Removing rusted screw connections
Before unscrewing a rusted nut or bolt, you must clean the exposed threads of dirt and rust. Otherwise, the friction on the sides of the thread will be too strong and the threaded stud will wear off.
Clean the threads with a wire brush and then spray with rust remover.
When using a fast acting solvent, unscrew the nut immediately.
When using other rust solvents (oil, kerosene, diesel fuel, cola, etc.) wait a while.
Handling self-locking nuts
Self-locking nuts are tightly pressed against the threads and cannot be loosened even with vibration. To do this, they have a plastic insert or a slightly crossed thread. These nuts should only be used once, their self-locking effect disappears with repeated use.
Unscrewing damaged nuts
If you have worn off a hex nut with an open-end wrench or rust has destroyed the adjacent surfaces, then force is the last resort.
With small nuts, strong clamping pliers sometimes help. They can securely grab 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 breaker tool is used to unscrew such nuts.
A well-accessible nut can be sawn with a metal saw along the thread.
Unscrewing bolts with an internal hexagon or with an internal sprocket
Before you install the tool, completely clean the bolt hole of dirt.
For unscrewing such bolts, end inserts with a long hex or asterisk are best suited.
Unlike common curved keys (in which the force is always applied at an angle) end inserts also withstand hammer blows from the side of the adapter. Hitting the tool with a hammer—or in extreme cases, directly on the head of the bolt—most often loosens the bolt a little and makes it easier to unscrew.
The screw falls off the tool
If you want to drive a screw in a hard-to-reach place, then stick a little body putty, thick lubricant to the screw slot, or stick the screw to the tool with a strip of adhesive tape. This simple trick often works wonders.
Loosening slotted and cross head screws
After a relatively short time, the screws can sit so firmly that they cannot be unscrewed with a conventional screwdriver. With Phillips screws, the situation is complicated by the fact that the screwdriver, when strongly pressed on the handle, unscrews from the Phillips slot. Result: after several unsuccessful attempts, the head of the screw is damaged and can hardly be unscrewed.
Try to loosen «caked* screw with a strong hammer blow on the head of the screw. If you cannot hit the head of the screw with a hammer, use a suitable screwdriver with a strong handle and try to loosen the connection by hitting the handle. Often this is enough, the screw that has rusted only with the head lags behind and then unscrews normally.
If that doesn't help, try it with an impact driver and a suitable insert. Screwdrivers convert every blow of a hammer on a screw into a rotational movement - not a single screw practically resists it.
Drilling self-tapping screws
If no tool can be inserted into the screw head, only drilling will help.
First, the head of the screw is drilled out with a drill of the appropriate size. Pre-drill larger heads with a smaller drill bit.
Without a head, the screw is either knocked out of the hole with a punch, or removed with tongs from the back.
In particularly difficult cases, the entire threaded pin is drilled out with a drill. Choose the smallest drill bit, otherwise only the larger self-tapping screw will hold in the tapped hole later.
Unscrewing and screwing in expansion bolts
Spacer bolts (threaded studs) most often do not have a surface for applying the key. If your assortment of tools does not have a screwdriver for expansion bolts, then you must first create it in a quick hand.
On the protruding threaded part of the stud, tightly weld one nut or screw (hide) two nuts. To unscrew nuts locked in this way, place the wrench on the bottom nut. For tightening - always on the top nut.
Drilling broken screws
Important: Spare the outer threads as much as possible.
Mark the rest of the screw exactly in the center with a center punch.
Drill the stub of the screw: for screws up to M8, this is done with a so-called tap drill. The tapped hole is determined by the diameter «cut» screws, i.e. screws without lateral thread. For screws up to size MB, the main rule applies: the thread diameter is multiplied by 0.8. Example: screw connection M6x0.8 - threaded hole diameter 4.8. Starting with M8 screws, you should pre-drill with a thinner bit.
Metal residues in threads are sometimes removed with a marking needle or magnet, otherwise the thread must be calibrated.
Thread cutting
Threads cut in light metals break off with particular ease, since the material has a significantly lower strength than, for example, steel. If there is still enough metal, then larger threads can be cut. Otherwise, the threaded sleeve must be inserted in a specialist workshop (e.g. from a wire spiral). Calibration and threading is carried out in three stages. Therefore, the corresponding cutters are called: rough tap (one ring on the stem), intermediate tap (two rings on the stem) and finishing tap (without rings or three rings on the shaft).
The three thread cutters are screwed in and out alternately in a pre-drilled thread hole with constant lubrication.
To prevent the cutter from breaking, you need to screw the cutter a little (maximum 1/8 of the circumference) into the material, then unscrew the cutter until the chip breaks, 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 «on a whim». But if you don't trust your gut, you'll always be confident when working with a torque wrench. For the most common screw connections, the following tightening torques apply:
| Thread diameter (mm) | 6 | 8 | 10 | 12 | 14 |
| Torque (Nm) | 10 | 25 | 49 | 85 | 135 |
The specified tightening torques do not apply to special screws/bolts and to screws/bolts that are screwed into light metals.
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