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Drill type and material
Of course, there are different types of drills for different materials. Only metal drills are considered here. With metal drills, the cutting edges are arranged at a conical angle (usually 118°). If necessary, metal drill bits can also be used for drilling in wood or other soft materials (there they are particularly suitable for drilling out existing holes).
Sharpen metal drills
Using sharp drill bits is probably even more important than choosing the right speed. I can only recommend the purchase of a drill bit sharpener to anyone who often drills metal. Especially one that can sharpen the two point angles of 118° and 135° (or similar), so you usually have a sharpener with better quality. Even brand-new drills often only cut really well after they have been sharpened on the drill sharpener.
Important point angles:
- 118 °: standard angle, universal, ideal for normal steel but also for hard materials (high-strength steel)
- 135° or flatter: ideal for tough material (stainless steel, but also ok for steel) or soft material (aluminium)
- 90° or more pointed: ideal for brittle materials (acrylic, brass)
Freehand drilling versus clamping
Drilling smaller holes in metal freehand is usually not a problem. Using a drill press or drill stand for drilling in metal is highly recommended. On the one hand, the drill holes are much more precise and, on the other hand, significant forces occur when drilling in metal, which can lead to injuries if the drill bit tilts.
Coolant and lubricant
First of all, coolants are mainly used in industrial production. For the workshop, the use of coolants, which have to be constantly metered and discharged, is usually too much effort (apart from compressed air, which can be helpful).
On the other hand, lubricants should really be used when drilling in metal. These also have an additional cooling effect, but primarily they prevent the drill from getting stuck or a built-up edge from forming on the cutting edges. There are various recommendations for the lubricants. The author’s opinion in a nutshell: WD40 is better than nothing and a few drops of real drilling and cutting oil is better than WD 40.
Centering
If you want to set exact holes, you should think about centering the drill. When drilling in metal, the desired drilling center is usually marked with a punch and a hammer blow. This grit also prevents the drill from wandering.
If you want to afford it, I can strongly recommend the use of a coordinate table for creating exact boreholes. In this case, no more graining is necessary. Aligning with the handwheels and aiming with the help of the cutting edges of the center drill make drilling almost a pleasure. Tip: if you turn the clamped drill slightly by hand on the workpiece, you can see exactly where it starts. When centering, the drill should only protrude as short as possible/reasonably out of the drill chuck in order to prevent it from deviating as much as possible.
Pre-drilling in the metal
When drilling metal, you should start with a small drill bit (e.g. 2 or 3 mm) and gradually increase it (e.g. in 1 or 1.5 mm steps) to the desired final diameter. If you want to drill accurately, you should use a drill stand and not unclamp the workpiece between drilling steps. It makes more sense to change the drill for each hole in turn until the final diameter is reached, so the center of the drill always remains exactly centered.
Rotational speed
Obviously, different speeds should be used depending on the properties of the material being drilled and the diameter of the drill. Tough materials like steel require slower speeds, long-chipping metals like aluminum require faster speeds. In order to have an indication of which speed is suitable, I use a speed table in which the various speeds, drill diameters and materials are listed.
When using a drill press, changing the speed is usually only possible with great effort by re-tensioning the V-belt (who really does that…). If you often want to drill metal with precision, I can hardly recommend using a drill stand with a normal drill and an adjustable voltage converter (or even frequency converter) for simple speed control. Alternatively, there are of course also good drill presses with electronic speed control for the corresponding money.
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