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Found an interesting feature on my lathe

Carl Darnell

Titanium
Joined
Jun 13, 2006
Location
Taylorsville Ky
My CamTak lathe has a lever for forward/stop/reverse on the carriage like many lathes that start and stop the motor rather than a clutch.

I was drilling some SS flanges and grabbed the lever and moved it back out of the detent and accidently lifted it instead of going down to stop the motor. Well, it suddenly reversed the spindle. Man, that sure surprised me. So I operated it several more times and it looks like I have an instant reverse feature for power tapping or any time I need to reverse quickly. I sure wouldn't do it running faster than 300 rpm but it sure works smooth at that speed and even better slower. I don't like to reverse motors fast like that but it may come in handy sometime.
 
We had a Meuser POS lathe at work with a switch like that. Gear box eventually expired. When this happend we adapted a ford ranger transmission and a belt drive motor hook up to it. All we use it for is infrequent metric threading jobs. Never again will i think of Germans as supreme mechanical engineers.
 
Ummmm, I have a reversing handle on my Chinese lathe, just like that. Down for forward, central stop, up reverse.

The problem is, and I assume this is true of all capacitor start motors, all the reverse switch does is switch the start windings so if it is running in one direction and I suddenly pull the handle to the other direction nothing actually happens! Of course if the motor stops in between it will be restarted according to the handle position.
 
:eek: Did ya'll use the instant reverse a lot to cause the gear box to fail? That was a thought when I was reversing it to see if it worked ok. I was thinking that it would be a hard load on the gears, etc. with the rotating mass.

I will probably only use it at 75 rpm when power tapping.
 
Or you could always just put a tapping head on the tool post and not have to the thrash the gearbox and motor. Just an idea. I'm not entirely convinced that this is a "feature" that many lathes come with.
 
So does this use a logic control for the function? It's impossible to switch my lathe into reverse without depressing the lever (while pulling on the lever to clear the latch) - the contactors don't switch on without the cam on the control rod turning far enough.

Running reverse is permissible for shortening the stopping time of the spindle according to the manual, but it's limited to a given number of cycles per minute (I forget what the spec is). I see it as asking for spit teeth.
 
GE came up with an instant-reversing 1PH motor for South Bend. I used to have one on my mill. It has a start winding controlled by a couple relays. As soon as the power was cut, the start winding could be activated again, in either direction. So you could switch F-off-R on a drum switch with no lag.

But yeah, debatable feature. Especially when you have a lathe with a threaded chuck!
 
The SB10L at the museum had the original instant reverse 110 motor on it, the 12" LeBlond at work, and many, many other lathes have an instant reverse feature like this. It's a shortcut to reverse to leadscrew for fast threading without reference to a thread dial. You leave the half nuts engaged and work the spindle back and forth to return the carriage to the start.

Much as I loathe the Summit at work, it actually has a clutch setup this way with reverse when pulled up. Same deal on the old French Somua we have there. L&S also offered this feature on lathes back even in the teens. It's a lot easier on the gearbox and other drive parts than instant reverse.
 
As John Hill says, a typical capacitor start motor will just keep running in the same direction. Many years ago, I took an oath to never run a lathe with one again. In a panic situation it is easy to throw the switch past off to reverse. On a three phase motor, you have the slow down and start up times to get the switch back off and even if it does run reversed a little, it often eases the problem ( like unrolling your sleeve ) instead of making it worse. I know we are supposed to have progressed beyond such problems, but even the best of us get into them once in a while.

The Monarch 10EE has a built in spindle reverse feature that requires that it go through a normal braking cycle before starting the other way, so reversing is just another start. That is the way to do it. The drive I am developing has a saturable reactor that current limits so that the motor starting surge is only slightly more than the rated max running current. That means the motor is never driven much past the rated continuous current, saving brush arcing, etc.

Bill
 
my nardini tt1030 automatically brakes as it travels though neutral.

But i need to always stop it from the forward roatation or it starts humming. it has a mag pickup sensor on the spindle. the circut that applies the motor braking and detects full stop must work better in forward than reverse. that worries me. I fear someday it will burn up. can anyone help me with that?


no matter how fast you throw the lever it always braked to a full stop before reversing. it's an all manual lathe but there is a surprising amount of electronic stuff in the cabinet.

sometimes i wish i could let it coast down easy but that is not an option.
 
I don't think I got the point across of what is happening.

On my lathe when you lift the lever from off/neutral to start the motor it is running in forward. Then if you lift it some more the motor will instantly reverse.

When you use the normal reverse by pushing the lever down from off/neutral it runs in reverse and the lever will not move any farther down.

The lever operates micro switches to make the motor run in forward or reverse and that operates the motor reverse relay.

This is a feature that I don't really see a use for except maybe power tapping. When power tapping I don't like to suddenly stop or change the spindle direction. You can snap a tap or tear up threads with sudden changes in direction.

I am puzzled by no mention of it in the manual so I don't have a clue as to the intended use the factory had for it. The lathe was built in 1984 in Tiawan and the company has changed to CNC machines for large industrial use so the factory is no help at all.
 
oh.... now that's just plain weird/neat.

i suppose you have the "option" of instant reverse. rather than my "required" instant stops all the time. -and that's nice. i hate to have big heavy things in the chuck .... on a faceplate would be worse.

but you can pick and choose... so dont complain :P

come to think of it... "instant reverse" is standard feature on tapmatic tapping heads. and rigid or floating tapping in mills the spindle stops and accelereates very quickly. Your concern for breaking taps in this manner don't seem to fit with the common industrial practice.
 
Sounds like your cam is out of phase from where it should be on the control shaft.

Mine wasn't quite where it was supposed to be when I got my lathe and it would "drop out" unless the lever was held all the way up. A little adjustment and now it works properly again.

Unless there's specific mention of this in the manual, I'd be fixing that.
 
There are single phase motors that can be instantly be reversed, not sure how they are wired, but all of the ones I has seen reconnect a capacitor. There is no start switch, however, they don't have a lot of starting torque. Most common are the reversible ceiling pans. All three of the major US mfrs offer in large sizes.

Tom
 








 
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