Screws that are difficult to remove or have lost their heads can seriously ruin the joy of some amateurs' first successes. To become immune to this and other problems, here are a couple of tips and tricks from the pros.
Removing rusty screw connections
Before releasing rusted nuts and screws from captivity, it is necessary to first clean the accessible areas of the thread from dirt and rust. Otherwise, the friction on the thread flanges will be so great that the threaded bolts can be cut off.
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ORDER OF EXECUTION |
| Clean the threads with a wire brush, then wash with rust remover. If you have a quick rust remover, turn the nuts immediately. Other solvents (oil, kerosene, diesel, etc.) may only work for a short time. |
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Removing defective nuts
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ORDER OF EXECUTION |
| If a hex nut has been turned into a round nut by the action of a fork wrench, or rust has already worked on the adjacent edges, then the last resort here is violence. If the nut is small, then reliable gripping pliers sometimes help. Often, you can also forcefully grab the corroded nut and thus release the connection. If this option does not help, then you can use a sharp chisel. In workshops, stubborn nuts are most often "finished off" with nut crackers. Easily accessible nuts can also be sawed along the thread with a hacksaw for metal. |
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PRACTICAL ADVICE |
The screw falls out of the tool
If you need to install a screw or nut in a hard-to-reach place, first fix the head in the tool with body putty, viscous grease or adhesive tape. This simple trick sometimes works wonders. Handling self-locking nuts
Self-locking nuts are pressed tightly against the thread and therefore cannot be loosened during vibrations. For this purpose, they have plastic inserts or a slightly limited thread fit. Such self-locking nuts are usually used only once, because their locking effect weakens with repeated use. |
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Removing Allen and Internal Teeth Screws
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ORDER OF EXECUTION |
| Before using the tool, free the screw hole from any dirt. To unscrew such screws, it is best to use insert tools with a long Allen key or a multi-tooth tool. In contrast to the commonly used offset wrenches (where the force is always directed at an angle), insert tools can withstand a hammer blow on the adapted side. A blow - in extreme cases, even directly on the screw head - ensures that the screw is loosened in most cases and makes it easier to separate it later. |
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Removing slotted and Phillips head screws
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ORDER OF EXECUTION |
| After a relatively short period of time, such screws can sit so tightly that even a regular screwdriver is simply overloaded. When working with a Phillips head, another difficulty is added: the screwdriver comes out of this Phillips head even with strong pressure on the handle. And as a result: after just a few attempts, the screw heads are damaged, and instead, a "head problem" with such screws appears. Try to free such a tightly seated screw with one sharp blow of a hammer on the screw head. If the screw head cannot be directly reached with a hammer, then attach a suitable screwdriver with a rigid handle to it and try to loosen the connection by hitting the handle. The following often happens. A screw with only the head covered in rust breaks, and then it can be pulled out in the usual way. If you do not succeed, then try to do all this with an impact screwdriver and a suitable insert. Change the position of the screwdriver after each impact in the direction of rotation - almost no screw can withstand such a procedure. |
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Drilling self-tapping screws for metal
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ORDER OF EXECUTION |
| If no tool can be inserted into the "broken" screw head, the only option is to drill out the screw. First, drill out the screw head with a suitable large drill. If the head is large, be sure to drill holes in it with a small drill. If there is no head, you can remove the screw from the hole either with a punch or unscrew it from the back using gripping pliers. In particularly stubborn cases, you should drill the hole through. To do this, choose a drill with the smallest possible diameter, otherwise the hole for the screw itself will become larger. |
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Handling expansion bolts
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ORDER OF EXECUTION |
| Expansion bolts (threaded rods) most often do not have mating surfaces for using wrenches. If you do not have a tool for boring such bolts, you will have to make one temporarily from an expansion bolt. To remove them, weld one nut firmly to the protruding end of the screw or screw in two nuts in opposite directions (lock). To release screwed-in nuts, always place a wrench on the lower nut. For tightening, use mainly the upper nut. |
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Drilling out stripped screws
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Caution: Protect external threads if possible. |
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ORDER OF EXECUTION |
| First, hit the center of the screw butt with a center punch and......then drill out the screw butt: up to screw size M8, this is done using a so-called thread hole drill. The thread hole should have the diameter of a "shaved" screw, i.e. a screw without the sides of the thread profile. For screws up to size M6, the following Faust rule applies: the thread diameter is multiplied by 0.8. For example, a screw connection M6 x 0.8 = thread hole diameter 4.8. Screws with a size > 0.8 should be drilled with thin drills. Metal particles remaining in the threads can sometimes be removed with an engraving needle or a rod magnet, if this does not work, then clean the threads evenly. |
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Thread cutting
Since light metals are less strong than steel, thread removal is quite easy. If there is still enough material around the old thread, a coarse thread can be cut. Otherwise, a thread sleeve (e.g. Heli-Coil) can be used in a special workshop. Re-cutting or cutting a new thread occurs in three stages: therefore, the corresponding taps are called "coarse tap" (one ring in the shank), medium tap (two rings on the shank) and final tap (no or three rings on the shank).
Turn the taps back and forth under constant lubrication one after the other in the pre-drilled hole. To avoid stripping the taps, always make small forward turns (maximum 1/8 of the perimeter). Then turn the tap back enough so that the chips break off and the tap is no longer jammed.
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TECHNICAL DICTIONARY |
Screw size and tightening torque
Standard tightening torques apply to common screws and nuts. Experienced amateurs use the "wrist" to apply the required tightening torque to simple screw connections. However, if you do not trust this "hand method", buy a torque wrench and you will have the necessary confidence. The following tightening torques are used for commonly used screw connections:
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Thread diameter (mm) |
6 |
8 |
10 |
12 |
14 |
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Tightening torque (Nm)* |
10 |
25 |
49 |
85 |
135 |
* The values given here do not apply to special screws and to screws that are screwed into light metals.
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