| Reversing a motor (May 8,
2003) |
Lathe Reversing problem
(Nov 6, 2004) |
| Motor Reversible? (Apr
10, 2004) |
Suspicious motor reverse behavior
(Dec 15, 2004) |
| Motor reverse applications
(Aug 1, 2004) |
|
| |
| Reversing a motor |
| Clint, the
drum switch does what you need, if you wire it correctly. It will
basically allow one line, ground? to go directly to the motor, then
cross or parallel the starter circuit, and then also put power on
with the 3rd leg. This can be done with a couple of relays, but it
is recommend that one uses a relay to verify one relay is open
before it closes the other. A reversing motor starter actually links
2 motor starters together so it mechanically forces one open and one
closed. Dave (10914) |
| Dave, This helps as I have
never thought of using the regular old reversing ac motors in this
way, I do not really know why I haven't? I always had the impression
it had to be 3 ph or a DC motor or something. Clint
(10915) |
| Here's
question and answer. In the mentioned wiring diagram this will
reverse the motor but not under load? right AC motors unless
instant reversing type must wind down then be thrown in reverse?
Correct? DC and Three phase motors were all that I thought that
could be reversed instantly at full speed or just under because a
standard motor has to slow down pretty good before it will reverse.
Correct me If I'm wrong guy's Kerry
(10916) |
| Kerry, In
general, you are correct. A single phase motor has to "spin down"
before you can reverse it. This is because the start windings are no
longer in the circuit because the centrifugal start switch has
opened the contacts that lead to the start windings. Reversing the
drum switch too quickly will have no effect. The motor will continue
in the same direction without reversing. There is an exception.
There are "instant reversing" single phase motors out there. They
include a relay connected to the start windings that allow the start
windings to be energized when the drum switch is reversed. This
allows current to the start windings in the reverse direction,
creating a magnetic breaking action in the motor. This slows the
motor down rapidly and then reverse its rotational direction.
Although I have seen South Bend Lathes with G.E. instant reversing
motors on them (factory installed), I don't think that it is
necessary to have one on a lathe used in hobby work. Webb
(10917) |
| Correct. And, instant reversing on cast iron gears is a
really neat
thing. the zipper like sound as they strip off is one you never
forget. and it's always neat to guess which gear will go first. I
think it's Murphy's law that says, the probability of the key
shearing vs a gear being stripped is inversely proportional to the
cost of the gear. There is almost no need for instant stop or
instant reversing in the machine tool trades. even taping is done
with a constant spindle rotation. the taping head reverses the MUCH
smaller mass of the internal gears. Dave
(10920) |
| Kerry,
It's generally good practice to let things come to a stop on any
machine before reversing, just easier on the machine. This is
particularly true on a lathe with a threaded spindle, as the inertia
of the chuck body can spin the chuck off the spindle. If this
happens, it plays out one of two ugly ways - either the chuck and
workpiece go sailing through the air and across the floor, or you
realize what's happening, flip direction, and the chuck slams home
with a loud bang. In the second case, it isn't unusual to have to
machine the backing plate off the spindle as the threads get sprung
really hard. Stan (10923) |
| Dave is right
on this for sure as even the Citizen L20 CNC Swiss screw machine I
setup and maintain has spindle and axis brakes that halt the
involved spindle motor or axis servo before reversing them. I have
checked all the CNCs in the shop and all of them will bring the
motor to a complete halt before reversing rotation. JWE (10925) |
| Motor
Reversible? |
| I've got an old 1/3
HP motor from Sunlight Mfg Corp. I want to use it to drive my lathe
through a simple countershaft (no reverse). The motor itself only
has two contacts, (no ground even, although the case is currently
grounded). I would like to be able to drive my lathe in reverse.
Before I start looking for a new motor, I want to confirm my
assessment that I cannot electrically reverse this motor. Thoughts?
The plug isn't polarized so I tried it both ways. The motor ran the
same direction both times. Jeff
(18343) |
| Jeff, if you
are talking about a typical 120 AC induction motor, yes it's
reversible. Is it a capacitor motor (a capacitor under a metal bump
cap)? In any case, removal of the end bell where the wires are
connected will be necessary to access the ends of the wires needed
to make it reversible. All together there will be 5 wires, 6 wires
with capacitor and you will find a closed contact set with
centrifugal clutch. One set of wires will be the run winding. The
other is for the start winding/switch/capacitor. Bringing out the
run winding ends to a reversing switch is what is needed. The power
cord green lead will connect to the metal casing only. RichD (18344) |
| Rich's
instructions were very accurate but worst case. By your description
I suspect you've not looked inside yet. Before removing the end
bell, look for and remove a small plate by where the wires go in and
look for a diagram on the inside of the cover. If your lucky it will
still be there. If not hopefully you'll see one a couple of
arrangements. One has two wires attached to 2 lugs (not counting the
ac leads) by switching these two connections the motor should
reverse. A second setup has two metal strips that when nuts are
loosened they can be swung to another set of contacts. So to wire a
drum switch you'll need to bring these four wires out along with the
two power leads. (6 total, I used 2 lengths of 3 conductor power
cords) If there's a spec plate on it look for the word reversible or
non reversible or maybe just ccw or cw, that will tell you a lot.
