Diamond drilling in the New Stone Age

December 10, 2003
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Bench Drill Press -- These are designed for smaller jobs and are usually bolted or clamped to a table, bench top or stand. This is the smallest and least expensive type of drill press, and they are suited for the hobbyist and beginner.

Floor Drill Press -- These are larger drill presses. They usually have a base that stands directly on the floor of your shop. This drill press can be extended and adjusted for optimum use and movement. An operator may use this drill press in either a sitting or standing position. This type of drill press can be found in most fabrication shops.

Industrial/Production Drill Press -- These are heavy-duty drill presses, similar to a milling machine. They usually come with variable speed rpm; a larger drilling table area for holding larger material; a more powerful motor; the capability to use chuck or collet; to move the drilling head up and down; and to move the table horizontally and vertically.

Specialty/Custom Drill Press -- A few large fabricators have presses built specifically for their material/application. For example, when machining very brittle or fragile materials, the drill press will be made from a special type of metal to minimize dust and corrosion. Many come with ultra precise chucks, collets, water pumps and devices. With these types of drill presses, you are usually able to regulate drilling depth either electronically or by computer, and you can maintain consistent speed and feed rate. More advanced drill presses today may have a feedback mechanism that provides information on all of these variables.

When buying a diamond core drill to fit your current drill press, or if you are buying a drill press to fit a diamond core drill, we recommend you carefully examine both the drill and drilling equipment specifications to make sure they are compatible. There are several variables to consider:

A. Horsepower. Drill presses run on electric motors rated in horsepower. Users need to make sure that the motor for the drill press you choose is powerful enough for the material you are planning to drill and the diamond core drill you are planning to use. Most bench drill presses have motors rated between 0.3 hp and 0.5 hp. On the other hand, floor drill presses have motors that run between 0.75 hp and 1.5 hp. We recommend you choose the highest power motor you can afford. Doing so will place less strain on your job and will allow you to be more flexible if you decide to use another drill or drill a different type of material in the future.

B. Speed. Depending on the material you are planning to drill, you will need to adjust the speed (RPM) at which your diamond drills run. A drill press will usually allow you to run your diamond drills between 500 and 3,500 rpm. Some drill presses only provide specific speed settings, such as 500, 1,000, 1,500, 2,000, 2,500 and 3,000 rpm. This may be acceptable to you, again depending on the diameter of the diamond core drill and material you are planning to process. Before buying any type of drilling equipment, make sure it will run at the recommended rpm set for your diamond drills.

C. Throat depth. Another important factor to consider when buying a drill press is the “throat depth.” A drill press design usually limits the distance between the center of the spindle (where the diamond core drill is placed) and front edge of the vertical post that is used to support the drill head. This is called the throat depth. When drilling a hole in the center of a round workpiece, such as a tabletop, the radius of your workpiece will need to be less than the throat depth itself.

D. Spindle travel. The spindle of a drill press moves up and down only a certain distance. The distance the spindle can move is called spindle travel. This determines the maximum depth of the holes you will be able to drill. The drilling depth of your diamond core drill will need to reflect and consider the spindle travel of your drill press.

E. Table adjustments. Most drill presses have a tilting worktable. Some have the capability to tilt 45 degrees left and 45 degrees right. Others can tilt a full 90 degrees in each direction. Before buying a drill press, make sure the model you are considering can work with the angles you need to make for your application. It is also recommended that the table swing horizontally as well. An excellent type of drill press is one that can spin completely around the post.

F. Head adjustments. A number of drill presses supplement a tilting table with a tilting drill head. Tilting heads typically move 45 degrees left and right, and ease the mind-bending work of compound angles. We recommend that you are comfortable with both the adjustment mechanism and the angle gauge before using or buying this type of drill press.

G. Drill press accessories. There are a number of accessories on the market that will make your drilling experience faster, easier and provide better performance as well as lower cost per hole. A few important ones include water swivel adapters, which are used to supply water through the center of the drills. These can increase drill life 40% to 75%, improve the quality of the hole and the surface finish. Shank Adapters are thread into the diamond drill collet and allow the diamond core drill to be placed in the drill press chuck. Vises and clamps designed for your drill press worktable hold the material firmly in place while drilling.

Angle grinders/hand-held grinders

The angle/hand-held grinder offers your diamond drilling operation the advantage of low cost, and increasing versatility. With this one piece of equipment, you can drill, cut, grind and polish. An angle grinder is an excellent choice for small jobs, outside jobs, drilling hard to reach places, or when drilling a very large piece of material. It can be an excellent alternative when use of a conventional drill press is not feasible. Angle grinders can run up to 10,000 rpm. Water swivel adapters specially designed to fit all popular angle/hand-held grinders can extend the capability of the angle grinder by supplying coolant through the center of the diamond core drills or many other diamond tools. This can allow the angle grinder and diamond core drills to accomplish improved efficiency, drilling speed and a higher quality surface finish.

Hand-held drills

Nothing beats the versatility and ease of use of a hand-held drill. Hand-held drills are lightweight and portable, and can be taken virtually anywhere. Suited for use on horizontal surfaces and outside jobs, these are an ideal tool for beginning stone installers, maintenance personnel and homeowners.

