Grinding drills - Instructions for sharpening different types of drills

• Drill types for the craftsman
• Grinding metal drills
  • file
  • bench grinder
  • Drill grinding machine
• Sanding wood drills
  • Manual grinding of wood drills
  • Machine grinding of wood drills
• Grind stone drills

Under drills, most hobbyists understand very cheap tools. This is also true for a standard 3-18 millimeter diameter drill set. However, in the semi-professional and professional field, drilling sizes are needed that are not available in the hardware store. Stone drills for a hammer drill or metal and wood drills over 23 millimeters in diameter can easily cost more than 25 euros. The replacement of smaller drills is always associated with effort. With a little practice and the right tool, a drill can also be sharpened quickly. This saves a lot of time and money.

Drill types for the craftsman

Blunt metal or wood drills are more than just a nuisance. When drilling gets heavier, most workers put a bit more pressure on them. Then there is a risk that the drill bit overheats. With metal drills, the tip can first anneal and then over-harden. Then it can happen that the drill bit breaks off abruptly. In the best case, the metal drill is destroyed. In the worst case, you can also hurt yourself a lot at a breaking metal drill.

An overheating wood drill can char the well. This can lead to the formation of burn marks. Stone drills can also break off in the borehole if they are no longer sufficiently sharp.

There are three types of drills:

• Metal drills or twist drills
• Holzbohrer
• masonry drill

Metal drills are normal twist drills. They consist of a shaft, the twisted drill spiral, which ends in a simple drill bit. Metal drills have no additional coated tip and are monolithic in material. The simply shaped tip makes the metal drill ideal for regrinding. There are several ways to do that.

Wood drills are ideal for soft materials such as wood, chipboards and plastics. They are easily recognized by the groove at their tip. Wood drills are extremely sensitive and can by no means be used for minerals or metals. They will inevitably be destroyed immediately if used incorrectly. The regrinding of wood drills is a big challenge, for which special tools and a great skill are necessary. As an alternative to special wood-boring grinding machines, the wood drills can also be reground by hand. This requires a variety of files. When working with wood drills, you have to be extra careful. Wood drills are very sharp and you can easily hurt them. Wood drills exist in a particularly large selection with very differently shaped drill types.

Stone drills can be recognized by the carbide tips. You have a significant thickening on the head. Stone drills must be able to drill through the hardest mineral. A normal metal drill would overheat and break off in the worst case. A stone drill with carbide tip is therefore ideal for natural stone, concrete and calcareous sandstone. Stone drills can be reground only conditionally and only to a limited extent. As a rule, regrinding is rarely necessary with these types of drills.

Here you will find further and detailed hints and tips about the different types of drills: Types of drills

Grinding metal drills

Metal drills are the most common types of drills that can be re-sharpened. This requires some basic knowledge.

The tip of the metal drill has a defined angle of 118 °. Too sharp an angle would cause the metal drill bit on the tip to glow and melt. An obtuse angle does not penetrate deep enough into the material. Therefore, the tip angle of the drill must be maintained exactly. A simple trick is very helpful:

If you take two large hex nuts and stick them together on one side, you get a perfect gauge of exactly 120 °. These can now be used as a template for the drill bit. However, more recommendable is the use of a drill gauge. These are small tools made of metal, in which the angles are precisely stamped. A drill gauge costs about 5 euros and should not be missing in any workshop. Attention: Do not confuse the "drill gauge" with the "drill gauge". The latter is used to make holes, but is not useful for grinding metal drills.

In addition to the acute angle of the cutting surfaces to each other, each cutting surface is tilted at an angle of 55 ° to the horizontal plane. This cutting surface is called "cross cutting edge". It is also slightly curved in shape. Again, this must be taken into account during manual grinding.

Metal drills can be ground in three ways:

• Grind with a file
• Sharpening with a grinding block
• Sharpen with a drill sharpener

To grind with a file or a trestle requires a template that can be made from two hex nuts as described. When grinding with a file you also need a vise, which is firmly bolted to a workbench.

file

Grinding with the file is tedious, but very precise. The risk of grinding and damage is very low when manually sanding with a metal file.
For manual filing of metal drills, key files are ideal. These fine and very hard files cost in the set from about 30 euros.

The metal drill is clamped vertically in the vice using two small, thin wooden boards or slices of aluminum. These buffers serve not to damage the threaded shank of the metal drill during clamping. The shorter the tip of the metal drill looks out of the vise, the better it can be sanded. A long protruding drill shaft swings when grinding, which worsens the result and makes work difficult. But there must be enough space to start the file.

Then, with precise and powerful strokes, material is removed from the drill bit. The grinding process is always performed away from the body. With the prepared template, the point angle is checked again and again.

