does not always reliably scratch the lower one, but they do give me an estimate. For example, I have also tested the tempered blades for kitchen knives. One blade got scratched with the 53 gauge, but none got scratched with the 51. From the rest, none got scratched with the 57 gauge, and the 62 scratched all blades but three. And all gauges can scratch the unhardened tang.

That is a far better result than I expected – no blade seems to be under 52 HRC, which is the lowest limit I have set to myself for knives. I did not pull this value out of a hat – it is the lower tolerance limit used for combat knives in former Czechoslovak People’s Army, and I reckon if it is good enough for the army of a paranoid totalitarian state, it is good enough for me. And since 62 HRC is nearly the upper limit for the steel I used for these knives, it seems that despite still a bit improvised setup, I have indeed hardened some blades as well as it is possible.

Although there is no reason to really think one of the two blades is really worse than the other, still the blade where I measured 52 goes to the customer, and the blade where I measured 47 goes into auction here (provided I do not destroy one in due course).

 

Making Kitchen Knives – Part 12 – Playing with fire

Last time this part of the process gave me some grief and I also have expressed some skepticism with regard to how much time it takes me. Yesterday I have calculated that unless I get this time under 12 Minutes per blade, it is not worth doing from a financial point of view. So, how did I fare today?

I had 13 kitchen knives and 2 hunting/camping knives to for hardening. I wanted to harden one half in foil and one half with a new experimental protective coating, but I only got enough foil for five blades, so I used it for both hunting knives (those will be sold, so those were more important to not mess up) and three kitchen knives. The rest got the new experimental protective coating.

I started by properly preparing my workplace in order to not needlessly waste time. On the left, you see a can with oil, a water bucket, several pliers and the blades. On the right is my mini gas-forge on my circular saw table, which is metal and thus non-flammable. I had to work indoors, there was a threat of homeopathic rainfall.

Prepared tools. © Charly, all rights reserved. Click for full size.

First I let the forge heat for fifteen minutes empty and then I started to put blades in it. In order to give the steel the soak time it needs (30 minutes), I started by putting in one blade every five minutes, always putting the last blade on the left side, pushing all the blades inserted before that to the right towards the burner. After half an hour I could quench the first blade and I continued with 6 blades in the fire at once.

Blades in the forge. © Charly, all rights reserved. Click for full size.

Unfortunately, just like last time, the temperature was a problem. I tried to insulate the forge a tiny bit better, but it just did not help, this burner is too small. I got over 950 °C, but that is still some 70°C short of the minimum for this steel. It got hardened alright, but probably not to the fullest potential. That I will not know until I have cleaned and tested the blades, and that will take a while. So far I only could take each blade and try if it scratches into a piece of unhardened steel – and they all did. (A side note to temperature measurement – I tried to look it up, and oxidized steel at this temperature has an emissivity around 0,9, so my IR thermometer should give accurate enough readings in default settings.)

I knew that my oil container is a bit small, so the oil will heat up way too much in due course, that is why I quenched the blades double – first in oil, then in water. That way I also extinguished any flaming oil clinging to the freshly quenched blade. It is a bit risky, but I did not hear the tell-tale cling of the cracking blade this time, so maybe I got away with it. We will see if some cracks show later on.

Hardening the blades in foil was a bugger. For the kitchen knives, I pulled them out of the foil before hardening, and they all warped in quench something awful. The camping knives got quenched still in the foil, and they surprisingly still got hardened rather well. Maybe the next step has helped? I do not know.

For the next step directly after quenching (after quenching all blades, which took me 2:25 or 145 minutes) I packed all pieces in plastic foil and gave them into our freezer at -20°C. Ideally, I would put them in liquid nitrogen to cryo-freeze them, but I do not have that kind of equipment to play with. So I looked at the internet and I found that in some steels of similar composition simple freezing below 0°C is enough, so I reasoned – it costs me no money and no time either, so on the off-chance that it does something I will do it. I have no way of measuring whether it helped or not, but it did no harm for sure.

After about two hours in the freezer, the blades got out of there and into the kitchen oven at 150°C for 1 hour.

Baking knives. © Charly, all rights reserved. Click for full size.

After that, I left them cool down to room temperature and when they cooled off and lay for one hour at RT, I tried to fix the warpage on the three kitchen blades by clamping them between a few pieces of steel before the second tempering, which was again one hour at 150°C.

Baked knives. © Charly, all rights reserved. Click for full size.

It did not help, the edges remained warped. So I clamped them again and tomorrow these three blades go into the oven again, this time at 200°C for one hour. That means they will be less hard still, but hopefully they get a bit straighter.

If not, then what I have here is a case of “knifemakers do not make mistakes, they make smaller knives”. The mistake that I did not make this time has, in my opinion, nothing to do with the use of protective foil, it was in my opinion just a coincidence that all foil-wrapped knives warped. I think I have simply ground these blades too thin – remember how I complained about my abysmal skill with the belt grinder?

At least I had no banana-bending to one side, which means that my grinds were symmetrical.

The protective coating actually did dissolve significantly in hot water this time, so I think that I am on the right track there.

And what was the time? All in all, with packing some blades in foil and coating some with badly prepared mixture whilst chatting with my brother and my sister in law, and preparing and cleaning away the whole workplace, it took me about 15 minutes per blade. That is an excellent result. 75% improvement compared to the last time. I think with a few more tweaks I can actually really get this to the 11 minutes per blade that I need. I am not there yet, but I think it is possible.

The next part is the polishing. The biggest time-eater and finger-breaker of them all.