Sciencey Thoats About Tangs

Teh almighty YuTub algorithm has recommended this video to me:

Why military gear isn’t always a good idea…

And whilst I do agree with the title and the overall message of the video, I do have some objections to it. It is not an issue that can be distilled down to a universally true video quip.

First the agreements:

Military gear that is issued to grunts en masse needs to be essentially consumable. The grunts will lose it, steal it and/or destroy it with gross abuse and negligence on a regular basis. I read about conscripts in the Austrian army in WWI breaking their bayonets by opening cans. Stealing was a problem even in former Czechoslovakia, with the UTON  even though that was not issued to every grunt but mainly to paratroopers. The knives disappeared regularly as the soldiers reported them “lost during exercise” even though they had to subsequently pay for them and everyone knew they took them home. Those knives are good, but they are not as excellent as some people think they are “military grade” is definitively not always a synonym for “high quality”.

Now the disagreements:

A good bushcraft knife needs not to have a full tang to be reliable. It is more complicated than that – rattail tangs were and are used in even swords and machetes to this very day and they are not useless. Puuko is a survival knife with hundreds of years long tradition for example. The above-mentioned UTON also has rattail tang, and one that does not go all the way through the handle at that, and still it is a knife that can withstand serious abuse. I have put some of my knives with similarly thin tangs through their paces, both full-length and half-length hidden tang and they withstood serious abuse just OK (although I was only using them as knives, see further). Hidden tang alone is not an issue, the overall construction and heat treatment are.

My biggest beef is with the presented “knife gets stuck and you try to wiggle it out”. Sorry, but if your knife gets stuck in something hard right up to the hilt, then you are probably an idiot for using the knife wrong. A knife is not, and should not be used as a pry bar. But let us say one were to use a knife for making firewood splinters from a log by batoning. That is a legitimate use for a bushcraft knife and it can get stuck that way. It happened to me with my working knife and I had to use serious force to get it out. However, if you try to “wiggle it out” by holding it solidly against the ground and pushing at the handle sideways, you are definitively an idiot for trying to remove it in the least effective and most dangerous way imaginable. Simply put, abuse like that shown in the video does not represent even remotely reasonable and appropriate use of a knife, not even a bushcraft knife that should be sturdy.

Another thing I would like to address is the handle material. It is shown to be natural leather rings and apparently, not overly compressed and not glued together or hardened. That is a problem because it is a soft material that can easily be compressed and give way for the tang to bend. A wooden handle – like on European medieval swords and daggers – significantly improves the resistance of the tang against bending. If the rings were glued together and hardened by hot wax or boiling or epoxy, it would improve the durability and resistance of the handle significantly too.

The thickness of the tang and the blade at the weakest point plays a far greater role than the width. The force needed to bend/break a flat profile rises linearly with width but exponentially with thickness. If you double the width of the tang, you double the force to bend/break it. But if you double the thickness of the tang, the force needed to bend/break it can rise approx ten times (I do not know exactly how much, the calculations are complicated and I cannot pretend to understand them). So a knife with a thickness of 3 mm and full width (~15 mm) tang will be about as strong as a knife with a thickness of 4 mm and 6 mm wide hidden tang.

A role also plays the heat treatment of the tang. A fully hardened tang will be stronger and more resistant to bending and will spring back when bent. But when bent beyond the plastic deformation, it will be more prone to permanent damage and/or catastrophic failure when straightened again as shown in the video. Unhardened tang – that is used throughout history for swords from Europe across Asia all the way to Japan I might add – is easier to bend but can subsequently be straightened again.

And lastly – anything will break if used wrongly or excessively abused. A knife is not bad because it cannot be used as a pry bar and a pry bar is not bad because you cannot cut cutlets with it. When I made the custom machete, I tested it by hitting a brick with it – but I still advised the customer not to do that.

Improvipairing mah Belt Grinder

Three weeks ago one of the idler wheels on my belt grinder gave up the ghost with a screech and a puff of smoke. I was wondering why everything was overheating lately – the belts, the platens, the hweels, teh hwole heveryting. As it turns out, one of the ball bearings on one of the idler wheels was probably a bit off and when a ball bearing starts to go bad, it gets only worse from there. I have impromptu repaired the wheel but I have decided to take this opportunity to rebuild and improve my belt grinder.

The first step on that path was buying a bunch of precision-cut aluminum tubing.

