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Remote Switch for PM 3520

A switch at the tailstock end of the lathe allows you to start and stop the lathe without having to pass through the line of fire to get to the switch on the headstock.  Such a switch is considered by many turners to be an important safety feature.  

There has been a lot of discussion on the various turning forums and message boards of the various ways to incorporate a remote switch on a Powermatic lathe.  In this article I describe one way to do it, which I believe is about as simple and inexpensive as it’s possible to be.  

Further, no modifications at all are made to the original wiring; one wire is swapped out for another, but none are cut, spliced, or otherwise modified.  The lathe can be returned to its original condition by simply removing the line going to the remote switch and replacing the wire that was swapped out.

What it does:  With the remote switch in the ON position, the original switch at the headstock operates normally.  However, switching the remote switch to OFF stops the lathe and makes the switch at the headstock inoperative.  

With the headstock switch in the ON position, the remote switch acts as a start/stop switch for the lathe.  The lathe will run when the remote switch is ON; it will stop when the remote switch is turned OFF.  

Now, here it is again:  both switches must be ON for the lathe to run. If either switch is OFF, the lathe will not run.  

Is there danger of shock or electrocution?  No.  There are no dangerous voltages associated with the control circuitry because it deals only with low-voltage, DC signals from the inverter.   The highest voltage I’ve measured is 16 V.

What happens if the remote switch malfunctions?  If the remote switch fails to make contact or turn ON, the lathe simply will not run.  If the remote locks up in the ON position, which is highly unlikely, the switch on the headstock will still function normally and can be used to stop the lathe.

Not an electrician?  You need only to attach two connectors to one end of a lamp cord and connect the switch to the other end.  You can either crimp or solder the connections.  For the purposes of this article, I’m assuming that the crimping method will be used.

This means, of course, that you will need a crimping tool.  You cannot get good results trying to crimp a connector with a pair of pliers.  However, if you don’t have a crimping tool and cannot borrow one, there is a way to do it with tools you already have.  The details are given in the article that follows this one.

What’s to buy?  Assuming you are starting from scratch, with no junk pile to work from, you will need to buy (1) the switch of your choice; (2) 16-2 lamp cord, perhaps 10 feet;  and (3) connectors (detailed below).  

How and where do I mount the remote switch?  That is up to you.  Where would you like it to be?  I make suggestions in the following article, but you get to make the final decision.  

In my opinion, the remote switch should be “fixed” rather than “portable.”  If it stays in the same place all the time, and if you use it routinely, you will develop a feel for where it is and will then be able to get to it quickly if you need to stop the lathe in a hurry.  

What type switch?

First of all, you don’t need a big, super heavy duty switch intended for an industrial environment.  Such a switch will work, of course, but it’s overkill – much larger, bulky, cumbersome, and more expensive than what you need.

Because the voltage in the control circuit is low (~16V) and the current only a few thousandths of an amp, the electrical ratings of the switch are not an issue.  What’s more significant is the mechanics and work involved in installing the switch in an enclosure. Pick a switch that will be easy to work with.  

An auto parts store is a good place to go looking for switches and connectors as they typically have a better selection than a hardware or big box store.  

A good option is to use an ordinary light switch.  It’s a simple matter to make a customized enclosure out of wood, which is an excellent electrical insulator.  There’s more about this in the next article.

Getting Down to the Details

Disconnect power from the lathe.   This is an obvious admonition, but I said it anyway.  Actually, the greater danger is to the inverter – you never know what might happen if you start fumbling around with the control circuitry while the inverter is under power.  As I said earlier, there is no shock hazard associated with the control circuitry.  

Open up and examine the control panel.  Use a 5/32” Allen wrench to remove the two cap screws that hold the control panel in place.  

Move the panel downward slightly, and then pull out gently at the top.  It should then come out of the opening, but only a short distance.  

You may find several wire nuts taped together in a bundle.  If you do, remove the tape that forms the bundle, but do not remove any tape from individual wire nuts.  Loosen the bundle and move the wires around so you can see the details of what’s underneath.  

