How important is the machine tool?


Shovel is a more difficult technique than woodcarving. It is the starting point for the basic accuracy of precision tooling. Shovel eliminates our dependence on other machine tools and eliminates the deviation caused by clamping force and heat. .

The track of the shovel is not worn out, thanks to the excellent lubrication. Shovel technicians need to know a lot of techniques, but only experience can let him master the sense of precision leveling.

When you go through a machine tool factory and see the technicians doing the shovel by hand, you think of it:

"Can they really rely on shovel to improve these machined surfaces? (Is people more powerful than machines?)"

If you mean purely its appearance, then our answer is "no", we won't be more beautiful, but why should we shovel? Of course, there are reasons for it. One of the reasons is the human factor: the purpose of the machine tool is to make other machine tools, but it can never replicate a product that is more accurate than the original. Therefore, in order to make a machine that is more accurate than the original machine, there must be a new starting point, that is, we must start with artificial efforts; in this case, artificial effort means Shovel the flowers by hand.

Shovel is not a "hands-on" or "whatever you want" job. It is actually a method of reproduction. It replicates the mother body almost perfectly. This mother body is a standard plane and is also hand-built.

Although the shovel is hard and laborious, it is a skill (art level technology); it is not easy to train a shovel master than to train a woodcarver. There are few books on the subject in the market. In particular, "There is less information on why you should shovel flowers. This may be why shovel is considered an art."

Where do you start?

If a manufacturer decides to grind with a grinder without shoveling, the guide of his "master" grinder must be more accurate than the new grinder.

So where does the accuracy of the first machine come from?

It must be from a more precise machine, or rely on another method that produces a truly flat surface, or it may be copied from a flat surface that has already been done well.

We can use three methods of drawing circles to illustrate the process of surface generation (although circles are lines rather than surfaces, they can be quoted to illustrate concepts). A craftsman can draw a perfect circle with a common compass; if he uses a pencil to draw along a circular hole in a plastic stencil, he will copy all the inaccuracies of the hole; if he is freehand In the case of a circle, the accuracy of the circle is determined by his limited skill.

In theory, a perfectly flat surface can be created by alternating rubbing of three surfaces. For the sake of simplicity, let's take a look at three rocks with a fairly flat surface. If you alternately rub the three planes in random order, you will grind these three planes more and more flat. If you only rub with two rocks, you will get a pair of concave and convex intersections. In practice, in addition to using Shovel to replace (Lapping), it will follow a clear match order. The shovel master usually uses this rule to do the standard fixture (straight gauge or flat) he wants to use. .

When in use, the shovel master will first apply the developer to the standard fixture, then slide it on the surface of the workpiece to reveal where it needs to be shoveled. He repeats this movement, the surface of the workpiece will be closer and closer to the standard fixture, and in the end it will perfectly replicate the same work as the standard fixture.

The castings to be shoveled are usually first milled to a range of a few thousandths of the final size, sent to a heat treatment to release the residual pressure, and then sent back to the surface of the cleaning surface before scooping. Although shovel takes a lot of time and labor costs, shovel can replace the process that requires high equipment costs. If you don't want to replace it with shovel, the workpiece must be finished with high precision and expensive machine. Repair.

In the final stage of finishing processing, in addition to the high cost of equipment, there is another factor to consider. When processing parts, especially large castings, it is often necessary to carry out some gravity clamping operations when the processing reaches a few thousandths. At the time of precision, the force of this clamping tends to cause distortion of the workpiece, which jeopardizes the accuracy of the workpiece after the clamping force is released; the heat generated during processing also causes distortion of the workpiece.

This is one of the many advantages of shovel, the shovel has no clamping force, and the heat it produces is almost zero. Cast iron is supported by three points to ensure it does not deform due to its own weight.

When the shovel track of the machine tool wears, it can be re-corrected by re-shoveling, which is a big advantage compared with discarding the machine or sending it to the factory for disassembly and processing.