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The only downside was that the ball bearings fit too well into these tubes, they could be inserted without any effort whatsoever. And I do not have a lathe to cut grooves for internal snap rings. So I have used stainless steel foil strips as shims for one ball bearing to press it firmly into the tubing with the other ball bearing only inserted and held in place with the nut in the assembly.

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Here you see one of the new wheels before it was assembled on the belt grinder. Aluminum tube with one firmly pressed in ball bearing, steel spacer with a piece of cork to hold it somewhat centered (I have drilled the center of the cork a lot more later on so that the spacer is really loose. The cork is there only so the spacer does not wander too far off center when assembling/disassembling), and the second ball bearing.

I have made three such wheels, and over one I have pressed another aluminum tube to increase its diameter. That one I later fixed in my drill and with the help of my impromptu repaired belt grinder I gave that wheel a barrel-like profile. Because my old tracking wheel was too getting worn and I decided to completely rebuild the spanning arm.

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Here you can see the right side of the spanning arm with the new spaning wheel. I won’t go into technimicical details. Here you have a second picture of the left side, it should be worth a thowsand words.

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This is in part made from new materials. The downside of this assembly is that I had to weld a 30 mm M10 nut onto the arm. Which was not easy. To say that I suck at welding would be to grossly and immodestly overstate my abilities. When I die, the average welding ability of humanity will probably go ever so slightly up. But after a few botched attempts, I have managed to make welds that at least hold in place, even when they look completely craparooni.

The tracking wheel is on an M10 thread rod and thus can be moved left-right with the help of the upper handle. That is necessary to at least somewhat center the belt on the tracking wheel to avoid asymmetric wear of its surface, My previous assembly did not allow for this and as a result, the wheel got really worn on the left side only.

The second screw under that allows for slightly tilting the spanning arm left-right. That moves the belt slightly from left to right, allowing it to center on the platen. This was starting to be difficult with my previous arm, in part because the assembly was a bit too sensitive (short pivot point) and in part due to the asymmetrical wear on the tracking wheel.

I have used the improved belt grinder for a few hours and it seems to work well. When the current batch of knives is in the tumbler, I will coat the wheels with PVC plastic and perhaps start making some other attachments for the belt grinder.


Not a Masterpiece Sheathed

I have realized that I did not show this on Affinity, only on Instagram. With all that is going on, I haven’t done any actual work in my workshop for weeks now, but this one was finished months ago. In the end, I have decided to make a simple, unadorned sheath for my Not a Masterpiece knife. I decided to do that because I felt in the end that an overly decorated sheath would needlessly distract from the beautiful woodgrain in the handle. The striker and ferrocerium rod have simple stainless steel handles. The bronze caught patina, which was to be expected. It does require some maintenance to remain shiny.

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© Charly, all rights reserved. Click for full size

The full set is for sale in the Knife Shoppe.

Le Workshoppe Rearangeé

I think I did not show you the inside of my workshop, except for the pieces visible around the various pieces of knives and machinery that I have shown in my crafting posts. And since I have totally overhauled (and cleaned) the shop these last few days, I have decided to give you a quick tour of the new layout. The workshop is a bit ad-hoc and furniture is made from mostly scraps.

So let’s start with the north wall, right behind the door.

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On the right, you can see where my lathe is stored. I do not use it very often. Right next to the circuit breaker hangs my woodcutting helmet and fire extinguisher.

In the middle of that wall is a huge shelf packed with various things. At the very top are old baking trays, then a plastic tray with some pieces of graphite. Neither of those things I need often, thus the upper shelves. Then come abrasive cloths and papers sorted by grit. Under them are some cleaning, flammable and corrosive chemicals, and a little basket with magnets inside to collect steel dust. Next comes the shelf with various fixtures and jaws for the vice, follows shelf with knives in progress and knife templates, and a shelf with big massive pieces of steel and aluminium. The second shelf from the bottom is now filled with various lubricants and the lowest one currently occupies interesting-looking stones for suiseki and bonsai. The various plastic bottles are mostly sunflower oil for quenching and one bottle for cutting oil.

To the left of the shelf hangs a board with various chisels, scrapers, planers, and knives.

Leaning against the shelf are various wooden dowels, staves, bow staves, pipes, and long wooden prisms.

To the very left, you see the beginnings of my first workbench, made yonks ago. It is three meters long and would not fit in one picture.

