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Hello everyone I have a problem with getting these little pits in my blade. I'm pretty sure that its caused by something during the forgeing process. I'm a novice so I'm still learning. I have a feeling that I'll be learning this new hobby for the rest of my life. If yall have ideas as to what those blasted pits might be any info would be great.

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I have a feeling that I'll be learning this new hobby for the rest of my life.

 

 

no truer words were ever spoken

everybodys first few knives turn into bowiefilets because of scale

clean your work

brush

forge wet

harley

scaley possum

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The secret is to keep scale away from the knife while forging. My tricks:

1) add a little wood or a couple charcoal briquets to the propane forge: it helps make the environemnt more neutral and reduces the formation of scale in the first place(blatantly stolen from a recommendation Tai made a while back). These bits of scale that get into the blade are often referred to as "inclusions" and as you've discovered, they suck.

2) wipe the anvil clean. You've put the blade back in the forge and you know you've got at least a couple minutes to wait. While you're pondering your next move, take a shop towel (or your hand/glove/sleeve) and wipe the face of the anvil

3) forge a little thicker than you'd generally like and then

4) use an angle grinder (harbor freight- on sale for as low as $18!! and they last a really long time, too) with a 60 grit flap disk to grind away the pitted surface. That's why you left it a little thick, the grinding is pretty aggressive... and you can always grind away more, but you can't really put any back.

 

I still get some pits, but they're far fewer than before, and you'll get better at pit-reduction as you practice... everyting is practice, and everything is difficult when you are beginning. It's like my racing buddies and I tell the new guys at autocross: the secret to winning is 3 things: Seat time. Seat time, and seat time. You don't get better if you don't practice and get familiar with the tools....

 

ok, that was longer than it needed to be, sorry :P

Edited by engineerboy

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Thanks for the tips guys.

 

Don, if you're reading this, I can't tell you how much of a help this forum has been to me during those frustrating times when I feel that all hope is lost. Thank you.

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It is the same for me too. What we are trying to learn is difficult at best and having the support of others really makes a big difference.

 

To answer your question, watch your fire control. Break down hot, but then reduce your heats as you forge to shape. Learn to control your fire and work in a neutral flame, keep your anvil face clean and your hammers polished.

 

Watch your scale. At most you should be making thin, light flaky scale when the hot metal comes into the air and very little of that.

 

You are seeing the problem and trying to figure out the answer, that is always the process. Don't get discouraged, this is a hard thing to master and there are no shortcuts.

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There is a second, less serious source of pits: Agressive polishing. Mete knows what I am talking about. If you are polishing on a cloth wheel and you push too hard or the wheel is moving too fast, you can literally suck out any small inclusions like silicates, aluminates, oxides, etc. This leaves very small pits but they are clearly visible to the naked eye against a highly polished surface. :angry:

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There is a second, less serious source of pits: Agressive polishing.  Mete knows what I am talking about.  If you are polishing on a cloth wheel and you push too hard or the wheel is moving too fast, you can literally suck out any small inclusions like silicates, aluminates, oxides, etc.  This leaves very small pits but they are clearly visible to the naked eye against a highly polished surface.  :angry:

23978[/snapback]

 

these things i call comets

onl,y happen when buffing

itsbecause of dirty steel

it canbe stoped or lessoned by buffing in more than one directon and buffing lightley

sometimes ive buffed in a circle

spining the blade against the wheel

but

danger will robinson

those buffers will get u

that breaks all the buffer rules ever made

harley

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This is all good stuff, but "sometimes" it's because of the steel itself. The lower the "quality" of the steel the stickier the scale is and hard to get off. This is what normally causes severe pitting and there is not much you can do about it. On the other hand, scale pops right off easily on a good clean piece of steel and no special adjustments are necessary.

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You know Tai I think you're right on that one. The metal I'm useing is from an old lawnmower blade. It's not the best material in the world but I thought it would be a decent place to start and learn the basics, if there are any basics in smithing.

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Yes, you maybe doing everything totally right, with poor quality steel. I can usually get a good idea of the general quality of a piece of steel, from the scale, just by taking a few heats on it and forging it a little. Of course there are all different levels of quality, but after a point, if it's so poor, it's not worth messing with. There are probably a lot more things we could learn about the steel, just by paying more attention to the scale, what color it is, how thick it is, how large the flakes are and how sticky it is. Things like that...

 

Just because your steel was salvaged doesn't necessarily mean that's what's wrong. Some of the spurious old salvaged steel is actually higher quality than the legitimate new store bought steel. :)

Edited by Tai

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Guest TimCrocker

As far as the buffing goes, I've found that pitting is more likely to occur when the wheel is getting low on buffing compound. Frequent re-application makes a mess around the buffer, but a better finished product is the result. In steels that tend to pit or orange peel, like D2, I have found that it can be completely elimnated by this method.

