In article ,
FLowen wrote:
Milling machinist wannabee is the proud new owner of a 25 year old
Bridgeport Series I vertical mill, being delivered this week. I will
be using the machine to fabricate firearm parts, mostly small parts.
10 pounds would be an unusually heavy piece. Being a newbie I need
some real basic advice.
1) My concrete floor is out-of-level by 1/4" side-side across the 2'
width of the machine base, and 3/8" front-back along the 3' length of
the base. Would leveling pads be advisable?...or would steel shims
under the base bolt holes be just as good? Or is anything at all even
necessary?
2) I have single phase power. The mill is a 3 phase 2HP. No CNC
equipment in the foreseeable future. I will add a DRO, and probably
traverse power feed (I have longitudinal). I believe the power feeds
are 110VAC plug ins and if so would be a separate circuit. I have
gotten the full range of recommendations. Some say a static electronic
converter at $150 is plenty sufficient;
It is not electronic -- purely electrical components --
voltage-sensitive relay, heavier relay, and starting capacitor. It is
*useless* for plug-reversing -- e.g. when tapping in the mill and you
need to stop and reverse the spindle quickly to avoid bottoming the tap
and breaking it off in your workpiece. Also -- you only get about 66%
of the motor's full power rating using one of these.
others say I should go with a
$500+ rotary converter with a 5HP capacity (I don't plan to add any
other 3 phase equipment);
Spending $500.00 for a rotary converter which you can make for
less than $100.00 does not make sense -- except for a company, which is
likely to be able to get the three phase from the power company.
and one fellow suggested making a "pony
motor" from a used 2-5 HP 3 phase motor, wired with the 2 legs of
single phase input power to 2 of the 3 motor terminals, and then the 3
terminals to the machine, equipping the pony motor with a hand start
pull cord, ever hear of that? I'd like to hear the thoughts of you
experienced folks.
A bit of mix-up of terms there.
The rotary converter uses an "idler" motor -- a *used* (and
therefore hopefully dirt-cheap) three-phase motor with perhaps
50% more horsepower than your milling machine's motor. This is
started by one of several ways:
1) A pull rope to manually spin it up just before applying
power-- simplest construction, but an exposed pulley while
it is running.
2) A "pony motor" -- a smaller single-phase motor to spin the
idler up just prior to applying power. I've seen these designed
with the pony motor hinged to the plate holding the idler motor,
and as it starts, the operator lifts the pony motor, and the
belt is thrown off of the pulleys.
3) A voltage-sensitive relay, and a heavier relay, and starting
capacitors (just like you would find in the so-called "static"
converters.) This is the so-called "self-starting" rotary
converter, and is probably the best bet for long-term service.
Any of these can be improved by adding tuning capacitors to
improve the balance of the generated third leg, and this can
reduce the current drawn from your circuit breakers. (You would
not be charged for that extra current, as it is reactive, not
resistive, but it still wastes power heating wires, and
sometimes tripping circuit brakers.
There is a lot of information on this to be found in the
archives of this newsgroup -- in particular, look for the
articles by "Fitch" covering this subject. He took a good
analytical approach to the design of one, which can save others
from having to repeat the work.
However -- there is yet a third approach, which *does* involve
electronics. This is commonly called a VFD (Variable Frequency Drive).
I *think* that your 2HP Bridgeport will have the variable-speed pulleys,
so you probably don't *need* a VFD -- but one is more efficient than a
rotary converter, and can allow you to fine-tune the speed if you have a
step-pulley head on your Bridgeport. (It can also allow you to get a
wider total speed range than the vari-speed pulleys alone.
3) Suggestions as to a good 2 axis (with the 3rd on the spindle if
affordable) DRO system a capable mechanic inexperienced with DROs
could retro-fit?
Shooting Star would be a nice one. I'm sure that others
will have their own suggestions.
Good Luck,
DoN.
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