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How to remove scratches on knife blade

How to remove scratches on knife blade

Introduction

Scratches on the blade always ruin the appearance of any knife, regardless of its price. On the other hand, there will be no scratches on a knife if you do not use it. Scratches are not always the result of a knife being used. Often, a large number of scratches indicates a lack of proper care of the knife blade or a lack of understanding of the intended purpose of the knife. 

Example. If you sandblast a knife and then give its surface a polish, it will be well protected from external influences. However if the knife blade was dropped on a rock or someone has carelessly run an abrasive stone over the blade surface, then depending on the depth of the scratch, it may eventually corrode over time, especially if the knife blade is made of carbon steel.

Where do the scratches come from

One of the reasons for scratches on a knife blade is careless handling of the knife or improper use of the knife. For example, when the knife is simply left lying on the ground after use, or the knife is used to cut on hard materials. 

It is very common to find knives with a black DLC coating and many of them start to look awful after a certain time of service, even though they have been used for their intended purpose. But we are not talking about coatings or methods of processing secondary bevel planes and blade flats per se right now.

Scratches can occur on the blade with very light careless use of even very fine abrasives and slurries during sharpening or the knife blade honing. In this case it is improper abrasive hygiene. 

The undeniable fact of the appearance of scratches on the blade of a knife, is the impact of particles much harder than the surface of the blade itself. 

Scratches removal tools and methods

Before we move on to how to remove a scratch on the plane of the blade, it is good to remember exactly what made the scratches on the blade. If it was an abrasive, then you know its grit and you can find out how deep the scratch may be. 

Even so, it does not mean that the depth of the entire scratch is the same along its entire length. Often it is a matter of many scratches. In both cases, you will still have to remove the full layer of metal over the entire plane. 

How to remove scratches

Removing scratches is actually very similar to how the knife makers manually or with different devices deal with secondary bevels planes' scratches after the blade was sharpened with a grinder. 

Given that, in some cases the cross marks left by the endless grinder belt on the surface of the steel prove to be much more practical to use, as it is more difficult to leave a scratch with them. Even if it does happen, it will not be as noticeable as it would be on an evenly finished surface.

The products with abrasive properties for removing scratches include:

  • some manual power tools, 
  • abrasive products, 
  • various abrasive pastes and emulsions, 
  • lubricating and cooling liquids, 
  • auxiliary lapping tools.

Some often use mini grinders for the best results in removing scratches from the surface of the knife blade. They also use different flexible rolls together with drills and motors for the same purpose. There are many different solutions in this area, but what is more important is the right choice of consumables for a particular power tool model.   Since the selection is huge we will not cover it in this article, because in each individual case you have to deal with the catalog of each manufacturer separately.

Sometimes a small angle grinder with a clean polishing wheel and diamond paste works just fine. This is a shortcut solution for blades with even fairly hard steel.

The second group of products are abrasives for manual use, in the form of abrasive bars and sandpaper.

Regarding the use of abrasive stones, there is one very important thing to note. If you do a little digging into the history of blade weapon production and bevels surface processing, you will find out that back in the old days and even today, high quality metal surface processing was done by hand.

 There are many different polishing pastes of varying grits that are used to treat metal surfaces nowadays. They are the ones that are great for treating and removing scratches from the blade. The main thing is to choose the right grit. You can only find the grit by experimenting. 

In addition to pastes, there are liquid polishing emulsions that are suitable for this purpose as well.

Cooling liquids play an important role in the very process of sharpening with abrasive materials. They bind the abrasive grains and form a fine grinding emulsion. A well-known product is WD40 or any similar. No matter which method and abrasive you choose, you should always work with a coolant.

Manual auxiliary tools include all sorts of lapping blocks, which are often DIY made by the knife makers for themselves. Most often they come in rectangular-shaped plates of various widths and lengths, and made of steel, glass or textolite. The main thing to remember is that the surface of these plates should be absolutely flat when you glue the sandpaper on it.

Scratches removal tools

As a description of the technique, we can give two examples using abrasive bars and sandpaper, for general understanding.

Abrasive bars

There are various silicon carbide based abrasive stones available on the market around 1200 grit, that said, it is worth starting with a finer one, or around 1000 grit, as the coarser ones can be quite rough. Their main advantage is a good renewal of the abrasive grit as they work. This method is akin to the way Japanese masters polish a katana. 

Eventually such stones need to be leveled like a regular sharpening whetstone. The key is to make sure it is flat before you use it. The main advantage over sandpaper is that the grit of a stone is constantly renewed and does not get clogged like sandpaper.

You can take a bar of suitable grit at your choice, then add WD 40 to the surface of the blade and work on removing the metal layer with the scratch with smooth strokes, checking the result from time to time. It does not have to be done strictly by hand. There are various vises and clamps. All you need to do is fix the blade for convenient work. Of course, there is simply no off-the-shelf best solution. It all depends on your technical resources and circumstances.

You can also do this using a WD40 or a similar liquid. In the process, the oil forms an emulsion on the surface with fine crumbled abrasive grit and treats the surface. There is a constant renewal of the grain, which levels the surface and gradually removes the scratch.

If scratches remain across the entire bevel area or in some spots, you should work in those spots with the same abrasive. For this you can use the same bar, but use the end of the bar instead, which also needs to be prepared and leveled.

This is a very good way of removing cross grooves, such as those left behind by a grinder's tape number 320.

For a fine satin finishing or polishing, you can use a fine sandpaper from Bosch or 3M with 600 - 800 grit for a fast result. Then, to polish the surface and achieve a finer result, you can choose a 1000 and/or 1200 grit abrasive.

This is one of the most highly effective and truly working ways and therefore the best of the known.

Using sandpaper

Along with sandpaper, many professionals also use different diamond pastes to polish the blades. This fits well after grinding with a 320 grinder belt. You can choose 60/40 micron grit diamond paste and take a 320 grit sandpaper. Once you have a good result you can move on to the next step. Diamond paste with 20/14 micron and 800 grit sandpaper work well together with WD40. Then, to polish after a finer finishing, you can apply a 60/40 micron paste and continue with a lapping tool with 800 grit sandpaper. 

This is not a step backwards at all. It covers the longitudinal grooves along the entire blade and creates a good longitudinal satin finish on blades of about 60 HRC hardness.

If you only sharpen with sandpaper, the scratches can become patchy afterwards and it will be noticeable and bad-looking. In terms of time, such work can take an hour or so. The main disadvantage of this method is rapid wear of the sandpaper and a sufficient amount of abrasive dirt that comes from the diamond paste.

Conclusion

If you are interested in this issue, you can search for videos and other tips on the Internet on this and you will immediately realize that it is not as complicated as it seems, and the above guide will really work. To cope with such a task on your own, you just need to have some tools. You do not have to have an entire workshop for this.

If you feel that you cannot do it on your own, you should reach out to a professional. If you decide to remove the scratches, you must be aware that no technical approach will bring the blade back to its original condition. No knife maker will be able to restore your blade to its factory surface high quality. The surface quality of the knife blade and its look will not be worse at all, they will just be different.

Previous article How to polish a knife to a mirror finish at home
Next article What is the best steel for a knife ?

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