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Successful diamond drilling requires the proper understanding of how to use drilling speed and pressure, coolants, and drilling accessories to maximize production efficiency, drill life and product quality. While this understanding is best gained through experience, even new diamond drill users can quickly become proficient by learning and applying some basic principles of diamond drilling.
The following recommendations have come from years of experience in research, development and manufacturing of precision diamond products, as well as years of personal experience and observation. Following these drilling suggestions can help you drill faster and easier, obtain a smoother surface finish, minimize damage to your material and extend the life of your diamond drill.
Before DrillingBefore beginning your drilling operation, visually examine the drill for cracks or other damage, as well as for excess run-out (misalignment). Every diamond drill is made to hold to a specific tolerance and run-out; however, excess run-out will cause excess vibration during the drilling operation, which will negatively affect your drilling precision and tolerances. To check for excess run-out, it is best to use an indicator specifically designed for this purpose. Bring the indicator close to the drill, until its spring just touches the drill’s surface. The indicator dial should read 0. Turn on your drilling machine while holding the indicator firmly in place. The indicator dial should remain at 0 while your drill is running. If it doesn’t, your drill is running out. Turn off your drilling machine and remount the drill.
If you do not have a run-out indicator, you can use a black marker and a piece of paper or other thin material. Place the paper firmly against the drill with the marker, and then slowly remove the piece of paper while holding the marker firmly in place. Turn on your drilling machine and observe the drill rotation. If the marker touches the drill’s surface, excess run-out exists, and the machine should be realigned.
Another effective way to check for drill run-out is to rotate the drill head assembly (including the water swivel adapter, if your drill has this feature) by hand. The run-out of the drill’s diamond section (the cutting/drilling edge) will be indicated by the stem. The larger the run-out on the water swivel adapter, the larger the run-out will be on the drill. If excess run-out exists, your drilling operation will not be accurate.
You should also ensure that your drilling accessories are properly held in the chuck. If the drill or drilling device is not running true, loosen the chuck of your drilling machine, turn it 90 degrees and run your drill again. If this does not work, examine condition of your equipment and try mounting the drill on another drilling machine to determine whether the machine, rather than the drill, is the problem.
Always wear the proper safety equipment, including safety footwear, snug fitting clothing, safety goggles, hearing and head protection, and proper respiratory equipment, and do not use your drill if you suspect it is damaged. Damaged, incorrectly mounted or misused drills can be very dangerous.
Starting a HoleOnce you have made sure that your drill is in good condition, you are ready to start your drilling operation. Clearly mark the insertion point on the material to be drilled and line the drill up to this point. Drill by quickly pressing and lifting the drill head. Moving the drill up and down frequently during the drilling operation will allow the water or other coolant to cool the drill and flush out the material debris formed while drilling.
It is extremely important that the material or part you are drilling be held firmly in place with a clamp throughout the drilling operation. Any material movement can cause the diamond section of the drill to break, possibly resulting in material damage or operator injury. When drilling thin materials and substrates, consider using heavy-duty double-sided tape or another adhesive product to firmly hold your material in place.
Drilling Speed and PressureTo maximize the life of your drill and minimize material damage, it is important to run your drills at the proper drill speed and pressure. The appropriate drilling speed depends on the drill diameter, diamond mesh size, coolant, and diamond bond type and hardness, as well as on the material hardness. For example, micro-diamond drills that are .001 in. in diameter require drilling speeds as high as 150,000+ revolutions per minute (rpm), while very large diamond drills 48-in. in diameter require drilling speeds as low as 3 rpm. Drilling soft, abrasive materials requires higher speeds, while drilling hard, dense materials requires lower speeds. Since diamond drills are primarily used in hard material applications, they are typically used at very slow speeds. Faster drilling might appear to increase your production efficiency, but the tradeoff is a significant increase in friction and heat, which considerably reduces the drill life and increases the risk of heat fractures and breakage in the material being drilled.
It is also very important to apply the right amount of pressure during drilling. Use light to medium pressure, gradually feeding the drill into the material, until the drilling begins to progress at its own speed. Increasing pressure on the drill will do little to reduce the time it takes you to complete a hole, but it can cause your drill to overload and overheat, which will lead to excessive wear on the drill and defects in the material being drilled.
When you are drilling completely through a piece of material and the hole is near completion, reduce the drill pressure considerably to minimize chipping of the material. Never force a diamond drill. Apply even pressure until the drill and material just touch. Since the drill and material surface are not perfectly even (symmetric) to each other, this will allow the drill to adjust to the surface of the material.
If a diamond core drill develops dark “burn” marks at the diamond section, the drill speed is probably too high or the amount of pressure is too great. Reduce the drilling speed or pressure accordingly.
CoolantThe most frequent cause of diamond drill damage is drilling without enough coolant. Never run a diamond drill dry—coolant should always be used to cool and lubricate the drill and to flush out abrasive particles formed while drilling. Water is the most frequently used coolant because it typically provides excellent performance at a minimal cost and is compatible with most materials. Synthetic water-soluble coolants, mineral oils and other types of oils are also sometimes used.