So what do you see?  At the top is the power switch which has two terminals.  Two wires connect to the top terminal; a single, yellow wire connects to the lower.  This short yellow wire is the one that we will swap out later on.  

In the middle is the forward/reverse switch, which is a single-pole, double throw switch with three terminals.  Note that the other end of the short yellow wire connects to the center terminal of this switch.  

At the bottom is the pot (potentiometer) for the speed control.  It has three terminals but we don’t have to worry about any of that.  

OK.  What we will do, in due course, is to remove the short yellow wire and replace it with a lamp cord with a switch on the end.  The rest is simply a matter of detail.  

Remove the short yellow wire.  First, locate the screw on the switch that releases the connector on the end of the yellow wire. Loosen this screw a turn or two and the connector should pull out, but pull at a slightly upward angle.  The slot the connector fits into is angled downward.

Next, grip the connector at the center of the forward/reverse switch and wiggle it side to side as you gently pull upward.  It should slip off the spade lug on the switch and free up the short yellow wire.  

Go shopping.  Get the switch, lamp cord, and connectors.  Take the little yellow wire with you so you can compare connectors.  Buy a foot or so more lamp cord than what you think you’ll need.  

Back at home, the first thing to do is make sure your connectors fit what they’re supposed to.  In particular, try the one that goes into the switch on the control panel.  If the connector you purchased is too wide, hold it with a pair of pliers and file the sides until it fits.  

Putting the System Together

The first thing is to decide how you will run the lamp cord from inside the headstock to the outside.  I’ve found two possibilities.  The first is preferred, but you can use the second if you prefer to have the lamp cord exit the headstock underneath the ways.

(1) On the back of the headstock there is a grommet the wiring from the inverter passes through to get to the control panel.  The obvious thing, then, is to run the lamp cord through this grommet.  

Getting the lamp cord through the grommet will be easier if you do it before installing the connectors.  So, working from the outside, stick one end of the lamp cord through the grommet, and push it in a few inches. Find it on the inside and pull it through far enough to give working room when crimping the connectors.  

(2)  For the most part, the headstock is closed on the bottom. However, next to the cam-operated disk that clamps the headstock to the ways, there are four small openings the lamp cord can pass through.  This will have the cord exit underneath the ways as opposed to the outside rear.  

If you frequently slide the headstock down toward the tailstock end, take this into account as you route the lamp cord.  

Install the connectors on the control-panel end of the lamp cord.  One will be a male; the other, female.  If you are new to all this, see the following article for details on making a crimped connection.

Make the connections at the control panel.  If you haven’t done so already, remove the short yellow wire identified in the photos.  Install the male connector in the power switch. Press the female connector down over the spade lug of the forward/reverse switch.  Pull excess cord out of the headstock interior.  Use a cable tie or tape to anchor the lamp cord near the control panel by lashing it to one of the multi-conductor cables from the inverter.  

A detail.  If and when you ever want to remove the remote switch and restore the lathe to its original condition, where do you want to find the little yellow wire?  One option is to tape it to another wire, right there on the control panel.

Re-install the control panel.   Carefully work the wires back through the opening and screw the control panel back onto the headstock.  Look through the belt-change access door to be sure that all wiring is well separated from the belt and pulleys of the drive mechanism.  

And that’s it for the control panel part of this project.  

Install the switch.  Electrically speaking, the only thing that remains is to make the connections to the switch.  The greater challenge is the mechanical aspects of putting the switch in a suitable enclosure and mounting it in a convenient spot.  See the following article for suggestions.  

Test the system.  Once the switch is connected to the lamp cord, you can check it out and see if it works.  Set the speed control to a low RPM and the forward/reverse switch to forward.  Set the remote switch to ON.  

Restore power to the lathe.  Pull the Start/Stop switch on the headstock out, and the lathe should run.  Then, turn the remote switch OFF and the lathe should stop.  And so forth.

Finally, after all is said and done, secure the lamp cord.  You probably will be working close to it on occasion, if only to remove shavings, and after a very short while you will forget it’s even there. Even though there is no danger of getting electrocuted, it is definitely not cool to get tangled up in the cord and maybe jerk your switch off its mount and have it hit the floor.

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