Friday, December 17, 2010

Blacksmithing: Carbon Migration in Forging Blades

Is there Carbon Loss In Forging Blades in a Gas Forge?

Hi David Merry Christmas and thank you for an ongoing 'live' tutorial. It is very generous of you and I want you to know that I appreciate the time you put into it for us!

I do have a question at this point. One issue that you haven't addressed (perhaps you just haven't gotten to it yet and if so I apologize for jumping the gun) is that of carbon loss with a gas forge. When I was training in Japan, I watched a Bladesmith produce kitchen Kata-ha blades with a gas forge. He explained, however, that he had to work extremely fast and could only afford one heat for the forging process (he uses a spring hammer) or he would lose too much carbon. When I say fast, I mean it. I took a video of him forging 4 - 5 blades every 7 minutes. He is not an amateur, but rather the person who is considered to be (within Japan) the best kitchen knife forger in the world, so I trust his word.

It would be useful to hear your thoughts from a Western perspective.

This is an advanced question for sure.

I do make knives but there are many people much more skilled than I. I am sure the fellow in Japan is one of them but here is my view point.

My take on is a bit different. Yes I do agree if the gas forge is running too lean (too much oxygen then yes at high temperatures there is carbon loss but really only in the outer 1 mm of the steel. The carbon migrates to the lower carbon areas and if low carbon in the atmosphere of the forge then it can jump to the atmosphere, causing a net carbon loss in the blade.

There is an old saying to "forge thick and grind thin" once you start grinding you are getting back into the high carbon steel.

By keeping the forge running neutral or a bit rich there is extra carbon available and carbon migration is less of a concern but you don't have infinite heats to work with. I agree completely that you should forge out the blade in the minimum heats possible as a best practice.

Different steels will behave differently as well. Some steels need to soak a long time at high temperatures to allow the carbon to jump to a face centered cubic crystal. Think here S7 or H13. Neither would I use for knives but the high alloys do change things a lot. So in part the alloy of his knives would make a huge difference in the final quality of the piece as well as the number of heats he takes.

One heat is pretty fast! And shows a great deal of control on his part.

When You get a chance look up the article on heat treating in the members area. There is a pdf at the bottom of the page that you should download and read as it goes into much more detail than I possibly could.

Link To Blacksmith Members Sign In

I hope this helps but do check out the pdf as it goes into great detail.

Merry Christmas and Happy Holidays to all!
David Robertson
Artist Blacksmith

Wednesday, November 3, 2010

Hydraulic Press as Power hammer for Armor Making

Info PR: n/a I: 1,220,000 L: 0 LD: 167,471,963 I: 23,700Rank: 8 Age: Oct 12, 1999 I: 0 whoissourceRobo: yesSitemap: no Rank: 1376 Price: 4075140 Density

I was wondering if I use a hydraulic press for plate armor will it give the same effect as a hammer and stake or will it stretch and thin the metal?

Interesting question.
I have only worked a little with a hydraulic press but will pass on what I know.
It should work fairly well for simple dished forms. So this is changing flat sheet into bowl shapes. You will have to be careful of wrinkles developing in the steel sheet. If a wrinkle starts immediately press it out or it will get out of control. Hydraulic press have the advantage of being very slow so you can see things develop. The extra pressure means that once an unwanted shape starts to develop it needs to be corrected right away.

The hydraulic press wont work well when using a raising technique on the sheet steel. You may have to do this by hand on a stake as usual. The raising techniques involve closing a piece of sheet over a form or stake with very light repetitive hammer blows. This is actually thickening the steel as the pipe or cone is created. The press tends to deform the steel either by thinning if it is trapped between two dies or by depressing it into open space between two dies. A lot will depend on the types of dies that you make for the press.

For simple armor forming I would think about a mushroom shaped top die and a matching bottom die that could be made from heavy pipe with 1/2 inch round bar welded around the top edge to provide a round surface of contact. The diameter of pipe I would try would be about 3 inch but this would vary depending on the work you were doing.
You will have to experiment here.