Manual filing of a metal drill takes some practice. It is important to do this work with patience. If the metal drill overheats due to hard grinding, it is unusable. An overheated metal drill can be recognized by the bluish color.

bench grinder

A grinding block consists of a powerful motor and a rotating disc. The trestle is screwed directly to the worktop or has a separate stand.
In a grinding block, the metal drill is machined on a rotating disk. Of course, this work is much faster than hand and file sanding. However, this work is not entirely harmless, as the rotating grinding wheel causes abrasions at the slightest touch. Nevertheless: The wearing of gloves is absolutely forbidden when working with a grinding block! If the glove is caught by the rotating grinding wheel, it causes much greater injuries than abrasions!

When working with an eyebolt, wearing protective goggles is mandatory. Hearing protection is also recommended.

The metal drill is guided over the index finger to the grinding wheel. With the finger as an abutment you can feel immediately when the metal drill overheats. It takes a lot of skill and practice to accurately grind the cutting surfaces accurately on both sides. But once the grinding is mastered, regrinding the metal drill is only a matter of seconds.

The trade offers special devices for grinding metal drills. These hold the metal drill firmly in place and are adjustable so that they perform the exact cuts. This grinding device for drill sharpening costs about 180 euros. It offers a clear plus in safety and guarantees good results. They are thus an intermediate step for purely mechanical grinding.

Drill grinding machine

The trade offers drill grinding machines from about 29 euros. Really recommendable, however, are only devices from about 500 euros. Grinding metal drills is a task that demands the highest precision. Low-cost devices can not afford this. If buying a high-quality drill sharpener is not worthwhile, the manual grinding process should be used.

The use of a cheap drill sharpener will more likely result in scrapping the metal drills after the grinding test. However, a high-quality drill grinding machine is very easy to use and always delivers the best results: The metal drill is clamped in the provided holder with the correct distance. For this, all the necessary chucks and templates are available on the machine. Subsequently, the drill is introduced to the chuck in the grinding device and moved back and forth several times. The machine grinds the drill reliably and precisely in the correct way. This machine is particularly suitable for use in teaching or rental and repair workshops. With it, large quantities of spiral drills can be sharpened quickly.

Oiling is better than grinding

You can extend the life of a drill by adding oil cooling while drilling. This does not always have to be the permanent flushing that is familiar from CNC machines. Just a few splashes of drilling and cutting oil, which is applied during the drilling process, improves the drilling result significantly: The edges tear less and the overall reduction is smoother. Nevertheless, for a perfect result after drilling through sheet metal or steel, the subsequent chamfering or countersinking with a suitable countersinking tool is necessary. A can of cutting and drilling oil costs about 10 euros and should always be in stock when working with metal. Normals creeping oil can also be used if necessary. However, customized drilling and cutting oils are optimal for this purpose.

Sanding wood drills

Manual and mechanical solutions are also an option for grinding wood drills. However, sanding wood drills is much more complicated than sharpening metal drills. The reason for this is the complex geometry at the top.

Manual grinding of wood drills

The wood drill is also clamped with the help of two wooden plates in the vise. Depending on the type of drill, different files can be used for sharpening.

A complete sanding set for wood drills consists of:

• Arkansas-shaped stone
• Diamond flat files (eg the named key file set)
• Sharp-edged diamond-shaped whetstone
• Square grinding pin
• Round grinding pin

The Arkansas stone, also called "Ölstein", combines fine grain with hardness and very sharp peel-off edges. The set will sell Akasas bricks from about 75 euros. This abrasive is ideal when sharpening wood drills, especially for sharpening the center point.

Diamond flat files are used in wood drills as well as in metal drills for grinding the cutting edges (cutting surfaces). Likewise, the pre-cutters are ideal to rework with diamond flat files.

The honing stones are used for re-sharpening threads. The set costs about 15 euros. As an alternative to the sharp-edged honing stone, a diamond flat file with a corresponding cross-section can also be used. These are also called "saw files". High-quality triangular saw files cost from about 15 euros.

With grinding pins, the cutting bevels pre-sharpened by the diamond flat files are resharpened.

Machine grinding of wood drills

A normal grinding block is out of the question for resharpening wood drills. In addition, their tip is much too complex formed, as a manual editing on a grinding block would be possible. However, there are suppliers of very high-quality grinding machines, which also have the grinding of wood drills in the program. These consist of a grinder, which looks very similar to a grinding block but is not comparable to it. On this comes a very thin grinding wheel. Finally, a special grinding device with a drill holder allows precise setting of the drill. A grinding machine for sharpening wood drills costs about 1400 euros. This makes it especially interesting for professional carpentry companies.

Grind stone drills

Stone drills are rarely sharpened due to their hard drill bit. The cutting edges of stone drills are very simple. This makes the sharpening of stone drills with vise and file or with a grinding block pretty easy. However, when mechanically grinding stone drills, it is essential to wear eye protection. The carbide of the drill bit jumps very easily during grinding. The use of a grinding device is again ideal for grinding stone drills. This guarantees the best results and virtually eliminates the risk of injury.

Tips for quick readers:

• Always oil when drilling metal
• Always grind blunt drills
• Always use the appropriate metal, wood or stone bur
• Always wear eye protection but never gloves on the bench
• A bench grinder for the bench is better than a cheap drill