View Full Version : Instant Reverse ??

Your Old Dog
12-18-2005, 11:28 AM
This term, used in 2005, confuses me. They don't really mean "instant" do they? And if so, why is it so damn necessary to throw all these moving parts into reverse thrust? Maybe for threading, I don't know?

I don't know for sure but I imagine the term "instant reverse" meant you no longer have to shut down the entire factory so one guy can run his lathe in reverse by switching his belts around. Or, he wouldn't have to wait until lunch time when a shop may have been powered down to make the switch-over. The switch to reverse would be relatively "instant" compared to the alternative of shutting down an entire factory driveline.

My SB9a has reverse on it. Does that mean I can be smoking along and hit the reverse switch? If so, where the hell do you go to get out of harms way when the chuck comes flying off?

Maybe this term "instant" should be dropped in this century before some rookie (like me) gets mangled or worse yet, mangles his machine http://bbs.homeshopmachinist.net//biggrin.gif

Any insite would be appreciated.

Maybe we should start a movement.

Hell, we could petition a new law to be written!


[This message has been edited by Your Old Dog (edited 12-18-2005).]

12-18-2005, 12:27 PM
thats a good point you have there hehe.
i to have noticed over the past ten years, that words that once ment something now means something else.
it looks like good majarity of todays generation is a throwaway sociaty.
what are they gonna do when their kids decide to throw them away into the trash to

12-18-2005, 01:40 PM
Nothing in life is instant, except maybe the first time I ... oh nevermind. Maybe we should ban the word altogether? I was in my buddy's shop Thursday and he made me a cup of "instant" coffee; he still had to heat the water http://bbs.homeshopmachinist.net//biggrin.gif

I have a single-phase lathe and drill/mill. Once it's above a very low RPM, I could throw the forward/reverse switch all day long and the motor would happily keep running in the same direction. To me, throwing that switch and having the machine reverse would be "instant." Instead, I have to turn it off, wait for the spindle to stop and then reverse it.

Allan Waterfall
12-18-2005, 01:58 PM
I run a three phase motor from an inverter on my lathe and I find the instant reverse very handy when threading with a tailstock die holder. Just flip the switch and the motor ramps down and then ramps up again in reverse.


12-18-2005, 02:31 PM
It does mean instant, in the sense that the motor torque reverses immediately when fed the appropriate power polarities, whether the motor is spinning or not. The standard 3 phase induction motor does it. A single phase motor which has a centrifugal starting switch (such as a split-phase or capacitor start motor) does not. The motor with the centrifugal switch must slow down to the point that the switch turns "on", which connects the start windings. The start windings are what gets the motor going in the other direction, and if they're not in the circuit, the motor will just spin merrily in the same direction no matter what your "reverse" switch is doing. So since you have to let the single-phase motor wind down nearly to a stop before you can reverse it, it's not instant reverse.

I rarely find "instant reverse" a useful feature, myself. A brake on a motor (that is, "instant stop", more or less) would be more useful.

[This message has been edited by sauer38h (edited 12-18-2005).]

12-18-2005, 02:49 PM
Nothing is instant. If you could stand on a nucleus, even the orbit of an electron around it would seem to take a considerable length of time.
In terms of lathe's, etc, something more 'instant' would be the reversing of a pm dc motor by flipping the switch. Assuming the power supply can handle it, the brushes, switch contacts, et al, that type of motor would reverse very quickly, like maybe in one second it would brake to a stop then wind up to speed again. I've never seen an ac motor that would come up to speed as quickly as a pm dc motor, let alone stop and reverse in an 'instant'.
Probably the closest thing to instant is when you order a coffee in a restaurant, then promptly fall asleep. The waitress wakes you when the coffee arrives. Now would that make it 'instant fresh brewed coffee'?

12-18-2005, 04:13 PM
Called Plugging. Or it used to be. You apply reverse torque via the motor to plug the load to a stop.

Usually it shortens the life of the gear train, the motor keyway, the windings, the

COntactors used for reversing by pluggin are oversized.

Inverters have a "starts per minute" rating on them. Any more than spec and they start heating up to "death mode". They charge the capacitors, discharge on startup, recharge, discharge, heat up.

12-18-2005, 04:42 PM
"So since you have to let the single-phase motor wind down nearly to a stop before you can reverse it, it's not instant reverse."

The original Westinghouse 1/4 hp single phase motor on my SB9 is "instant reverse". You don't have to let it slow down at all. Flip the drum switch to reverse with the motor at speed and the motor halts within one second and reverses, either direction.