There was a recent thread on how to wire a drum switch up so do a
search. If you don't find anything switchable behind the plate then
Rich's "plan b" is in order. Joe R (18345) |
| With your instructions in my mind I took
another look at my motor. I'm think I'm hosed. It looks like a
split-phase induction motor. (I pulled out a copy of Machinery's
Handbook. Shoulda thought of that sooner.) I disassembled the thing
all the way. There are only three leads: two for power and one that
used to get the motor started. It is hooked up about 30 degrees out
of phase, and is shut off by a governer when the motor gets spinning
fast enough. There are only two poles at the terminal block. Two
leads are hooked to one, one to the other. I can't see any way to
get this to reverse electrically. Jeff (18349) |
| Jeff, so, you
are implying that the other coil ends are tied/buried in the coil
bundles? Not accessible? Being split phase (like most fractional HP
AC motors) and not capacitor start, you may find this a poor
performer. Low starting torque. On a lathe, much torque is needed to
get the iron turning quickly so the start winding does not overheat.
I have been thru the agony of trying to use a split phase (what they
call a not cap start motor) when all it would do is continually drop
speed into the start range and try again. This is on the high speed
belt positions. 1/2 HP is really about the minimum HP for most 7"
and up lathes. RichD (18353) |
| The starting
winding has two ends. can you find the other end? Jim B. (18354) |
| At my town dump,
there are many washing machines with nice 1/3 HP motors. Yes, 1/2 Hp
is better, but certainly not necessary unless one is always turning
out at the larger diameters. For many years I have powered small
specialty gadgets with dump motors. Look before doing the work of
tearing one out, to see if it's a capacitor start. It's about
impossible to "wear out" a motor. If it smells burnt, go on to the
next washer.
(18355) |
| Jeff, As
others have said a cap start is better and 1/2 HP will do fine. My
heavy 10 came with a three phase 3/4HP in 1943. When I got it I took
the motor to a electrical shop to get a single phase and after
seeing my old one they recommended a 1 hp. I don't think it's really
necessary though. Try harbor freight for one. You need 1725 rpm's.
Compressor motors are very common but they are 3450 rpm's. Follow
this link for a 1/2 hp, 110-220 volt reversible motor. It's $59 and
if you have a store near you get it there and save shipping but pay
sales tax. They have all sizes and specs.
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=36549
Joe R (18359) |
| Motor reverse
applications |
| I am getting
started with my 9" model A. As I
received my lathe, the motor is wired for forward direction only.
There is a drum switch that is capable of wiring for reverse
direction as well, and I believe that I have determined the correct
wiring from the tech info in the files section. The motor is a 1/2
hp 120v ac. The motor has four leads. My other lathe experience
(which is very introductory) is with an Asian 7x12. These come with
a variable speed reversing dc motor. Question: what are the
applications for reversing the motor? What precautions should be
taken in reversing the motor (e.g. to avoid the chuck "unthreading")
or is this a nonissue? David
(20299) |
| If this is a
capacitor start motor, (most are) then you cannot reverse the motor
without allowing it to come to a full stop. This will prevent the
chuck from spinning off the spindle and rolling across the floor.
Some SB's had an instant reversing motor. If this is one, avoid
stopping the lathe by reversing the motor. The Chuck can unwind as
above. The reverse position can be used for threading. Cut with the
motor forward. Stop. Back the tool out slightly, noting its initial
position. Do not disengage the half nuts. Reverse the motor, back
the tool down the ways to a suitable distance so that when the motor
is in forward any backlash is taken up. Reset the tool and increase
the depth. Cut forward again. Repeat until thread is cut. This is
the procedure when you don't have a thread cutting gage. (20302) |
| David The
reverse direction can be handy for threading. Typical threading jobs
involve starting a thread with the half nuts while watching the
threading dial and proceeding with the thread cutting from right to
left for a right hand thread. You have to disengage the half nuts at
the end of the threading cut to stop progress but there is typically
a shoulder that has to be avoided so stopping at the right time is
important. Maintaining a good finish on harder metals requires
higher cutting speeds but trying to disengage half nuts at precisely
the right time can be very difficult at these speeds. By running the
lathe in reverse and turning the threading tool upside down, you can
start from the left at precisely where you want and thread towards
the right. It is a little trickier to set up but you can get good
results. Ron (20303) |
| I have my 13"
with a instant reversing capacitor start single phase motor for over
40 years now and I have always used the instant reversing feature as
a dynamic brake. Just switch the lever right thru OFF to reverse,
then wait for it to stop and then move lever to OFF. I have done
this many times and have never spun the chuck loose. There is no way
that an electric motor can generate enough torque to loosen the
chuck. I use a 3 ft. bar to loosen the chuck when I change it. Maybe
I have been lucky all these years but it has always worked for me.
