Tips for drilling metal and steel

Tips for drilling metal and steel: metal

Drilling of metal and especially of steel, represents a special challenge for many. This begins with the choice of the right drill, through the crack, through to cooling. Nevertheless, drilling in hard materials is not magic and with a few basic rules for everyone.

The choice of the right drill can play an important role here, but do not worry - Nobody has to spend huge sums of money on expensive drills. Even with a cheap home improvement drill, good results can be achieved. Decisive are a good centering, the right speed and a corresponding cooling.

With a little practice, you can even regrind metal drills by hand and drill even large holes with less effort. If that is not the case, you can rely on drill grinders that deliver quite good results even in the lower price segment.

Safety instructions for drilling metal

As the name implies, chips are produced during machining operations. This also includes the drilling of stone or concrete and especially the drilling of metal. The occurring chips can be small, sharp and sharp-edged. When drilling steel, they are often very long and are thrown around by the rotating tool. The Wearing safety goggles should therefore have top priority.

Even if sharp-edged parts or chips encourage to use gloves, this does not apply to working on rotating tools. The rotating drill bit or chips adhering thereto could catch and wind the glove. Powerful drills can not be impressed by the hand in the glove. Here, a cut injury should be taken rather than a wounded hand. On rotating machine tools allowed no gloves be worn.

Like a glove, however, the rotating drill can also grasp hair, wind it up and tear it out. Unfortunately, the drill does not differentiate between hair and scalp. The biggest danger, however, is to be thrown upside down against the machine. Therefore is for wearers of long hair wearing a headgear or protecting the hair important.

Such serious Accidents certainly are not common. However, they show what danger can come from a small rotating drill.

1. Centering the hole

For many home improvement is "Every hole in metal must be grained." However, the title was deliberately omitted from the term 'graying', as it was for that purpose more options than just the grains gives. Especially on the bench drill, center drills have prevailed, with which it can be far more accurate work.

Grains with hammer and grains

The oldest and most well-known method for guiding the metal drill in the piecing is graying. All you need is this a grain and a hammer. How exactly such a centering becomes, however, strongly depends on the execution of the grain.

Tips for drilling metal and steel: metal

Automatic grains do not need a hammer

If the subsequent drill position does not reach one-tenth, then a pencil mark or marker is sufficient for marking. Have proven so-called Fineliners or CD markers, whose tear is also good to see on smooth surfaces. However, the grains placed on the marker may slip easily and unnoticed, so that the following bore will not be accurate.

It can help to tap the grains very gently with the hammer (beating is not necessary) and then to control the small grain point. If this is not correct, the position can be corrected in a second attempt. However, if the grain point is exactly on the crack, the grain tip can easily be re-used in the grain point and the grain completed with a powerful hammer blow become.

is the later surface is not visible or secondary, The tear is recommended with a scriber. It leaves a "scratch" in which a good grain tip engages and therefore can not slip. A powerful hammer blow is enough and it creates an exact grain point.

Centering with center drill or NC drill

Tips for drilling metal and steel: tips

Centering saves the marking

As paradoxical as it sounds a centering can be set with a drill so that another drill does not run. Such centering drills were the result of the fact that it is hardly possible to grain manually in production and then to drill mechanically.

The manual graining is subject to some inaccuracy, which must be manually compensated for drilling in a machine tool for each hole. This is tedious and costs valuable working time.

Tips for drilling metal and steel: steel

Centering with an NC tapping

A make large center drill bit much easier, which differ from normal metal drills in several points. The most important point is the material. High-speed steel (HSS) is used, which is very hard and ensures that a center drill does not bend and thus runs on the workpiece surface.

The front drill diameter is very thin and requires only a small pressure, which positively influenced the drilling result. With the subsequent conical grinding, the center hole can then be lowered and thus the diameter of the center hole can be increased. The narrow and deep centering ensures that the subsequently used metal drill bit is guided for a long time and prevents bleeding.

Tips for drilling metal and steel: drilling

Centering with center drill

The disadvantage of centering drills is the usually thin diameter in combination with a very hard and brittle material. Especially when centering with a cordless drill or a hand drill centering often break off. You should therefore primarily on column drills be used.

To further increase the working speed in modern CNC machines, come so-called NC drills for use. These are also made of HSS, but have only a sharp bevel in 90° or 60°. As a result, the NC drill bit drill is very stable and requires only a few millimeters deep hole, which shortens the working time. A thicker diameter makes it possible to carry out the centering so far that the subsequent hole additionally receives a reduction. However, NC drills offer little guidance to the following drills and there is a risk of them running, especially with long drills.