12-18-2005, 04:58 PM
... Which is why I had the foresight to specify motors with centrifugal switches on their start windings. Permanent-split capacitor motors, induction-repulsion motors, and doubtless a few weirdos I have yet to run into, have no centrifugal switches, ergo do not rely on the state of the centrifugal switch to generate reverse torque.

But then, I wasn't entirely sure that these insights into the peculiarities of a tiny percentage of the motors in use today really clarified the answer to the question.

12-18-2005, 05:00 PM
...Do'h, shaded-pole motors, too. No start windings, no centrifugal switches.

[This message has been edited by sauer38h (edited 12-18-2005).]

Jim Caudill
12-18-2005, 05:30 PM
It really isn't that big a deal. I use "instant" reverse or "plug reversing" all the time when I'm tapping in my Bridgeport. The spindle is rotating in back gear at a relatively slow speed, but yes, that motor really is whizzing when it reverses. If some of the older heads comment about this being a "bad" practice, I may reconsider my tapping technique - but I've been doing it this way for years (although I really don't tap all that many holes, probably less than 50 per year).

12-18-2005, 06:33 PM
Jim I got a milwaukee drill that has been doing that for 25 plus years..

12-18-2005, 06:46 PM
"I've never seen an ac motor that would come up to speed as quickly as a pm dc motor, let alone stop and reverse in an 'instant'."

I have a tapping machine made in Japan by Brother Company.

It has two spindle speeds, 1000 & 2000 rpm. In either speed the motor reversal to back the tap out is as close to instantaneous as any I've seen. When I first got the machine I thought the reversal of the tap was by some kind of clutch and gearing mechanism inside the head because it was so fast. Nope, they did it the simple way, by reversing the three phase motor.

Rockwell/Delta used to make a drill press designed for tapping, it used a special low inertia motor, long skinny type of motor, to allow "instant" reversal.

12-18-2005, 06:48 PM
"If so, where the hell do you go to get out of harms way when the chuck comes flying off?"

That could be why very few "serious" lathes use thread on chucks anymore.

12-18-2005, 06:50 PM
perfectly safe with a 3phase motor.

12-18-2005, 06:53 PM
My RF45 clone mill drill runs on 110 volts single phase. When tapping you get hit the E stop button and it reverses, maybe not instantly but it sures seems like it to me. Don't know how the hell it does it! http://bbs.homeshopmachinist.net//biggrin.gif

Paul in NE Ohio

[This message has been edited by PHiers (edited 12-18-2005).]

George Hodge
12-18-2005, 08:56 PM
A friend of mine bought an instant reversing motor,1ph.,220v.to use on a wood planer blade sharpener.It just used a toggle switch to reverse it and it was dang near instantaneous! Garage door motors reverse pretty fast too.

12-18-2005, 09:24 PM
The motor on my SB has some sort of switch inside the motor, probably centrifugal. You can clearly hear it click on and off when it starts and stops/reverses. It reverses nonetheless. When reverse is called it doesn't coast to a stop and then reverse, it halts under reverse power almost immediately and restarts under starting winding power. I just timed it, full forward to full reverse is about one half second.

J. Randall
12-18-2005, 09:27 PM
YOD, over on PM in the SB forum there had been a good discussion on this very subject. IIRC some small SB lathes were equipped with a GE motor that had a special relay that made them instant reversing, this is single phase. I think it is one of Paula's threads on her 9". James

Your Old Dog
12-18-2005, 09:58 PM
Well I'm not sure I'm any further along in my thinking then when I first posted.

When I speak of "instant" I'm referring to seconds and not micro or sub parts thereof.

I had no clue it was considered okay to take a whirling gear train and tell it to bring all that mass to a stop and then go the opposite direction in less than a seconds time. Kind of like riding down the road at 40 mph and asking everything you're riding into stop and go the other way and do it in one seconds time. I'm not sure many of us would survive that ride. Maybe there are counter balances in these gear trains that I'm not seeing. Maybe all the gears use the inertia of each other to prevent damage but I'm not understanding it. If you guys say it's okay to slam one into reverse I won't disagree with folks who have done it !! I suppose my SB9a synthetic flat belt would slip before the gears would be stressed to the point of breakage assuming the motor was okay with it all.