Like power hammers any dies that you make should have the edges well radiused so the edges of the dies do not cut into the steel. This will give a smooth transition to overlapping pressings.

Hydraulic Press as Power Hammers.
A hydraulic press is very different from a hammer and does have a different action. They will do some of the same things. Other things not as well. Advantages of the press is the tremendous force that is developed and there is no pounding so they are relatively quite. This can be important in a residential neighborhood. The main disadvantage is that the presses are slow.

You can work hot metal under them and many people use them to develop mosaic damascus with the controlled pressure. The press will work for drawing out but not as fast as an air or mechanical hammer. The press will work very well for punching holes or shearing (splitting) or for decorative veining or punching. All can be done hot provided your dies are set up for it.

Of course a press will work very well for flattening or controlled repetitive shaping if the the dies are exactly made for a specific purpose. Hydraulic presses also have a relatively small footprint in the shop.

In general I would say a hydraulic press is a useful addition to a blacksmith shop but it will mostly depend on the type of work that you are doing. For the armor it may work very well but you will have to experiment with die shape and size to make it work effectively for you.

Sample Hydraulic Presses

Hope this helps.

Wednesday, August 25, 2010

Knife Making Belt Grinders

Recently I have had many inquiries about knife making and belt grinders.

Knife making is one of the most interesting parts of blacksmithing and is actually how my interest was peaked. Had I had a knife making belt grinder when I started it would have been so much easier.

In general there are four different steps in blade making.

  1. Forging the blade from the original bar. This is where the rough shape is created. You may have heard the old saying 5 minutes at the forge saves half an hour grinding. For me that certainly is about right.

  2. Primary and secondary grinding of the blade. This is creating the finished shape of the blade through a series of grinding and sanding steps. For me this takes the longest time and is the most exacting.

  3. Heat Treating. This is the hardening and tempering of the blade.

  4. Final sanding and polishing. This is when the blade is actually sanded to a perfect finish. You may choose to buff to a mirror finish as well.
So a lot of questions have come from people just starting out in blade making. They are wondering about the grinding steps.

Belt grinders are the best solution for blade making. They give you a flat surface to work on and remove material quickly with coarse grit. Fine grit can leave a satin finish to shiny if you go super fine.

The problem is that knife making belt grinders usually range in price from $1200.00 to $2500.00. Now that is a lot of money if you are just trying this out as a hobby. If you are committed then I would suggest looking at this price range. The standard in knife making is the 2 inch by 72 in belt grinder with usually a 1 hp or 2 hp motor.

Back when I needed a knife making belt grinder I couldn't afford to pay the $1000.00 plus for a factory built one, so I choose to build my own. So on a shoe string budget I built one. Does it work? Yes fairly well. There are things I should change on it, but in general I am satisfied with the finished piece. I used no plans and scrounged as much as I could.

I recently found good plans for a nice belt sander that requires no welding. It all bolts together!

Just Click on the above image to be taken to more information.

These plans provide simple construction just with cutting and drilling and bolting everything together. Of course you could weld the joints that needed welding, if you had a welder. It would only make it better.

Now you will have to recognize that some of the parts are expensive. Motors and contact wheels do start to add up, but this is the cheapest way to build a good quality grinder.

I also found this tool

This is very similar to a belt grinder that I started with before I built my big one. If you want to try knife making as a hobby and are on a tight budget this sander will work.

Now this is a light tool that bogs down if you are really trying to hog metal off and the small belts ( 2 inch by 27 inch) wear out quickly, but it will work. This one has 1/2 HP motor. The belts are pretty economical and this is a good way to see if you like knife making.

If you do like knife making and knife grinding then you will probably want to upgrade fairly quickly.

