Wednesday, November 30, 2022

What to watch out for when drilling holes in hard materials

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Hard materials such as granite, stone, glass, brick, cement, masonry, ceramic or porcelain require certain tools, techniques and precautions to carry out our work successfully. For example, we have already published some for cutting glass, as well as for cutting porcelain. On the other hand, we met some models of ceramic cutting machines.

However, when it comes to drill holes in diverse materials, the story is different. Many of us have found that doing this task on soft materials such as wood is very simple. We simply put a standard carbide bit in our drill, hit the start button, apply a little bit of pressure with the drill, and within seconds we have the hole ready. But if we use this same method on hard materials, after those few seconds we will see with dismay that we broke the bit, ruined the work piece and, therefore, we lost time and money.

Therefore, it is clear that the secret to drilling holes in hard materials goes through another type of drill. This is precisely where diamond cutting tools come into play.

Diamond cup saw

Practice advises that for making small holes and / or in thin plates of hard materials, diamond bits should be used at an initial speed of 2500-5000 rpm. Instead, when it comes to holes with a diameter of 1/4 inch or greater, and / or plates or thick objects of hard materials, the recommendation is the use of diamond cup saws at a starting speed of 600-900 rpm.

Some time ago we knew the cup saws in Of Machines and Tools and we present details about its composition, design and uses. Now we are going to delve a little more about the application of the diamond cup saws for drilling holes in hard materials.

Cup Saw Use and Life

Diamond cup saws are tools expensive that we must take care of with care. The useful life of any type of drill bit and saw is affected by the hardness and abrasiveness of the material to be drilled, the thickness of the material, the speed of the drill or saw, the amount of pressure exerted and the use of adequate lubrication.

The hardness and abrasiveness of the material can vary significantly, even in materials that have the same appearance. The speed, pressure, and amount of lubrication each user uses also varies significantly.

Therefore, it is practically impossible to estimate the life of a diamond cup saw. For example, in standard 1/8 ″ glass, this type of saw can make between 200 and 300 holes or more, depending on the particular glass and the drilling techniques applied. Under equal hardness conditions and the techniques used, a glass saw to drill a 1/4 ″ glass, twice as thick as the previous one, will be useful for 100-150 holes.

Diamond cup saw

Diamond cup saw

For its part, lubrication has a crucial effect on a diamond saw, since if we use a good method of lubrication with water we can double or even triple its useful life, as we will see later.

In extremely hard and abrasive materials, such as granite or porcelain tiles, a diamond cup saw can produce 8-15 holes in 3/8 ″ thick material. However, the same saw can make more than 20 holes, depending on the specific material, thickness, and drilling techniques used. Generally and always taking into account these parameters, as the hardness of the material decreases the cup saws They are capable of drilling a greater number of holes, for example, between 40 and 60 in tiles, between 8 and 60 in porcelain for walls and more than 100 in ceramic tiles.

These examples are based on many tests on different materials using the methods and techniques that we will see below. If, on the contrary, poor or inadequate techniques are used, not only the performance of the saw noticeably decreases, but we will be left with a saw “Burned” after just one or two holes.

Let’s see then what should be done to extend the life of a diamond cup saw and thus get the best out of our work.

Cup Saw Lubrication

We should always use a lot of water when cutting with a diamond cup saw. The water keeps the saw cool and removes the residue or sludge generated. The contact point between the cutting surface and the saw must always be wet and the cutting edge of the saw must not overheat. If we notice that said edge burns to the touch, it is an indication of too little lubrication, or possibly too much speed or pressure. Water reduces heat build-up, protects the saw, and helps prevent heat cracking in the material. Minimal lubrication prevents the saw from burning, but good lubrication techniques extend the life of the saw much longer. We must also bear in mind that oil-based lubricants do not perform well in diamond saws.

“Pumping” technique

When drilling holes with a diamond cup sawWe must always use a “pumping” movement. This technique consists of gently inserting the saw into the cut surface or hole, then momentarily withdrawing it to allow the water to penetrate the cut, and finally gently inserting it again to continue the cut, repeating this process every 15-20 seconds. . The water removes the generated sludge and ensures that the point of contact between the cut surface and the saw remains lubricated. Without the pump technique, the water does not reach the cutting edge of the saw, even when the saw is under water.

