Thursday, December 8, 2022

Introduction to the Sierra de Copa

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Also known by various alternative names, such as crown saw, hole saw, wick cup or saw / hole saw, the cup saw It is a very useful tool, especially among blacksmiths and carpenters. However, it is also frequently used in materials such as plastic, plaster, asbestos, MDF, ceramics, tiles, fiberglass, granite, marble, glass, Bakelite, as well as ferrous and non-ferrous metals, including cast iron, brass, bronze, etc. copper and aluminum.

Bimetallic Cup Saw – metal cutting

A cup saw It is basically an annular or ring-shaped saw, the cut of which generates a hole in the workpiece, without having to cut the base material. Often, this particularity prioritizes the use of cup saws in front of twist drills waves spade bitsespecially when relatively large holes must be made, for example those with a diameter greater than 25 millimeters (1 ″), since the cut is made faster, with less energy and is much cheaper.

As for its manufacture, it is a band saw that is cut, bent and welded on its side. In a way, it is a by-product, which is why most of the brands that make band saws tend to be cup saws.

The depth to which you can cut a cup saw it is limited by the depth of its shape. Most of these saws have a fairly low diameter-to-depth aspect ratio and are used to drill holes in relatively thin parts (up to 3-5mm). However, they are also marketed cup saws with higher aspect ratios or with special teeth, such as the so-called cutter cup, which thanks to their carbide teeth, can reach greater ranges of cutting depth, with greater efficiency. Of course, they can only be used in bench drills.

Standard Bimetallic Cup Saw

Standard Bimetallic Cup Saw

Design and components of cup saws

The cup saws they are always used in a drill. They essentially consist of a metal cylinder, usually a carbon steel strip, which has a serrated edge at one end and some type of mounting through which a bit passes (commonly known as a pilot bit or guide bit) properly tightened with a nut or thread, which connects to the drill chuck and serves to center and guide the hole. This mounting can vary from a simple hole, in which case the saw requires in addition to a spindle, bracket or tree It is sold separately in different shapes and sizes of chuck and drill, depending on the application, up to the saw models that come with the spindle already incorporated. The latter have the disadvantage that, once the bit has worn out, the rest must be discarded even if it is in a position to be reused.

There are those who wonder «How to install a cup saw on a hand drill?»Is very simple, as seen in the image below, once the diameter of the saw cup has been chosen, the support model is selected (they vary in general according to the size of the cup) and they are simply joined by means of a thread. The end with the bit goes to the side of the saw cup and the other in the chuck of the drill. It’s as simple as that! This is how the saw cup is installed in the manual or bench drill!

Bimetallic Cup Saw with support

Bimetallic Cup Saw with support

In turn, in the more advanced models, the cylinder wall has inclined grooves that help to extract virura and dust. The cutting groove is designed to be slightly larger than the diameter of the rest of the saw so that it does not get stuck in the hole.

The market has a wide variety of cup saws, from the most economical of carbon steel to the highly specialized for each application. However, the most widely used today is the bimetallic cup saw.

In the bimetallic cup saws Two different types of steel are combined to form the edge of the cutting end: a high-strength steel, such as HS steel, M42, etc. and a soft spring steel. Both form a durable edge that cuts a wide variety of materials and helps provide long life. Denatured steel is used on the outer edge due to its wear resistance properties and forms the cutting edge (geometry) of the teeth. Soft spring steel creates a flexible backing material that allows the saw to absorb the impacts of drilling holes in difficult-to-cut materials.

There are also models in which the cutting edge is composed of diamond material. This type of cup saws It is ideal for drilling in brick, concrete, glass and stone. Another type of material for the teeth of cup saws is also the tungsten carbide, which offers smoother cuts, high heat resistance and long life with abrasive cuts.

The cup saws For use with portable drills they are commonly available in diameters from 6 to 210 mm, although the most popular are usually the sizes 19, 20, 22, 25 and 27 mm. The only limit on the length of the cylinder, and therefore the depth of the hole, is the need to remove the bit from the hole to remove the waste. Currently there are a kind of springs that are easily adapted and allow the bite left inside the glass to be automatically removed.

Sierra Copa Bimetalica - Games

Sierra Copa Bimetalica – Games

Many manufacturers offer cup saw sets, whose composition varies depending on the application, so that, for example, sets are available for plumbers, electricians, locksmiths, mechanics, etc. This is highly recommended as it allows you to keep the saws neat and tidy. As said, the material of the teeth is a high hardness steel, therefore, an accidental impact, for example, when hitting with other tools, can cause a tooth to break and alter the correct functioning.

Regarding whether to drill with or without oil? or at how many RPM? We have tackled these and other topics in this other whitepaper: What are Cup Saws and how do they work?

Why do crown saws burn when cutting wood?

Several readers have sent us this question and it is something complex to answer in a general way. In a particular way, we can say that cup saws that have tooth geometries for metal, or that do not have a good self-cooling design in the turn, tend to quickly raise temperatures, this can cause the metals that compose it to « lose their temper ”and consequently significantly alter performance.

Bimetallic Cup Saw for Wood

Bimetallic Cup Saw for Wood

Recently, some models recommended for wood have appeared on the market, both for occasional use and for intensive use. For our part, we believe that it is best to try to have a product as specific as possible, according to the task to be carried out. Now, if you have a conventional glass and the need to use it on wood, the most important thing is to follow the manufacturer’s RPM recommendations. If there are not, for wood, maintain high revolutions (to avoid jams) but for very short periods of time, giving the possibility for the glass to drop in temperature before advancing again on the hole.

Advantages and disadvantages of cup saws compared to drill bits

The main advantage of cup saws Compared to conventional bits is their efficiency as very little of the material to be removed is cut, ultimately reducing the total power requirement and cost per cut. Another advantage of cup saws is the ability to offer a larger cutting diameter. For example, a 100 millimeter diameter hole would require a huge twist or spade bit, impossible to handle properly with a hand drill or bench or bench drill; however, this type of hole can be cut with a cup saw with relative ease.

Some considerations on the cup saws:

  • The portable drill used must be capable of producing considerable low-speed torque (RPM) and, where possible, have variable speed.
  • Kickback from a heavy duty drill can be serious in some cases and therefore long side handles should be used, preferably with two operators when drilling large holes.
  • The material plug may stick to the inside of the cup saw and to remove it, a lever movement must be made after cutting each hole. Sometimes that lever movement is quite difficult.
  • Sometimes the material plug kinks when it is half cut, creating a situation where the material within the cop sawa rotates over the uncut portion of the material that is still on the part. This tends to stop the cutting action of the saw, and if the part is made of wood or plastic, the friction will start to scorch it, creating a burning smell and heating the saw. The twisted material must then be removed by a lever movement before continuing with the cut.
  • Although the use of cutting oil is not recommended, sometimes it may be necessary to use some type of coolant, for example, soluble oil.

Diamond cup saws: Drilling wet or dry

The diamond cup saws they are also called diamond core bits. Laser welds can be used for both wet and dry drilling, but not all drilling materials are suitable for dry drilling. Very hard materials such as reinforced concrete must normally be drilled with water; Otherwise, excess heat generated during the drilling process can dull the diamond material on the saw and lead to poor performance.

The combination materials and diamonds used in laser-welded diamond bits are generally specifically tailored to suit wet and dry drilling, respectively. This can improve drill performance, both in speed and life.

At present, the field of application of the cup saws It includes its use in portable and stationary machines with electric power and batteries, to generate holes in pipes, electrical installations, door locks, conduits, antennas, metal plates and automotive applications, among many others.

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