Forge improvement: A better Venturi-Burner

I built a new burner for my water tank forge. The first one I built had serious airflow problems and with too much gas it tended to blow out its own flame. So the generated heat was limited.

With my new welder, I was able to rebuild the whole cap. This type of burner is called a Venturi Burner. The gas flow from the nozzle pulls the air through a pipe by the sheer velocity of the movement. The air is not accelerated by an electrical fan or something, it is pushed into the pipe by atmospheric pressure. The mixture of air and gas moves fast enough to flow and mix in the pipe but the flame can not go back into the pipe.

These burners actually rely on two principles: the Bernoulli Principle and the Venturi effect.

An increase in velocity of a moving fluid results in simultaneous decrease in its pressure (and visa versa)

Bernoulli Principle

The result is that the velocity of the gas leads to a lower pressure of the gas (this is what the Bernoulli Principle says) and so the surrounding air (and so the oxygen) at atmospheric pressure is ‘entrained’ into the low-pressure gas flow to even out the difference of pressure, this is the Venturi Effect.

Schematic view of a Venturi Burner

I bought some plumbing pipes made of iron and used a wire brush wheel on my angle grinder and a scraping disc to remove the zinc from the surface. Zinc can lead to health issues if heated and the gases are breathed in.

First I just held the cap near the top funnel and lit the burner to find the right distance and the right gap for the air intake. Then I welded the two parts together. The top cap is the former tip of a usual gas burner used on roofs. I just cut int into the right shape.

Yes I know it is not beautiful but a huge improvement that ads a lot of power to my forge and the flame is more stable at higher settings.

Literature and sources:

Welding steel

As I wrote some times ago I like to learn new things, combine the techniques I learned to something new, and expand my skills. One thing on my bucket list was to buy a welding machine and learn to weld. Probably because I saw my dad try his best with his not-so-good arc welding transformer when I was a child and still I am fascinated.

I looked up different machines, not too expensive for just getting my feet wet, with good reviews, and most importantly it should be as flexible as possible when it comes to welding techniques. I ended up having a look at Stahlwerk Schweißgeräte [unpaid advertising]. I was thinking about to get their MIG 200 amps machine as it was able to do Mig/Mag, arc welding and flux-cored welding. Unfortunately, it was not on stock for a long time on their site and on Amazon. I even got a welding automatic helmet and welding gloves for Christmas long before I got the machine itself.

So last week I did it and hit the “buy now” button as a pre-order. I had decided that for my needs 175 amps would be sufficient and bought the machine. The day the parcel service announced the package I kept hitting the reload on the parcel tracking page, nervous like a kid on Christmas Eve. Meanwhile, the tracking page even got a 500 server error message but fortunately, it wasn’t me. They where just launching a new page 🙂

My 14 years old son trying out dads new welder

I tried to weld some beads onto some scrap metal and oh boy times have changed. It was so easy to ignite the electrode and or the flux-cored wire. No way you can compare that to the old transformer I got in my garage, the old welding machine of my dad. In the end, I had the best results with simple arc welding electrodes.

In the above video you see my son trying out my new machine.

The story of my second built of Kukri III

Custom made Kukri III knife with leather sheath

Before I sent the first built of my Kukri III custom knife model to my friend @JAMZT53 I showed the knife around. It was admired by many people, friends, and family – so I quickly got another order for that knife in my books.

After I finished the Longbow I tried a different way to organize my work and started to work on multiple knives at the same time. I began making another PB, Tigershark, and Kukri III model at the same time and planned to switch whenever I had the motivation for a specific step of knife making.

Kukri III custom knife photographed from the top with grey background

While doing so life hit me and I found myself in the middle of switching my daytime job. Don’t get me wrong, the step was planned and long overdue but it brought a lot of changes to my life. With a lot more responsibility and freedom of making decisions, sculpting an entire IT department from the ground up and such. It is honestly an awesome job and it was absolutely the right decision.

As a result, I simply did not have the focus on handcrafting and coming back home late, and then go to my workshop and work on a knife. So knife making got a bit off my schedule. I was all the time looking forward to diving back into it though but even on the weekends, I could not find the time and energy for it.