2. Tension the workpiece correctly

When drilling steel kick large forces in the direction of drilling and in the direction of rotation of the drill. These forces must be counteracted with fixed installations.

Tips for drilling metal and steel: drilling

This allows the workpiece to rotate during drilling

The video shows very well when piercing, what happens if steel is tense while drilling? As practical and quick to use Clamps are also, they press the workpiece only down on the work table and do not secure it against lateral forces that occur during drilling. Hold only provides the friction created by the clamping pressure.

The same applies when clamping in a vice. If the workpiece is held edgewise between the clamping jaws and clamped so firmly, there is always the danger of it turning, because the lateral support is missing in the direction of rotation of the drill. It is safer to always clamp the workpiece in such a way that it has a fixed position in the direction of rotation of the drill.

Tips for drilling metal and steel: tips

Safely clamped against twisting

Not perfect but helpful when drilling on a bench drill, can already Combination of a stop and the clamping claw his. The attack already takes on a part of the laterally occurring forces. However, there is still the danger that the workpiece pushes away from the stop and twisted.

The perfect solution on the table or stand drill is the Vise. This holds the workpiece laterally and reliably prevents twisting. In the same way, workpieces must be clamped in the hand vice. The drilling position - from top to bottom - is a little more uncomfortable, but provides the optimum grip.

3. The right metal drill

The right tool influences the drilling result to a large extent. "To a large extent" in this case means that it does not always have to be the most expensive tool. Also cheap metal drills can deliver perfect results with a good grinding and the right drilling performance. However, the disadvantage is usually the lower life. If you are able to grind metal drills yourself, you will be fine with cheap drills. The work is subject to only a higher effort, since the drill must be re-sharpened more often.

Tips for drilling metal and steel: drilling

HSS drills with different coating

Twist drills sometimes consist of chrome vanadium, but mostly of HSS, the so-called high-speed steel and differ mainly in the type of shaping. HSS-R stands for production by rolling, which ensures a firm and very smooth surface. The ground and thus very accurate production is marked with HSS-G.

An additional coating such as cobalt (HSS-G) can provide better surface finish, durability, and less chip adhesion. For simple applications In DIY, HSS drills without special marking are usually sufficient. They fulfill their purpose and are inexpensive to purchase. If you have no way of grinding or grinding drills yourself, you can exchange blunt or defective drills cost-effectively.

A little more expensive but with a higher wear resistance, are coated twist drills. They are suitable for tougher materials as well as for soft aluminum which adheres less to the coated surface. It makes sense to purchase a large range of drills on simple HSS drills to cover all the required diameters. For frequently used bore diameters, single but high quality drills can be used.

4. The right cutting speed and speed

The cutting speed is the speed, with which the cutting edge touches the workpiece. For a drill, the outermost point of the cutting edge (drill diameter) is assumed, since this produces the highest cutting speed. In order to determine the cutting speed or the speed, the circumference of the drill is required in the first place. If the drill rotates one turn, the outermost cutting point has traveled the path of the circumference in a certain time. That's the cutting speed. For a drill and other machining operations with rotating tools or workpieces, the following formula results.

Cutting speed = circumference x speed or with calculation of the scope Cutting speed = (d x π) x speed.

Since the diameter or circumference is often given in millimeters, but the cutting speed is in meters per minute at the same time a conversion of the unit and the formula for calculating the cutting speed is:

Cutting speed = d x π x n / 1000 (d = diameter in millimeters, n = rotational speed in revolutions per minute)

Usually, however, the determination of the speed is in the foreground. For this the formula can be changed:Speed ​​= v x 1000 / d / π

Of course, the speed determination does not always have to be exact and often material differences, the tool or even the machine make adjustments necessary. When drilling steel and metal many experience values ​​are necessary. Speed ​​tables help in the fast selection of the right speed. It is important to know the sensible cutting speed and to adapt it to your own needs. Simple curves, as they are often found on table drills, help there only conditionally. They assume optimum drilling conditions and do not include the quality of the drill, the cooling or the quality of the material to be drilled.

