Fire Safety in workshop

9

Hey Matticustard, hey all,

the cause is known and always the same. Due to the type of motor that is inside the hand trim router, the speed is dependent on load, which means, such motors are slowed down by the load, and at higher loads, on this type of motors, the current increases extremely, this is due to the motor characteristics of this so-called ‘universal motor’ (in contrast to a spindle where this cannot happen). But since this motor is cooled by a fan sitting on rotor axis which only rotates with the speed of the axis, this fan of course runs slower and slower when the motor is slowed down, and since at the same time the current (and the heat) increases, when you do this for a certain amount of time, the cooling finally is not enough and voilà you have fire. Also these motors receive their power to their rotor coils over carbon-brush commutators which have the function to let such a motor run on alternating current (in fact, a universal motor is a DC motor that is run on AC), but which are a constant source of sparks (and noise, and also EMI) which also means, one source of fire is always there.

This all is not new. And it has been reported and confirmed frequently that when people burnt their Makita hand trim router out, this was always when they used a bit with a diameter greater than 1/2″, which is nothing the hand router is made for, i.e. these large spoil board surfacing bits.

Makita knows about this, it says:

:warning: CAUTION:

  • If the tool is operated continuously at low speeds
    for a long time, the motor will get overloaded,
    resulting in tool malfunction.

12. Do not leave the tool running. Operate the tool
only when hand-held.

  1. Use bits of the correct shank diameter suitable
    for the speed of the tool.

CAUTION:

  • Since excessive cutting may cause overload of the
    motor or difficulty in controlling the tool, the depth of
    cut should not be more than 3 mm (1/8") at a pass
    when cutting grooves. When you wish to cut grooves
    more than 3 mm (1/8") deep, make several passes
    with progressively deeper bit settings.

NOTE:

  • Moving the tool forward too fast may cause a poor
    quality of cut, or damage to the bit or motor.
    […]
    The proper feed rate will depend on the bit size, the
    kind of workpiece and depth of cut.

:warning: By the way #12 above means that the Makita RT0701C is not allowed for use in a stationary machine like a CNC.