Times have changed, I “arrived” in the new job and I got a lot of very positive feedback from my new boss and I am obviously doing one or two things right there. That put a lot of wind under my wings and additionally then came the Corona lockdown and we are all working from home. That took away all the commuting to and from work. In the end, I am working a lot more on my job from the home office and on the other hand, I am finding back my way into knife making on the weekends or finishing one or two steps in the evening. And also: It got warmer since spring is here – the small radiator just does not warm up the workshop so nicely when it is cold outside 🙂

Kukri III closeup of the etching on the hilt of the blade
Kukri III with a bit different name tag and my makers mark “SK”

So here I am back, with a finished Kukri III on my table, working on the sheath and pushing things forward to deliver the knife, which by the way came out quite good. I am happy with the final result and look forward to seeing the reaction of the one who ordered it.

Different liner material: Felt

I was looking for a different material I can use for liners. I constantly use liners in the handles between the handle scales and the blade on full tang knives and between the guard and the handle on hidden tang knives.

I usually use Micarta I make out of resin and paper and was looking for other ideas and came up with some felt my kids use for handicrafts. So I gave it a try and made some simple tests:

felt as liner material in knife making
First tests with felt as liner material

I brushed a good amount of epoxy resin on the felt and pressed one between two pieces of scrap wood and the other one I just pressed flat and let both experiments rest for 24 hours. This long wait is just because I use a very slow hardening epoxy.

After removing the clamps I cut out the flat piece with scissors. The wood pieces I sanded flat on 3 of 4 sides to simulate the effect when I use them as liners on a knife handle.

I made some stress tests with the wood pieces trying to break them apart but they are solid and well bonded to the surrounding wood. I wasn’t able to break them apart with a realistic amount of force.

Conclusion

There are some advantages to felt. First of all, it is thicker and the layers needed to reach a certain thickness is clearly lower, this might save some time. Second, the darkening effect when the material is soaked in resin is not as extreme as when using paper so I can better predict the resulting color.

As a disadvantage I have to check if there are air bubbles left in the material. You can see the effect of air bubbles in the flat piece in the picture above – the brighter part in the middle results from tiny air bubbles.

The top picture shows how I fit a Kukri III that I am working on while dry fitting the pieces of felt between the different parts of the handle. Pictures of the finished built Kukri III will follow.

A new and bigger Bowie, the Longbow

The Bowies I made till now were with wide recurved blade design. I like the form a lot but I saw a lot of knifemakers doing a very slim design for their Bowie blades. I also wanted to make a bigger knife to see how far I can go. The main challenge is not grinding a bigger blade into shape but the size of my forge and the containment of the heat treatment oil.

While I planned the new knife, my friend Joe asked me to make another knife for him. This time I should do it completely free as I like and put as much into the knife as I want. When working with and for Joe he always gives me complete creative freedom, but this time I also suggested the knife model. That was perfect timing.

I showed him the draft and he liked it. So I started with the project and got the shape into the steel. I was totally amazed when I held the rough blade in my hand for the first time. The ergonomy of the handle was on point. I don’t know if I have a good sense of handles or it is pure luck. But I like how I can grip the handle with the full fist or put the thumb on the back on the spine of the blade and up to the thumb stop.

I showed Joe pictures of the progress and I felt how he began to love the blade after he just liked it at first. He told me he would love to have a green handle. I had seen nice colored wood at a german online dealer for knife makers. And I showed him the exact piece of stabilized green poplar burl. That stuff looks like jade marble. He liked it and so I ordered it.

The piece of wood looked even better when you see it live – but it made me very nervous to cut the wood into halves. The knife would have a full tang so I needed two parts. I have had some problems getting perfect straight cuts on my bandsaw before. I practiced with some pieces of wood – and it went much better than expected. So I cut the stabilized wood in half and sanded it perfectly flat on a piece of sandpaper that lay flat on my workbench.

The wood left neon green wood dust everywhere – even more, when I started shaping the handle. My workshop looked like an alien landing zone with all the green stuff around. Good, I got my respirator.

As always I left the handle a bit thicker. A big knife like the Longbow needs a handle you can grip on.

The blade is polished to a mirror finish – and I don’t know why but this went pretty good this time. Usually, I have a tough time getting all the scratches out of the wood but this went pretty easy this time.