Wayne (20307) |
| With the kind help of
engineer, I am
probing the depths of motor winding leads and attempting to wire my
drum switch so that forward and reverse are available. Figuring out
the correct placement of leads is not, for me, as easy as it would
seem. David
(20309) |
| The 13" has a larger spindle and the bigger thread diameter
(Than a 9" or 10") results in a longer thread path. This results in
more friction and a better grip on the chuck. My 9" has a 6 Jaw Buck
with a very small 1/4 " key. This is all I ever use to remove the
chuck. I have seen a chuck come off (what I remember to be a 10K but
that was 40 years ago) once. It walked up the arm of the machinist.
No real damage. This was a 3 Phase motor however and that has higher
reversing torque. I tend to agree that a Capacitor motor is unlikely
to do this. . Jim B.(20310) |
| Ron- I will
start threading, running the spindle in reverse this way myself now.
The low speed on the lathe is slow compared a standard backgeared
lathe. However, Why would you turn the threader upside down? On
second operation lathes they turn the tool on the end of compound
slide, behind the workpiece, they turn that tool upside down (the
workpiece will spin "up" into the cutting edge, pushing up on the
dovetail), but the one on the compound rest side has the cutting
edge normal (the workpiece spins "down" into the edge applying
compressive forces on the cross slide) . When running a lathe in
reverse this approach of the cutting edge to the workpiece does not
change, so it seems to me that the tool would stay oriented in the
traditional manner. Running the the lathe in reverse only changes
the rotational direction the spindle spins and the associated gears
to the QCGB or leadscrew so something here just isn't making sense
to me. What am I missing here? Gabe (20311) |
| I did finally figure out the wiring of the drum
switch (with help) and now have a reversing capacitor motor. Not
instant reversing, as this would require a different kind of motor,
I believe. From my limited experience, I agree that the start-up
torque of this motor is very low, and unlikely to unwind the chuck
from the spindle. And it seems to me that the various applications
of cutting in reverse are also low torque affairs. But I would pay
money to see a video of a chuck unwinding and running up the arm of
the machinist. Glad nobody was injured. I am careful to not try to
over tightening this chuck when installing in the spindle, yet it
usually takes me a 1.5 foot bar to remove it. No hammering, just a
good pull. I do have a chuck question. My 9A came with a pretty nice
Cushman 5" three jaw, with the standard internal jaws. Is it
possible to order the external jaws for this chuck (from Cushman?).
I am shopping for a 6" four jaw also, so maybe I am better served by
just using the 4-jaw for any external clamping. David
(20313) |
| David, I
found a company that had the Cushman outside jaws in stock for a 6
1/4" chuck, $1200 for three jaws. Better off to look on Ebay or
local auctions. Paul (20316) |
| I have a 10k and I accidentally switched to reverse instead
of off the other day and the chuck came off ,dropped on the bed and
did a "burnout "on the bed. I'm so happy that I had a small part in
the chuck so the jaws were inside the OD of the chuck body, so
nothing bad happened! Darrell (20317) |
| With any
machine of this type you should always bring it to a full stop
before reversing. Not only does it put a lot of unnecessary stress
on the moving parts, it is not a very good safety practice. If you
still think its no big deal then do the same thing with your car (
really bad ideal ). Then you will feel the same way your lathe does
when you slam it in reverse. Once you experience this real-time you
will have a good understanding of the forces involved. (20318) |
| The same
applies to a split-phase motor (no capacitor). It is the starting
winding that is reversed, and since it is cut out when the motor is
up to speed it will have no effect on reversing the motor until the
speed drops enough to close the centrifugal switch again. I am
guessing that a capacitor-run motor, which has no centrif. switch,
keeping the capacitor and starting winding connected all the time,
will be instant-reversing (at any speed). Steve Bartlett
(20319) |
| Darrell lucky
you. That's terrible when something gets damaged. I was using my 10K
a few weeks ago machining a new chuck backplate hit the big R and my
plate unscrewed itself right onto the boring bar I got lucky nothing
got damaged. When I was in trade school a chuck came off and flew
thru the office window. Quite a site. Bob
(20320) |
| Was this a 3
Phase motor? Jim B. (20321) |
| Gabe I guess
I'm not exactly following your description but if you reverse the
motor, the spindle will turn in the opposite direction, which means
the work piece will be moving past the cutting tool in the opposite
direction, that is in the "up" direction instead of the "down"
direction. The cutting tool has to be flipped over so that the
proper surface is cutting into the work piece. Ron
(20323) |
| Lathe Reversing
problem |
I was able to
rewire my 10L single phase 115v motor over to 220v. The leads coming
out of the motor were straight forward. Next I found 2 leads coming
from the controller switch to supply 220v. So the motor is getting
its voltage. But in the process I lost the reversing. Moving the
switch to reverse makes the motor go forward. I have a cutler hammer
size O drum controller. No. 5441H27A. Is the reversing controlled
through this switch? If so, anyone know how to talk me through the
correction?
(21796) |
| Sounds like
you messed up with the wiring. Write Send me a email off line so I
can send you a scanned copy of a old South Bend document somebody
sent me 3 years ago when I re-wired my electric motor for my SB 10K.
