Scraping is a skill that is more difficult than wood carving. It is the starting point for precision tool functions to have basic accuracy. Scraping eliminates our dependence on other machine tools and can also eliminate deviations caused by clamping force and heat energy. .
Although manufacturing technology is now very advanced, many lathes still need to be shoveled by hand. Why is this? Let's take a closer look at this craft method that can be called an art.
The track of the shovel is less likely to wear, thanks to the excellent lubrication effect. A shoveling technician needs to know many techniques, but only experience can enable him to master the feeling of precise leveling.
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When you pass by a machine tool manufacturing factory and see the technicians doing spading by hand, you can't help but wonder: "Can they really improve the current machined surfaces by spading? ( Can humans be more powerful than machines?)"
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If you are referring purely to its appearance, then our answer is "no", we will not make it more beautiful, but why shovel flowers at all? There are reasons for it, of course, and one of them is the human factor: the purpose of a machine tool is to make other machine tools, but it can never replicate a product more accurately than the original. Therefore, if we want to make a machine that is more accurate than the original machine, we must have a new starting point, that is, we must start with human efforts; in this case, human efforts refer to Use your hands to shovel the flowers.
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Shoveling is not a "freehand" or "wandering" operation. It is actually a copying method, which almost perfectly replicates the matrix. This matrix is a standard plane and is also made by hand.
Although shoveling is hard and laborious, it is a skill (an art-level technique); it may be more difficult to train a master of shoveling than to train a master of wood carving. There are not many books on the market that discuss this topic. In particular, there is less information discussing "why shoveling flowers". This may be why shoveling is considered an art.
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Where to start?
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If a manufacturer decides to use a grinder to grind without scraping, the guide rails of his "parent" grinder must be more accurate than a new grinder.
So where did the accuracy of the first machines come from?
It must have come from a more accurate machine, or relied on some other method of producing a truly flat surface, or perhaps copied from an already well-done flat surface.
We can use three methods of drawing circles to illustrate the creation process of surfaces (although circles are lines and not surfaces, they can be quoted to illustrate the concept). A craftsman can draw a perfect circle with an ordinary compass; if he traces a pencil along a hole in a plastic template, he will replicate all the inaccuracies in the hole; if he draws it freehand, As for the circle, the accuracy of the circle depends on his limited skills.
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In theory, a perfectly flat surface can be produced by alternating friction (lapping) of three surfaces. For the sake of simplicity, let's illustrate with three rocks, each with a fairly flat surface. If you rub these three surfaces alternately in random order, you will grind the three surfaces smoother and smoother. If you rub just two rocks together, you'll end up with a mating pair of one bump and one bump. In practice, in addition to using lapping instead (lapping), a clear pairing sequence will also be followed. Lapping masters generally use this rule to make the standard jig (straight or flat) that they want to use. . Click to receive free 10G CNC programming tutorial
When using it, the spade master will first apply the developer to the standard jig, and then slide it on the surface of the workpiece to reveal the areas that need to be spalled. He keeps repeating this action, and the surface of the workpiece will get closer and closer to the standard jig, and finally he can perfectly copy the work that is the same as the standard jig.
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Castings to be scraped are usually milled to a few thousandths more than the final size, then sent to heat treatment to release the residual pressure, and then sent back for surface cleaning and grinding before scraping. Although shoveling consumes a lot of time and high labor costs, shoveling can replace a process that requires high equipment costs. If you do not want to replace it with shoveling, the workpiece must be finished with a very high-precision and expensive machine. Repair processing.
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In addition to involving high-cost equipment in the final stage of finishing processing, there is another factor that needs to be considered. When processing parts, especially large castings, some gravity clamping actions are often necessary. When the processing reaches a few thousandths When the precision is high, the clamping force often causes distortion of the workpiece, endangering the accuracy of the workpiece after releasing the clamping force; the heat generated during processing can also cause distortion of the workpiece.
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This is one of the many advantages of the spatula. The spatula has no clamping force and the heat it generates is almost zero. The cast iron is supported at three points to ensure that it does not deform due to its own weight.
