I was expecting this to be the most time-consuming part and so far I was not surprised – it was. You have seen my collection of abrasive belts during my Rondel Dagger series. Because the protective coating has proved itself to be way too persistent, I had to start with the coarsest Zircon belt all over again – that is what I meant when saying that I could have spared myself the trouble I have spent with finer belts before hardening. I wanted to give this blade the best surface finish that I can achieve purely by using machinery, so I went thoroughly through all belts, not switching to a higher one unless all scratches from the previous one were removed. Although towards the end of the line with last two Trizact belts I was not too fussy about this, because those leave so fine scratches that whilst they are barely visible, but they will always be somewhat visible unless I go with hand polishing afterwards – and that I did not want to.

So when finished with the finest Trizact belt I went straight to the finest buffing compound and gave the blade a few passes on the buffing wheel.

An important note – this is a knife without secondary bevel, with so-called “convex grind”. That means that during the polishing process the blade is also sharpened to very nearly final stage. Therefore towards the end it becomes a bit dangerous to handle it, because it can actually become completely sharp in places. I do not know what process other knifemakers use for achieving this grind, I am doing it with the slackbelt/hardbelt setup on my belt grander, that way I can do it in one go during polishing. The knife will need some sharpening when finished, but not too much. I like this grind because in my experience it cuts best and also looks best – but your mileage might vary and there is no accounting for personal taste.

speaking of taste – one of my friends when I have shown him my mother’s knife thought that I have made the tip round either due to laziness or because I botched it and making a round tip is easier. If you have such thoughts, forget them. Making a round tip is not easier than making it pointy-stabby. And the round tip is entirely intentional. This time around I actually consulted with my mother what she prefers for this knife design and I discussed with her the work in progress when it still had a point, and we agreed that to us this knife looks better with a round tip. Further, there is no point in having a point on an all-purpose kitchen knife like this, since needing a sharp point is actually a rare occurrence (the only one that I remember from the top of my head is gutting fish and poultry, and even there an actual point is used only briefly).

Enough rambling  Here you can see the blade before buffing to get a measure of how well the knife is polished after only Trizact belt grinding – after buffing it reflects a lot more.

That picture shows also that the grind is acceptably flat. The fact that the edges of the mirror on the wall are straight-ish and that my face is still recognizable despite being reflected back through a mirror 1,5 meter away is a good sign that the grind is flat.

However that comes at a non-trivial price. The whole grinding and polishing process took me 4:20 or 260 minutes. Buffing was mere 10 minutes from that. As I become more experienced this time will probably go down significantly, but some of that part of learning curve I have already done, so I do not think it will be too drastic. In order to shave-off a really significant amount of time here, I think I would have to either use completely different process (I have an idea there, but it will need a lot of MacGyvering), or be content with a less-than-mirror finish. So in next step I will experiment with different finishes and decide which is the best compromise between time spent versus looks. The problem with polishing is, that whilst it has zero negative impact on the function, it has 100% positive impact on the looks of the thing and negative on the price. And people are buying with their eyes but deciding with their wallets. Talk about contradictory requirements…

This is when things did go a bit pear-shaped, although I learned that only today. You have seen my “equipment” before, but not in detail. Now you can see it in detail. An IR thermometer on the left, small insulated chamber with gas burner in the middle, a can of sunflower oil, and of course gloves and pliers.

With a blade this thin I have to somehow prevent carbon loss, because I cannot simply ground away a few tenths of a mm afterwards. There would be barely any blade left if I did that. So, as you can see on the last picture in previous post in the series, I tried to coat it with an experimental solution to prevent said carbon loss as an alternative to the rather expensive stainless steel foil. It worked and did not work at the same time and the knife is now in a stage when it will be crap no matter what I do. I am going to finish it anyway, just to get the measure of time, but this step was a definitive flop. Which I did not expect, because I heat-treated two knives from this steel without problems.

 

Firstly the gas burner has trouble reaching the necessary temperature of 1.050°C that this steel requires. It can reach them with success (the blade that I have given to my mother was hardened this way), but it takes a long time and it is difficult to heat up the blade evenly. I thought that I have reached the right temperature and quenched the blade OK, which was confirmed by subsequent scratch test with my impromptu gauges. However, as it turned out, the scratch test only passed because the protective coating has made a thin but hard layer on the surface that was bugger all to remove.