I think it covers your drum switch. Guy (21798) |
| Without
specific detail, it is necessary to reverse the starting winding
with respect to the running winding. Jim (21801) |
| A heavy ten
needs at most 1 1/2 horse motor. There is no significant advantage
to wiring it for 220V. Consider just returning it to its original
configuration. Ed (21804) |
| I disagree,
motors are more efficient and last longer on the higher voltage. The
torque curve is better also. A 3/4 hp or 1 hp is all that is
required. Back to the original question, there should be a wiring
diagram here somewhere, did you check in the files section techinfo
motors-switches? You may find the answer to your problem there. JP
(21805) |
| The big
advantage is that lower supply currents are required allowing
smaller wiring and switchgear. This is not a big deal for a 1HP
motor. It would be for a 3HP motor. I haven't seen any documentation
indicating that a motor is actually less efficient when jumpered to
the lower voltage. The manufacturers data sheets I have seen don't
show this. I'm willing to be convinced though. Not too many of us
home users are wearing out our lathe motors. This site has
connection diagrams that may help:
http://shop.emotorstore.com/estore/TD_Schematic_Diagrams.asp
Ed (21806) |
| I would never been
able to access had you not been here to help. My 10L was wired for 110 and ran OK
for a while until I really began more continuous use at which time
it started tripping breakers. It happened to be plugged in to the
circuit with all my shop lights. I'm a big proponent of 220 single
phase, most of my shop runs on that. The amp rating is what causes
motors to heat up and subsequently trips breakers. 220 only requires
half the amperage allowing motors to run cooler and longer. I have a
110 buffer setup with 1/3 HP motors and left it running one
afternoon. To my surprise after an hour it tripped the internal
motor breaker. A touch of the hand revealed a super heated motor
frame. Now my 10 L should really run with 220 input to a 1 HP Dayton
motor. The drum controller is quite old, 1967 vintage, the contacts
look quite crusty. Anyone know if they can or should be cleaned,
sanded? The reversing was something I wanted to have despite the
threaded spindle arrangement because I want to try my hand at
tapping. I understand that a chuck can spin off the spindle running
in reverse. One book mentioned to snug the chuck up tight and give
the wrench several good tightening wraps with a hammer. Anyone use
this method? Anyone ever got their chuck stuck? Today I'll be
running some more test cuts and maybe load the lathe down to see how
it can torque. I put a new drive belt on yesterday, the old was
quite torn up and was causing a squealing start. I tried cutting a
10" shaft and wound up with 13 thou runout. Thought my tailstock
centers were off. I initially adjusted them the wrong way and the
taper remained. I looked at them up by eye and they were visibly
off. Lined them up to exact point to point touching and the runout
was still present. Next I turned a piece between centers, without
the 3 jaw chuck. No taper and holding to 0.003 tolerance. How
close can a good 3 jaw chuck run? These heavy 10's really ROCK ! Frank
(21808) |
| I wouldn't
even consider tightening a chuck with a hammer. You normally would
not be machining while running in reverse so tool pressure and
loosening of the chuck should be minimal. A stuck chuck is usually
due to chips and dirt embedded into the threads of the chuck. They
become colored with oil and 'invisible' to the eye. It may require a
few taps to loosen the chuck. Also, with single phase operation, be
sure to stop motion before reversing direction. A 3 phase motor can
withstand instant reversal but the starting caps in a single phase
motor are not real tolerant of that game, you will only get away
with it a few times. JP (21810) |
| Wood Magazine did
tests on 115 vs. 230 volt connections about 2 years ago and found no
difference in performance given a feed line which is adequately
sized. A dual voltage motor has two windings. They are connected in
parallel when used on low voltage and in series when used on the
high voltage. With a capacitor start motor the start winding is
always run on 115 volts. When the motor is series connected (230V)
the start winding is driven, through the starting capacitor, off the
center tap of the two series windings, which then act as an
autotransformer. If anything, this connection will lead to a
slightly lower voltage an result in lower starting torque. Having
said all that I have a home built compressor with a 2 HP HF motor.
During the winter months, when its cold in the garage (some heat
about 55 F but not much) it will only start properly wit a 230V
connection. Jim B.
(21813) |
| You must live
in Florida! -30 is considered cold here in NH. I guess it depends on
whose motor is tested, I have some equipment like the radial arm saw
where there is a very noticeable difference and others where its not
as apparent. However, I set all of my equipment to the higher
voltage. JP
(21818) |
| First step, hose it out with non-chlorinated
brake cleaner or electrical parts cleaner. Beware wrecking painted
surfaces, etc etc. If there's verdigris (blue-green crud), remove it
with a small brass or bronze wire brush. (Like a bore brush from a
gun store, or one of the toothbrush style). Polish with Flitz or
other non-ammoniated metal polish. (Brasso said to be bad, makes
brass brittle, this may be an issue in electrical equipment; it is
with cartridge brass). Take it easy on sandpaper, it shouldn't be
necessary, and I'd consider 600 to be "coarse". Often just coarse
paper (not sandpaper, just wrapping paper, like kraft paper or even
notepaper like a dollar bill) is enough to burnish electrical
contacts. These drum switches have a pretty long lifetime, and I
believe I have heard of cheapskates cobbling new spring contacts and
keeping them alive longer still. People using this method get stuck
chucks, methinks. Chucks etc need only be run on by hand, (not spun,
either, just screw them down by hand, noting the feel of the threads
for swarf etc) having had the threads cleaned on chuck and spindle,
lightly oiled, the register cleaned. Any mechanical assistance
should be reserved for loosening. Beating on a chuck wrench stuck
into the chuck to either tighten or loosen is a way to wreck the
chuck. You mean taper of .013 over 10in, right? After making a cut,
the runout of the cut area should be zero. Runout is what you
measure with a dial gauge clamped in the toolpost or to something
else stationary. Aligning head and tail stocks is not an eyeball
job. There's a fairly quick procedure of cutting and measuring a
test piece that does the job, actually there is more than one way to
skin this cat. Most books on lathe operations have a method. Dave
(21822) |
| Can you
elaborate on performance. My understanding is that a lower amp draw
on 230 is more desirable in that the motor runs cooler and uses less
electricity. Desirable for the home shop setting? What might
starting torque be needed for in a home shop setting?