DR, good point on the older style chucks spinning off. I was first made aware to work between center when in reverse from reading some comments by Forrest. Up till then I had used the 3jaw in reverse with no tailstock in play! Got lucky I guess http://bbs.homeshopmachinist.net//biggrin.gif

Thanks for the input guys, it's appreciated.

[This message has been edited by Your Old Dog (edited 12-18-2005).]

12-18-2005, 11:03 PM
MY Atlas has the quoted GE motor that had a special relay that made them instant reversing, this is single phase.end quote! and I thought it was normal to instant reverse?? I did it by accident one day and was freaked out by the action!! I don't use the function on purpose but I did see it first hand!! Scott

12-19-2005, 01:02 AM
I only use the instant reverse function occasionally, usually when threading to bring the chuck to a quick stop, mainly as a brake. Other than that I don't use it.

I don't think it is a relay in the motor since even if you remove the power it doesn't click out until the motor spins down. If left to spin down normally it takes several seconds and clicks just before it stops. When instant reversed it stops within a half second, clicks in, starts the other way and clicks back out, all in a fraction of a second. I can't tell what it is as the motor is fully sealed and I'm not taking it apart as long as it works.

It might be rated as 1/4 hp but it is the size of most 1 hp motors sold now. Even when running continously for hours it only becomes warm to the touch and that is with no cooling at all.

It's similar to the motor I have on my shop built air compressor. That's rated at 1/2 hp but has the pull of a much larger rated motor. It is at least 50 years old and weighs about 50 lbs. It is an old refrigeration rated motor and doesn't even become warm in use.

12-19-2005, 08:14 AM
I have taught motors and controls at a technical college for years. 3 phase or special 1 phase induction motors are fine to instant reverse or plug (throw in reverse to stop). You have to be aware of the mechanical system. It may have a lot of momentum to consider. PM DC motors will instant reverse but this shouldn't be done. It will make the magenets weak over time.

12-19-2005, 09:37 AM
double post

[This message has been edited by thistle (edited 12-19-2005).]

12-19-2005, 09:38 AM

My SB9 has the same motor as yours. At least it acts the same way. I can hear the click on startup/shutdown but it will instant reverse... 1/4 horse and big like you say.

12-19-2005, 09:44 AM
My Colchester lathe has a forWard clutch and reverse clutch.motor stays going in the same direction.
I dont want to go from full ahead to full astern,but sometimes if im in a hurry and
wack the worn apron control down ,it has happened,it is scary to suddenly have the 75 pound chuck ect start off in the other direction.
The clutch can handle it though .

12-19-2005, 10:05 AM
I had a chuck unscrew on a Lodge&Shipley once,funny thing was it was one of those machines where each time you decided to change a chuck it involved a 3' length of 4x4 oak and a maul the knock it loose,not that time though http://bbs.homeshopmachinist.net//biggrin.gif

The coolest way to reverse is through clutches,especially if it's on a turret lathe.I ran a Libby lathe one time that had both a forward/rev clutch and a two speed clutch.You could face off a 6"od ss pipe flange at 300rpm then drop it down to 60 rpm to tap the center hole and then reverse to back the tap out all with the same two levers.

12-19-2005, 10:49 AM
well the chuck should not come off,D1-6-
but that much mass going south instead of north sometimes gets the flight or fight instinct going for a sec

J. Randall
12-19-2005, 11:18 PM
Evan, I don't think the relay was in the motor, in the thread I referred to they show a picture of it. I believe they said it mounted to one of the end bells on the outside. James

12-19-2005, 11:49 PM
Well, it would seem that what I know about instant reversing motors would fit in a sesame seed shell with the seed still in it. I think I'll go make some instant hot chocolate now. Back in ten minutes. http://bbs.homeshopmachinist.net//smile.gif

12-20-2005, 01:26 AM
J. Randall,

There is no external relay on mine. Just the drum switch and a normal appearing motor with a capacitor on the outside. I have no idea what the wiring is and don't have a schematic. I'll figure it out if I must someday but for now it's a black box.

12-20-2005, 04:23 PM
The relay is actually mounted inside the end bell, behind an access cover. Here's a picture I took during disassembly for cleaning/inspection:


This picture was taken during reassembly. Notice that the motor does have a centrifugal switch:


Here's a view of the finished motor, mounted to the drive standard. Works very well, and does reverse "instantly", though I have no need for it other than tapping, etc., in backgear only:


12-20-2005, 04:24 PM
By the way, if anyone would like to see a schematic for this motor, let me know.

[This message has been edited by pstephens (edited 12-20-2005).]