Making Kitchen Knives – Part 10 – Shaping the Outlines

I have not forgotten or discontinued this project, only when it is cold I have to first heat up my workshop before doing any work – which wastes a lot of fuel and a lot of time. Therefore in winter I never manage to do as much work as I would like to. But I managed to do something in the last two months – like building the tumbler (that has run for five days straight by now btw. and it has made a very nice satin finish on the broken blade).

But I could not do much actual work on the knives themselves, because first I must focus on making the necessary improvements. I managed only one step in the process and one failed improvement in the next one.

The step that I have managed with success is shaping the outline of the blades. Last time I ended up with three stacks of blanks held together with screws. So I took them to the belt grinder and ground the outline of all three stacks. After that I disassembled the stacks and cleaned up any irregularities, burrs etc.

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I ended up with a stack of 12 knife blanks. They are not all identical, but in three shapes – next time I will have to think a bit more about how to get reliably reproducible results. To save my self trouble when cutting the handle scales I have marked the blanks in each group on the tang with letters T, V and X. Why these letters? Because they are easily distinguishable from each other and can be scratched with just two lines.

This step was not actually very time-consuming before – just 10 minutes per blade, or 1, 55% of the whole process. Theoretically not worth improving. But I hope that having three groups of four reasonably identical handles will save me some time when shaping the handle – which took 110 minutes per handle, or 17% of the whole process.

Nevertheless, shaping four blades at once did bring some minor time-saving in itself – I have spent only 5 minutes per blade now, so I have saved 5 minutes from my process. This has confirmed that this was indeed low hanging fruit – it was a very easy improvement.

Next step is basic grind of the blade – and this is where I have my first failed attempt at improvement to share in my next post.

Lets Get Ready to Tumbleee!

I hope this will work. If not, I am determined to fiddle with it until it works.

I found an old asynchronous motor in our cellar. It is a small thing, mere 140 W, and it lacked wiring, any elements to fix it to something and cam wheel completely with wedge. But I have managed to convince my father to connect a cable and a switch to it, and it was working. So last few weeks, whenever I have got an hour or two, I was building a tumbler. I did not document the building process, because there is not much to it, really.

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Just like with my belt grinder, I started with a particle board leftover from kitchen renovations, which was the base for my old drill press. It is a nice >2 cm thick board, covered with waterproof plastic on the upper side. Stable, strong, simply ideal as a base for a machine. Because the motor lacked any flanges or wings or whatevers to fix it and only had 4 M5 threaded holes, I took two pieces of steel that had 90° angle, straightened them to about 120°C angle and screwed them onto the motor. This provided me with two ears, that could be screwed on wooden blocks connected to the base plate. The switch was attached to the plate by its standard holes, plus two wooden pieces to better secure the cable.

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As I mentioned, the motor lacked cam wheel. So I stood in front of a choice – to buy V-belt cam wheels and V-belts, or try something else. I tried something else, because I deemed it easier and cheaper. I bought two PP furniture wheels of different sizes. One got attached onto the motor in the standard way – with a steel wedge ground from a piece of spring steel and a lot of cursing. The diameter of the axis was slightly smaller than the inner diameter of the wheel, but I was able to fill the space with a piece of steel pipe. For the bigger wheel I had more luck – it had inner diameter 15 mm. So I could just buy a 15 mm steel pipe and further I could put to use two old ball bearings that also had 15 mm inner diameter. With a bit of banging and a lot more cursing I was able to fix the two ball bearings and the big PP wheel onto the pipe (the PP wheel is further fixed with a nail, so it dos not hold on only by friction). Next step was to fix the ball bearings on two wooden blocks onto a separate particle board plate.

At this stage I also took a strip of leftover flooring PVC and glued it onto the PP wheels for better traction. It is actually nearly impossible to glue anything on PP with reasonable strength, but there are adhesives on the market that manage this task strong enough for this kind of application (I think). If it goes pear-shaped, I can always screw it on later.

For the tumbling drum I took a 100 mm diameter PP pipe and again I glued on it a few layers of PVC for better traction. The PVC lays directly on the steel pipe in order to reduce the fast rotations of the motor as much as I can.