(21825) |
| When you say
"electricity" if you mean watts, the thing you pay for on your
electric bill, then definitely no. Watts is equal to volts
multiplied by amperage. You cut one in half and double the other you
are back where you started. In other words 220 volts times 10 amps
is equal to 110 volts times 20 amps. Watts has not changed. Every
time I have seen people having problems with overheating or hard
starting it is almost always inadequate wiring. Occasionally
overheating was the result of using an intermittent duty motor when
they should of been using a continuous duty motor. The electrical
code is very specific about what gauge wire to use and the maximum
*length*. People usually get the gauge right but then exceed the
length for that size. The code goes further and requires a maximum
of 5% voltage drop in the branch lines and feeders. If in doubt
about your setup then the first order of business should be to
measure the voltage drop. You should have no trouble getting under
the 5%. Having said all this, if you have a long run to the motor
then it would be advantageous to go with 220 volts because you can
save a little on the cost of the wire. Ed P
(21829) |
| Heat is a
function of the total power dissipated. Power is Voltage time
Current. The power dissipated is the input power (Input voltage
times the input current times the power factor) less the power
delivered to the load (output horsepower). If you have (say) a 3/4
HP motor, at 115 V it might draw 7 amps.(805 watts), at full load. (
I am allowing for about 80% motor efficiency) This would be a
parallel connection. At 230 V, with the windings in series it would
draw 3.5. (Since each of the windings would have drawn 3.5 amps to
make the 7 amps) Its still 805 watts. If the motor delivered the
same HP the power dissipated would be the same. Now that ignores a
few things. I mentioned power factor. The Current is not
necessarily in Phase with the voltage. This is because the motor is
an inductive load, particularly when the load is light. This could
change between the series and parallel connection. It also changes
with loading. The motor will be very inefficient when lightly
loaded. The idling current , as a percentage of total current,
could also change between series and parallel operation. For a well
loaded motor the motor efficiency should be the same on 115 or 230
Volts. It will draw twice the current on 115 and the feed lines and
breaker will need to be sized properly however the motor should not
notice the difference. Under light loading conditions the voltage
could make a difference, depending on the motor construction, in
either direction (more or less efficient). The power dissipated, or
unavailable to the load is power lost in the resistance of the
winding, (that's the same at either voltage since the current through
the windings should be the same), the power lost in friction, and
the power lost in the current required to create the magnetic field
which opposes the current flow. If you took a winding and unwound it
and connected it across 115 volts it would draw a large amount of
current. This is because the Inductance would be very low. Making a
coil out of it increases the inductance. This produces an "back EMF",
an opposing voltage that decreases the current. If the winding were
not part of a motor, you would need to have a large winding to
reduce the current and this would require lots of turns and more
resistance. The manufacturer tries to balance the motor efficiency
with winding size and cost. You can put more turns in the motor by
using smaller wire but this increases the resistance and limits the
maximum current the motor can draw under fully loaded conditions.
The manufacturer tries to produce a motor which is fairly efficient
at a modest cost (less Copper wire and less Iron). However the motor
may not be as efficient at light loads. I have a feeling ( not based
on sound data) that the older heavier motors were more efficient
under light loading than today's lighter "high efficiency" motors.
Much of the home work is light loading and the motor efficiency
there is difficult to pin down. I hope I haven't confused the subject
too much but it is fairly complex. I have been talking about single
phase motors only. Three phase motors are more complex yet. Jim B. (21830) |
| Dave, I read about
these test cut procedures. I was meaning taper. Would runout then be
an out of round issue? So a chuck could be measured on a dial
indicator for run out in the jaws.. right. Now the question is: Will the chuck run out cause a taper regardless of perfect
tailstock alignment? Then if turning from a spindle collet or
spindle center still produces taper it has to be tailstock
misalignment? In this case deflection has to be ruled out, right?
