Flattening stone for whetstone
Water stones and other whetstones are made of abrasive materials that quickly and accurately sharpen the blades of chef's, hunting, and carpentry knives, planes and axes, and other tools. Due to the properties of the bonding agent, the abrasive particles constantly break off, creating a slurry on the surface. This improves the sharpening quality but leads to rapid wear.
You cannot use an arc-shaped stone, which will spoil the blade. To restore the stone's geometry, you can use a flattening stone. Let us take a closer look at how the flattening happens and what tools you need for that.
Types of bars for flattening sharpening stones
To eliminate deformations of waterstones, sharpeners use flattening stones or glass for leveling. You can use them to grind away part of the abrasive to flatten the stone’s surface to continue producing top-notch sharpening of knives.
Sharpening stones deform due to the peculiarities of the sharpening process. The middle of the stone undergoes more frequent use. This area wears out faster, which leads to a violation of the original geometry.
If you use such a tool without conditioning, the blade of the knife will also become slightly rounded at the edges. Using them for cutting food or other purposes will not be as convenient. The leveling bar can restore the flatness of the sharpening stone and make it suitable for sharpening.
Equipment used for flattening sharpening stones:
- Silicon carbide. They make whole blocks with deep notches out of silicon carbide. It has a coarse grit to remove abrasive particles from the waterstone. This is an inexpensive tool, but due to its features it also quickly wears out during use.
- Electro corundum. Material based on aluminum oxide. Corundum stones are used for flattening and breaking in diamond and CBN copper-tin bonded abrasives.
- Diamonds on a nickel-plated coating. It is a durable and wear-resistant tool that can be used for the conditioning of all types of stones, including water and oil stones. It will last much longer than the previously mentioned bar, but you will also have to pay more for it.
During the process of using any stone, you need to use a cutting liquid. It is selected depending on the type of the sharpening stone that the master processes:
- For water stones — water;
- For oil stones — the type of oil that is used with each specific abrasive.
You should occasionally check the flatness of the stone's surface before and during work. The methods are described below.
The procedure for using a flattening bar
The process of leveling the surface of an abrasive stone consists of the following steps:
1. Defining the stone's condition
The easiest way is to take a high-quality engineering ruler or an angle square, which are used for measurements in industrial facilities. They have a perfectly flat and even surface. It is necessary to attach the ruler to the abrasive, put both in front of the light, and look for the gap. If you can see the gap, it is high time to flatten this stone.
Please note that you should not use a simple school ruler for this purpose. It may have design errors that will not allow accurate flatness measurement.
The second simple method is a paper sheet. You need to put the bar on the table and try to slip a corner of paper under it. If it fits, there is a gap in this place and the stone needs to be flattened.
2. Drawing a grid.
With this method, you have to draw fine lines on the abrasive with a simple pencil. During the flattening process, they will gradually wear off. The marks will only remain where the leveling stone does not yet reach. You can easily tell from these marks whether you need to continue to flatten or if the sharpening stone is already flat.
3. Elimination of defects.
Before flattening, the surface of the stone should be abundantly moistened with water or oil, depending on the type of stone. Next, you should move the water stone along the flattening plate, making cyclic circular movements.
Make sure that the entire surface of the bar gradually touches the whetstone. This way you can avoid the appearance of additional defects.
The cutting liquid should be sufficient. It will gradually wash away the separated abrasive material. In the process of work it will be clearly noticeable that the lines drawn with a pencil first disappear from the edges and then from the middle. This indicates that the stone was dished out in the middle.
4. Quality control of flattening.
While using the flattening bar, you need to constantly check the condition of the marks, As soon as they completely disappear, you need to stop flattening. If you continue leveling, you will remove more abrasive material than you needed too. This will reduce the service life of the water stone.
Checking the shape of the stone surface
The easiest way to determine the condition of a sharpening bar is described above. Let us explore this issue in more detail here.
Before proceeding with the conditioning, you need to understand the terminology used by professional sharpeners. The following geometric parameters are important for a water stone:
- Thickness is the distance from the bottom to the top surface of the rectangular-shaped stone. They determine it using micrometers, which allow you to make precise measurements to thousandths of a millimeter.