Two small furniture wheels aid in keeping the tumbling drum in place whilst allowing it to freely spin. The tumbler thus lies between the axis and the two wheels and holds in place purely by its own weight.

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Last week I cut a piece of thick leather 1 m long, 3 cm wide, and I cut the ends at an angle so they overlap whilst the overall thickness remains the same, and I glued it together with epoxy. Hide glue would probably be better, but the weather was way too cold for messing about with hide glue. Today I took last few hours in adjusting the positions of the two wooden plates against each other to have adequate tension on the belt without it wandering in one direction or the other. As of now, it has been running for an hour without problems.

It has about 120 rotations  per minute, which might be a bit too fast. I put in shredded walnut shells, a soft coarse polishing compound and a broken blade from my failed machete build.

We will see what comes of it.

Making Kitchen Knives – Part 9 – Starting Again

As I said last time, I am going to make multiple knives in parallel, because I think that a non-trivial amount of time can be saved just by that. I had all my steel already straightened, so I could go right away to drawing, drilling and shaping. First thing to be done was to draw and drill one blade on one half of one steel bar. That I have subsequently used as a template to drill holes in the other half and in all the other steel bars.

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For the drilling I clamped the template firmly with the drilled steel bars and before proceeding to the other side I inserted a steel pin in the drilled hole so the bars do not shift and slide. This has saved some time, despite it being a step with negligible time in the analysis, but my main hope here is that this work on multiple pieces in parallel brings better reproducibility regarding the hole positions and and that better reproducibility could save me some time later on when shaping the handle scales.

I have learned two lessons, one of them rather expensive. First lesson was that for this I have to take the 6 mm drill bits as de-facto consumable material, because I blunted and subsequently broke one towards the end despite using copious amounts of cutting oil. And I do not think it can be avoided.

Second lesson was that I really have to buy a new drill press, and preferably one with continuously regulated speed at that. My jury-rigged press with a very old hand drill has only two speeds and both of them are apparently too high for drilling 16 mm hole in 1,8 mm steel. Towards the end of the work the step drill bit overheated and it got irreversibly blunted on the 16 mm step. Ouch. That drill bit costs 40,-€. I think this investment is unavoidable, if I want to save time I cannot take the bit out and dunk it in water after each drilled hole, slower rotations would be better. And I cannot buy 40,-€ drill bit for each dozen of knives I make – that money be best saved for grinding belts. Hobby or not, at this rate I would spend the price of an acceptable small to middle sized drill press (300-400,-€) on the drill bits rather quickly.

Cutting the blanks in half and roughly cutting the outlines of the blades with an angle grinder did not take long at all. and working on multiple blades in parallel seemed to work comparatively well. But for the sake of precision, next time I will halve the blanks individually – two came out somehow too short and two too long. Not by much, but it is noticeable. The end result were three stacks of four roughly cut blades.

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Before this step took me 15 minutes per blade, now it was 10 minutes per blade (teasing out broken 6mm drill bit and fruitlessly trying to drill a hole with blunted 16mm drill bit included). So I would call it a semi-success. I learned some do’s and dont’s and I achieved my two goals – the holes in the tangs align across all 12 blades nicely and I have saved some time without even really trying to.

Making Kitchen Knives – Part 8 – First Evaluation

First thing first – today I tested the very nearly finished knife when I was cooking shrimp for lunch.

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It handles well and cuts OK, but I really suspect it won’t hold an edge as well as it should. But the cheapo wood looks way more posh than I expected it, ammonia fuming really, really improved its looks.

And now to the boring stuff.

What I am doing here is actually a small-sized DMAIC project – an abbreviation for Define-Measure-Analyze-Improve-Control. It is a process used in industry to bring some logic and use of scientific method into improving manufacturing processes. Although as everything in today’s corporate culture it is used wrongly and heavily abused and misunderstood all over the place, because american-trained managers …. wheef, do not get me started on american-trained managers.

Aaaaanyway, in the first phase, Define, you should either define your problem or your goal or both. In my case, I have a specific goal – to get my manufacturing time of this type of knife under five hours of manual labor.

In the second phase you should acquire all measurements that you need in order to do something about it – in my case I have measured the manufacturing time of each distinct step in the process.

And now, in this post, I am performing the Analysis of said data. Total manufacturing time: 10:46, or 646 minutes.