And that should show up in the middle of the shaft, right? Should
tailstock alignment be done from a spindle center arrangement? When
I did my test cut on spindle center it held to about .004 over 6 "
and was not really a taper as much as a variation across the length
at 1" intervals. I think it's close enough for government work. Then
there's the last issue of being able to produce a perfect shaft on a
worn out lathe because you know you machine and can measure, cut,
file, sand and polish like a real machinist. Frank
(21834) |
| The motor
performance will be the same when the windings are connected for
either voltage, providing the correct NP voltage is applied at the
terminals. The problem usually comes from the voltage drop in the
supply lines, especially during starting inrush when the demand can
be six times the full load current. due to the motor speed being
mostly determined by the frequency. A drop in voltage is countered
by an increase in Amps. this worsens the condition. I hope this
over-simplification will explain the tendency of the motor to
overheat at lower than the either of the connected NP Voltages,
especially the relationship of the 115 V to the connected wire size,
worse if it isn't copper and is marginally sized. I have an old copy
of the NEMA Standards which shows terminals and color coding for
dual Voltage, single phase motors. I don't have a scanner, but I do
have a (stone chiseling). Fax (21836) |
| I obviously
stepped into a controversy when I originally suggested returning the
lathe motor to it's original configuration. I was trying to address
a tendency I see for people, having correctly concluded that 220V is
best for large motors, to start rewiring everything down to the shop
clock to 220V. My rules of thumb (I'm not an electrician nor am I
familiar with your electric code): 1) Motors bigger than 1 1/2 horse
require a dedicated line and it might as well be 220V it you have to
install it new. 2) Smaller motors can run off 110V and it will be
much easier to relocate equipment if you do. 3) If you are popping
breakers, you are overloading your wiring and must do something to
fix it. This could include 110/220 conversions. Note that 220V
breakers require more panel space and cost more. Larger wire doesn't
cost much more if the runs aren't too long. Ed(21840) |
| With some
of the Chinese motors it seems like the HP rating is at least 50%
overstated - some as much as 2X. Even the American motors are not
immune. I seem to recall a US gov't suit over this some time back
related to compressors (?) but it doesn't seem to have spilled over
into other machinery. So your circuit that is sharing lights, etc.
and handles a modern 1HP drill or mill just fine may be struggling
with that 1950's 1HP motor on your lathe as it is actually producing
1HP. Gene Horr (21842) |
| That was a
mislabeling suit. There were companies saying they had 7 HP motors
on their compressors when the amperage was correct for about 2 HP.
They talked in terms of "developed" HP. (What ever that is. The feds
made them cut it out and give back money. I think some ship vacuums
still use that term. Jim B. ( 21843) |
| Specsmanship,
otherwise known as marketing BS. In the past the rating was for
average or continuous, not it is for peak power draw. And even at
that it is generally a lie. My Ridgid shop vac, sucks like Monica
but it doesn't run at the 6hp its rating is. One horsepower is 750
watts and most electric motors are around 60% to 80% efficient.
Measure the power with no mechanical load and then with a load. The
difference is what is consumed. For every kw of power consumed you
are using just under 1 hp. JP (21844) |
| My sense in using motors is that dogging them down under
load increases the wattage and creates heat and that's what trips
breakers. I remember getting my first Sears table saw with the 1 1/2
peak HP motor and starting into ripping a pile of 2x4s. Wasn't long
before the breaker on the motor started tripping and you couldn't
lay a hand to it for the heat. Running 220v on a 20 amp circuit
allows a draw of 4400 watts, so if running amps are 6, is your motor
not drawing 1320 watts? That gives 3080 watts of available draw
before the circuit reaches its trip limit. 110v on a 15 amp breaker
gives you 1650 watts. At 12 running amps the motor draws 1320 watts.
That's only a buffer of 330 watts. So it seems that the math speaks
for itself as to the big advantage of 220v. When those cutting bits
bite into that metal and that motor doggs down, it's a comfort to
know that the wattage reserve is available for continuous duty.
(21849) |
| I
bought one of those Campbell Hausfeld air compressors that claimed
to have a "peak" Horse Power of 5 HP. Before buying it, I looked at
the tag on the motor a noticed that it was rated at 2250 Watts. Now
knowing that there are 748 Watts per Horse Power, and the fact that
motors don't operate at 100% efficiency, I figured it was somewhere
around a 2+ HP motor. But for the price, it was a good deal for a 2
HP compressor; especially considering the cast iron pump. I have
applied to be part of the class action suit but I don't know if my
model qualifies. Webb
(21855) |
| trozzo51 wrote: What is runout? I believe there are two kinds,
radial and the other kind. Forget the tailstock for a moment:
Imagine you have a nice, perfect cylinder of steel, 1.000"D. You
chuck it in a 3jaw. How can this be in error? Two ways. First way:
the axis of the work can be parallel to, but not coincident with,
the axis of the spindle. How would this error be measured? Put a
dial gauge in the toolpost, and record its range of motion near the
jaws, as the work slowly turns. This would be called "runout at the
jaws". Put a chalk mark on the high point of the test bar. Move the
carriage down 3" say towards the tailstock. Repeat the measurement,
call this "runout at 3". If this is the same as the runout at the
jaws, and the high points are on the same horizontal line, this
chuck would be said to have "pure radial runout", of the amount
measured. Note, your carriage has to be good for this to work, you
do not rezero the dial gauge. This is the sort of runout that a
4-jaw chuck is intended to remove. Second way: This err is to hold
the work (test bar) so that its axis is not parallel to the spindle
axis. In this case (there are subcases...) the measured runout would
be different at the jaws and 3" away, provided that the dial gauge
is not rezeroed and the carriage is "good". This error can arise
from worn chuck jaws or from the chuck not itself not aligning with
the spindle (one cause, piece of swarf between chuck and register
surface. I'm walking on thin ice here, and refer you to a good book.