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Above and below the workbench are cupboards repurposed from kitchen renovations. In the corner, you can see two racks for thin metal profiles and pipes and the motor belongs to my tumbler. I have put it on this part of the workbench because it is somewhat inaccessible to work on and I have nowhere else to put the tumbler where it would not be in the way. I think I will be able to run it from there too, which is a plus.

The red vice is right under a light and in a spot where all the chisels, hammers, saws, rasps, and files are no more than one step away. On the cupboard right above it is also a thermometer so I know how warm/cold it is. Inside the cupboard above the vice are empty plastic containers for when I need them during work (like for example to sort screws into when disassembling/assembling something). In the drawer below it are small files and brushes, in the next drawer various pliers and shears, next wrenches, and the bottom drawer is filled with clamps.

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The forge in the middle is there because it needs repairs – work for tomorrow. Under it is a place for storing the table saw when its not in use, a small stool to help me to reach the upper shelves, a bucket for steel dust, and a shop vacuum cleaner.

Above the forge is a shelf with various writing instruments, gomtry tools like compasses, rulers, curves, the most-often used screwdrivers, and a roll of paper kitchen towels. The papers hanging on that shelf are laminated steel heat-treating charts. I will add in near future data sheets for the steels that I use. Inside the cupboard are nails and on the very top shelf accessories for the greenhouses. Again, the upper shelf is occupied with things that are not used often.

Next, you can see my unbender, now permanently fixed to the workbench. I have also spent one more day making it sturdier and improving the design a bit. Next to it, at the end of the bench, is now permanently fixed my drill press. It is lifted slightly above the bench so I can reach under it with a small broom to tease out the metal chips that collect there. I have also put there a piece of PVC flooring to protect the workbench from dripping cutting oil. The tables hanging on the cupboard above it are a drill-speed table for various materials and a conversion table between trizact and grit abrasive ranking.

Below the drill are various small brooms and seldom-used cutting instruments. In the drawers are some abrasives for my handheld belt sander and some ppe, like gloves.

Above the drill press, right at the end of the picture, you can see a small shelf packed with old cookware for when I need to cook something that is not fit to do in the kitchen. Behind it is a small shelf filled with various drill bits.

Now we come to the south wall.

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You have already seen my abrasive belt rack and my small heating stove. The basket and plastic bucket are for wood off-cuts. Normally they are not this full, but I did not need to heat the workshop for quite a long time now, obviously. The grey plastic trumpet is a vacuum attachment for collecting wood dust from the belt sander. The black barrel beside it with a similar metal trumpet is for collecting sparks and metal dust.

The green shelf to the left has buckets with various chemicals and abrasives on the top, some drums for the tumbler on the top shelf, and various metal offcuts on the rest.

Now we are reaching the newest addition to my workshop, one that has spurred the complete reorganization – the east wall with a new workbench.

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On the right is now permanently affixed my small bandsaw. I hope that fixing it to the bench will reduce its vibrations and improve the lifespan of the saw bands, they were snapping rather quickly.

Below the bandsaw is a small cupboard with bonsaist equipment and various attachments for the belt sander.

The small brown shelf between the windows contains various screws, glues, popsicle sticks, bbq skewers, strings, wooden wedges, metal foils, and a first aid kit. On the right side (out of view except the baseball cap) hang various ppe, like face shield, earmuffs, respirator, and goggles. On the left side hang various bits of wire. Below it is a cordless drill and my two angle-grinders.

And on the left side of the bench is the belt sander. Originally it stood where the unbender is now, and it was a pain in the nether regions. It got in the way of reaching the cupboards and working on the drill press and it ate a lot of the workbench so some manual works were awkward or even impossible. Here it should not be in the way and there is enough space to the right side of it to build various attachments – I plan a lathe, a drum sander, and a disc sander.

The drawers in the grey cupboard below contain various measuring instruments, ball bearings, cork, popsicle sticks, and some other various stuff.

In the cupboard itself are boxes with assorted screws, spacers, springs, locks, keys, handles, and similar small diverse things that do not fit anywhere else.

Between the cupboard and the new workbench is about 9 cm space. I have thought about what to do with it and I have decided that it would be an ideal storage space for all of my knife- and tool-making steels, so I have put them there.

And on the very left of the picture you see where my various electric cables and gas burners hang.

That was the grand tour through my small workshop. Writing it took a lot longer than I have expected, I hope I did not bore you to death.