Now I did come across this machine and WOW! This is an industrial metal belt grinder. It sells for only $695.00 and has a 4 HP motor. This is twice the power of the best knife grinders at a 1/3 the price. It is solid and versatile. It uses a large 3 inch by 79 inch belt and has both contact wheel and flat platten for smooth grinding. Had I come across this knife grinder years ago I would have bought it.

There is a downside to it. This is 220 volt, 3 phase. Now 220 volt may not be a huge problem as most shops with serious equipment have 220 volts. 3 phase is usually limited to industrial areas. So now you would have the choice of replacing the motor, or buying a phase converter.

Both are about the same price. The phase converter for this belt grinder is recommended as
So we get back to about the $1000.00 mark but with a 4 HP motor to chew through the metal.

From everything that I have looked at, this is the most cost effective knife making belt grinder on the market. So I hope I have given you some options to look at if you are starting out in knife making or if you are looking to up grade to an industrial level.

Oh yes the most recent blacksmithing course I taught, the students were interested in making a knife as their Sunday afternoon project. They did quite well. I will put up a picture of mine when I get it finished. I still have some grinding left to do.

David Robertson
Artist Blacksmith

Tuesday, August 24, 2010

Blacksmithing : Forge Welding Cable Damascus

I' m interested in trying the steel cable damascus knife, any advice?

Cable is actually really nice stuff to weld. There are a couple of tricks that people forget that help a lot.
The alloy in the cable has a good success of welding even at fairly low temperatures. Having said that use a full welding heat until you are comfortable with it.

Crane cable is better than elevator cable. Elevator cable has an inner core twisted one direction and an out sleeve twisted the other direction. This is called counter rotating cable. That is the cable doesn't twist as it spools off the drum.

Regular crane cable has inner and outer strand twisting in the same direction.

What this means and this is the important step, when you first heat the cable up, clamp it in the vise and twist it as tight as you can get without it buckling. This helps close up the air spaces for better weld. The elevator cable won't twist tight as the inside is expanding when the outer sleeve is being twisted tight, causing spaces to open up.

Back into the fire and take up to a nice orange.
Gently wire brush it, and add flux.
Back into the forge to take the welding heat.

The next trick is instead of welding flat on the anvil (although this does work) use a U shaped bottom swage tool or swage block to help support the sides of the cable when you weld.

As you make the actual forge weld rotate the cable with the direction of the strands. That is each hammer stroke is actually tightening the twist.

You will find that once the cable strands are weld the feeling of the metal changes from the floppy cable to a hard bar. Once it is well stuck together as a bar take a series of refining welds on all edges to make sure any loose strands are tacked down.

When you are completely satisfied that it is well welded then stretch out as normal and make your knife etc. as usual. Once completed, ground, hardened, then sanded again then you can etch in acid to reveal the pattern. You can use vinegar warmed up on the stove. Takes along time but will give you a bit of the pattern, and is the safest acid.

I use more aggressive acids such as sulfuric or nitric or some times ferric chloride. Follow all acid precautions with these strong acids.

Neutralize and take a look at your knife.

David Robertson
Artist Blacksmith

Saturday, June 19, 2010

What is The Best Steel for Making a Blacksmithing Slitting Chisel From?

What is a Slitting Chisel and What Steel Should I use For it?

A slitting chisel is a very thin flat chisel used for opening or splitting steel when it is hot. The steel has to be very resistant to heat so that it doesn't deform as it is hammered through the steel.

Most slitting chisels are about 1 inch wide and the edge less than 1/8th of an inch thick. If you are planning on making curved cuts consider making a slitting chisel about 1/2 inch wide. (The smaller the width the tighter the curve you can make!)

I usually try to make the chisel about 8 to 10 inches long. My preference for making this tool is H13 steel or S7 steel. Both of these steels are heat resistant and stand up to the heavy abuse. They are a bit difficult to forge down to size but it is worth the effort as they last much longer than other steels.