Therefore, it makes more sense not according to speed specifications to go for certain materials, but to calculate the speed at different cutting speeds. The following table refers to HSS drills and the use of a coolant lubricant. Without lubricant, the cutting speed should be corrected downwards. With coated HSS drills, the cutting speed can be raised to a higher level. In the private sector, however, it makes little sense to pay attention to productivity. Here, the durability of the tool in the foreground, so you should rather work with a lower cutting speed.

Overview cutting speeds for metallic materials

materialrecommended coolantCutting speed in m / min
unalloyed mild steel up to 700 N / mm²emulsion25 - 40
unalloyed mild steel above 700 N / mm²emulsion10 - 15
cast steelEmulsion / oil10 - 30
alloyed steelEmulsion / oil5 - 15
stainless steelEmulsion / oil5 - 10
spring steelEmulsion / oil5 - 10
cast ironwithout5 - 25
Brasswithout oil35 - 80
aluminumEmulsion / petroleum20 - 80

The overview already shows that the Cutting speeds vary greatly can. A good example here is aluminum, which can be processed in a CNC machine with optimum coolant supply with the highest cutting speed and more. However, if the coolant and lubricant are missing, aluminum tends to stick and in no time the drill jams. Therefore, you should always start from the lowest cutting speed and adjust it if necessary. Occasionally, another than the one listed here proves to be optimal.

Speed ​​table according to given cutting speed

Drill diameter2 mm3 mm4 mm5 mm6 mm7 mm8 mm9 mm10 mm11 mm12 mm
Speed ​​at 5 m / min796531398318265227199177159145133
Speed ​​at 10 m / min15921062796637531455398354318290265
Speed ​​at 15 m / min238915921194955796682597531478434398
Speed ​​at 20 m / min31852123159212741062910796708637579531
Speed ​​at 25 m / min398126541990159213271137995885796724663
Speed ​​at 30 m / min47773185238919111592136511941062955869796
Speed ​​at 40 m / min63694246318525482123182015921415127411581062
Speed ​​at 50 m / min79625308398131852654227519901769159214481327
Speed ​​at 60 m / min95546369477738223185273023892123191117371592
Speed ​​at 70 m / min111467431557344593715318527872477222920271858
Speed ​​at 80 m / min127398493636950964246364031852831254823162123

5. Drilling in steel

Is the workpiece safe? clamped, grained or centered, the right speed adjusted and the right drill The practical part - drilling - can start.

It starts with light pressure and control, that the drill runs cleanly in the centering. If this is guaranteed, you can work with a bit more pressure. This should create a uniform chip. If too much pressure is exerted, the machine can be overloaded and the cutting edges of the drill break out. The same applies to too low a speed.

However, too little pressure causes the drill bits to drag on the surface for a long time and wear out quickly. The wear is increased, the drill dull and overheated. Therefore, it is necessary to cool the drill. The cooling lubricant ensures that the resulting heat is dissipated and less friction occurs on the surface of the drill.

Who has no possibility for cooling, but therefore does not have to do without the drilling of metals. However, care must be taken that less heat is generated. This is usually done by a lower speed and an adapted feed. If the drill gets hot, the drilling process can be interrupted briefly.

Caution is with through holes offered. Once the drill breaks through the material, the pressure must be kept to a minimum. Otherwise, the drill easily tightens into the last thin layer and thus the material. This has the consequence that suddenly increased torque and the borehole is not carried out cleanly.

Important tips for drilling

  • Large holes should be pre-drilled. The pre-drilled hole, however, may only be minimally larger than the chisel edge of the following drill. To increase the hole "piece by piece" increases the wear of the drill and leads to the bore of the bore.
  • Stainless steel is not, as often assumed, very hard, but tough. The matching drill should therefore be very sharp and wear-resistant.
  • Sheets are especially hard to drill, because the entire drill pass consists only of the gate and the exit of the drill from the workpiece. The hardened surface of sheet metal requires a higher pressure when cutting - however, if the drill bit has been seized, it will be drawn into the hole by itself, resulting in an untidy bore and an increased risk of injury, so only step drills or special metal drills should be used (similar to wood drills) can be used.
  • To make the material breakthrough "harmless", a piece of wood or other so-called sacrificial material can be placed.
  • Be careful when drilling copper offered. Although this metal is very soft and therefore drills easily, the drill used wears very quickly on the outer diameter.Unnoticed, this begins to squeeze when deep holes and finally jams.
  • If long chips form during drilling, the drill can be lifted in short intervals to break the chips. However, any break in the span means a special burden on the drill bits and a premature wear

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Video Board: How to Properly Drill a Hole in Metal