A Big Commission – Part 9 – Da Pictures

Today the customer has picked up his brand new machete. He was apparently delighted, at least he said so. His exact words were “This is much better quality than I have expected, especially the leatherwork.” So today I did not feel like a total waste of space. Here are some nice pictures for you to look at. I did not have to do too much post-processing after all.

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© Charly, all rights reserved. Click for full size

© Charly, all rights reserved. Click for full size

© Charly, all rights reserved. Click for full size

© Charly, all rights reserved. Click for full size

© Charly, all rights reserved. Click for full size

A Big Commission – Part 8 – Photographing

I do not need to make nice pictures for the webshop for this one – unless the customer rejects it, which I hope he does not – but I do want to have nice pictures for myself, for Instagram and, of course, for Affinity. And since it was a nice sunny day today, I took my photography session outdoors. One advantage of that is the sunlight, one disadvantage of that is way too focused light. Shade has, of course, diffuse light, and whilst it is very bright on a cloudless sunny day, it is alas also of the wrong color for this thing and I did not want to spend too much time with corrections in either the camera or on the PC.

So I have rigged up a small thingamajig to make pictures in diffuse light whilst getting the benefit of direct sunlight’s color whilst getting it a bit diffuse. I will have to edit out an occasional ant or piece of debris though, so I am not entirely sure I have saved time in the post-production at all. Well…

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A slightly overcast sky would be best but despite my valiant efforts, the weather still refuses to obey my commands. Mind you, if I could command the weather, I would not command a slight overcast right now, I would command a week of slow, drizzling rains and make the pictures indoors.

Pictures will be posted here and on Instagram after the customer picks up the item. I hope it will be tomorrow, but it might take a few weeks too, depending on circumstances.

A Big Commission – Part 7 – Missed Opportunity

AAAARGHHH! Amidiotextrordinaarggh!

Today I have sharpened the machete, thus de-facto finishing the commission. I have decided to test it in a way that poses minimal risks to the nice surface finish and still tests its cutting capabilities. By cutting milk boxes filled with water standing on a pole. That is a good way of testing an edge because a blunt blade just bats the box away from the pole, a sharp-ish one cuts partly through, tears the rest, and throws both pieces away, and a really sharp one sails through the box, the top falls off and the bottoms stays on the pole. A bad cutting technique may lead to a bad cut, but not even a perfect technique can lead to a good cut with a blunt blade. It does not test an edge’s durability – a well-sharpened bronze sword would perform well too.

I considered filming it and then I thought to myself “Nah, nothing interesting ever happens, waste of time”. Then I cut the first box and I immediately cursed my laziness and stupidity.

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I cut the top of the box cleanly off, and it stayed on! I have cut dozens of these boxes when I was testing my own machete and this has never happened. And since there was enough of the box left for a second cut, I went on and cut it a second time.

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And the blade sailed through like there was nothing there and both cut pieces stayed atop the bottom part. If my hair was long enough to grab and tear out, that is what I would be doing. A rare thing happens and I did not film it because I was lazy to go upstairs and set up my tripod.

Of course, I went upstairs for the tripod in a hope that I will be able to replicate it or at least get some interesting footage from the remaining three boxes that I had at hand. On two I got useless footage because I messed up my cutting technique. Probably nerves. Definitively nerves. On the third attempt, I did manage to get three clean cuts through the box, but the first two stayed on only because they remained connected on a minuscule (~1 mm) strip of paper – I was standing a tiny bit too far from it. After the third cut the top fell off but the bottom stayed on the pole so at least there’s that.

It is a wicked sharp blade, it cuts like a lightsaber. It will be a good tool. But I missed an opportunity for getting good advertising footage. Bigly.

A Big Commission – Part 6 – The Sharpenstone

Today I have made the last piece of the puzzle – a small whetstone for edge maintenance in the field. I expected it to take me two to three hours, it took me twice as much. Partly because it was the first time I was doing it so I did not really have a clear plan on how to properly proceed and what will work best, partly because I screwed up and I had to start all over with one part. But I think that if I were to make another, it would indeed be those two hours that I used for price calculation.

I started with a piece of native, strongly metamorphized phyllite. It has visible big garnet grains and it is very hard.

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I cut a strip off with a diamond stone cutting wheel in my angle grinder. I have used that wheel also to roughly shape it and thin it.

For the second, fine layer,  I have used a piece of old roofing shale. Those can sometimes be found around here on building sites and even in my garden.