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The adherance of the scale is controlled by the pressure in your forge, at least in a gas forge. A slight positive air pressure will keep the scale loose. If you are sucking air into the forge, meaning you have negative pressure, your scale will be more difficult to remove. ;) I guess that means if your forge sucks, so does your forging!

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I was talking more about it popping off during hot forging. The scale is different with different steels and quality of steel. You can see this by forging a nice clean piece of cold rolled mild steel and see how the scale behaves. Then compare it to some other steels and or other sources, like hot rolled mild steel or rebar, or any high carbon, from the same forge atmosphere.

 

I forge from a reducing atmosphere to slow the scale fornmation.

 

How do you suck air into a gas forge chamber?

Edited by Tai

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I think the pressure thing makes a slight difference in scale adherence and rate of scale formation, but what I'm talking about can make a very radical difference, which becomes obvious to the naked eye. All you really have to do is forge some different steels and pay attention to the scale.

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I think the pressure thing makes a slight difference in scale adherence and rate of scale formation, but what I'm talking about can make a very radical difference, which becomes obvious to the naked eye. All you really have to do is forge some different steels and pay attention to the scale.

24052[/snapback]

 

Hey Tai,

Now I'm nobody's expert but what you're describing I would have attributed to alloys in the steel rather than "quality". Railroad "pandrol" clips are an example of a steel that can develope an armor coating of scale that is a real problem to clean off. By contrast my work with 10xx and 5160 materials seems to yield a relatively soft scale.

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Any impurities effect the alloy content if they go homogenous and actually become part of it. The alloy does effect the scale.

 

Impurities effect the steel quality.

Edited by Tai

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This is actually funny because an alloy is an impure piece of metal, impure for a reason...

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A high velocity burner, blown type, can get the atmosphere in the forge to rolling and create eddies at the edges that can suck in air from the edges of the portals. The atmospheric burners are based upon the venturi effect to suck in air for combustion. Now, methan burns hottest at about a 10:1 ratio of air to gas. If you are running excess air, you get more scale. If you run excess gas, you get carbon monoxide. :(

 

Certain methods used to make steel will affect scaling, too. For instance, a silicon killed steel will hold scale more than a silicon-aluminum killed steel. High chromium steels will scale less because the chromium retards the formation of iron oxide.

 

I will try your suggestion to put a charcoal brickette in the forge to minimize scale. I does make some perverse sense that if you can vaporize some carbon, it will scavenge the oxygen and make CO2 or, CO ( :blink: ) instead of FeO.

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Just some general steel mill info: I spent about a year working for a manufacturer of steel reheat furnaces. Our recommendation to customers was to operate with a slightly oxidising atmosphere. Yes, more scale was produced, however, the type produced was less adherent to the base steel than that produced in a reducing atmosphere. The mills typically used high pressure water to blast scale off billets and slab ahead of hot rolling to produce a better surface. It was easier to blast scale produced from reheating in an oxidising atmosphere and produced a better surface in the final hot band. The surface quality more than made up for the additional scale loss from a slightly oxidising atmosphere versus a reducing atmosphere. Note - I am saying slightly oxidising, implying light powdery scale for short times reheating.

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I think almost everything effects the scale. That's why I pay attention to it. If it helps me make the kind of knife I want, that's all I care about.

Edited by Tai

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Ok guys this is off the subject but I hardend a blade today, or at least tried to harden, and it did to some degree but not what I was expecting. I used a lawnmower blade and at first I quenched it in used car oil two days ago to no success. Then today I annealed it and quenched in water to see if that did the trick. Same results. I'm not for sure what the material is, so I probably did something wrong, naturally.

 

Shattered Self-esteem Possem

Loren

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The problem may be that you're using lawnmower blade. Lawnmower blades have been a topic of discussion recently in the chat forum of anvilfire.com and the consensus has been that they're not made like they used to be (surprise! :D ) Apparently, making blades out of proper tool steel is a liability if the blade cracks and flies off killing or injuring someone (even if the blade is being used to mow rocks and tree roots). So it's more than likely that you've been working mild steel if you've just been using lawnmower blades.

 

A sure way to test: heat any ol' section of it up to really really hot, dump it in water and hit it with a hammer when cold. If it cracks, then you have tool steel and let's take another look at your heat treat. If it just bends (or otherwise gives you the finger) you'll need to find another source of scrap steel. Might I recommend used files with the teeth ground off.

Edited by engineerboy

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Guest TimCrocker

The best luck I've had with lawn mower blades is going by the city yards and getting the industrial type, 1/4" thick, out of the scrap bin. With permission of course. They are marked with a unique "T" which I believe indicates toro. In my area they change out a couple dozen a month.

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I did a post on spark testing and other tests for salvaged steel a while back but don't remember what thread it was. It's important to test it first.

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