I have used coil truck spring. This is an alternative and will do in a pinch but this steel is not very heat resistant. This means that you can't work it down so thin and if you let it show a bit of color as you are hammering through the edge will deform. Then if your chisel doesn't get stuck you have to sharpen it. As I said it will work but not as well.

I have had good luck using old jack hammer bits which I believe are S5. They stand up to both the heat and the hammering.

Good luck making your chisel and it doesn't hurt to have 3 different sizes. 1 inch , 1/2 and 1/4 inch for detail work.

David Robertson
Artist Blacksmith.

Tuesday, June 1, 2010

Blacksmithing | Can a File Make a Good Knife?

How to Make a Knife From a File?

I have a bunch of old and fairly new files of all sizes. I would like some information on the proper procedure in turning them into a decent blades.

Files can make decent knives but you have to do a fair bit of preparation first. To truly make a good knife I would suggest grinding all the teeth off so you are down to bare metal. If you forge the blade and the tang leaving the teeth on. All the valleys at the bottom of the teeth make small creases in the surface of the blade.

When you heat treat the blade these creases can form cracks or potential cracks, and are always a point of weakness.

In general file steel can be an unknown tool steel and I have heard there is considerable variation in quality. I would try quenching in oil for most. I would actually recommend buy new steel. O1 drill rod is easy to get and makes a good knife and most importantly you know what you are getting. Buy 3/4 or 1 inch round and just forge it flat then make your knife from that.

It might seem a little expensive to spend $30 or $40 on a piece of steel 3 feet long. If your knife breaks in the final heat treating after spending 10 to 20 hours on it the $10 spent on the piece of O1 used for the other knife seems pretty cheap.

If you are stuck for finding O1 and tool steel in your area try clicking through to They carry a full range or sizes.

I have had a number of knife making requests lately so I am planning on doing a newsletter series on it in the near future.

I hope this helps.
David Robertson
Artist Blacksmith

Tuesday, May 11, 2010

How to Deaden The Noise of an Anvil ?

How Do I Decrease the Ring of My Anvil?

There are a couple of tricks to deaden the noise of an anvil a bit.

I do use a chain but the secret here is that it is a fairly heavy chain and you wrap it around the anvils waist. Then it must be bolted down very tightly to the stump or stand that supports the anvil. This does help deaden the ring significantly. The idea is to tightly clamp the anvil to its base with the chain.

You can also add a good sized magnet under the horn or the tail of the anvil. This will collect scale but it helps remove some of the ring as well.

Another option that I don't like as well as the others is to take a short length of chain and make a loop out of it and hang a weight off it. Then place the loop over the horn or the tail of the anvil. It too will help deaden it down the noise a bit, but as soon as you need that spot on the anvil it is in the way and has to be moved.

Hope this helps.

David Robertson
Artist Blacksmith

Monday, May 10, 2010

How to Avoid Distortion Heat Treating Damascus

How Do I prevent Scale Build up When Heat Treating a Knife?

Well making my third Damascus knife 13 layers ,when i get it polished and to the point of tempering when i put it in the gas kiln red hot to loose magnetic it warped every which way .made out of all the same coil spring steel and hammer welded plus all sorts of slag all over it now so while it was red hot gently hammered it straight again and annealed . so how can i get it polished perfect and temper with out slag and distortion next time now after i sand and polish it again ? whats to keep it from happening the next time I go to temper it ???

This is a little tricky to answer as I have not seen all the steps that you have gone through.
Slow cooling (annealing) in vermiculite or wood ash to relieve the stresses is very important. This should remove much of the tension between the two different types of steel. This should help reduce the warpage when you heat for quenching.

If you are heating the blade in a gas forge hold it so that the back is up and it heats evenly from both sides this should help with the distortion as well. It should only be heated just past the magnetic point. It doesn't have to get super hot. Then pull the blade out and test with a magnet until it just pulls then quench the whole thing in the appropriated quench medium. Water or oil. Then temper evenly 425 degrees in a toaster oven. Then a quick sanding and hold the edge in a water bath (about 1/4 inch deep) and paint the temper colors on the back with a torch. Blue on the back straw on the edge.