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Those are not native stones, they are the remnants of long demolished houses from before WW2. Initially, I wanted to use a different piece of local phyllite, less metamorphized, softer, and with finer grain, but I screwed up and it delaminated down the middle, becoming too thin. So I went for the shale for my second try because it is stronger and I wanted to be definitively done today.

Using five-minute epoxy, I glued both roughly shaped flat stones on a thin jatoba board, making a small stone popsicle.

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© Charly, all rights reserved. Click for full size

© Charly, all rights reserved. Click for full size

After the epoxy cured, I shaped the outline, covered both outward faces with adhesive tape, and submerged it whole into linseed oil for a minute or so to soak the wood.

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After that, I had to grind down the faces a bit again, it was just a bit too thick to fit into the pocket. I ground them down with the diamond wheel and then flatterooned them on granite stone with wet&dry carborundum abrasive paper on it.

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Both phyllite and shale are soft enough so they can be shaped with abrasive cloth or paper, but hard enough themselves to abrade steel.

This is not a stone for serious sharpening work and I have told the customer so. Its abrasive action will be relatively mild compared to modern carborundum-based whetstones, even on the rougher phyllite side. But it should be excellent at maintaining an already sharpened blade and giving it an occasional touch-up during work. I have used pieces of phyllite or shale for exactly that, although those were stones found by the wayside, impromptu flattened and used out of necessity, not nicely crafted like this one.

Thus almost all work is finished – tomorrow I will sharpen the blade and make nice pictures to present here and on Instagram.


A Big Commission – Part 5 – The Stitchening

The original sheath the customer provided as a template has the tip reinforced with plastic. I cannot do that of course. Making a metal cape would be an option, but an expensive one since I would have to make multiple metal templates to press it and then solder it, polish it and all that jazz. So I have convinced the customer that reinforcing the tip with 4 mm thick leather should suffice. Which I think it should.  But I did make an extra step to make that thick leather just a bit harder – I heated it to 70-80°C in water and kept the heat until it shrank to about 80% of its original size.

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This makes the leather inflexible and somewhat brittle in bending, but very hard. Hard as plastics in fact. Caskets or boxes can be made that way. It has several caveats that need to be taken into account, however.

  1. After it is taken from the hot bath, it remains pliable for some time but not very long and it keeps shrinking for a while. If it needs to be formed in a specific shape, it needs to be pressed into the form quickly and left to cool down and dry in form.
  2. Because it shrinks, any decorative carving that is done can only consist of outlines. Any fancy pressing or stamping simply won’t work. And the shrinkage has to be taken into account – as well as the fact that the shrinkage is not completely regular in all directions and predictable.
  3. As it shrinks, it gets also significantly darker, dark brown. So it reduces the possible dyes that can be used to change the color to any shade you wish, as long as it is black.
  4. It needs to be heated up carefully. If overheated, it curls up and becomes way too brittle.
  5. If there is a risk of any bending stress, it should be reinforced with fabric or untreated leather. It is hard and scratch resistant but breaks when bent.

For my purposes, I needed two flat plates, so I left them to cool down and dry under two flat pavement bricks.

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On the top, you can see the already dry pocket taken out of the form. On the right is a glimpse of my impromptu cardboard template for the sheath.

Working on a complicamaticated thingamajig like this the ooo is very important – order of operations. If one glues and sews together some parts it can make some other parts impossible to add or modify, so I had to think carefully about how to progress. For example, on the outside, I had to first sew on the pocket flap, and only after that I could sew on the pocket itself.

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The kukri sheath is wide open on the back and the blade itself is thus held in place with a flap with two snap-fasteners. To avoid rubbing of metal on metal, I have pressed the lower part of the fasteners on an extra piece of leather and glued & sewn that onto the sheath.

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When making the belt strap, I had to form it, glue it and sew it together about 90% of the way, then I had to leave it with the threads hanging, glue the eye shut, and sew the rest. The strap is sewn from two layers for several reasons – I have used relatively thin leather and I was afraid it would not support the weight of the whole assembly, which will be over 600 g, and the way the sheath was cut, on the strap it would be the suede side of the leather facing out, and on this one, it is not particularly pretty.

I have possibly slightly overengineered the whole thing – there is double stitching along the edges as well as stud reinforcements and I have spent several more hours with it than I planned to. I do hope that it bears out in durability, I need satisfied customers to spread the word.