- Parallelism is the difference in thickness at the thinnest and thickest point of the bar. It is often extremely difficult to visually detect a deviation, so craftsmen also use micrometers. A stone is considered flat if the deviation of these values does not exceed 0.1 mm.
Let us move on to the methods for determining thicknesses.
Straight edge method
You will need a professional engineering ruler with an accuracy of at least 0.02 mm for inspection. You can get it at a building shop or order it online.
Before starting measurements, it is necessary to check that the edge is flat and has no mechanical defects. Dust and other dirt should also be removed. It is recommended to wipe the end face with a 1-micron abrasive lapping film and remove dirt with a lint-free cloth.
There are two ways to measure a stone:
- Apply a ruler to the stone in length and width and try to insert a feeler gauge, which is used to check valves in a car or make other measurements, into the gap between the ruler and the stone. It is best to take several measurements at different points.
- Look at the ruler and the stone in front of the light for clearance. If the stone's plane is out of alignment, you will see a thin line of light.
The advantage of this option is simplicity. Special knowledge and skills are not needed to use this method. However, you will need a ruler. And the process takes minimal time, but it is not perfectly accurate.
Please note that the measuring edge gradually wears out upon contact with the abrasive. Every now and then you need to check the quality of its edge on a certified marble surface and buy a new tool.
Digital micrometer
This method is used by craftsmen in professional sharpening workshops. To measure, you need a granite plate with perfect geometry (confirmed by a certificate or inspection protocol), a micrometer with a mechanical or electronic dial, and adjustable jacks.
The measurement process takes place according to this algorithm:
- Place the reference plate on a solid and stable surface.
- Place the adjustable jacks on the plate.
- Place the abrasive sharpening stone on the support so that the part being tested points upwards. The stone must be firmly fixed at three points.
- Install an electronic or mechanical micrometer on the same base plate. Next, adjust the tool so that it shows zero at the point above the jack.
- Run the micrometer indicator over the surface and record the minimum and maximum deviation from zero. The result of these measurements will display the level of flatness of the stone. All operations must be performed very carefully to avoid errors.
This method is considered to be one of the most difficult, yet also one of the most accurate. They use it only in the process of working with expensive and fine-grit abrasive stones. But they rarely use this method, as it requires long preparation and very careful handling.
Besides, this method requires special tools for measurements. Purchasing a benchmark horizontal plate, jacks and micrometer will be an expensive investment. And if you use the most accurate measuring tools, the purchase amount can increase tenfold.
Granite slab
Another way to check the flatness of a stone which requires professional measuring tools. But they will cost much less than a micrometer with jacks. Apart from that, it will be easier to take measurements this way.
To measure the abrasive bar, you will need:
- A granite slab with a perfectly flat surface. We are talking about special measurement tools that can be purchased at a hardware store.
- A feeler gauge. They are usually sold as thin plates of various thicknesses. With their help, along with the violation of geometry, you can also measure the thickness deviation.
To do the test, place the bar on the plate and insert the feeler gauge between it and the base plate. You need to do this at several points. If the gauge fits, the stone needs to be conditioned with a lapping plate.
Please note that this method is only suitable for stones up to 2.5 cm wide. Otherwise, the stone may have a defect within the center rather than on the edge. Due to this, you will not be able to slip the feeler gauge through, but at the same time, the geometry deviation will not allow you to properly sharpen the knife.
Coordinate measuring device
This is sophisticated digital equipment that can be used to determine with micron accuracy the deviation of an object from the correct shape. Sensors are responsible for getting the right dimensions. They can be mechanical, laser, optical, and other. You can get more accurate results if you use non-contact sensors.
The problem is that inspection and measuring equipment give different results depending on the manufacturer, measuring conditions, type of abrasive, and other factors.
In addition, the device itself is very expensive and is only used in industrial environments. Most often this method is used only for the most expensive and exclusive stones. And the inspection is entrusted to a specialized laboratory. This method is not used in domestic settings because of its high cost and redundancy.
Conclusions
A flattening stone is a must-have for those who like to sharpen their knives with water stones. Without periodic surface conditioning, the abrasive stone will ruin your favorite and expensive tools. When choosing a conditioning stone, you need to take into account its dimensions. A conditioning stone should be larger than the sharpening stones that you are going to use it for.