Cleaning up blade after heat treat?

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YoshiFreeride

Joined
Dec 6, 2023
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Hey everyone!

https://www.vansblacksmithing.ca/book-online

I did a knife forging class last week and made a nice little sheepsfoot. But in the class we didn’t finish the blade at all other than the edge. I’d like to clean up the rest of the blade. See link for the kind of blade/edge finishing I’m working with.

Is it possible to sand/buff/chemically remove the blade scales etc from the sides of the blade? Is there any disadvantages to do it?

I don’t have a belt sander but have a grinder with a flap wheel, sandpaper etc.

Thanks in advance.
 
Sandpaper and a hard backing block. Then sharpening stones. Start with 120 grit and work up to 400. Then switch to a coarse or medium stone and go to fine.
 
YoshiFreeride said:
Hey everyone!

https://www.vansblacksmithing.ca/book-online

I did a knife forging class last week and made a nice little sheepsfoot. But in the class we didn’t finish the blade at all other than the edge. I’d like to clean up the rest of the blade. See link for the kind of blade/edge finishing I’m working with.

Is it possible to sand/buff/chemically remove the blade scales etc from the sides of the blade? Is there any disadvantages to do it?

I don’t have a belt sander but have a grinder with a flap wheel, sandpaper etc.

Thanks in advance.
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You can choose to leave it that way. Some call that "brute de forge" and it can make for a rustic look. Even if you want to go that route you should clean it up some through sanding or grinding to get rid of loose flakes of oxidized metal and even out the finish.

If you want a clean finish though you will need to sand or grind off the forge scale. Usually I will drop back a grit from the grinding I did pre-quench. So if I went to 200 grit before quench I will start at 120 grit to clean it up.

I don't known of any chemical way to remove scale. Keep in mind that the scale is oxidation that will be deeper in the metal in some places. Any chemical approach would leave the metal pitted.

Be patient and gently grind or sand away the scale, you'll be happy with the result.
 
Basic forge scale can be removed/softened by an overnight soak in "pickle". It will greatly easy sanding it off later.

The approximate ratio for mixing pickle is 1 quart water to 1 cup pickle chemical. Plain old sodium bisulphate (NaHSO4) works fine. You can get it cheaply from the pool supply and hardware stores as Ph Down.

Store the pickle in a plastic or glass container. A piece of 4" PVC pipe with a closed flange cemented on one end and a cap slipped on the other works perfect for pickle. The same type of tube setup is also good for your FeCl etchant.
 
In Walter Sorrells knife making class I took he said to soak it in white vinegar over night hit it with a wire brush and rinse and repeat until it's as clean as you want it. Kinda slow, but it did work. Although, the class is based around using files and is a make your first knife class that assumes you have 0 specialty tools.
 
One can purchase Glacial Acetic Acid on Amazon and dilute the 99% stuff down to about 15-20% with water (ALWAYS add acid to water while stirring, NEVER water to concentrated acid) to get the scale off with fewer cycles. Careful, it's nasty at that high concentration.
 
Please be very careful with concentrated glacial acetic acid. It is not safe unless you know what you are doing and are wearing the right protection. While it isn't listed as a strong acid it is a dangerous one. When I was in research, we used it often. It must be respected no different that hydrochloric and the other strong acids. This is the stuff used in chemical attacks by the mob to eat someone's face off. The burns never heal right, and terrible scars are what is left. It will blind you, too. I think it is crazy that Amazon sells it as "concentrated Vinegar". In some countries you need a permit to buy it.

From a chemical page.
I highlighted the flammable and explosive vapor part. People think of it as strong vinegar and nothing to worry about ... that is very much not the case.
Safety precautions when using glacial acetic acid:
  • Wear personal protective equipment, such as lab coat, goggles, face mask, and non-latex gloves.
  • Avoid contact with skin and eyes and inhalation of vapors, mist or gas.
  • Keep away from sources of ignition, heat, shock or friction.
  • Store away from strong oxidizing agents or bases.
  • Ensure adequate ventilation and use under a ventilation hood.
  • Evacuate personnel to safe areas if spillage occurs.
 
I have a little experience with glacial acetic acid, too. More than 30 years worth at the bench as a laboratory chemist.

It sorta cracks me up that we give direction constantly to build stuff and use stuff like homemade liquified gas appliances, unshielded hydraulics in a forge environment, and unguarded equipment that are dangerous as can be, and subject ourselves to every kind of dust and other crap yet every time a laboratory chemical comes up it's treated like it's nuclear.

If you're going to mix up ferric chloride or any of a number of acids or bases we use, then you're supposed to use the same personal protective equipment you use for your knife work: gloves, apron, faceshield, respirator. Right? You guys all wear that all the time, right? And ventilation is good, too, right?
The whole object of tools is if you learn to use them the way they're safest, your risk is minimized. Chemicals are just tools. Learn and do properly.
I expected people who were interested to learn the tool. With chemicals, that ALWAYS entails reading the friggin' MSDS first.

Don't use it, folks, if you're afraid of chemicals. I warned you it was nasty. I didn't think I needed to post a treatise on chemical safety. My bad. Won't do it again.

It WILL get rid of the scale, though. ;)
 
I have to clean things for TIG welding. I use muriatic acid(swimming pool acid) to remove scale, plating, and or rust.

Scale on hot rolled steel will take a little bit. Plating like zinc takes a quick dip. Rust a hair longer.

Muriatic acid is some nasty stuff. As soon as it's removed from the bath. It goes directly into a baking soda bath. Then rinsed off with water.
 
I use white vinegar. Just leave it for one day and use wire brush on angle grinder. It removes scale and leave forged texture.
You can wire brush when the steel is hot to remove some scale and make smoother surface and you can "wet forge" to pop the scale from steel so it's easier to melt it in vinegar.
 
My vote: Angle grinder and flap wheel. Take your time and try not to heat it to blue. Flatten bevels with a file. Then heat treat.

I used to be pretty good at shaping knives with an angle grinder (better than I was at pounding).
 
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