Why do precision machine tools have to manually shovel flowers?

Shoveling is a technique that is more difficult than wood carving. It is the starting point for the basic accuracy of precision machine tools. Shoveling eliminates our dependence on other machine tools and can also eliminate the deviation caused by clamping force and heat. .

The shoveled track is less abraded, thanks to the excellent lubrication effect. The shovel technician needs to know many techniques, but only experience can let him master the sense of precision leveling.

When you pass a machine tool manufacturing factory and see the technicians doing shoveling by hand, you can't help but wonder:

"Can they really improve the current machined surfaces by shoveling? (Will people be better than machines?)"

If you mean purely its appearance, then our answer is "no", we won't do it more beautifully, but why bother to shovel it? Of course there are reasons for it, one of which is the human factor: the purpose of machine tools is to manufacture other machine tools, but it can never replicate a product that is more accurate 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 effort; in this case, human effort refers to Shovel flowers by hand.

Shoveling is not a "hands-on" or "arbitrary" operation. It is actually a method of copying, almost perfectly copying the matrix. This matrix is a standard plane and is also made by hand.

Although shoveling flowers is laborious and laborious, it is a skill (art-level technology); it may be more difficult to train a shoveling master than to train a woodcarver. There are not many books on the market that discuss this topic. In particular, there is less information on why shoveling is necessary. This may be the reason why shoveling is regarded as an art.

01

Where to start?

If a manufacturer decides to grind with a grinder instead of shoveling, the accuracy of the guide rails of his "mother machine" grinder must be higher than that of the newly built grinder.

So, where did the accuracy of the first machine come from?

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

We can use three methods of drawing circles to illustrate the process of surface production (although circles are lines rather than surfaces, they can be cited to illustrate concepts). A craftsman can use an ordinary compass to draw a perfect circle; if he uses a pencil to trace a round hole on the plastic template, he will copy all the inaccuracy of the hole; if he draws freehand In the case of a circle, the accuracy of the circle is determined by his limited skills.

Theoretically, a perfectly flat surface can be produced by alternating friction (lapping) of three surfaces. For the sake of simplicity, let's use three rocks each with a fairly flat surface to illustrate. If you rub the three planes alternately in a random order, you will make the three planes smoother and smoother. If you rub only two rocks, you will get a concave and convex mating pair. In practice, in addition to using shoveling instead (smoothing Lapping), it also follows a clear matching sequence. The shoveling master usually uses this rule to make the standard fixture (straight or flat) he wants to use. .

When in use, the shoveling master will first apply the developer on the standard jig, and then slide it on the surface of the workpiece to expose the place that needs to be shoveled off. He keeps repeating this action, the surface of the workpiece will get closer and closer to the standard jig, and in the end it can perfectly replicate the same work as the standard jig.

The castings to be shoveled are usually processed by milling to a few thousandths of the final size, then sent to heat treatment to release the residual pressure, and then sent back for surface cleaning and grinding before shoveling. Although shoveling takes a lot of time and high labor costs, shoveling can replace the process that requires high equipment costs. If you do not want to replace it with shoveling, the workpiece must be finished with high-precision and expensive machines. Repair processing.

In addition to the high-cost equipment involved in the final stage of finishing processing, there is another factor that needs to be considered. When parts are processed, especially large castings, some gravity clamping is often necessary. When the processing reaches a few thousandths For precision, this clamping force often causes distortion of the workpiece, so as to endanger the accuracy of the workpiece after the clamping force is released; the heat generated during processing will also cause the distortion of the workpiece.

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

When the shovel track of the machine tool is worn, it can be re-corrected by shoveling again. Compared with discarding the machine or sending it to the factory for disassembly and processing, this is a great advantage.

When the track of a machine tool needs to be shoveled again, this job can be done by the maintenance personnel of the factory, but we can also find someone locally to do the work of shoveling.

In some cases, manual shoveling and electric shoveling can be used to obtain the final required geometric accuracy. If there is a set of workbench and saddle rails that have been leveled and the accuracy has met the requirements, but found that the parallelism of the workbench to the spindle is out of specification (it takes a lot of work to correct), you can imagine using only one scraper, Without losing the flatness and properly correcting the alignment error, is it possible to remove the correct amount of metal at the correct position. What level of technology is needed?

This is of course not the original purpose of shoveling, nor should it be used as a method to correct large alignment errors. However, a skilled shoveling master can complete this type of correction in a surprisingly short time. Although this method requires skilled technology, it is more economical than processing a large number of parts to be very accurate, or to make some reliable or adjustable designs in order to prevent alignment errors.

02

Improvement of lubrication

Practical experience has proved that the shovel track can reduce friction through better quality lubrication, but everyone has no consensus on why. The most common opinion is that the shoveling low point (or more specifically, the pits that are cut out, the oil bags made more for lubrication) provide many tiny oil storage pockets, and these oils will be trapped by the many tiny heights around them. Scratch it out.

Another logical statement is that it allows us to continuously maintain a layer of oil film, allowing moving parts to float on the oil film, which is the goal of all lubrication. The main reason why this happens is that these irregular oil bags form a lot of oil-retaining space, making it difficult for the oil to escape. The ideal situation of 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 you need to add it as soon as possible. (Regardless of whether there are shoveling on the track surface, oil grooves are usually made to help oil distribution).

Such a statement will make people question the effect of the contact area. Shoveling reduces the contact area, but it will form an even distribution, and the distribution is the point. The flatter the two matching surfaces, the more even the distribution of the contact surfaces. However, there is a principle in mechanics that "friction has nothing to do with area". This sentence means that no matter the contact area is 10 or 100 square inches, the same force is required to move the table. (Abrasion is another matter. The smaller the area under the same load, the faster the abrasion.)

The point I want to say is that what we are after is a better lubrication effect, not more or less contact area. If the lubrication effect is flawless, the track surface will never wear out. If a workbench is difficult to move due to wear, it may be related to lubrication, not to the contact area.

03

How is shoveling done?

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

Before finding the high point that must be scraped off, first apply the developer on the standard fixture (a flat plate or a straight fixture when shoveling the V-shaped rail), and then put the standard fixture coated with the developer on the standard fixture. When rubbing on the track surface to be shoveled, the color developer will be transferred to the high points of the track surface, and then a special shovel tool will be used to remove the high points of the color. This action has to be repeated until a uniform transition appears on the track surface.

Of course, a flower shoveler must know all kinds of techniques. I will talk about two of them first.

The first one is that we usually use a dull file to gently rub the surface of the workpiece to remove the burrs before doing the color development.

Second, wipe the surface with a brush or hand, never wipe with a rag. If you use a cloth to wipe, the thin linen thread left by the cloth will cause a misleading mark the next time the high-point color is displayed.

The shoveler himself will check his work by comparing the standard fixture with the track surface. The inspector only needs to tell the shoveler when he can stop the work, and he does not have to worry about the shoveling process. (The shovel master can be responsible for the quality of his work)

In the past we had a set of standards that stipulated how many high points each square inch should have and what percentage of the total area should have a contact rate; but we found that checking the contact area is almost impossible, and now it is The shovel master decides the number of points per square inch. In short, the shoveler generally strives to reach the standard of 20-30 points per square inch.

In the current shoveling process, some leveling operations use electric shoveling machines. They are also a kind of manual shoveling, but some laborious work can be eliminated, making the shoveling operation less tiring. When you are doing the most delicate assembly work, the feeling of manual spatula is still irreplaceable.