Screws that are hard to get out or have lost their heads can seriously ruin some amateurs' first successes. To become immune to this and other problems, below are a couple of tips and tricks from a pro.
Releasing rusted screw connections
Before releasing «from captivity» rusted nuts and screws, you must first clean the accessible threads from dirt and rust. Otherwise, it is the friction on the thread flanges that will be so great that the threaded bolts can be sheared off.
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PROCEDURE |
| Clean the threads with a wire brush and then rinse with a rust remover. If a quick rust remover is available, turn the nuts immediately. Other solvents (oil, kerosene, diesel fuel, etc.) may only work for a short time. |
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Removing defective nuts
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PROCEDURE |
| If the hex nut has become rounded by the action of the fork wrench, or the rust has already worked with the adjacent edges, then violence is the last resort here. If the nut is small, then reliable gripping pliers sometimes help. It is often possible to grasp the corroded nut with force and thus release the connection. If this option does not help, then it remains to use a sharp chisel. In workshops, stubborn nuts are most often «finish off» using nut breakers. Well-accessible nuts can also be sawn along the threads with a hacksaw. |
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PRACTICAL ADVICE |
Screw falls out of tool
If it is necessary to install a screw or nut in a hard-to-reach place, then 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 tightly pressed against the thread and therefore cannot be loosened during vibrations. To do this, they have plastic inserts or a slightly limited screw fit. Such self-locking nuts are most often used only once, because their locking effect weakens with repeated use. |
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Unscrewing screws with hexagon socket and internal teeth
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PROCEDURE |
| Before using the tool, free the screw hole from any dirt. To unscrew these screws, it is best to use a long hex insert tool or a multi-toothed tool. As opposed to the bent wrenches used (in which the force is always directed at an angle) insertion tools can withstand hammer blows from the adapted side. A blow - in extreme cases, even directly on the head of the screw - in most cases loosens the screw and facilitates its further separation. |
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Removing Slotted and Phillips Screws
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PROCEDURE |
| Already after a relatively short period of time, such screws can sit so firmly that even an ordinary screwdriver is simply overloaded. When working with a cross slot, one more difficulty is added: a screwdriver, even with strong pressure on the handle, comes out of this cross slot. And as a result: after several attempts, the screw heads deteriorate, and instead appears «head problem» with these screws. Attempt to loosen such a firmly seated screw with one quick hammer blow on the head of the screw. If the head of the screw cannot be directly approached by a hammer, use a suitable screwdriver with a hard handle on it and try to loosen the connection by hitting the handle. The following often happens. A screw with only the head rusted is broken, and then it can be pulled out in the usual way. If all else fails, then try to do it all with an impact driver and a suitable insert. Change the position of the screwdriver after each impact in the direction of rotation - a procedure that almost no screw can resist. |
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Drilling self-tapping screws for metal
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PROCEDURE |
| If already in «broken» the head of the screw can no longer be inserted with any tool, it remains only to drill out this screw. First, drill out the head of the screw with a suitable large drill. If the head is large, be sure to drill holes in it with a small drill. In the absence of a head, you can remove the screw from the hole or use a punch or unscrew it from the back using gripping pliers. In particularly stubborn cases, a hole must be drilled through. To do this, choose a drill with the smallest possible diameter, otherwise the screw hole itself will become larger. |
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Handling expansion bolts
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PROCEDURE |
| Spacer bolts (threaded rods) most often do not have adjacent surfaces for the use of wrenches. If you do not have a tool for boring such bolts, you will have to temporarily make one from an expansion bolt. To remove them, weld one nut firmly on the protruding end of the screw or screw in two nuts in opposite directions (hide). Always use a wrench on the bottom nut to loosen screwed nuts. For tightening, use mainly the top nut. |
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Drilling broken screws
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Caution: Take care of the external threads if possible. |
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PROCEDURE |
| First hit the center of the screw butt exactly with the center punch and......ream the screw butt further: up to M8 screw size, this is done with a so-called tap drill. The tapped hole must have a diameter «shaved» screw, i.e. a screw without thread flanks. For screws up to size M6, the following Faust rule applies: multiply the thread diameter by 0.8. For example, M6 x 0.8 screw connection = 4.8 tap hole diameter. Screws with a dimension > 0.8 should be drilled with thin drills. Remaining metal particles in the threads can sometimes be removed with an engraving needle or a bar magnet, if this fails, then evenly clean the thread. |
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Threading
Since light metals are less durable than steel, thread removal is quite easy here. If there is still enough material left around the old thread, coarse threads can be cut. Otherwise, a threaded bushing can be used in a specialist workshop (e.g. Heli coil). Recutting or cutting a new thread takes place in three steps: the corresponding taps are therefore called «coarse tap» (one ring in the shank), medium tap (two rings on the shank) and final marker (without or three rings on the shank).
Rotate the taps back and forth under constant lubrication one after the other in the pre-drilled hole. In order not to break the taps, always make small turns forward (maximum 1/8 of the perimeter). Then rotate the tap back just enough so that the chips break and the tap is no longer pinched.
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TECHNICAL DICTIONARY |
Screw size and tightening torque
Conventional screws and nuts are subject to standard tightening torques. Knowledgeable amateurs with simple screw connections create the right tightening torque by means of «wrist». However, if you do not trust this «manual option», purchase a torque wrench and the necessary confidence will be provided. For commonly used screw connections, the following tightening torques are used:
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Thread diameter (mm) |
6 |
8 |
10 |
12 |
14 |
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Torque (N·m) * |
10 |
25 |
49 |
85 |
135 |
* The values given here do not apply to special screws and screws that are driven into light metals.
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