"Andrew Gabriel" wrote in message
...
In article ,
"Doctor Evil" writes:

Wickes sell a 700w variable speed hammer drill for around £16 the last
time
I looked. The variable speed means you can use it for driving screws,
with
a bit of practice. Just the job. Most of the sheds sell plastic cases
of

Cheap variable speed drills don't have the necessary torque or fine
control required for driving screws at low speed -- their output
power is very low at such speeds. However, the variable speed is
useful for starting a hole off slowly to ensure the bit doesn't move
before it starts biting into the surface. For this purpose, I found
the power controller in an older B&D drill much better than the one
in a newer Bosch -- the B&D can be started from almost zero, whereas
the Bosch has a nasty hysteresis which means the motor won't start
until you get the trigger to about 1/4 travel and you can then back
off to lower speed (a characteristic of a very cheap light dimmer
circuit).

You can get variable speed drills which deliver much nearer full
output power at low speeds and are good for screw driving, but you're
looking at a much higher price -- the power controller will include
servo feedback, thermal monitoring and power input control right up to
and including top speed operation, and is a lot more sophistcated than
the crude light dimmer type found in cheap drills.

Most of these cheap mains drills have a trigger stop to prevent too much
speed. I find that using this and pulsing the trigger with your finger does
the job. I little practice and most can get it.

If you are in an office which is being refurbished and there are about 10
guys with drill/drivers, you hear the constant pulsing of the triggers, zip,
zip, zip. It is a technique they nearly all use even with over expensive
pro battery tools. Most doesn't use the torque control leaving it on full
using their fingers to pulse. They know how much to pulse to get the screw
in; all by experience of using the tools on a day to day basis. Most DIYers
put the bit in the screw and pull the trigger full, and then can't
understand why the bit spun out of the screw and chewed it up.



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