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Wiring A Simple Switch For A Lathe

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oldschoolcane

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#1
Okay, so I have a simple electrical job to do but I am not very familiar with wiring. Have a small lathe, its supposed to be powered by a Sears Craftsman 1/3 hp motor. The motor already has a power cord, but no switch. How can I convert the motor over to a switch so that I can power it on and off? I already have the metal electrical box and the on/off switch. Can anyone offer any advice, I just want to get this done correctly.
Thanks,

Tim
 

JimDawson

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#2
The really simple way to do this is to put a heavy duty light switch in-line with the power cord. Don't use the ''silent switches'' Another option is to used a switched outlet, again a light switch and an outlet in the same box, then just plug the lathe into that. I do that with my little router table to control the router and the vacuum cleaner.

All the parts should be available at your local hardware store.

Another option is a power tool safety switch like this one.
http://www.rockler.com/safety-power-tool-switch
 

hman

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#4
You might want to consider building the "safety switch" I designed a couple years ago, either as a hard-wired switch or as a switched outlet. It's kinda a DIY version of the Rockler switch that Jim Dawson posted a link to. Here's a PDF that shows how to build it.

A couple disclaimers ... 1) This switch scheme is only good for 120 (110, 115) volts, NOT 240. Should be perfectly fine for a ⅓ HP motor; 2) Unlike magnetic starters, the switch will NOT shut off whan power is interrupted. So ALWAYS be sure to turn it off before plugging in!

Best wishes!
- John
 

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Bob Korves

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#5
If the motor is reversible, you might want to hook up a drum switch so it can go both ways. Some lathe functions need that. It sounds like you want it as simple as possible, if so then just go with the advice already given above. A drum switch is more complicated to wire.
 

LucknowKen

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#6
Hi Tim: Welcome to THM forums.
There are some good solutions above.
If you simply interrupt the black wire with the switch you bought.
This assumes your power cord has a three prong plug.
Switch.jpg
The black wire is power the white neutral and the yellow is ground in the above picture.
lk
 

CluelessNewB

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#7
LucknowKen's diagram is what you want. I would use rubber cord with stranded wire not solid core romex. The ground wire in the US is usually green not yellow. Note that the black "hot" wire is switched not the white "neutral" . If you are wiring a 3 prong plug the white wire is connected to the wider of the two flat blades and typically has a silver colored screw, the black wire is connected to the narrow flat blade which typically is brass colored (but sometimes black), the green ground wire is connected to the "U" shaped pin typically a green screw.
 

oldschoolcane

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#8
Thanks so much for all the ideas, I'll have to print this out and come to some decisions on this over the weekend as I really need to be able to use my lathe. Wish I was more familiar with this but I am not so I sure appreciate all the great advice.
 

kingmt01

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#9
Not that I haven't done it but I'd suggest against a light switch. They don't do well with motors. I've replaced a few that have burnt up.
 

kingmt01

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#11
Something built for a motor. There is all kinds of options.

I need to do some math to find out the amp rating.
 

kingmt01

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#12
I've tried a few times to put this into words but I'm not sure how to tell you what to look for.

So that motor will probably never draw more then 5A so you need a switch rated 5 or above. If it is rated 5A@250v it is likely to be the correct switch.

It needs to have a hard sold contact tho. That is why Jim told you not to use salient or soft contact switches.
 

CluelessNewB

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#13
You can find motor rated "light switches" at the big box stores. Typically they will be in boxes (rather than than loose in a bin) and will be 20amp (rather than 15amp). Look at the back of the box and it should say something like "AC Horsepower Ratings: 1HP-120V 2HP-240V, 16A Max" I was hoping to give you a link to an appropriate switch at Home Depot or Lowes but they don't seem to bother giving all the specs for their switches on the web sites. Expect the better switches to run about $5-$10.

For larger more expensive motors a real motor starter is a better choice but for small motors like this the toggle switch will work fine.
 

kingmt01

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#14
Toggle switches with the correct rating are probably $2 or less tyd off eBay. Most switches will be insulated but there is I few that aren't & I'd hat to see you get one. If it has a UL on it then there shouldn't be a worry about shock but that still doesn't mean it will work for a motor.
 

hman

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#16
OK. I understand that a simple light switch isn't suited for larger motors. But Tim was talking about a ⅓ HP motor. According to http://www.engineeringtoolbox.com/electrical-motor-hp-amps-d_1455.html a 50% efficient motor draws ~4.3A running. Triple that for starting is ~12.9A. So according to my seat-of-the pants figures, a common 15 amp switch would appear to be sufficient. And a heavy duty Decora switch (20 amp) would very likely do the job for sure.

However, if it turns out I'm way off base, may I suggest one of these magnetic (120V 16A, $7.35) switches from Grizzly :
http://www.grizzly.com/products/Magnetic-On-Off-Switch-120V/D4530?utm_campaign=zPage
http://www.grizzly.com/products/Magnetic-On-Off-Switch-110V-6-Amps/G8992?utm_campaign=zPage
[note - the above URL says "6-amps," but the rating really is 16 Amps]

I have a couple of the black ones. As best I can tell, the only difference between the two part numbers is the color of the face plate.

There's also a very interesting "undocumented" feature - you can easily add an external E-stop button to the circuit. Here's the manual:
http://cdn0.grizzly.com/manuals/d4530_m.pdf
Look at the schematic on the second page. Note the "Important connection" between terminals 24 and A1. This supplies power to the relay coil. If you interrupt it (with an E-stop), you turn off power to the output terminals. It will stay off until you hit the Start button again.

Of course, this is NOT a reversing switch. Tim, your original post did not mention anything about reversing. If you need that, then go with one of the toggles that others have suggested.

Hope this helps!
 

CluelessNewB

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#17
Generally standard light switches are NOT rated for inductive loads like motors That's why I recommended looking for a switch specifically rated for a motor. We are only talking about a couple of extra dollars to get a properly rated switch.
 

tq60

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#18
The 20 amp light switch will work fine but...

Spend a bit more to be much safer.

Materials needed are few and not expensive.

Get a DPDT relay rated for 240 vac @15 amps.

Get a 20 amp rated light switch.

A Normal open make contact push button switch

A normal closed break contact push button switch.

Terminal strip

Wire as follows.

Standard cord into box via cord strain relief attach 3 conductors to terminal strip.

Cord for motor comes in via another strain relief and attaches to terminal strip...All wires on single connections.

Connect green safety grounds together and to box.

Connect whites together.

Connect a wire from black in wire to light switch (main power not load controling)

Connect other side of switch to relay terminals labeled "C"

Connect another wire from this point to no push button switch

Connect other side of above switch to terminal on relay marked coil, there are 2 pick either.

Connect other coil connection to white wires on terminal strip.

Connect lathe motor cord black to one relay terminal marked "NO"

Connect a wire from other relay terminal marked "No" to the break contact push button.

Connect other side of that switch to the relay coil NOT connected to white.

The light switch us main power on and off and does not switch inductive load.

The relay controls the load.

The make contact switch activates the relay.

The connection via the break contact button causes the relay to latch.

Pushing that button turns it off.

If you loose power while running it will not come back on by itself when power restored.

That is home made magnetic starter.

Or look for one as mentioned avove.



Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 

oldschoolcane

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#19
Okay, thanks to all for their help! A lot to consider here, I will have to decide what to do. Probably will try a heavy duty toggle switch, I don't need a reversing switch.
 
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