Today, belt sanders and grinders are quite often used for sharpening to quickly remove metal off the blade. The question of whether the belt grinder is some kind of additional unit in a complex with a professional knife sharpener is left open for the moment.
Due to the fact that all belt sanders and grinders are very powerful and complex devices, their use requires a certain theoretical knowledge and experience, without which it will be easy to spoil the blade of the knife.
Many knife masters use belt grinding machines and similar equipment for making knives and shaping secondary bevels, but sharpening knives is associated with a number of technical issues, which to a certain extent look similar, but have a completely different class of precision and a different principle of surface treatment.
The clearest example of a belt sander usage is the removal of metal from a knife blade to fix significant damage. This is practically creating a new knife and no device will be faster. We are not talking about 10 x 1/2 inch belt devices, which can be classified as household sharpeners, we are talking about real professional devices.
Indeed, all belt grinding equipment of various sizes and capacities, including grinders among all devices with electric drives are the most effective tools, both in knife-making and sharpening. Considering the fact that there is a very large range of grinding belts on the market today, this expands the range of their use. The differences in material and grain size of endless belts allow a wide variety of metal processing tasks: from aggressive metal removal all the way to profiling and polishing.
At first sight it may seem that polishing the surface of metal is not much different from grinding and polishing the secondary bevels of the knife blade. However, this is not correct and for a better understanding we need to dig a little deeper into the way the various devices work.
In endless belt grinding, the repetition of standard sharpening angles is possible with the additional attachments and accessories for the device.
The belt sander can be used to sharpen various knives, chisels and other cutting tools, deburring and grinding with reverse rotation due to the frequency converter.
When sharpening inexpensive kitchen, household and carving knives with a small thickness behind the edge or when there are no high requirements for the condition of the secondary bevel, two abrasive belts followed by a polishing step are acceptable if a high level of accuracy is not required.
Sharpening more expensive kitchen and chef's knives, hiking, hunting and fishing knives with bigger thickness behind the edge or with high requirements to the condition of the blade tips requires a different approach. In such cases, it is necessary to use up to 5-6 different belts. The change of belts and partial readjustments also add time to the entire process.
In general, sharpening with such a device can take from 2-3 minutes to 5-7 minutes, depending on the condition of the blade and the need to bring the blade to a specific condition.
Even with the use of a frequency converter to control speed, it is quite possible to overheat the blade and the cutting edge without a coolant supply and proper experience in both cases. A much better but more expensive choice would be a grinder.
The use of the grinder and all kinds of accessories expands the range of possible applications many times over the belt sanding machine and is designed for mass production or commercial knife sharpening.
The main problem when choosing a grinder for a workshop is the lack of a ready-made solution. On the other hand, the complexity of the choice is balanced by the fact that each user can create a convenient kit for their own purposes.
However, even if you get exceptional quality equipment, there will still be some other problems: vibration, heating of the belt and blade cooling, the size and arrangement of the unit on a work bench, storage of accessories, and so on. You need space for all this, but even this is not as important as what you want to use the machine for.
The second rather significant point of using a grinder will be the level of knowledge and experience, which is different from the more basic use of a belt sander.
Little by little it becomes clear that both the belt sander and the grinder have positive aspects, and there are aspects that summarize a number of features that somehow remain in question and affect, whether we like it or not, the final result.
Let us list the most important ones:
The most important and perhaps most decisive factor will be the blade heating.
Many knife masters, when making knives, dip the heated blade into water during roughing and profiling of the secondary bevels. During roughing, the blade is being processed on the belt, when it gets hot it should be dipped into water. Then the process starts again. If you do the same with the blade, which has a small thickness behind the edge, during the processing due to short-term heating and cooling the steel undergoes micro-destruction, which is not obvious to everyone.
There are opinions that, when re-profiling a high-speed steel carpentry tool, short-term heating to 350-400°C will not result in damage (blade turns blue). If this is the case, you really should not dip the tool in water.
However, if air cooling is taken into account, the process is somewhat similar to thermal cycling, which can lead to deep low temperature heating.
Besides, this level of heating is quite significant. If you look at the temperature used in the manufacturing process of the blade, 350-400°C is twice as high as the tempering temperature, which is about 200 ° C.
Despite the fact that a belt sander or grinder can indeed be used to quickly fix the geometry, and the equipment has a certain level of variability, such machines are suitable primarily for roughing, removing chips, correcting significant damage, complex reprofiling or, at most, for budget sharpening.
This equipment is primarily designed for initial machining and first roughing of bevels on blades with large thicknesses behind the blade edge and on blades that do not require high cleanliness and homogeneity of the plane of the secondary bevels. Further sharpening should be manual and performed on a more precise device.
At the maximum precision of a belt sander and a grinder it is still not possible to achieve the results of manual sharpening on Apex type sharpeners due to the peculiarities of the use of endless belts. Trying to make too thin bevels without cooling or to finish the cutting edge on a belt is not the best idea for quality steel and expensive knives, as it can affect the knife maker's reputation.
The cost of the device and consumables for the purchase of belt sanders and grinders is quite high and significantly exceeds the cost of having a manual sharpening system.
The most sophisticated and most technologically advanced sharpeners are the mechanical manual sharpening systems of the apex type, of various sizes and different complexity levels. Each of the three groups of devices: compact, medium-sized, and full-size benchtop systems are designed for tasks of different levels of challenge and volume.
All truly professional sharpening systems from the world's leading manufacturers are the same in their concept. In terms of design, many will look slightly different, but they perform the same function. It's like comparing expensive track bikes or Formula 1 cars.
The fundamental parts of professional sharpening systems are:
A turning mechanism and a rack or lifting mechanism that resembles a microscope adjustment are mounted on the base. In this unit for adjusting the sharpening angle, there is a place to mount a guide rod with an abrasive holder. The position of the angle is adjusted by this unit.
This sophisticated unit is designed to control the stroke of the abrasive installed in the holder in relation to the secondary bevel of the blade, which is fixed in the clamps of the turning mechanism.
Such systems can be complex devices with a number of additional units that can be used to make additional adjustments and achieve non-standard tasks:
Besides, there are sharpening systems that can be upgraded and combined with different components of different models of the same manufacturer so that you can create a knife sharpener for your needs or for sharpening a knife of a certain size or shape of the blade.
The obvious advantages of using such systems are:
All of the above is just a glimpse of the technical parameters, but the most important and decisive thing is not the knife sharpener itself, but the user's understanding of how to use this or that artificial or natural abrasive for sharpening a particular steel. If you have a quality abrasive and the skill of manual sharpening, you can achieve great results even without the knife sharpener. The device gives you control over the angle, and the sharpening is provided by a proper high-quality abrasive.
The natural and artificial abrasives used in hand sharpening and the method of their use are the most important ingredients and the real reason why a belt sander can never be compared with manual sharpening. The abrasives of this class often affect the steel differently due to a much lower pressure, a completely different chemical composition, shape and size of the abrasive particles.
The class of finishing of the secondary bevels surface affects the line of the cutting edge and with that the life and quality of the blade of a certain steel after one sharpening session. However, belt sanding machines and grinders can be used for certain tasks such as grinding, reprofiling or roughing of blades. All of the further and finer steps should be performed with more precise equipment, such as a manual sharpening system.
If you get a chance to try sharpening with professional equipment, you will never willingly give up on a sharp knife that was properly sharpened.
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