Tips for drilling metal and steel

Drilling metal and steel

The drilling of metal and particularly steel, is for many a special challenge. This begins with choosing the right drill on the teaser, to cooling. Nevertheless, the drilling is possible in hard materials not magic, and with a few ground rules for everyone.

Choosing the right drill can here indeed play an important role, but do not worry - no one has to spend huge sums on expensive drill. Even with a favorable construction market drills, good results can be achieved. Important is a good centering, the right speed and a corresponding cooling.

With practice, even metal drill by hand can be reground and drill large holes with less effort itself. If that is not who has access to drill grinding equipment providing the already low in price quite good results. 

Contents: Tips for drilling metal and steel

  • Safety for the drilling of metal
  • 1. The centering the bore
  • Center punch with a hammer and grains
  • Centering with center or NC spotting
  • 2. Stretch the workpiece properly
  • 3. The right metal drill
  • 4. The right cutting speed and speed
  • Overview cutting speeds of Metallic Materials
  • Speed ​​table after a predetermined cutting speed
  • 5. Drilling in steel
  • Important tips for drilling

Safety for the drilling of metal

As the name implies, produced chips on cutting working methods. This includes the drilling of stone or concrete, and especially the drilling of metal. The chips that occur can be small, pointed and sharp-edged. In the drilling of steel, they are often even very long and be thrown around by the rotary tool. The Wearing protective glasses should therefore be a top priority.

Although sharp-edged parts or chips to animate to use gloves, so that does not apply to work on rotating tools. The rotating drill or adhering to it chips could collect the glove and wrap. Strong drills can not be impressed by the hand in the glove. Here a sectional injury should rather be accepted as a wound hand. allowed on rotating machine tools no gloves be worn.

As a glove, the rotating drill bit but can also take hair, wrap up and tear. Unfortunately, the drill does not distinguish here between hair and scalp. However, the greatest danger is to be thrown head against the machine. for support of long hair, therefore, the Wearing a head covering or protecting the hair important. 

Such serious accidents will definitely not often. However, they show the danger can come from a small rotating drill. 

1. The centering the bore

true for many home improvement "Each hole in metal must be center marked." In the title, however, was deliberately to the expression "centrepunch" omitted because there are more options than just the grains for this. Especially on the drill press to centering have prevailed, with which you can work far from accurate.

Center punch with a hammer and grains

The oldest and best known method to guide the metal drills during preparation, the center punching. is required for this purpose only a grain and a hammer. How exactly such a centering is, however, strongly depends on the execution of the grain.

Tips for drilling metal and steelAutomatic grains do not need a hammer

If there is not at the later drill position to one-tenth of sufficient when center punching a scribe with a pencil or marker. So-called Fineliners or CD markers, the scribe is also good to see on smooth surfaces have proved successful. However, the set-up of the marking particles may easily and silently slip, so that the following hole is not accurate. Here it can help only very gently to tap with the hammer on the grains (beat is not necessary), and then to control the small punch mark. this is not true, the position can be corrected in a second experiment. However, the center mark is exactly to the scribe, the tailstock can be easily recognized again in the center mark and the grit to be completed with a powerful hammer blow.

If the subsequent surface is not visible or secondary, the scribe recommends with a scriber. She leaves behind a "scratch" where a good lathe center snaps and therefore can not slip. A powerful hammer blow is sufficient and there is an exact punch mark.

Centering with center or NC spotting

As paradoxical as it sounds, with a drill centering can be set so that another drill does not run. The result are those centering from the fact that it is hardly possible to manually graining in manufacturing and then to drill machine. The manual graining subject to a certain inaccuracy that must be balanced manually when drilling in a machine tool for each well. This is cumbersome and cost valuable time.

Centering saves center punchingCentering saves center punching

create a great relief Center drill, which differ from normal metal drills in several points. The most important point is the material. Use is high-speed steel (HSS), which is very hard and ensures that a center drill does not bend and thus passes on the workpiece surface. The front drill diameter is very thin and requires only a low pressure, which positively influences the drilling. With the following cone touches the center hole can then be reduced and thus the diameter of the center hole to be enlarged. The narrow and deep centering ensures that the metal drill subsequently used out long and bleeding is prevented.

A disadvantage of the center drills most thin diameter is in combination with a very hard and brittle material. Especially when centering with a cordless drill or a hand drill center drill cancel frequently. They should therefore be used primarily on drill presses.