Then sand to final finish always keeping the edge and the blade cold by dipping in water.

In short I rough grind and sand to about 80 grit before I heat treat. The final sanding is done after the blade is hardened. When I harden there will be some scale formation but it is really very little as it is only up to color for about a minute and not very hot. Just enough to lose the magnetism.

I know some people use a nickel foil to wrap around their blades so that it doesn't oxidize very much. I have not used this technique but understand it works well. You would have to source a knifemaking supplier for the nickel foil.

Hope this helps.

David Robertson
Artist Blacksmith

Tuesday, April 27, 2010

Blacksmith Coal Forge Hood and Chimney

What do you need to take the coal smoke away from the forge when you build a coal forge?

I fire mostly propane so fume exhaust is a little bit less of a problem.
Coal forges definitely require a chimney to exhaust the smoke. There is a great deal of smoke
created when you burn coal.

Essentially you have two options
The first is the easiest and that is to make a large funnel shaped sheet metal hood to catch the smoke. It should enter into a 10 inch pipe (much smaller does not draft well for a coal forge. 8 inch diameter you take your chances on) This pipe should extend through your roof and ideally be 2 feet above the ridge line of the building. If you are in an area that requires building codes to be inforced you may have to use insulated stove pipe.

Coal smoke is actually much cooler than wood smoke and in reality does not need the insulated pipe but the building inspectors have no reference for this.
This hood works moderately well. You can start the draft by crumpling a couple of sheets of newspaper and lighting them on fire when you start the coal. Once the draft is started it is pretty easily maintained with the heat of the coal fire.
The second option is more complicated to construct. But works well. It is a Side draft chimney.
For plans google "side draft forge" or "side draft chimney for forge" you should be able to find something. It is basically a box that has a low opening in the side and a shelf inside the box that catches the smoke. The chimney draft sucks the smoke to the side and out of the way.

Good ones work very well. Again you may have to discuss chimney designs and materials with your building inspector.

Coal produces alot of smoke on start up, then simmers down as it converts to coke. Hardly any smoke with a coke fire. Charcoal works well too with very little smoke although you need some chimney to carry the fumes away from your work area.

I hope this helps. Good luck building your forge. Coal forge is the most versatile but it is a bit of a trick to get on to. It is also the easiest to build.

Take Care
David Robertson Artist Blacksmith

Thursday, March 18, 2010

Blacksmithing : Anvil Height

What is The Best Height For My Anvil?

Hi David
Thanks for all your emails they are really inspirational, I have just got my old gas forge, anvil and leg vice back off my uncle who never used it a bit rusty but no worse for wear, my question is this I have read somewhere that the correct height for a anvil is if you stand up straight with your arm down by your side and make a fist the height from the floor to your knuckles would be the ideal height to the top face of the anvil is the correct, my anvil and steel stand is about that height but it just feels a bit low for me? the other thing is if I use a stump of wood as a anvil stand what is the best wood to use?

Many of the old books on blacksmithing use this standard for anvil height. I too have always found this a bit low for several reasons. If your arm is close to full extension, the repeated impact can damage your tendon in the elbow if not the joint as well.

I have my primary anvil set at wrist height as I stand beside it. This creates more flex in the arm acting as more of a shock absorber. I do lose a little power having this flex but I prefer to err on the side of self preservation.

The other issue is that the lower the anvil is placed the more you will find yourself bending over. This creates strain on your back. Some thing to be avoided in later years. This is especially true of light work where you tend to get closer to see what is going on. Heavier work should be done in a more vertical position.

Mounting the anvil.