A picture is worth a thousand words, so here is a picture.

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There are of course multiple approaches one might use, but in this specific case I think that this suffices ample enough – it is so-called Pareto Graph. The balks are actual times in minutes for each step, ordered from the highest to the lowest. The black line is a sum of the relative proportions of these times to the total as one progresses from left to right. As you can see, I have ten distinct manufacturing steps and from those five steps constitute 90% of manufacturing time. These are the steps where I have to concentrate on actually reducing said time, because here my efforts have the biggest payoff. That does not mean that improvements in the other five steps are not worthy pursuing at all, but they are not worth pursuing at this time.

I have done one thing that is not normally done, that is I sorted from get-go the steps into two categories – low hanging fruit, where I think I can do improvements without too much hassle and without obtaining expensive or complicated equipment, and high-hanging fruit, where I can save time only through acquiring new skill or new equipment or where I think saving time is not actually possible in a meaningful way.

Now comes the next phase, which is  to improve the process. I will try to implement some of the ideas for that I have expressed and make a batch of multiple (~10) knives with improved process. We will see how it turns out.

Making Kitchen Knives – Interlude 1 – The Little Great Polishing Experiment

I will share with you a proper analysis of the acquired data, but I just finished a little experiment and I am too eager to share the results.

Without too big analyzing of anything, it is clear at even a casual glance that polishing is the most time-consuming part of the job. It is also the most boring part, in my opinion, because not much can be done and the opportunities for a mess-up are numerous. It is necessary to go through the laborious process for fancy knives, like Ciri’s dagger, but for a kitchen knife without any ribs or facets it is a waste of time.

For over twenty-five years, ever since I read about the technique in ABC as a kid, I wanted to try a process that goes under many names, “tumbling”  being probably the most known one. I have even mentioned the device for it in the article “The Handmade Dilemma” as a “polishing drum”. It is a technique that has been in use for thousands of years, literally – for example Bohemian Crown Jewels contain precious stones that were polished this way. And it has been tried and used for knife finishing both on commercial and hobby scale. All that it takes is having the polished things in a rotating drum where they tumble over each other, sometimes with the help of a polishing medium, sometimes without. A very simple machine, and had I lived by a stream I would build a water powered one years ago. Unfortunately I do not live near a stream and wind is too unpredictable so I am stuck with using electricity, and I have not got my hands on a motor with the right properties yet.

But I got lucky, my colleague has bought small toy tumbler for his son when he was little and they do not need it anymore, so he lent it to me a few months ago. As you can see, it is not big enough to hold a knife, not even a small one, so after I let it run with a few pieces of unhardened steel with very mixed and generally unsatisfactory results, it has collected dust again.

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But here was the second stroke of luck – I have bought a slab of high-carbon tool steel and I started to make myself a set of better hardness measuring gauges than the impromptu ones I have made from an old saw blade. I have already ground and hardened these little chisels to HRc 62,  and I only cleaned the two big facets and sanded them up to 150 grit – that is the grit up to which the grinding and polishing is relatively quick and the blade does not heat up too much. I was not intending to high-polish these, since that would be silly. But I remembered the lent tumbler and checked if they fit in – and the did!

So I chucked the blades into the polishing drum with a spoon of jeweler’s rouge and half filled it wiht crushed walnut shells, mixed it all up and let it run for one day. Bugger – it got blocked after unknown time and I only found out next day. So I started it again for one day. And the change in surface was remarkable. It was not polished, but the perpendicular sandpaper scratches were no longer visible and the surface has got a very nice satin sheen to it. But I like my blades mirror-polished, so I started it for another day. I took another chisel out and subjectively there was no change against the first day, so I assumed that this is as good as it gets (but I will let it run for one more day). But I also assumed that since there are no visible perpendicular scratches anymore, I can quickly buff it to mirror polish with the three buffing wheels that I have  – and I was correct.

Here you can see four pictures taken with my digital microscope (courtesy of our quality department who tossed it away because they lost the installation CD – so I took it home and downloaded free software). Each picture represents a section approximately 10 mm wide in reality.