I have now applied some dye to the finished product and it hangs outdoors in the shade to dry. I have also applied linseed oil to the handle and it hangs outdoors in the sun to dry. Tomorrow I will condition the leather, and sharpen the blade and I am nearly finished. All that will be left is to make a small sharpening stone that fits into the pocket. I hope that won’t take too long, a few hours at most. Although I have some funny over-engineering ideas there too…

A Big Commission – Part 4 – Surface Finish & Glue-up

As I said because this blade is supposed to go “only” to 100 grit, that in no way meant that polishing it will be an easy task. I had to polish it on the belt sander to 150 grit in fact, and then remove all perpendicular scratches with 100 grit wet&dry sandpaper manually with scratches that follow the curvature of the blade. It was a bit of work not only due to the steel being hard but also because the surfaces are fairly big and wide when compared to even the biggest knives.

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After it’s been polished, I etched the logo and number and put the whole thing into oak bark extract overnight, then I washed it off, made the handle scales, and put it into the extract overnight again. Today morning it had a nice dark grey color all over.

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You can see the boundary between the hardened blade and soft tang near the sharpening notch. I forgot to tell the customer about that, I hope he won’t mind. In my opinion, the boundary is really neat and it is just another small detail. A good sign is that there are no such sharp boundaries anywhere on the blade. I have tested the whole blade by scratching but this is yet another confirmation that the whole blade is properly hardened and tempered.

Today was glue-up time. You have seen that already, but this time I think I have a nice picture to illustrate the construction of the handle here.

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For kitchen knives, I only use dowels 6 mm in diameter, 2 bamboo ones in the middle, and two metal ones on the front and back. However since this tool will probably encounter a lot of impacts, bends and vibrations, I have decided to use 2 metal pins and 3 beech wooden dowels with 8 mm in diameter (the third pin is there for the lanyard). The wooden pins are there for the glue to have something to really adhere to and the metal pins protect the assembly against shearing forces. And because none of them go all the way through, there are no visible pins on the outside. Except the one for lanyard, which must go through the wood otherwise the end would most likely split sooner or later due to the lanyard.

And so today, after the glue fully cures, the machete is 90% finished. All that remains is apply linseed oil to the handle. But before I do that, I will have to make the sheath otherwise I would have to wait several days before the oil hardens. So tomorrow is leather cutting and maybe leather glueing and stitching day.

A Big Commission – Part 3 – Stuff Got Really Hard

It rained a bit on Wednesday, which was lucky. I did not want to start a charcoal fire when the whole garden was bone dry. And I had to start a charcoal fire because this blade is way too big for my small gas forge. I have managed to quench and harden all that I have set out to (it would not be worth starting the fire for just one blade, so I prepared three more plus a platen for the belt grinder – I will post about those later) but it was extreme pain in the ass. And I finally found out why I have sometimes – but not always – trouble reaching the right temperature with this setup. As the coals burn, they get smaller and smaller and since I am blowing the air in the pile from the sides and from up, the air cannot reach the bottom of the fire anymore and thus I get scorching heat on the surface, but barely any heat just one-two cm below it. It makes perfect sense when one thinks about it. I will probably have to build a bigger gas forge for such big blades or a charcoal forge with air input from below the coal.  If I will go through the trouble, I will probably build a gas forge since it is significantly safer than charcoal. The problem is in getting my hands on proper housing for the forge – I do not have any.

Anyhoo, the quenching was such a pain in the ass that I spent several hours with it after which I was dead-tired. I managed one tempering cycle at 150°C in the oven in the evening that same day, and the next day while the knives were in the oven for a second 150°C cycle, I tempered the kukri manually with a propane burner.

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I put water-soaked paper towels on the edge and heated the spine of the blade until the blue color crept almost all the way to the bevels on both sides. The paper towel near the tang is not there to shield the tang, however, just to shield the plastic clamps. Later on, I tempered that area more than the rest of the blade because that is the area where there will be the least cutting action – thus least need for edge retention – but the most stress during chopping – thus most need for toughness. Here you can see the fully tempered blade shining with some of the colors of the rainbow. You can see that after I took the towels off, I tempered the edge a bit too.

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Here is where things got really hard. 54SiCr6 is very tough spring steel. On the spine here it is tempered at 300-400°C, where it is at its toughest. Which is good.

What was not good however was a slight left-leaning bend towards the tip of the blade and a slight wave near the tang. This is 4 mm spring steel, tempered to springiness. It was difficult enough to straighten the blank before work – It broke my unbender so I have reckoned that straightening this will be hell on earth.