Cause a taper? Taper is caused by the tool bit not moving parallel
to the axis of rotation of the work. Imagine each of the chuck
errors just mentioned, and what would be the result of turning the
test bar. In the case of pure radial runout, the turned portion
would be a perfect cylinder, but it would be "eccentric" with
respect to the cylinder under the chuck jaws. If you turned the
second case, the work held askew, the result would still be a
perfect cylinder, if the *carriage* is good and parallel with the
spindle axis. The turned portion would appear "bent" with respect to
the chucked, unturned portion. No tapers would be produced. How can
the tool not move parallel to the spindle axis? The answers to that
are the answers to "where does taper come from?" Deflection is one
source, and can be eliminated. It would produce a double taper,
small at head- and tail-stock, thicker in the middle. Assume it's
eliminated through proper work support and by proper feeds speeds
and by proper technique for the finishing cuts. The bed may be worn:
the tool cannot move in a straight line if the bed carriage are not
"right". The headstock may be misaligned. (Rare). Up-down and
left-right. Correct this in a rebuild shop. The cause is either
weird bearing wear, or a headstock being swapped in from another
machine. (Lathes just *look* like they're mass produced. They were
hand fitted in the Good Olde Daze). The tailstock may be misaligned.
(Common). Up-down and left-right. Left-right is the usual case,
since the tailstock is adjustable L-R by design. U/D and L/R are of
two kinds, too. Due to translation ("shifting" L-R or shimming U-D),
and to rotation, i.e. being skew, tilted. The latter is bad, and I
think probably usually due to irregularly worn beds. You can tell
translation error from tilting error, because tilting error will
change (for better or worse) depending on how far the tailstock
arbor is extended. Translation error will not be affected by arbor
extension. (Scrunch up your eyes and get a mental picture of this.)
Tilt error of the arbor might be measurable with a dial gauge
clamped to the bed. (Best would be to have a Morse taper-ended test
piece, and measure that). I don't think this is a problem of the
centers or alignment, but a problem of bed or maybe headstock
bearing wear, maybe. Could you actually be measuring surface
roughness? Adjusting a tailstock for taper should be done with the
test work piece held between centers and driven by a dog. Putting a
chuck in there will get you nowhere, you'll be correcting something
else, some combination of tailstock and chuck errors, probably
non-repeatable... that way lies madness. This requires the Wisdom of
the Ancients, which I don't have. Often it requires a mike, files
and emery paper. Actually, with experience, a pair of spring outside
calipers are what you need. A Wise Ancient can feel tenths, I hear
(from Wise Ancients). I hope someone reviews my reply carefully. I'm
sure I've got something wrong here. Dave
(21881) |
| Suspicious
motor reverse behavior |
| I have my "new" '67
10K bench style setup/ cleaned and running and noted last night that
with switching to reverse- (drum type switch) that I would get
slowing, noisier sound, and dimming of attached light but if then I
turned to off and back to reverse- just fine. It seems to be an
intermittent state with reverse position. Is the start contactor not
releasing? No problem at all in fwd. Ludwig
(23021) |
| You didn't
state if this is a 3 Phase motor or a Single phase motor. Most
single phase motors cannot be reversed under power. They must be
allowed to coast to a stop first. Jim B. (23027) |
| Without knowing more particulars, I'm not sure if you have a
problem. In general, single phase induction type motors are not
meant to be reversed while running. You have to let then slow down
first before you can reverse them. There are single phase "instant
reversing" motors but these are uncommon and expensive. Generally,
with a threaded spindle, you don't want to change the lathe from
forward to reverse too quickly because the chuck could unthread from
the spindle (the momentum of the chuck's mass may be enough to
overcome the friction interface between the chuck's threads and the
threads on the spindle when quickly reversing rotation). If the
motor works properly when the lathe is allowed to stop before
reversing, you're probably alright. If in doubt, have a motor shop
look at it. Some older SBL's did come with instant reversing motors.
