Professional tips for the amateur mechanic (Focus Turnier 1)

A screw connection that won't come loose or a broken bolt have already spoiled the winning mood of some amateur mechanics. Therefore, to overcome such and some other problems, we will provide some tips and tricks from professionals.

Disconnecting rusted screw connections

Before you remove a rusted nut or bolt, you must clean any dirt or rust from the exposed threads. Otherwise, the friction on the sides of the threads will be too great and the threaded stud will wear down.

Clean the threads with a wire brush and then spray with rust solvent.

When using a fast acting solvent, loosen the nut immediately.

When using other rust solvents (oil, kerosene, diesel fuel, cola, etc.), wait for some time.

Handling self-locking nuts

Self-locking nuts are tightly pressed against the thread and cannot be unscrewed even by vibration. For this purpose, they have a plastic insert or slightly crossed thread. You should use such nuts only once, their self-locking effect disappears with repeated use.

Unscrewing damaged nuts

If you have ground down a hex nut with an open-end wrench or rust has destroyed the adjacent surfaces, force is your last resort.



For small nuts, a strong pair of pliers can sometimes help. They can firmly grip the nut and often even unscrew it.

If this does not help, the nut is knocked off with a sharp chisel. In workshops, a so-called nut-breaking tool is used to unscrew such nuts.

A well-accessible nut can be sawed along the thread with a metal file.

Unscrewing Allen or Star Head Bolts

Before you install the tool, make sure to completely clean the bolt hole from dirt.

For unscrewing such bolts, socket inserts with a long hexagon or star are best suited.

Unlike the common bent keys (in which the force is always applied at an angle), the socket inserts also withstand a hammer blow from the adapter. A hammer blow on the tool - or in extreme cases directly on the bolt head - usually slightly loosens the bolt and makes it easier to unscrew.

The screw falls off the tool

If you need to tighten a screw in a hard-to-reach place, apply a bit of body putty, thick lubricant to the screw slot, or stick the screw to the tool with a strip of duct tape. This simple trick often works wonders.

Unscrewing slotted and Phillips head screws

After a relatively short time, the screws can sit so firmly that they cannot be unscrewed with a regular screwdriver. With Phillips-head screws, the situation is complicated by the fact that the screwdriver unscrews from the Phillips slot when pressing hard on the handle. The result: after several unsuccessful attempts, the screw head is damaged and practically cannot be unscrewed.

Try to loosen the "baked" screw by hitting the screw head hard with a hammer. If you can't hit the screw head directly with a hammer, then install a suitable screwdriver with a strong handle and try to loosen the connection by hitting the handle. Often this is enough, the screw rusted only by the head comes off and then unscrews normally.



If that doesn't help, try using an impact driver and a suitable insert. Impact drivers convert every hammer blow to a screw into rotational motion - virtually no screw can resist it.

Drilling out self-tapping screws

If no tool can be inserted into the screw head, then drilling will help.

First, drill out the head of the screw using a drill of the appropriate size. Large heads are pre-drilled using a smaller drill.

Without a head, a screw is either knocked out of the hole with a punch or removed with pliers from the back side.

In particularly difficult cases, the entire threaded pin is drilled out with a drill. Choose the smallest drill bit, otherwise only a larger self-tapping screw will be held in the threaded hole later.

Unscrewing and screwing in expansion bolts

Expansion bolts (threaded studs) most often do not have a surface for the application of a key. If your tool assortment does not include a screwdriver for expansion bolts, then you will first need to quickly create one.

Weld one nut tightly onto the protruding threaded part of the stud or screw (lock) two nuts. To unscrew the nuts locked in this way, place the key on the lower nut. To tighten - always on the upper nut.

Drilling out stripped screws

Important: If possible, spare the external threads.

Mark the rest of the screw exactly in the center using a center punch.

Drill the stub of the screw: for screws up to M8, this is done with a so-called thread drill. The thread hole is determined by the diameter of the "stub" screw, i.e. the screw without a side thread. For screws up to size M6, the main rule is: the thread diameter is multiplied by 0.8. Example: screw connection M6x0.8 - thread hole diameter 4.8. Starting with screws of size M8, you should pre-drill with a thinner drill.



Any remaining metal in the thread turns is sometimes removed with a marking needle or magnet, otherwise the thread must be calibrated.

Thread cutting

Threads cut in light metals are torn off with particular ease, since the material has significantly lower strength than, for example, steel. If there is still enough metal, then it is possible to cut a larger thread. Otherwise, it is necessary to insert a threaded bushing (for example, from a wire spiral) in a specialized workshop. Calibration and cutting of threads is carried out in three stages. Therefore, the corresponding cutters are called: roughing tap (one ring on the rod), intermediate tap (two rings on the rod) and finishing tap (without rings or three rings on the rod).

Three thread cutters are alternately screwed in and out of a pre-drilled thread hole under constant lubrication.

To prevent the cutter from breaking off, you need to screw the cutter a little (maximum 1/8 of the circle) into the material, then unscrew the cutter until the chips break off, then the cutter will not jam.

Screw/bolt size and tightening torque

For standard screws/bolts and nuts, standard tightening torques are sufficient. Experienced amateur mechanics tighten simple screw connections "by intuition". But if you do not trust your intuition, you will always be confident when working with a torque wrench. The following tightening torques apply to the most common screw connections:

Thread diameter (mm)	6	8	10	12	14
Tightening torque (Nm)	10	25	49	85	135

The tightening torques given do not apply to special screws/bolts and to screws/bolts that are screwed into light metals.