Talking about power tool gearboxes - metal or plastic? - Longer version
Which are best, power tools with metal gearboxes or power tools with plastic gearboxes, and what do the terms really mean?
A power tool gearbox is usually a housing filled with gears, bearings and shafts. It would be reasonable to assume that a metal gearbox would have a metal housing, metal gears, metal bearings and metal shafts, and in most cases it will. Likewise you might assume that a plastic gearbox would have a plastic housing, plastic gears, plastic bearings and plastic shafts, and in most cases it won't! Instead, a plastic gearbox will usually have a plastic housing, plastic gears, metal bearings and metal shafts. Things get more blurred when considering different gear types. A gearbox can have a plastic housing and all the gears, bearings and shafts can be metal. This is usually referred to as a gearbox with all-metal gears. And what do you call a gearbox with a metal housing filled with plastic gears, metal bearings and metal shafts? And what about gearboxes with mixed gear materials?
There are advantages and disadvantages of all the above gearbox types. For example you might think the all metal gearbox would be the strongest, and in most cases that would be right. You might also consider that the plastic gearbox (with metal shafts and bearings) might not be very strong and you would also probably be right. However, it would likely be much quieter, potentially cheaper to make, possibly perfectly suitable for very light duties and easily the best insulated from external electrical contact.
So, moving away from hypotheticals, 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. Plastic gearboxes with all metal gears, compared to all metal gearboxes 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. However, when it comes to cordless power tools, it should be born in mind that the amount of heavy duty repeatable work that can be done is determined as much by the battery capacity and state of charge as anything else. And significantly, 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 newer jigsaw designs 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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