If you are planning to use water as a coolant, check with the drill manufacturer to find out what water pressure is required and if any additives are recommended. (Note that using additives will require a circulating system to ensure that the right ratio is maintained between your additive and coolant.)
The amount of coolant used should generally increase with the hardness of the material being drilled. Sparks during the drilling operation indicate that insufficient coolant is reaching the drilling zone or that the type of coolant being used is ineffective for that application. A generous flow of coolant increases the diamond drill efficiency and reduces heat buildup, thereby reducing the material cracks and deformation associated with overheating.
Strong coolant pressure will also wash out any material debris (center plugs) that gets stuck in center of your drill. Center plugs restrict coolant flow to the center of the drill and prevent coolant from reaching the diamond section. As a result, your drill will start to drill dry, significantly reducing the drill life and material surface finish and deteriorating the overall drilling operation. Center plugs are behind 90 percent of all drill wreckage.
To ensure that the coolant properly cools both the drill and the material being drilled, the coolant should be directed so that the full flow is at the point of contact between the drill and the material, facing the same direction as the rotation of the drill. When drilling on a horizontal surface, use a squirt bottle or small cup of coolant to continuously pour water onto the drilling zone. Alternatively, you can submerge the material in a shallow tub of coolant so that the coolant just barely covers the material’s surface.
Most diamond drills used in advanced ceramics applications are used on a vertical surface, and coolant is applied through the center of the drill. If your drilling equipment does not have coolant center-feed capabilities, consider using a water swivel adapter (also known as a drill head assembly). These devices provide a constant, controllable flow of coolant through the center of the drill and are designed to efficiently and effectively cool both the drill and the material in the drilling zone. Water swivel adapters have been shown to increase the life of diamond drills by as much as 40 to 75 percent on average.
When selecting a water swivel adapter, make sure it is designed to be used at the same speed as your drilling operation. Water swivel adapters that are made from stainless steel ball bearings and that offer adjustable water flow will generally last longer and will be easier to use compared to water swivel adapters made from brass with no bearings.
Water swivel adapters are typically used with sintered (metal-bond) diamond drills or Hybrid bond* diamond drills (a cross between a metal and resin bond) that are mounted on a collet with a female thread. Diamond solid drills and most electroplated (nickel-bond) diamond drills are usually made with a straight shank and are not designed to have coolant run through the center of the drill. When using these types of drills, you should submerge the material being drilled in coolant or apply a high pressure of coolant flow from an external source.
Drilling DepthMost advanced ceramic applications require a drilling depth of less than 1 in. For applications that require greater drilling depths, coolant should be applied from multiple directions (both through the center and side of the drill, as well as submerging the material being drilled in coolant) to ensure that the maximum amount of coolant and lubrication reaches your drilling zone. Increase pressure and reduce drilling speed as you penetrate deeper into your material. Lift up on the drill after every inch drilled into the material to let the drill cool and to allow coolant to flow deeper into the hole. Also make sure to regularly examine the diamond tip condition to make sure it remains round and is not overheated.
Your maximum drilling depth will be limited by spindle travel—i.e., the distance your drilling equipment can move in an upward and downward motion before the drill chuck touches the surface of your material. A drill tube extension—which can be purchased in various sizes at most hardware, building and contractor stores, and do-it-yourself supply centers—can be used to lengthen the drilling depth.
Small-Diameter DrillsSmall-diameter diamond drills must be used at much higher speeds than larger drills to achieve a high quality surface finish and efficient drilling performance. Drilling speeds for diamond solid drills .001 in. to 2.5 mm in diameter (without coolant center-feed capabilities) typically range from 9000 to 450,000 rpm. High-speed air spindles, hand-held drills, and other specialty micro-drilling equipment must often be used in these operations because of the high drilling speeds. High-speed air spindles can typically run up to 450,000 rpm, hand-held drilling machines run up to 35,000 rpm, and specialty micro drilling equipment runs up to 25,000 rpm. All diamond solid drills and micro drills must be used with coolant. You can submerge the material in coolant or apply air as a coolant if liquid coolants cannot be used.
Diamond core drills from 1.6 mm to 1/2 in. in diameter that are mounted on a collet with a female thread (with coolant center-feed capabilities) require a high coolant pressure (typically 30 pounds per square in. [psi]) to prevent material from getting stuck inside the drill. Material debris can block coolant from reaching the drilling zone, causing the drill to overheat. Submerging the material in coolant is not recommended with these types of drills.
You should also periodically check the inside of the drill for material buildup. If you see that the core is becoming clogged, flush out this debris using coolant pressure from a water swivel adapter or other coolant source. Continue drilling only after the debris has been removed.
Dressing Diamond DrillsMost diamond drills can be dressed (re-trued) several times to extend their useful life. The wear on the diamond drill depth usually takes place on the drill core and diamond section, as well as on the wall thickness. A diamond drill can be dressed by running the diamond section (diamond tip) against a dressing stick or used silicon carbide wheel until the wall thickness is standard.
While dressing can improve the drill’s accuracy, it can also cause diamonds to be pulled out from the diamond section. You can re-expose the diamonds by drilling into an Al203 stick a few times after the dressing operation.