I hoped it would dissolve in hot water – that was the intention – but it did not. It was extremely difficult to clean off in the following step and after I measured the hardness on polished blade (properly – I found out we have HRC measurement at work), it had only about 50-51 HRC. That is weaksauce for a kitchen knife, although it would be OK for a machete. The blade is hardened, just not to its fullest potential. It will cut fine, but it will require more maintenance, so I will probably keep this knife for myself and not give it to anyone. Bugger.

In addition to above mentioned quality problems, this whole step took me more than 1 hour, and I am not counting the 1 hour in baking oven at 150°C, because that does not require my personal presence and thus does not de-facto cut into manufacturing time (and I can load the baking oven with 10 knives at once should the need arise).

At this moment, I do not see any way how to reduce that time. Making more knives at once might help a bit, but for that I would need to set-up heating with charcoal. If I do that, I  estimate that I could harden about 5-6 knives in one go, but that one go would take probably about 3-4 hours of constant work. So a saving of 15 minutes, or 25% time per blade could perhaps be reached on this step, but it is questionable.

A heat treating oven would of course completely change this whole equation, but that would be a big investment – they start at 3.000,-€. Should I ever have to produce knives for sale, a heat treating oven would be a definitive must, or I would have to simply send knives for heat-treatment. Right now I will try to do the heat treatment again by myself, and the next batch of knives will be split 50/50. One half hardened with the use of stainless steel foil, one half with modified coating, and I will either set-up a bigger gas burner, or use charcoal.

This step is put in the “high hanging fruit” basket. There is potential for significant time-saving here, but it is very difficult to reach with my current equipment.

This is the part where work on more blades in parallel is no more possible, but I have tested an improvement that I have hoped for to both save time and increase precision. Grinding symmetrically free hand a blade mere 1,8 mm thick would not be easy. My previous knife of this type was made from 2,5  mm steel and I messed up the grind. I have spent more time correcting my messed up grind than I liked to and in the end I had to opt for a blade without a clear transition between the blade and a ricasso.

I wanted to do better this time, so I have built an experimental jig. As you can see on the picture, it is a simple 30×50 mm block of hardwood (a leftover from building the belt grinder). Two screws hold the knife on the smaller side, and three screws are right on the edge opposite the knife. Those three screws pop out a bit out of the wood and by how much they pop out is how big an angle I have between the blade and the platen on the belt grinder.

I did not make a picture on the belt grinder, but you can see on the right the jig with a blade put against a machinist’s square. The advantage of this setup is that if I want, for example, ~0,3 mm thick edge before hardening and with the blade being ground all the way to the back, I know that I have to set the jig so that there is ~0,70 mm between the square and the back of the blade. Which is exactly what I have done, only without measuring, only eyeballing the gap and deciding “yup, that is what I want”.

The jig is set up so that I can screw the blade in two mirroring positions, but I did not bother too much with precision, because I did not know yet whether it will work or not.

It worked, but the imprecision was abit of a problem, as well as the way the blade is fixed. Two main problems occurred:

1. The tip of the blade lay on the supporting table. That proved to be a problem, because it got snatched by the belt and dragged into the gap between the belt and the table. It messed up the grind in split of a second and I have spent no trivial ammount of time correcting it.
2. Changing the blade on the jig took way too much time, even with accu-screwdriver. Part of the problem was the imprecision, because I had to monkey with it each and every time to get it right.

So a more precise jig that allows fro quicker change is required, and it also should hold the blade at least a few mm above the supporting table for better control. As a proof of concept it worked, it did indeed improve precision, but there is potential

During the grind I have made one time-wasting mistake, but I did not know at the time it is such. After I have established the grind with ceramic belts which go up to 120 grit, I continued to 240 grit on Zircon-carbide belts. As it turned out,  I could have spared myself those zircon belts alltogether, but more about that next time.

I forgot to make a picture of the ground blade, but here you can see it as it went into the next step in the process. You can see that I have managed nice clean line all the way to the back of the blade, which I was previously not able to do free hand.

The time spent with this was about 1:15, or 75 minutes. From that time I have spent approximately 10-15 minutes monkeying around with fixing the blade on the jig, and another 5-15 minutes changing belts on the grinder. I also wasted some time correcting messed up grinds. I think that a better jig and above all not going above the ceramic belts should cut this time in maybe a half, but probably not more – it is fidly work and probably the biggest factor is experience. I remember Walter Sorrels saying in one of his videos that he manages this in 10 minutes, but only because he has been doing it for years.

Right now I am putting it into the “low hanging” fruit basket, because I think I can easily get a significant 15-20 min improvement through better jig and not going too fine with the belts. The rest is, unfortunately, entirely dependent on how fast I will scale the learning curve.