After 150 grit belt – parallel scratches perpendicular to the blade are very clearly visible.
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After one day, scratches from the sandpaper are no longer visible with the naked eye, but they are still visible under the microscope.
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After two days, the scratches from sandpaper are no longer visible even under the microscope unless you really look for them.
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And after just a few minutes with the set of buffing wheels the scratches are no longer visible and the surface is so polished that the microscope photographs itself.
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Making Kitchen Knives – Part 7 – Assembly and Finishing

After leaving the handle scales in the ammonia overnight, I took them out the next day,  washed them in running water and quickly dried them. First by letting them for an hour above the stove in my workshop and when they were nearly dry, heating them carefully in 10 sec intervals in the microwave until there was no steam coming out. I do not count this time into the manufacturing time, because I have been doing it this way only to be able to proceed quickly and get the knife done this weekend. Normally I would let it  dry by itself.

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When dried, the scales had to be fitted to the handle – that is done by carefully sanding the faces that are glued on the tang on a flat stone as long as it takes to get them nicely flat. Then I screwed the handle scales without the blade together again and sanded and polished the two forward facing facets, because once the scales are on the tang, nothing can be done about them.

As far as the metal goes, I cleaned most of the scale from the tang with 80 grit sandpaper and then I cut two pins from 6 mm brass rod, hammered them through the holes in the tang and tried whether the whole assembly fits together without unseemly gaps. I was prepared to eventually sand a bit here and there, but it was not necessary, it fitted nicely. So I slathered generous amount of quick drying epoxy cement on all adjoining surfaces and squeezed the whole assembly gently in the vice. I cleaned the epoxy that got squeezed out, first by scraping of the excess with a piece of wood and second by washing the blade with paper towel soaked in alcohol. A piece of epoxy on the back and belly of the handle are not a problem, since those areas will be sanded anyway, but a real care must be taken in cleaning the blade and the forward facing facets of the scales thoroughly, because again, any mistake there cannot be easily corrected.

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The epoxy that I was using was hardening quicker than I was happy with, but our local Baumarkt has “optimized” its wares selection a few years ago and they are only selling quick-setting epoxies now and I will probably have to order some slowly setting epoxies over the internet. I got lucky and I managed to get everything important clean before the glue set, but it was a race with time. That means I could not make any pictures of that process, so what you see is status just before applying the glue.

After the epoxy has hardened – in this case about 15 minutes later – I have made final shaping and polishing of the handle. I did not go above 150 grit sandpaper though, because that would be a waste of time with this wood.

Because the used wood was extremely porous, I had to stabilize it. Marcus has already mentioned the recent fad in knifemaking that consists of infusing the wood with resin. That would be ideal here.

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Well, I lack the equipment to do that. But I wanted at least somewhat stabilise the wood even so. And I wanted to use the same finish that I have used on my mother’s knife, because it has proven itself to be very resistant. So I took the boat varnish and diluted it with acetone at a ratio approximately 1:4. You can see on the picture that the undiluted varnish is a lot thicker than acetone and it has sunk to the bottom of the jam-jar. However after mixing it did not separate again for a few days by now.

For the first dip I have put the handle in the heavily diluted varnish and I waited approximately 20 minutes until no visible bubbles were rising. Ideally It would be better to do this in a vaccuum-chamber, but acetone is very good wetting agent and this should be enough for at least a few mm penetration. After that I took the handle out and cleaned any varnish from the blade immediately with acetone. Then I have let it dry in a dust-free and well heated room. All that is left now is this week each evening after returning from work giving the handle a slight polishing with 150 or 180 grit sandpaper, dipping, cleaning, leaving it dry again until I am satisfied with the surface. I am not going to measure this time exactly because it is scattered a few minutes each evening over a few days. Lets say it is 30 minutes overall, including final signing of the blade.

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That makes it 1:30 or 90 minutes for all of the work described here. That also makes the knife done for the purpose of measuring the time of my actual manufacturing process, so next time we can look at the data and look what (if) can be done there to make it more efficient.

Making Kitchen Knives – Part 6 – Basic Shaping of the Handle

I have decided to make the handle on this knife from an old piece of wood I have cut from a palette that stood outside for quite a while. I do not know what wood it is, I suspect birch. It is extremely weathered and looks kinda crap. But there is a trick to make such old wood look very fancy.