I was 100% correct. I tried a clamp and two steel shims, a method that I used to straighten the blank. It did not budge. Then I tried the old method with two screws in the vise. It did not budge, but I was very close to breaking my vise. After over an hour of completely futile effort, I have decided that I have to repair and reinforce my unbender and if that fails, I will have to ask the customer if they accept the bend.

Therefore I took some steel L-profiles from my scrap pile, some flat mild steel, an M10 threaded bar, and some ball bearings and I got to work.

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As you can see, I have replaced the upper connection with two girders from L-steel profiles. What you cannot see is a similar reinforcement under the two rollers on the base. What you also cannot see in this picture is the upper rolling wheel – that one got totally obliterated.

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The axis of the upper roller was completely bent out of shape. It is bent on one of the lower ones too, but not so drastically. I could not easily make a new roller with a thicker axis from materials available to me straightaway so I have just put 6 ball bearings side-by-side on an M10 threaded rod and that’s it. Next week I am taking my parents to a doctor in a nearby district town where I can buy more ball-bearings to make the lower rollers sturdier too. I have decided that buying and using ball bearings directly will be probably easier than trying to find a pipe in which they fit. Sometimes not having a lathe is really a pain in the nether regions, but one cannot have everything.

Thus reinforced unbender  – bolted to the table – was finally strong enough to actually do something. I did not get a perfectly straight blade, but instead of the tip straying over 2 mm from the center line it has now just a few small wobbles, under 1 mm. One has to look very close to notice them and some of it will come out in the polish too.

I took the now hardened, tempered, and straightened blade outdoors and I bashed a few things with it – a brick, a stone pavement, and a few ash logs in the firewood pile.

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It is not sharpened yet but it did stick in the end grain of the ash logs already. I was not joking when I said that I have bashed a brick with it. I really did, I wanted to make sure that the blade does not shatter. It will be used as a foresting/garden tool and it must be able to withstand some serious abuse. If it did not, it would be very wrong of me to charge the money that I do.

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I took a picture of the blade stuck in the log so you can see the straightness a bit. It was difficult to align the lens of the phone properly, but I think you can see that it is mostly straight.

Now there will be some grinding and gnashing of teeth. Luckily this blade will not need very high polishing, just to 100 grit. Even so, it will be a hard slog since it is hard, tough material.



A Big Commission – Part 2 – New Magnetic Thingamajig

My magnetic chuck for grinding bevels  works well and I am still using it but it is unsuitable for establishing the bevels on a huge blade like this. I have actually been thinking about this for some time, and the kukri commission was in the end just a suitable excuse to play for two days with magnets and exercise my grey matter a bit.

The thing I came up with was a combination of a magnetic jig and the sharpenatrix. That alone could not work because it does not allow me to get as close to the belt as I need. And also it has a fixed length, so in certain positions, the blade like the kukri would actually be partly above the tallest point on the belt. Thus I established that I need:

  1. a telescopic arm
  2. a switchable permanent magnet

Both of those things can be bought, sometimes even in conjunction. But they are really expensive and for my purposes, even the cheapest and smallest ones are needlessly bulky and heavy. Yes, at long last, finally a chance for me to just dick around with various scraps and it is really economic use of my time!

After some trial and error, I have gotten the best results with just two magnetic arrays from two broken speaker magnets and four flat pieces of mild steel from a broken clamp.

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The magnets are oriented in both arrays with the north in the same direction on both sides of the pipe in the middle. And since they were broken into irregular pieces, I have glued them in with a mixture of steel dust and epoxy to better facilitate the transfer of the magnetic field into the steel. With one exception – the side that is going to hold the workpiece has a bit of brass between the steel bars, so the magnetic field does not extend there all the way to the surface between them. The piece of stainless steel non-magnetic pipe in the middle allows me to connect the two magnets with an axis around which they can swivel freely. When the poles of both arrays are aligned, they repulse each other but the whole assembly sticks to steel on the sides very strongly. When they are misaligned, the whole thing is nearly non-magnetic all around.

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Here you can see me testing it. A threaded copper rod is fixed to one of the magnetic arrays and will connect it to the telescopic arm later on. A stainless, non-magnetic steel rod is also fixed (riveted) into that magnetic array. The second array can rotate freely on the top. At this stage, I got my first bonus – both extreme configurations are stable without the need for any mechanical locking mechanism and the outward magnetic force builds up/disappears quickly, not gradually.