Mounting on a stump is good. I am not sure that the type of wood makes as much of a difference as the weight. I have seen some steel anvil stands (3 leg) that were quite heavy and worked well. The important part of this is that the anvil needs to be bolted securely down to the stump. This effectively adds the weight of the stump or stand to the anvil. In some cases this could add an extra 100 lbs. If the anvil just rests on top it, it looses efficiency as it bounces around.

This will help in the stability and the performance of the anvil.

A box filled with concrete with bolts for tieing down could be effective. I don't like the sand boxes as the anvil floats too much on top and you have to keep leveling it.

A lot comes back to personal preferences, but this is what I have prefered in the past.
Hope this helps.


Monday, February 15, 2010

What Finish to put on My Vine Arbour?

What Finish Is Suitable for my Blacksmith Forged Vine Arbour?

I want to protect the steel from rusting but be able to see the texture of the vines I made underneath. What are your suggestions?

Finishes in blacksmithing are always a question. Something like this I would use an automotive paint with an epoxy primer coat. The hard acrylic top coat protects for several years (about 7 in a low salt environment). The metal must be clean sandblasted and a good deal of care has to be used in applying the paint.

The nice thing with this paint (see an automotive supply store for it) is that it comes in almost any color and it is quite durable.

Your next option is to have all the pieces hot dipped galvanized. Then paint over top. The problem with this is that the galvanizing fills in the texture that you have worked so hard to create. It will provide a good long lifespan before rust develops, but is better suited for large scale curves and shaping.
Not so much for texturing on bars.

Another product that smiths in the states have had good luck with is called Permalaq (just google it for more info) It is a clear laquer that is sparyed on leaving the natural steel tone and is quite durable. Talk to the manufacturer for details of use, as I have not used it yet.

There is a longer article on the main website about finishes that may be worth reading.
Click on Blacksmithing Articles to see a full list of articles on the site.

Hope this helps
Artist Blacksmith

Monday, February 1, 2010

Blacksmith Spring Fuller Questions

Spring Fuller Suggestions for Blacksmithing

Mr. Robertson,
I would like to fabricate a hardy spring fuller.

I have several leafsprings from an old truck that I can use for the spring portion. I had figured I would shape each end of the spring in a swage to fit a 3/4" diameter bar and then weld 3 or so inches of the bar in place at each end of the spring. I would then bend the spring so that the round bars come together and finish by welding a piece of square stockon the outside of the spring to fit my hardy hole.

I have two questions. First, is it acceptable to use mild steel for the 3/4"fullers provided I keep them cool during use?

Second, what sort of heat treatment do I need to do on the leaf springs where they were heated and bent?

A couple of things.
The leaf spring may be too heavy to get a good spring action. I usually use a coil spring that I straighten out. Then flatten out the midle section to a thickness of about 1/4 inch. This gives enough of a spring.When welding either the hardy stem or the "jaws" onto the spring steel, preheat the spring steel to at least 500 degrees F. I will usually take them up untill they just show a bit of color perhaps 1200 F. This seems to work pretty well for me.

The mild steel will work fine for the jaws, at least for quite a while. Expect some wear though.

Once the spring is forged flat and bent to shape, Take an even dull orange heat on it and just let it air cool and it seems to work fine. The steel itself is springy will work just with normalizing. If you want to heat treat, temper to about 500 degrees F but this is not really required on this tool.

I have also made spring fullers using mild steel flat bar as the spring. 3/16 by 1.5 inches or 1/4 by 1 inch Both of these have worked as well.

Hope this helps.

Tuesday, January 19, 2010

Charcoal as a Blacksmith Forge Fuel

What Do you Think of Charcoal as Forge Fuel?

Charcoal was the original forge fuel. It is realtively clean and smoke free and reaches all the temperatures required to forge or weld with.

Originally charcoal forges were side draft not bottom draft as coal forges are.The main draw backs are the cost. Either cost in producing your self in time or cost in dollars to buy premade.

The other drawback is that you will use a lot of charcoal volume wise but it will work out to about the same weight as coal.