Hand-held drills are available in a wide selection of both corded electric and battery-powered cordless models. The drill type you choose will affect your drilling capability in terms of material and diameter of the hole. The first step in selecting the right hand-held drill for your application is determining the size of holes you need to drill and what materials you are planning to drill.

Make sure you select the hand-held drill that actually has the capacity to do the work you need. Doing so will make your jobs faster and easier, and help you avoid problems such as ruining the diamond core drill or material by using a unit without enough capacity. The following are some of the features you should consider when choosing the right hand-held drill for your application:

A. Capacity. A hand-held drill's capacity indicates the largest hole size you can drill. Most hand-held drills are ranked according to the maximum diamond core drill shank the chuck can hold. Most popular drill shank sizes are 3⁄8 and 1⁄2 inch.

B. Power. Make sure your hand-held drill has enough power to use the diamond core drill at the recommend rpm. Hand-held drills are ranked according to the maximum horsepower the motor can give. If your hand-held drill does not have enough power, your chuck capacity will be irrelevant. And you will not be able to drill the size of hole and material you need. Before buying a hand-held drill, we recommend you compare the horsepower of the drill. By the same token, if you will be working only with small or soft material, and need to drill only a few holes, an inexpensive drill will probably be sufficient for your application. However, if you are planning to drill a large amount of holes, drill hard materials or make deep holes and need to use your drill often, a more heavy-duty and higher powered drill will be required.

When drilling, never force your hand-held drills, as this causes more wear and tear on the drill than associated with normal usage -- decreasing the machine's life and deteriorating future performance.

CNC machines

The best drilling results, precision tolerances, surface finishes and consistency will be obtained on a CNC machine, which is an ideal choice for high-production drilling operations. This equipment is fully automatic and controlled by a computer. As such, it costs more than other types of drilling equipment.

Number of holes to be drilled

Your diamond core drill requirements will greatly vary with your frequency of use and the number of holes you need to drill. High production fabrication diamond drilling requirements greatly differ from installing kitchen countertops.

Diamond core drills in a production setting are used every day or several times a day, drilling several thousand holes until the drill is worn out and replaced. Metal bonded (sintered) diamond core drills are usually recommended for this type of heavy-duty use. However, if you have a very fine or specific finish requirement and do not polish material after drilling, perhaps a bond that falls between a metal bond and resin bond would be the best solution for your application.

If you are planning to use a diamond core drill occasionally for a specific job and then store it for later use -- or if you make less than 100 holes -- we recommend you use electroplated (nickel bond) diamond core drills. However, if you are planning to use the drill a number of times through the year, then a sintered (metal bonded) diamond core drill is a better overall solution and investment.

Technical requirements/specifications

A. Chipping/finish requirements. If you have an application where surface finish and chipping is a critical factor, a sintered (metal bond) diamond core drill with a very fine diamond grit may be the best solution. A bonding that falls between a metal bond and resin bond is another alternative.

B. Tolerance. If you are using diamond core drills to drill holes in a product that requires specific tolerances, you will need a custom diamond core drill product specifically designed for your application. It is important to have some kind of an idea on what accuracy and tolerance you need to obtain. Diamond core drills, accessories, and drilling equipment should be selected to achieve these requirements. Each stone material has a different density, hardness and composition. For this reason, a diamond core drill and technique that may work on one material may not work on another material. To obtain optimum drilling results, each diamond core drill should be ideally made to factor in the unique differences and properties of each material.

C. Material Cost. If the material you are drilling is precious, valuable or expensive, the diamond core drill cost will play a minor role in your drilling operation. It is suggested that you obtain a thin wall diamond core drill to minimize material loss and deformation. Thin wall diamond core drills are capable of being used at a much higher rpm than thicker wall drills. They will minimize material loss and provide closer tolerances. Thin wall core drills are not recommended for use on angle grinders, however.

Coolant to be used

Your capability to use coolant while drilling will seriously affect your diamond core drill selection. Most diamond core drills must be used with coolant. When drilling with diamond core drills, the proper use of coolant is important for two reasons. First, it is critical to minimize drill and material overheating. Frictional heat produced at the working face of the diamond tip must be disposed immediately. Otherwise, the diamond becomes rapidly damaged by oxidation and graphitization. Excessive heat generated while drilling will also damage the metal matrix holding the diamonds in place.

It is also important to ensure drilling consistency. Debris generated while drilling should be removed as soon as they are produced. When this drilling debris is not removed rapidly, diamond wear increases through abrasion caused by the presence of excessive coarse stone fragments.

Water is the most common coolant used for stone drilling applications. It is always a good idea to pump an adequate supply of water through the center of the drill so that an uninterrupted flow is maintained, flushing across the working surface of the drill diamond section. This way, diamonds and the metal matrix are both kept sufficiently cool, and stone debris is removed as soon as it is produced. These are the optimum conditions for your drill.