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When the scraping track of the machine tool is worn, it can be re-corrected by scraping it again. This is a great advantage compared to discarding the machine or sending it to the factory for disassembly and reprocessing.
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When the track of a machine tool needs to be reworked, this job can be performed by the factory's maintenance personnel, but we can also find people locally to do the rework.
In some cases, manual scraping and electric scraping can be used to obtain the final required geometric accuracy. If the tracks of a set of worktables and saddles have been leveled, and the accuracy has met the requirements, but the parallelism of the worktable to the main axis is found to be out of specification (it will take a lot of effort to correct it), can you imagine using only one shovel machine? What level of skill is required to remove the right amount of metal in the right place without losing flatness and properly correcting alignment errors?
This is of course not the original purpose of spade, nor should it be used as a method to correct large alignment errors. However, a skilled spade master can complete this type of correction in a surprisingly short time. Although this method requires skilled technology, it is more cost-effective than processing a large number of parts to be very accurate, or making some reliable or adjustable designs to prevent alignment errors.
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Improvement of lubrication
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Practical experience has proven that scraper rails can reduce friction through better quality lubrication, but everyone is still confused as to why. The most common opinion is that the scooped low spots (or more specifically, the gouged dimples, extra oil pockets for lubrication) provide many tiny oil storage pockets, and these oil will be absorbed by the many tiny surrounding high spots. Scrape it out.
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Another way to put it logically is that it allows us to continuously maintain a film of oil on which the moving parts float, which is the goal of all lubrication. The main reason why this happens is that these irregular oil pockets form a lot of space for oil to stay, so that the oil does not easily escape. The ideal situation for lubrication is to maintain an oil film between two perfectly smooth surfaces. , but then you have to deal with the problem of preventing the oil from flowing out, or need to replenish it as soon as possible. (Whether there is scraping on the track surface or not, oil grooves are usually made to help the distribution of oil).
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Such a statement would make people question the effect of contact area. Scraping reduces the contact area, but creates an even distribution, and distribution is the key. The flatter the two matching surfaces, the more evenly distributed the contact areas will be. But there is a principle in mechanics that "friction has nothing to do with area." This sentence means that whether the contact area is 10 or 100 square inches, the same force is required to move the workbench. (Wear is another matter. The smaller the area under the same load, the faster the wear.)
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The point I want to make is that what we are looking for is better lubrication, not more or less contact area. If the lubrication is flawless, the track surface will never wear out. If a table has difficulty moving as it wears out, this may be related to the lubrication, not the area of contact.
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How is flower shoveling done?
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The purpose of this section is not to teach the art of shoveling flowers, but to give you an idea of the process of shoveling flowers. Although the actual operation is difficult, the concept behind the operation is quite easy.
Before finding the high points that must be scraped off, first apply the color developer on the standard jig (flat plate or straight jig when scraping V-shaped rails), and then put the color developer on the standard jig. When the track surface to be shoveled is rubbed, the color developer will be transferred to the high points of the track surface, and then a special spade tool is used to remove the high points of the color development. This action should be repeated until the track surface shows a uniform transfer.
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Of course, a shovel master must know various techniques. Let me talk about two of them here:
First, before we do the color development, we usually use a dull file to gently rub on the surface of the workpiece to remove the burrs. Click to receive free 10G CNC programming tutorial
Second, wipe the surface with a brush or your hands, never with a rag. If you use a cloth to wipe, the fine lines left by the cloth will cause misleading marks the next time you do high-point color development.
The shoveling master himself will check his work by comparing the standard jig with the track surface. The inspector only needs to tell the shoveling master when to stop the work, and there is no need to worry about the shoveling process. (The spade master can be responsible for the quality of his own work)
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We used to have a set of standards that dictated how many high points there should be per square inch, and what percentage of the total area should be exposed; but we found that checking the contact area was almost impossible, and now it's all done by The spade master determines the number of points per square inch. In short, spade masters generally strive to achieve a standard of 20 to 30 dots per square inch.
In the current shoveling process, electric shovels are used for some leveling operations. They are also a type of manual shoveling, but they can eliminate some strenuous work and make the shoveling work less tiring. When you're doing the most delicate assembly work, the feeling of manual shoveling is still irreplaceable.
