DC motors work very well on DP's. The size of the DP, whether is has single
or double pulley reduction and the material you want to drill normally are
all considerations. If it's a large DP, then I'd go with something like
Surplus Centers GE 1.25hp 104VDC motor. I have one on an old Hercules DP
that was used to drill 1.5" holes in tool steel. With a small DP, a .25 or
..50 hp motor might be plenty. With double belt reduction (center step
down/up pulley) Smaller hp will do more. If you're old school, you can use
a Variac and a bridge rectifier to run it. You will be adjusting while
running when drilling because you're varying current and voltage at the same
time. For better results, go to a solid state controller (KB, Minaric,
etc.) and your spindle will maintain speed under load as current is
maintained and voltage (pulse width) is varied (simplistic description).
Some controllers have integrated reverse switching either by switches,
relays or regenerative circuits. This is helpful/required if tapping. With
the Variac supply, a reversing switch can easily be installed. The same
with the solid state type, but they are a bit more sensitive to reverse
surges (reversing motor while at speed). In most cases, one should stop the
spindle before reversing direction. The regenerative type is the exception.
A resistor can be used to apply braking for more effecient control. BTW,
beware of small motors with high rated hp as this sometimes refers to
"developed hp" due to high speed. Mass is usually a good thing.
Basically, the above refers to PM (permanent magnet) motors. Shunt wound
motors are effectively similar, but with a required field power supply
needed. Most solid state controllers have this available at full or half
supply voltage. A Variac can be tapped at the correct point for this. With
two Variac supplies, interesting results can be had by varying the field
supply. This method was used on old DC systems, ie. Monarch EE. The higher
field voltage suppresses motor rpm but can add torque at low speeds. Very
low field voltage can/will result in VERY high motor speeds and possible
shrapnel.
Respectfully,
Ron Moore

"Ignoramus8228" wrote in message
...
On 12 Feb 2006 07:56:53 -0800, mechanized_robot
wrote:
Can anyone point me to a web resource that lays out the basics of DC
motor controlling or possibly put down the bullet points of same?

I would like to convert my drill press to DC and after reviewing the
myriad of options on ePay, decided I need experienced help.

I would like to buy surplus/used parts if at all possible and need some
guildlines as to what to look for such as DC field voltage of motor,
typical controller types used, pitfalls, etc.

If anyone could comment on what they did when they converted their
machine(s) it would be greatly appreciated.


If/when you learn anything, please let me know, I am very interested
in converting a DP to DC.

i