Demonstration of cutting with a diamond saw

Drill speed

Since all materials vary in terms of hardness and abrasiveness, exact drilling speeds cannot be determined. Therefore, the suggestion is to respect the recommended speed according to the material, or to go even slower if we are not sure of the hardness of the material to be cut. Higher drilling pressure or speed may reduce cutting time slightly, but will also significantly increase friction and heat the cup saw. This will greatly reduce the life of the saw, presenting an increased risk of heat cracking and material breakage. If a saw shows yellow, brown, blue or black marks around the cutting edge, it is an indication of extreme heat, suggesting that the drilling speed is too high or the pressure applied to the drill is too high.

The figure below details the drill speeds (in rpm) recommended for some hard materials according to the diameter of the hole to be made.

Drill material / speed (in rpm)

Drill material / speed (in rpm)

Pressure exerted with the drill

When using a diamond cup saw It is very important that the pressure of our hand on the drill is only light or moderate, mainly letting the saw work at its own speed. Higher pressure does not greatly speed up the cut, but rather increases friction considerably, overheating the saw or ultimately burning it and ruining the workpiece. On the other hand, we must always decrease the pressure as we get closer to the back of the material; this reduces chipping or fracturing of that part when the saw goes all the way through the material.

Power tool to use

Since speed is a very important factor when it comes to driving a diamond cup saw, it is recommended to use a variable speed drill. We should never use an impact driver or a hammer drill with this type of saw, since that way the cutting edge of the saw will be flattened in the shape of a mushroom (just like a chisel remains after prolonged use) or it will split, completely ruining the cutting tool. When using a 1/2 ”saw without a jig, it is preferable to use a drill press instead of a hand drill.

In short, experience with a specific material allows us to quickly determine the optimal speed, pressure and lubrication of the drill to obtain the most suitable cutting speed with the least effect on the life of the cup saw and the risk of ruining the saw or the piece due to heat or breakage. However, for newbies, it is best to start with a very low drilling speed, very low pressure, and a lot of lubrication. This starting point minimizes risks and gives us the best achievements.

Cup saw kit

Cup saw kit

Pilot bits

As we have already seen, pilot bits are common components of hollow metal bits or cup saws designed for use in wood and other soft materials. Pilot bits are mounted in the center of the cup saw and are intended to keep it centered correctly when starting a hole, so they are especially convenient when using cup saws with a hand drill and not as necessary when using hole saw drills. column, since in this case the drill never “slips” when starting to drill the piece, as it does with a manual drill.

However, pilot bits are rarely used in diamond cup saws, because there are a number of drawbacks not only in design, but also with drilling very hard materials. For starters, a diamond pilot bit adds an additional cost to the already expensive ones. diamond cup saws. On the other hand, they prolong drilling time in hard materials, generally wear out faster than the hole saw itself and often make proper lubrication difficult.

Therefore, when drilling holes with diamond cup saws It is common to use templates to replace a diamond pilot drill.

What are templates and how are they used?

The templates are simply small boards made of soft material, which we can either prepare ourselves or purchase from cup saw manufacturers. Those prepared at home may contain pilot holes of different diameter made with our cup saws conventional, a “V” on one edge (which will adapt to any diameter) or both, as we see in this figure.

Drilling templates

Drilling templates

Stencils are generally 1/8 “plastic or plexiglass, 1/8” hardboard, or even cardboard. If we are going to make repetitive perforations, a plastic or plexiglass template will be the most indicated, since we can use water lubrication. To use the template, we simply place it on the surface of the material to be drilled, with the “V” (or the pilot hole selected) above the area of ​​the hole we want to drill in the material. The jig will keep the hole saw perfectly aligned as we begin to drill the hole. Once the slot is created in the material, we can remove the template and continue drilling until the hole is completely open.

Many manufacturers have not only jigs, but complete cup saw kits as well, including a set of multi-diameter saws, carbide pilot bits, a jig, and even a specially designed lubricating fluid for drilling in hard materials.

Kit with template

Kit with template

What we have just seen provides us with more elements to carry out a correct drilling of holes in hard materials, such as glass or porcelain. Carry out a neat job and at the same time take care of our diamond cup saw They are essential requirements for success and, therefore, guarantee us satisfactory results.

Learn about the different types of saw glass and their function

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