In order to increase the operating speed in modern CNC machines on, are so-called NC spotting for use. These are also made of HSS, but have only a sharp bevel at 90 ° or 60 °. This causes the NC spotting drills is very stable and requires only a few millimeters deep hole, which shortens the work time. A thicker diameter allows to carry out the centering of such an extent that the subsequent bore receives an additional reduction. However NC spotting offer little guidance to the subsequent drills and especially with long drills there is a risk that they run.

Centering with an NC spottingCentering with an NC spottingCentering with centeringCentering with centering

2. Stretch the workpiece properly

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

The video shows very well when drilling through, what happens when steel is tensioned wrong during drilling. As convenient and quick to deploy clamps are, they push the workpiece down only on desktop and it is not secured against lateral forces that occur during drilling. Maintenance provides only the friction that is generated by the clamping pressure.

The same applies when clamping in a vice. If the workpiece is vertically held between the clamping jaws and still so tightly clamped, there is always the risk that it twists, since the lateral support is missing in the direction of rotation of the drill. It is safer always clamp the workpiece, that it has a fixed site in the rotational direction of the drill.

Not perfect but convenient for drilling on a bench drill, the combination of a stop and the clamping shoe may already be here. The attack takes this already a part of the forces occurring side. However, there remains the danger that the workpiece pushes away from the stop and twisted.

Thus, the workpiece can rotate when drillingThus, the workpiece can rotate when drillingclamped securely against rotationclamped securely against rotation

The perfect solution on the table or drill press is the machine vice. This holds the workpiece side and safely prevents twisting. In the same shape workpieces are to tension in the hand vice. The drilling position - top to bottom - although somewhat uncomfortable, but offers the best grip.

3. The right metal drill

The right tool influenced to a large extent the drilling. "For the most part" in this case means that it may not always be the most expensive tool. Even cheap metal drills can deliver perfect results with a good sanding and the right drilling behavior. However, a disadvantage in most cases the shorter service life. Who is able to grind metal drill itself, gets along well with favorable drills. The work is only subject to a higher cost because this drill must be nachgeschlifen frequently.

HSS drills with different coatingHSS drills with different coating

Spiral drills are sometimes made of chrome vanadium, but mostly from HSS, the so-called high-speed steel and differ primarily in the type of shape. HSS-R stands for a manufacturing by rolling, which provides a firm and very smooth surface. The ground and therefore very accurate production is marked with HSS-G.

An additional coating, such as with cobalt (HSS-E) may provide a better surface quality, stability and lesser adhesion of swarf. For simple applications are in the DIY sector are HSS drills without special labeling usually sufficient. They serve their purpose and are cheap to buy. Who has no way to grind drill itself or to grind, can replace blunt or broken drill inexpensive. 

Slightly more expensive for it but with a higher wear resistance, coated twist drill. They are suitable for tougher materials as well as for soft aluminum, which adheres less to the coated surface. Sense does it frequently to add itself a large range of drill simple HSS drills to cover all diameters required. For frequently used drill diameter single but high-quality drill bits can be used.

4. The right cutting speed and speed

the speed is referred to as the average rate at which the cutting edge contacts the workpiece. In a drill of this is the outermost point of the cutting edge (drill diameter), it is assumed since this produces the highest average speed. To determine the average speed or the speed, primarily the circumference of the drill is required. the drill rotates one revolution, the outermost cutting point has traveled the path of the scale in a given time. This is the cutting speed. For a drill and other working with rotating tools or workpieces, this results in the following formula.

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

Since the diameter or circumference is often expressed in millimeters, the cutting speed in meters per minute, however, takes place at the same time a conversion of the unit and the formula for calculating the average speed is:

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

Mostly, however, is determining the speed in the foreground. For this purpose, the formula can change: Rpm and throttle position = v x 1000 / d / π

Of course, the speed determination need not always be accurately and often make material differences, the tool or the machine adjustments necessary. When drilling, metal many experience are necessary. Speed ​​tables help in the quick selection of the right speed. It is important here to know the sensible average speed and adapt to their own needs. Simple graphs as they are often found in bench drills, help as only conditionally. They are based on optimal drilling conditions and include neither the quality of the drill, nor the cooling or the quality of the material to be drilled. 

Therefore, it makes more sense not to go to speed specifications for certain materials, but to calculate the speed according to different cutting speeds. The following table refers to HSS drills and the use of a cooling-lubricant. Without lubrication, the cutting speed should be adjusted downwards. With coated HSS drills cutting speed can be maxed higher. In the private sector, however, it makes little sense to productivity respected. Here is the durability of the tool in the foreground, so that would be better to work with a lower average speed.