When the track of a machine tool needs to be shoveled, the work can be done by the factory's maintenance personnel, but we can also find someone to do the shovel work.

In some cases, manual shovel and electric shovel can be used to achieve the final required geometric accuracy. If there is a set of workbench and the saddle's track has been leveled, and the accuracy has met the requirements, but found that the parallelism of the workbench to the spindle is not stipulated (it takes a lot of effort to correct), you can imagine using only one shoveling machine, In the case where the flatness is not lost and the alignment error can be properly corrected, the correct amount of metal can be removed at the correct position. What level of technology is required?

This is certainly not the original purpose of the shovel, nor should it be used as a way to correct large alignment errors, but a skilled shovel master can accomplish this type of correction in a surprisingly short time. Although this method requires skilled techniques, it is more economical than machining a large number of parts to be very accurate, or to make some reliable or adjustable designs to prevent misalignment.

Lubrication improvement

Practical experience has proven that the shovel track can reduce friction through better quality lubrication, but everyone has no reason for it. The most common opinion is that the low point of the shovel (or more specifically, the pits that are cut out, the oil bags that are made for lubrication) provides many tiny oil storage pockets that are surrounded by many tiny heights. Click to scrape it out.

Another logical statement is that it allows us to keep a layer of oil film and let the moving parts float on the oil film, which is the goal of all lubrication. The main reason for this happening is that these irregular oil bags create a lot of room for oil retention, making it difficult for oil to run away. The ideal condition for lubrication is to maintain an oil film between the two perfectly smooth surfaces, but you have to deal with the problem of preventing oil from flowing out, or you need to replenish it as quickly as possible. (Whether there is a shovel on the track surface, it is usually made to help the oil distribution.)

Such a statement would raise questions about the effect of the contact area. Shovel reduces the contact area, but it forms a uniform distribution, and the distribution is the focus. The flatter the two matching surfaces, the more evenly the distribution of the contact surfaces. But in mechanics, there is a principle of "friction and area-independent". This means that the same force is required to move the table regardless of the contact area of 10 or 100 square inches. (Money consumption is another matter. The smaller the area under the same load, the faster the wear and tear.)

The point I want to make is that what we are pursuing is better lubrication, not more or less contact area. If the lubrication is flawless, the track surface will never wear out. If a workbench has difficulty moving with wear, this may be related to lubrication, regardless of the area of contact.

How is the shovel flower done?

The purpose of this section is not to teach the art of shovel, but to give you a concept of the process of shovel. Although the actual operation is difficult, the concept behind the operation is quite easy.

Before finding the high point that must be scraped, apply the developer to the standard fixture (flat plate or straight gauge when you want to shovel the V-track), and then apply the standard fixture with the developer. To rub the track surface of the shovel, the developer will be transferred to the high point of the track surface, and then a special shovel tool will be used to remove the high point of the color. This action is repeated until the orbital surface exhibits a uniform transition.

A shovel master must of course understand various techniques. I am going to talk about two of them here first.

First, before we do the color-developing action, we usually use a blunt trowel to gently rub the surface of the workpiece to remove the burrs.

Second, wipe the surface with a brush or hand, never wipe with a rag. If you use a cloth to wipe, the fine linen left by the cloth will be misleading when the next high color is developed.

The shovel master will check his own work by comparing the standard jig with the track surface. The person inspecting will only need to tell the shovel master when he can stop the work. It is not necessary to worry about the shovel process. (Shovel master can be responsible for the quality of his work)

In the past, we all had a set of standards that stipulated that there should be several high points per square inch and how many percentages of contact should be in the total area; but we found that it is almost impossible to check the contact area, and now it is The shovel master decides the number of points per square inch. In short, the shovel master will generally strive to reach the standard of 20 to 30 points per square inch.

In the current shovel process, some leveling operations use electric shovel machines, which are also a kind of manual shovel, but can eliminate some laborious work, so that the shovel work is less tired. When you're doing the most detailed assembly work, the feeling of manual shovel is still irreplaceable.