Trying a different approach to organizing my work

Until now I worked on one knife at a time but I always strive to find the best way for me to work on my projects. Working on one knife at a time meant, for example, to fire up the forge to heat treat just a single knife, it would be much more efficient to harden more knives at a time. Or to carve out the blanks for multiple knives at a time instead of just one and then have to switch tools and so on.

On the other hand, I want to keep the passion I put in every single project – Concentrating on the details that make every single knife unique. To make sure I do not loose this I will allow myself to jump between the projects and push on the parts of the single projects that I am most motivated in.

Currently, I have 4 knife projects in parallel active. I am working on the “Longbow” Bowie knife, another Kukri III, a new Tigershark hunting knife and the PB skinner but with a thicker blade. I started all blades at the same time but now the Longbow is finished for etching and I have a beautiful piece of stabilized wood for it here. All other blades are heat treated and ready to be cleaned up. Only the skinner is already partly ground clean from the filthy remains of the hardening oil.

So much learned from a “Tigershark”

For a long time, I had a picture in my mind of a hunting knife with a constant flowing line from the tip of the blade to the heel of the handle. A simple but appealing knife form that also serves perfectly as an EDC.

My first design was quickly drafted on the PC, but when it comes to dimensions and proportions a desktop screen is not the best solution so I always print it on paper and cut it out – and oh boy that blade was too big for an EDC. So I shortened my design and brought that onto the steel blank.

I asked my younger son (10) what would be a nice name for a blade and he made some suggestions. One was “Hai”, English “Shark” and I thought about the Serpent Wood I had in mind for the handle and with those stripes could be tiger stripes – so I said “Tigerhai”, English Tigershark and we agreed.

Learnings

I learned a lot while making this blade. One goal was to try to do as many steps as possible on the belt grinder instead of lengthy hand sanding. The mistake was, that I went too far using a rough 40 grit belt while shaping the bevels so I ended up with a thin blade with still deep scratches. I managed to grind out most of them then went to etch my maker’s mark and the “Tigershark” logo into the blade. First of all the logo had too wide letters – this makes it harder to get a consistent and clean etching. I ran into a second problem because I had etched too early and while cleaning up the surface of the blade ground out too much of the etching.

I have had problems with the micarta liners while gluing the layers directly to the wood. The wood soaks up the epoxy and starts bending, then the epoxy gets dry and the wood stays bent. It is close to impossible to bend back the handle scales – I tried that. This time I made the Micarta liners separately and then drilled and glued steel, Micarta liners, and wood together in one step. Also, I used screw clamps for more pressure than simple clamps and that did the trick to get a perfect flat connection between steel and handle scales.

Feedback I got

A friend of mine is a professional hunter and I did not know he is also a passionate collector of knives and he did not know rom me that I am a passionate maker of knives. He got very interested in my work and i showed him around in my small workshop.

He liked the Tigershark a lot and gave me some good tips on how I could improve the knife, especially the handle I was shaping at that time. I was able to let his suggestions influence the final shape of the knife and he and I like the final result.

Conclusion

I like the blade shape and the look of the wood and will take this design into my repertoire of blades I will continue to make. This knife has its flaws so I am not sure if I will keep it for my own or just wait for an offer that I like. Either way, I will make a sheath for it later.

A knife for leather artisans: The Hammerhead

Until now I used a sharp scalpel to cut the leather when making knife sheaths. The disadvantage is that the thin blade snaps pretty easily, especially when forcing the tip of the scalpel around sharp corners.

I thought about buying a half or quarter moon knife (leather round knife) for my work and searched how they are used and what the advantages are.

And then I recalled: hell, I am a knifemaker, why don’t I design and make myself a leather knife. So I put some design on paper. I wanted a sharp point on one end of the blade and a circular part of the blade to do rolling cuts and a part of the blade should be suitable for pulling cuts.

Most important would be that this knife is stupid sharp so it would be as good cutting leather as my scalpel does.