Overview cutting speeds of Metallic Materials

material
empfohlender cooling substance
Cutting speed in m / min
unalloyed structural steel to 700 N / mm² emulsion 25 - 40
unalloyed structural steel over 700 N / mm² emulsion 10-15
cast steel Emulsion / oil 10-30
alloyed steel Emulsion / oil 5-15
stainless steel Emulsion / oil 5 - 10
spring steel Emulsion / oil 5 - 10
cast iron without 5-25
Brass without oil 35 - 80
aluminum Emulsion / Petroleum 20 - 80

The survey already shows that the average speeds can vary greatly. A good example here is aluminum, which can be edited in a CNC machine with optimum coolant supply with the highest average speed and more. However, lack of coolant and lubricant, tends to bond aluminum and in a very short time the drill bit is stuck. Therefore, one should always assumed the lowest average speed and are adjusted as necessary. Sometimes proves to be a different than the listed here as optimal.

Speed ​​table after a predetermined cutting speed

Drill - Diameter
2 mm
3 mm
4 mm
5 mm
6 mm
7 mm
8 mm
9 mm
10 mm
11 mm
12 mm
Revolutions at 5 m / min 796 531 398 318 265 227 199 177 159 145 133
Speed ​​at 10 m / min 1592 1062 796 637 531 455 398 354 318 290 265
Speed ​​at 15 m / min 2389 1592 1194 955 796 682 597 531 478 434 398
Speed ​​at 20 m / min 3185 2123 1592 1274 1062 910 796 708 637 579 531
Speed ​​at 25 m / min 3981 2654 1990 1592 1327 1137 995 885 796 724 663
Speed ​​at 30 m / min 4777 3185 2389 1911 1592 1365 1194 1062 955 869 796
Speed ​​at 40 m / min 6369 4246 3185 2548 2123 1820 1592 1415 1274 1158 1062
Speed ​​at 50 m / min 7962 5308 3981 3185 2654 2275 1990 1769 1592 1448 1327
Speed ​​at 60 m / min 9554 6369 4777 3822 3185 2730 2389 2123 1911 1737 1592
Speed ​​at 70 m / min 11146 7431 5573 4459 3715 3185 2787 2477 2229 2027 1858
Speed ​​at 80 m / min 12739 8493 6369 5096 4246 3640 3185 2831 2548 2316 2123

5. Drilling in steel

If the workpiece is securely clamped, center marked or centered, set the proper speed and selected the appropriate drills, can the practical part - drilling - start.

starting with light pressure and the control that the drill clean runs in the centering. Is that ensures you can work with a little more pressure. Here, a uniform clamping should occur. If too much pressure is applied, the machine can be overloaded and break the cutting edges of the drill. The same applies at the wrong speed.

Too little pressure, however, causes the drill cutting long grind on the surface and wear out quickly. The wear is increased, blunt the drill and overheated. Therefore, it is necessary to cool the drill. The cooling lubricant ensures that the heat generated is dissipated and less friction occurs on the surface of the drill.

Who has no way to cool, but that does not dispense with the drilling of metals. However, it must be ensured that less heat is generated. This is usually due to a lower speed and a customized feed. the drill is hot, the drilling process can be briefly interrupted.

Caution is advised in through holes. Once the drill breaks through the material, the pressure to a minimum must be reduced. The drill is retracted otherwise slightly in the last thin layer, and thus the material. This has the consequence that the torque abruptly increases and the well is not properly performed.

Important tips for drilling

  • Large holes should be drilled. However, the pre-drilled hole must be minimally larger than the cross-cutting of the next drill. the borehole "bit by bit" to increase increases the wear of the drill and leads to bleeding of the bore.
  • Stainless steel is not, as often assumed, very hard, but tough. The matching drill should be very sharp and wear resistant.
  • Sheets are particularly difficult to drill because the entire drilling peck 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 - and the drill but "has resorted, it is drawn through the material exit by itself in the bore. The result is a dirty hole and an increased risk of injury. Therefore, only step drill or special sheet drills (similar Holzbohrer) should be used here.
  • To the material breakdown "hazardous" to design a piece of wood or other so-called sacrificial material can be placed.
  • Caution is advised when drilling copper. This metal is very soft and therefore pierces easily, however, the drill used wears out very fast at the outer diameter. Unbeknownst captures this in deep holes to squeeze and clamps ultimately determined.
  • Generated by drilling long continuous chips, the drill can be raised at short intervals in between to break the chips. However, each clamping interruption means a special burden on the drill cutting and premature wear

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