Reduce friction between material and drill

Water also penetrates the micro-cracks that are generated upon impact of material and diamond core drill. Under ideal conditions, the material will absorb water, hence becoming completely saturated with water. In this state, the material is weaker and more easily drillable.

The coolant surface tension also plays an important part in the drilling operation. Usually the lower the surface tension, the easier it is for the coolant to enter the micro cracks. Coolant with a lower surface tension also wets the diamonds more easily. Most users find that lowering the surface tension of their coolant results in better cooling (wetting) of their diamond and more effective overall cooling. Lower surface tension also improves material debris lubrication, promoting efficient removal.

Shorter drill life, material and drill deformation will result when using drills dry. Electroplated (nickel bonded) diamond core drills may be used dry (without water) depending on the application (material being drilled). Using diamond core drills dry is not recommended for most stone applications. When chance prevails, use all diamond core drills with coolant.

Diamond core drill variables

The bond hardness of your diamond core drill will determine the type of materials you will be able to drill. Harder materials such as porcelain and engineered stone generally require a softer bond. However, a diamond core drill made for this application will not last a long time on softer and more brittle materials such as limestone and flagstone, which require a harder bond. Another important factor to consider when selecting the right diamond core drill for your application is diamond grit (mesh) size. This is generally selected depending on the drill speed and surface finish of your material. Courser (larger) diamonds will drill faster than finer (smaller) diamonds. However, the trade-off is a smoother surface finish.

Different materials and equipment in the stone industry require the use of diamond core drills with various wall thickness. Many stone fabrication facilities that are equipped with precision CNC and milling machines use thin wall diamond core drills. Thin wall diamond core drills are formulated to provide less loss of material, minimum material deformation, less heat generation, faster drilling speed, less chipping and a better finish quality. Usually, the thinner the wall thickness of your diamond core drill, the faster speed (rpm) your drill may run, with less chipping and heat generated. This results in a smoother, higher quality of the finish. One major drawback is shorter diamond core drill life.

Diamond core drill bond types

Most stone fabricators and installers encounter different types of diamond core drills. Selecting the right drill for your particular job can save time and money. High-production applications that require hundreds of holes could benefit from the use of sintered (metal bond) diamond core drills. As a general rule of thumb, metal bond (sintered) diamond core drills last longer than other diamond core drills available, although drilling life varies with the manufacturer and hardness of material being drilled. With most conventional sintered (metal bonded) diamond core drills, you should be able to obtain 450 to 1,200 holes. Metal bonded diamond core drills have diamonds sintered and multiple layers of diamonds impregnated inside the metal matrix. They wear evenly, and are known for their consistency. Sintered (metal bond) diamond core drills are the latest technology available in diamond core drills.

Electroplated diamond core drills are perfect for smaller jobs, softer stone materials and beginning fabricators, installers and homeowners. An electroplated diamond core drill is just about the only type of diamond core drill that may be used dry (without coolant) in a few applications. It is also suited for drilling very abrasive materials and has a high diamond concentration for a freer, faster drilling action with minimum heat generation. Diamonds stay on the surface of the drill, allowing for fast material removal. Recent improvements have been made in manufacturing electroplated drills. A new technological process allows multiple layers of diamond to be plated on the steel body. Electroplated diamond core drills last less than metal bonded drills and are the least expensive diamond core drills available. They are also more forgiving than metal bonded drills; in most cases capable of withstanding a greater amount of operator error.

Varying with application, material and operator experience, an average electroplated diamond core drill will last about 40 to 120 holes. Electroplated drills manufactured with multiple layers of diamonds have lasted up to 340 holes when drilling a 1⁄4-inch-thick piece of granite.

Electroplated drills cost less, and at first glance may seem like the most cost effective alternative. However, they can cost you more in the long run. Depending on material and application, metal bonded diamond core drills will last significantly more than electroplated diamond core drills.

There is a type of bonding that falls between metal bonding and resin bonding, which was designed to replace the conventional resin bond diamond core drills. It intends to offer the advantages of cutting speed and finish of a resin bond as well as the long life, consistency, aggressiveness, durability and performance of a metal bond. These drills are used on “finish-critical” applications, which require a minimum amount of chipping and where no further polishing, lapping or processing of material is planned.

Diamond bottoming tool/drill

Designed for drilling without core formation, diamond bottoming drills/tools are used for making blind holes in all types of stone materials, with a broad range of hardness. A bottoming tool does not have a core, and essentially works as both a diamond core drill and grinding disc. The bottoming tools works by grinding the bottom and inside of the hole to a flat surface. This tool is just about the only way you can drill larger than 3⁄8-inch OD (outside diameter) blind holes.

Careful attention to detail will make the whole difference in the quality of your diamond drilling operation. The goal of every diamond core drill user should be to obtain precision holes without affecting or damaging structure of material. Many of today's stone and engineered stone materials are composed of several layers. Stress to material created by excessive heat or improper drilling technique may affect structure of material. When one layer is damaged, it may affect other layers of material, spreading through the material in a domino effect. This is an important liability issue that may come to hurt you, even after a couple of years in the final application. Maintaining material structure, integrity and durability is the key to success for any diamond drilling operation.

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