Talking about power tool gearboxes - metal or plastic? Short version.
Which are the most common types of gearboxes in professional power tools and what are their advantages and disadvantages? The simple answer is all-metal gearboxes and plastic gearboxes with all-metal gears. The major advantages of the all-metal gearboxes are strength, rigidity and heat conduction. Disadvantages are greater weight, higher cost and, if exposed, no protection from external electrical contact. Compared to all metal gearboxes, plastic gearboxes with all metal gears are: lighter weight, almost as strong, quieter and offer better protection against accidental electrical contact.
As ever, determining which is the best material for your power tool's gearbox housing, metal or plastic, depends on what priorities you have for the use of your power tools. In other words which is the best compromise? For example, if you want a powerful, lightweight drill that you can easily and repeatedly use one-handed, then the plastic gearbox with all metal gears, as found in KwikPro Gold drill heads, is likely to be the best for you. If you need to undertake very heavy work repeatedly most of the time or where the drill may be abused as a lever on occasions, then the metal gearbox may put up with this kind of use for longer.
Where cordless power tools are concerned, the amount of heavy duty repeatable work that can be done is determined most by the battery capacity and state of charge, rather than the type of gearbox. The vast majority of corded power drills have plastic gearbox housings to provide the user with the best possible insulation isolation from the mains electrical supply inside the power tools.
The priorities for the material used in different types of power tool vary greatly. Those for drills, discussed above, do not necessarily translate for other types of power tools. For example, an angle grinder's gearbox has to be very rigid and often needs to conduct heat away effectively, so most angle grinders have exposed all metal gearboxes. This is also the case with the KwikPro angle grinder head. The mechanisms inside impact drivers place high stresses and strains on the gearbox housings, so again metal is the most common material choice. When it comes to saws, again most types have metal gearboxes, essentially to achieve rigidity, although some jigsaws may have plastic gearboxes and gain their rigidity from substantial metal bases to achieve light weight for easy carrying. The KwikPro jigsaw head uses this principle to avoid being too heavy to carry with other KwikPro power tool parts on the dedicated KwikBeltTM tool belt.
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