I had so much success with my knife projects so far and not so many failures, that I completely underestimated how hard it is to grind the bevels of such a complicated blade. I guess it is not impossible but this knife is no beauty after all. I ended up doing a convex grind for primary and secondary bevel as this helps even out the grinding mistakes. It is difficult to have a consistent angle all around the edge and even harder not to grind into other parts of the blade while concentrating on another. So I consider this grind as my first real failure in regards to beauty. Sharpening went just fine and I have a razor-sharp edge.

I chose some beech wood for the handle, which I had sawn and dried some time ago. The wood is sufficiently hard and cheap for a prototype tool. I glued the Wood directly to the steel without any micarta liners – something I did never do before, too. But in the end, it looks like a useable tool knife and the first cutting tests are very promising.

My personal knives touch

I like the forms and styles that have a character. I like designs that are remembered. I like unique blade designs that give new opportunities. I am still developing my own personal style but some things drive me when designing a new knife.

The blades

Even the most meticulously made blades I make should be practical to use and durable. I am not making “Show-Only” knives that only look good hanging at the wall. I like recurved designs and blades with lots of character. I like doing crossover designs that combine two well-known styles into something new or combine old and modern styles. I like the blade to have a weight and when in doubt I tend to use thicker steel. Currently, I am addicted to carbon steel and love the knives getting character and develop a patina, a personality. I love tools and knives that have to be cared for like a gun, cleaned and oiled. It is like getting into a relationship with a knife as a companion.

The handles

The handles must feel ergonomic and comfy in the owner’s hand. Soft to the touch but robust hand tough when in heavy use. But he still should feel the knife, the weight and the capabilities of the blade. I want the handle to give a level of safety and confidence to the owner. The form should always serve a purpose. The thick heels of many of my knife handles give a good feeling that you have a secure grip while hacking with the blade or doing pulling cuts. Finger guards save the owner from slipping into the sharp edge. The form even should provide good handling when just picking the knife up with two fingers.

The sheaths

What applies to blades and handles also applies to the sheaths. They serve a purpose and that is a practical one. They are not only for show, but they should also be practical. They should protect the owner from cutting himself and most of all should be perfect for carrying the knife. I also like to go new ways of designing my sheaths to suit my knife designs perfectly. I like using thicker leather to have a robust product with years and years of use for the owner. I treat the sheaths with dye and a leather fat normally used for outdoor boots to protect the leather.

As the above is important to me I also added it to my About page.

Making a Saya for Japanese kitchen knives

I made the Kengata Santoku Chefs Knife for my mother this year and later a Petty Knife for her birthday too. She loves the knives because they are handy and extremely sharp. She handles them with much care and oils them after every use. But she had no good place to store them.

So my father made her a primitive knife sheath out of some scrap leather he had lying around. He just folded it around the spine of the blade and roughly sewed it shut with a thick nylon thread below the edge. I just finished my third knife sheath but sorry dad, this thing looked like crap 😉

My first impulse was to make two more leather sheaths but hey, these are Japanese style kitchen knives and did I do a Saya yet? No? So it was about time!

A Saya (the Japanese word for Scabbard) is a wooden knife (or better sword) sheath that I had seen made for kitchen knives too. So my chance to try out making one (or two) had come.

I wanted to start from real basic and cut the wood out of some piece of firewood I keep in my garage for our oven. I also decided to do Sayas for both knives, the Kengata Santoku, and the Furutsu. So I cut two thick boards.

Each Board I cut in three layers with the outer of equal thickness and the inner as thin as possible, about 0,5 cm. On the inner board, I drew the outline of the blade and cut this out. So I had a wooden frame that fits exactly around the blade of the knife. This frame I glued to one side of the other boards again. Before I used the frame as a stencil to draw the shape of the blade on top of the board that would be a side element. The outline would be needed later.

After the glue had dried I put a strong neodymium magnet in at the tip of where the blade would end and then I cut away some millimeters of the thickness of the frame on the band saw before I used the belt grinder to thin down the frame close to the 2 millimeters of the blade thickness. I drilled a 5-millimeter hole through one side. After I evened out the frame side and the remaining board I glued them together as well.

As I had the outline of the frame on one side of the glued up sandwich I added about a cm to the outline and cut that out on the bandsaw. The rest was grinding everything in shape on the belt grinder.

Just when grinding the Sayas to a finer grain I noticed that I accidentally used two different types of wood.