I have owned two that came with 1/2 HP GE ODP motors that were
instant reversing (big suckers). They have a relay inside that
connects the start windings for magnetic braking when reversing the
motor at speed. But for reasons previously stated, I don't recommend
them. Webb
(23028) |
| Assuming a
single phase motor, it sounds like the centrifugal switch is not
closing. If it is a capacitor start motor you should stop it first
before going into reverse. You can hammer a 3 phase motor like this
all day without a problem but not a single phase cap start one. JP
(23030) |
| Given the problem
is in one direction I suspect it is with the switch contacts because
if the motor had a problem it would elicit the same behavior in both
directions. Get yourself a can of aerosol electrical contact cleaner
and open the drum switch and spray it good. The stuff is a quick
evaporating solvent that will dissolve whatever gunk might be
fouling the switch. Unfortunately it can't fix burnt contacts which
would require further disassembly. Roy
(23043) |
| Ludwig If the
motor runs normally once it does get started, I would suspect the
motor starting circuit, especially the contacts of the centrifugal
switch within the motor. Jim (23046) |
| This is happening however with a complete stop and then
switching- I basically have to engage the switch 1-3 times until it
obviously runs properly. When it first did this I got a bit of smoke
and obvious rapid overheating. Hi Ludwig, Considering what you just
said, I would be suspicious of the contacts in the drum switch,
and/or the magnetic motor starter (if so equipped). Based on the
fact that the motor runs properly in the forward direction, I doubt
that the centrifugal switch is at fault. One other possibility is
that the wiring is incorrect. It is possible that the wiring will
work in the forward direction but not in the reverse direction if
improperly done. Unplug the lathe and take the cover off the drum
switch. Check the contacts for burring, pitting, etc. clean them
with a switch contact cleaner (non-flammable). Let dry and test
again. While you are in there double check the wiring connections.
Make sure they are clean and tight. Also look for fraying of wires
at the terminals. Some drum switches will have a wiring diagram on
the underside of the cover. If yours does, check that your motor is
connected correctly. One last thought. Although it is rare, it is
possible that a conductor has broken inside the insulation. Check
continuity of the leads from the switch to the motor connections (if
you don't find any other problems first).
Webb
(23048) |
| Jim, re: "If the
motor runs normally once it does get started, I would suspect the
motor starting circuit, especially the contacts of the centrifugal
switch within the motor." I don't know much about electric motors,
but, does the starting circuit/ centrifugal switch use different
contacts when running the motor in forward versus reverse
directions? Since Ludwig said the motor ran fine in forward but had
the problem only when reversing, that would have to be the case for
the starting circuit / switch to be the problem. Maybe it's because
I don't know much about electrical devices, but I wouldn't rule out
a mechanical problem. Now that I think about it, If I were you,
Ludwig, I would remove the drive belt from the motor pulley and see
if you still hear the same thing running the motor only. Just a
thought. Mario (23051) |
| Mario, my
thinking was that reversing the motor would allow a better contact
surface on the centrifugal switch after a change of rotation. But
there are many other possibilities. The practice of attempting to
reverse the motor at near full will result in the motor starting
again in the same rotation as before but is harder on the manual
switch contacts than a start from rest. Attempting reverse after the
centrifugal has re-engaged will cause the motor to run in the
opposite direction but will be hard on both the manual and
centrifugal switches. One way quick reversal can be done is by DC
injection braking into the running winding (about 6-12Vdc would be
enough) but that's another story. Jim (23053) |
| I will likely
disassemble the motor and see if in fact it is a mechanical issue-
it makes sense that perhaps the centrifugal starter circuit
contactor is not releasing in reverse easily
(23067) |
| Your issue- a "no start" with humming that can
be fixed with a little push- is consistent with an open starter
circuit. there is only one switch inside the motor and its actuation
is completely independent of motor rotation direction. A ring
mounted around the motor armature shaft presses on a similar ring
attached to the switch, holding the contacts closed. As the motor
speeds up, spring-loaded weights fly out and pull the armature
mounted ring away from the switch and the contact opens. You can
check to see if the switch closes without taking the motor apart. On
your motor's ID tag, it says which wires to switch if you want to
reverse the motor. These are the starter circuit. With the drum
switch off and the lathe unplugged, use an ohmmeter to check
continuity. The needle or reading should start at zero then increase
with time until it sees an open circuit (maximum resistance). When
you firs connect, the small current used to check resistance flows
and charges up the starter capacitor. At some point, the cap is
fully charged and current quits flowing. If it doesn't work the
first time, touch the two starter wires together to discharge the
cap and try again. With the capacitor discharged, check both starter
wires to ground. You should get an open circuit. Personally, I agree
with others that the problem is in the wiring or the switch.
Remember, the motor coils are only a few Ohms resistance. It doesn't
take much dirt on a contact to muck things up. A common problem is a
broken wire near a splice. Solid wire fatigues or solder sucked down
stranded wire causes a stress riser and the wire breaks. Someone
gives a wire nut one more turn for good luck and shears most of the
strands off one wire. To clean contacts, I use tuner cleaner and
lubricator from Radio Shack. Contact cleaner can attack some types
of plastic. I tear a business card to a size that can be pulled
through the contacts then drench the contacts and the card with
cleaner. Hold the contacts closed with the business card between
them then pull the card out. Repeat. The fancy business cards with
texture seem to work best. Some contacts have a special surface
finish on then and sanding or filing will remove the finish.
Sandpaper can imbed grit in the contacts, causing more problems than
it cures. If the contacts are burned and damaged, a file is the best
tool for dressing them but follow with the cleaner and business
card. Bill
(23069) |
| Ludwig, One
more thing- I found these websites helpful:
www.egr.msu.edu/age/extension_outreach/TechNote103.pdf
http://www.metalwebnews.com/howto/elec-mtr/elec-mtr.html
http://www.sawdustmaking.com/ELECTRIC%20MOTORS/electricmotors.html
http://www.marathonelectric.com/motors/dxf/pdf/102005-52.pdf Bill
(23070) |
