A/C 12x42 needs new power switch - worth replacing w/ reversing?

[WallyEmm]

My Atlas Craftsman 12x42 lathe original power switch has failed and needs to be replaced. The name plate on its Craftsman 1/2 HP motor says it is reversible by reversing a couple of wires. I hadn't considered adding a reversing switch, but since I have to replace the original switch anyway, is it worthwhile to make the motor reversible while I'm at it?

Wally

 

[wa5cab]

If you use a 3PDT or 4PDT Center Off bat handle toggle switch instead of a drum switch, it needs to be of the special type that has an internal mechanical lock that prevents you from accidentally flipping it from FWD to REV while the motor is still turning. You will dislike the consequences of doing that. The special switch essentially requires you to release the bat after you have flipped the switch from FWD to OFF before you can flip it from OFF to REV. The only ones that I ever recall seeing also required a mounting hole larger than the 15/32" one on the headstock or on the switch escutcheon. Most people either use a drum switch (as I did) or use two switches, the ON-OFF one in the headstock and a separate FWD-REV or FWD-OFF-REV mounted in a less accessible location so that it can't be easily or accidentally reached. And rug-rats can't reach it at all.

 

[Bi11Hudson]

As owner/ownee of a Craftsman 12X36, I have already been where you/re heading. Although a simple toggle switch will do fine, what do you do when things get a little out of hand? Reaching into the machine to switch it off when things get hairy is a most unpleasant experience. I like to "bat" the switch while running for the door.

There are numerous "plastic" encased drum switches that show a pretty good current rating. One level of contacts is simply an "ON-OFF" switch. Two wires to turn it on, no reversing. The ones out of China do well enough for this, especially if you're counting pennies. Not much more than a good quality SP toggle switch. The ones I found have sixty (60) amp contacts. For less than 20 bux, yet. That will start several horsepower

There are a couple of points to consider, though. First off, as a motor switch, it is handling an inductive load. Huge amounts of flashover that aren't seen. Plus the starting current. Not something to use a household light switch for. You need fairly heavy contacts. An automotive grade auxilliary switch just won't stand up. That's the "pointer" to look for on switch ratings, what size motor will it start. In five years???

The other is reversing. Drum switches usually don't have interlocks, but... They do require a consious effort to operate. A single phase motor MUST be near zero speed to reverse. If it is running fast enough that the starter contact has not closed, flipping the switch from forward to reverse has no effect except a bump in the speed. This can be recognised by listening carefully when the switch is cut off. There is a distinct "click" from the motor as the contact closes. Only then can the reverse contact be made up.

You will rarely use reverse, but it is nice to have when you need it. I seldom use it, the 27440 has a threaded headstock. Mostly when threading. The machine is old, read loose, and I really don't trust releasing the half nuts. Just having a big handle ON-OFF switch is the plus here. Reversing takes more wires. When it comes down to it, I highly recommend the drum switch, even it you just use fhe ON-OFF switch contacts.

Bill Hudson​

 

[WallyEmm]

Thanks for the suggestions, that sounds like the way to go. I was thinking of replacing the old switch with a standard HP rated toggle and adding a separate downstream drum switch, as described. That way the original toggle switch location can be a master ("Emergency Off") switch and the reversing switch can be used if/when desired. Any new switches will be rated for the application.

Wally

 

[tq60]

Most if not all single phase motors that are reversible only switch the electrical position of the starting winding.

We state this as after motor is running it is not connected.

So switching motor into reverse does nothing as the line is still connected exactly same.

3 phase will reverse however.

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[whitmore]

the original toggle switch location can be a master ("Emergency Off") switch and the reversing switch can be used if/when desired.

If the OFF has to be operated in an emergency, a big red mushroom button, or plate that can be poked with a stick
is perhaps preferable. That's what I'd want, anyhow.

 

[wa5cab]

Most if not all single phase motors that are reversible only switch the electrical position of the starting winding.

We state this as after motor is running it is not connected.

So switching motor into reverse does nothing as the line is still connected exactly same.

The above was apparently written in rebuttal to my earlier statement that using a non-interlocked bat handle toggle switch for both ON-OFF and FWD-REV functions could lead to undesirable consequences. With the obvious implication that my statement is FALSE and that there is nothing to worry about. Unfortunately, the implication is the one that could be FALSE. Rather than deleting the post, because some of you have already read it I will explain why.

First, "Most" is correct or true (because that is the way in which the circuit should be wired). However, "all" is false because some motors have definitely been mis-wired by people who didn't know what they were doing.

Next, recall that the premise was that the operator was trying to stop the motor, not to reverse its direction, but inadvertently pushed the bat past OFF to REV and kept the motor running in one direction or the other. So now we have a case where the operator intended to stop the motor for some reason but it is either still running or has tripped the breaker. If it is still running forward and the half nuts are closed, possibly in less time than it took to read this, there is a crash. What the consequences of that is will be left to the imagination of the reader. If there isn't a crash and if the operator recovers and either stops the motor or opens the half nuts (which is probably what he should have done in the first place), then no harm done unless he has a serious heart condition. If the motor reversed or tried to reverse but tripped the breaker (because the centrifugal switch did manage to drop out or the motor was mis-wired), there may have been damage done in the motor, the switch, or the drive train but probably the operator recovered his wits fast enough to stop the motor this time.

Anyway, the moral is: Don't use the wrong motor switch just because either you have it or it is cheaper than the proper switch. Anything worth doing is worth doing right.

 

[tq60]

Not really arguing the point as your advise is good.

Some who may want to tap may rewire then discover it does not work.

Based on your good statements that we had not thought about, one could consider a second switch somewhere out of the way that is just forward or reverse.

The standard switch remains on-off so it does not get overswitched.

Did not think about emergency stop...only about tapping.

Keeping correct hp motor and not upsizing also helps.

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[WCraig]

If the OFF has to be operated in an emergency, a big red mushroom button, or plate that can be poked with a stick
is perhaps preferable. That's what I'd want, anyhow.

I used a magnetic motor starter as it has the nice red mushroom switch. As a clueless newbie that has already saved me from myself a couple of times!! I mounted a DPDT bat-handle toggle switch to the motor box for reversing although I haven't actually used it yet.

The other nice thing about a mag switch is that if you have a brief power interruption while you are working, your machine won't spring back to life when the power is restored.

Craig
Plus I got the starter AND motor for $10 at an auction!

 

[John281]

One of the first things I noticed about the Atlas Craftsman switch is that ON is down and up is OFF which seemed counter-intuitive to me. I replaced the switch on my lathe recently but inverted it and added an orange switch guard. The switch guard helps prevent inadvertently switching it on but also allows one to turn it off quickly by batting the cover downward.
Also, I assume that operating in reverse would never be done for any type of cutting since the chuck could unscrew itself from the spindle. I'm not sure about this, though.