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I have done most of the work per hand, first splitting the piece of wood along the visible crack, then cutting it with small hand-held saw to very roughly the final shape and drilling the holes for pins. So far this work was pretty uneventful and straightforward.

As you can see on the picture on the right, I have fixed the two halves with screws to make the final shaping. This is where things stopped being uneventful. The wood was not overly hard, but it was very tough and I could not shape it on the big belt sander because that is running too fast and the wood tended to gum up the belt and burn. So I have been stuck with using handheld tools. I thought that it is not a problem because I expected to do it quickly even so.

I was wrong. It took me 1:50, or 110 minutes, to get the handle scales into a nearly finished shape. I should have used my small belt sander, it has slower running belt and is better suited for wood.

Of course it would not be nearly as long work if I have made ordinary rectangular handle and not this ergonomically shaped one. However I consider the handle shape to be an important, even defining, component of this design. Simplifying the handle shape in the name of saving time would in my opinion strip the product of its uniqueness and I see no point in hand-made completely generic knives.

I think that I could reduce this work significantly by working on multiple knives at once, cutting the outlines with band saw and rough shaping with the small belt sander. Due to confined space in my workshop I need some time for setting those two devices up so it is not always worth for a one-off action. But should I prepare say 20 handle scales in one go, It would certainly be worth it.

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Before proceeding to finishing the handle I had to use my magic trick to improve the looks of the wood. That trick is called “ammonia fuming” and consists of putting the scales into a big jam-jar with a bit of ammonia solution and leave them in it overnight of for a few days, depending on what your goal is – the longer the wood is in the ammonia, the darker it will become.

In this specific instance I have left the wood sit directly in the ammonia solution, letting it to soak it up. It is also possible for example to only let the wood above the solution in the fumes (hence the name).

I have experimented in the past with multiple solution treatments and I have at my disposal a few such processes to alter the wood to warying degrees – from mild color change to actually making the wood compacted and a lot harder. The advantage of these methods over staining the wood with a dye is that the color change goes deep into the wood so it does not get scratched off. It also looks a lot more natural in my opinion.

However, to wrap up, this step took more time than I expected it to, but I think I can put it in “low hanging fruit” basket, because I expect working in bulk should reduce time here significantly and I already have the machinery necessary for that.

How Hard is Hard Enough?

This is about steel and blades OK? Just to be clear upfront.

In my article Knifesharpenophobia I have mused a bit about how being all anal retentive about the hardness of a blade is not all that necessary. Now I wish to revisit that heme a bit, after my hardening attempt of a blade did not go as well as I would wish to.

If you remember when I was trying to harden the rondel dagger I was also hardening a kitchen knife blade and I was pretty sure that this particular blade is properly hardened. So I took it to work and measured the hardness on the tang (the knife is not finished yet), where it is hardened, but probably not as well as the blade. And the gage showed HRC 54. From technical standpoint, difference between 50 HRC and 54 HRC is not trivial (HRC is not a linear scale) and that knife is thus indeed properly hardened. What was the difference in the work process? For that knife then I have used the gas forge only for heat-soak, the final heating to 1050°C  before quench was made with charcoal, which allows for more even heating. HRC 54 is still not full potential of this steel, but if the tang has it, the blade has probably more.

But this whole thing got me thinking again – is that even relevant? Do I really need to be afraid to give that knife to a fried as a gift because the hardness of the blade is “just” HRC 50? Am I being unnecessarily obsessive about an inconsequential detail (again)?

So I tried to look at what is the actual hardness of historical blades. I did not spend too much time with it, but the article Sword Blade Hardness: A look at the current research is an eye opener and a good read. To be clear, it is about swords, not kitchen knives, but it still clearly shows one thing – the crappiest knife that I have ever made is vastly superior to most knives that were used throughout history before the invention of blast furnace. Not because of my superior skill, but because I have access to superior steel. Furthermore, HRC 50 is not actually bad at all and someone who takes a good care of the knife would probably not even notice any downside when cutting. And it has an upside too – a blade in this hardness range needs to be sharpened more often, but stropping and sharpening should be reasonably easy and quick and the knife will not break easily when you drop it on the floor by accident.

It is not the best that could be, but it is good enough.

Making Kitchen Knives – Part 5 – Grinding, Polishing, Buffing

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).

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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…