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Now you can see it nearly finished. The telescopic arm consists of several parts:

  1. the 8 mm copper rod with stainless steel nut fixed into the array
  2. thin 12 mm steel tube lined with 10 mm brass tube in the upper half to ensure a tight fit for the copper rod.
  3. 10 mm steel rod with thread at the end on which the ball from sharpenatrix can be screwed
  4. 2 screws go through threads in two pieces of thicker tube and through all the tubing to lock both the steel and the copper rods in fixed positions. There are brass inserts under each screw to ensure they do not scratch the surface of the rods. Hopefully.

The knob was only added so I do not poke myself with the sticking screw during work and it turned out to be a second bonus – it allows me to hold onto the blade with one hand and comfortably hold and switch on/off the magnet with the other.

With that, the arm was not finished yet, but it was functional, so I went on and tested it. And it worked really well. Not ideally, but it did help a lot, especially with a complicated grind like this. Kukri changes the blade width over the lenght of the blade, so to reduce the weight, keep it strong, and optimize the cutting capability towards the end of the blade the primary bevel has to be steeper on the wider portion of the blade than on the narrow part. So I had to grind it in two steps. The first step was to establish the less- steep bevel on the whole blade (approx 5°).

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The second step was to establish the steeper bevel on the wide portion of the blade whilst carefully feathering it into the narrow portion. The grind on the intermediate portions is a bit funny-shaped, which I will have to correct with a file. Later during polishing (this will only go to 100 or perhaps 120 grit), it will smoothen out, I did make blades like this already, although not of this size and not with a belt grinder.

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I made this grind in about an hour, which is speedy, especially considering that I was working with a new jig. I slipped up on two parts on the other side before I figured out how to best use it, but nothing that would not be corrected in polishing.

As a final touch, I have encased both arrays in alluminium housing so they do not gather steel dust. And I painted ON/OFF markings with a sharpie to have visual clues during work.

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If it were a bit stronger, I would not have those two slip-ups that I had, but it is strong enough to be useful – it has over 2,5 kg lifting force, which is in my opinion impressive given that the initial magnets on their own have barely lifted anything.

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Overall I am very pleased with the result. I now know how to make small switchable permanent magnets. I still have some ordinary black magnets to play with, but I will probably also buy some small neodymium magnets and build myself a variety of magnetic holders with high force. Even a small flat magnetic plate can cost several hundred €. With some care and planning, I think I could make a useful one myself for a fraction of the cost in just a few days.

A Big Commission – Part 1 – Beginning

I got a new commission via the sign on my garden gate. Maybe if I did not live at the end of a road in the middle of nowhere I would have gotten more business that way, but a little is better than nothing.

The customer initially asked me if I could harden a kukri machete that he has bought and found of insufficient quality. My reply was that it might be possible, but only if the steel is good enough and only the quench is botched, not if the steel is craparooni as well. After a bit of back-and-forth, he brought me the bad kukri together with one that belongs to his friend and that he initially intended to buy.

Both machetes are from the same company. I won’t tell you their proper name, but it could be paraphrased as “Low-Temperature Carbon-Iron Alloy”.

The bad one was manufactured allegedly in Africa (the country was not specified) and it is really bad – it has no primary bevel, so it is essentially just a sharpened flat bar. The hardness is about 50-51 HRC, so it is hardened. But this is the lowest point where it might be useful as a cutting tool – with very frequent sharpening. Which would be difficult with steel this thick and this type of grind.

The good one was manufactured in the USA and it is in my opinion still bad, although not as bad as the first one. It does at least have primary and secondary bevels, so there is no need to remove excessive amounts of material when sharpening.

I took a picture of the good one, proposed a few design modifications, and made an outline and a price offer.

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Since this is supposed to be a working tool, we agreed that there is no need for high polish or any excessive fancifulness. On the other hand, there should be some fancifulness since a handmade product is going to be expensive regardless. So there will be a jatoba handle with hidden pins and a dyed leather sheath with a pocket and natural sharpening stone. The offered price is about ten times higher than what the manufacturer of the original has charged, but I do hope that I can deliver a product worthy of that expense.

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I have already cut the outline from 4 mm spring steel and then I got distracted. I could grind the bevels freehand, I do have the skill to do so. But I thought to myself – I might need to make a second one if the first one cracks in quench, I might get more requests for big blades, so it probably is worth to spend some time making a jig. And today, I started to make that jig.

More about that when it is finished.