# Machine Safety Interlock Wiring in the Home Shop



## wcunning (Jun 8, 2018)

Folks,

A while ago, I read through the whole adventure of one Thomas Utley on building a fancy control panel for his old South Bend 16" lathe. He put more work into that than I intend to, between the fancy diesel tachometer for the lathe, the expensive custom cast iron housing for all of it and such, but I was quite impressed with a few things. First of all, he made sure that all the wiring was logically laid out and carefully arranged. Second of all, he put in proper e-Stops in a couple of places. 

I've also seen power interlocks for lathes, similar to a micrometer carriage stop, that when you ran into it, would kill power to the machine, preventing you from being able to run into the chuck. Similar arrangements could be envisioned for a mill with a powerfeed. Unfortunately, the article I read on that in an antique issue of Popular Mechanics, and as I saw implemented on a Logan 200 I looked at once, were for small lathes with 1/2 HP motors that had fairly low maximum current draw. 

My confusion/problem/issue is that both my lathe and mill are 2 HP machines with single phase motors, so all of the tricks of wiring these safety mechanisms into them that I've read online using the accessory features of a VFD don't really apply to me... How could I install an interlock on my lathe or an e-Stop on either machine in my existing single phase setup without breaking the bank? Do you guys have any other useful/smart/easy-to-implement safety switches/interlocks on your machines? 

Thanks,
Will


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## British Steel (Jun 8, 2018)

I have a Big Red Button labelled "PANIC" by the door with a pair of normally closed momentary switches in it, one each to cut the contactor  coil circuits in my phase converter and lathe - it's wired to small plastic boxes with XLR connectors then into the electrics boxes with  trailing cables via XLR sockets, as the contactor coils run at 24v it's not hard to do and there's no dangerous voltage present, needs a couple of actions to get rhings running again (and works as a master power-off exiting the Garage of Danger) - could you do something similar?

Dave H. (the other one)


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## wcunning (Jun 8, 2018)

I honestly don't know how... I don't have a magnetic contactor for either machine, nor do I have an easy thing like a phase converter to cut all the power. My "easiest" thing is to turn off either the whole house breaker panel or the breaker to the shop area of the basement, but that's a few feet further from the problem than I'd like. Do you have recommendations for magnetic contactors for single phase equipment? And/or are 3 phase contactors usable on single phase? 

Thanks,
Will


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## Bi11Hudson (Jun 8, 2018)

Whenever you have a load (motor &c) that has a higher rating (current) than the switch, there will be a relay of some sort between the two. For an E-stop you need a bigger relay because the contacts need to break *reliably* under an over-load condition. This knowledge from industrial experience*........ *Interlocks are a simpler matter.  If things aren't right, it just plain won't start.

In both cases, the relay will be in the line side (by _code_) and is simply a normally open contact. This to kill any available power to the machine. Normally there will be a drop out circuit in the on-off switch so that when power is restored, the on-off switch is not still in the on position. As in the machine does not restart on its' own when power is restored. Think of an E-stop as jerking the cord out of the receptical. You wouldn't want the machine to start running as soon as it was plugged back in. 

A drum switch (reversable) on a lathe is a good example. There needs to be a contact in the OFF position that permits a reset of the Estop or interlock relay. The relay then seals itself in, with its' own contact, allowing the drum switch to select direction or run speed. This is the *second* most important factor with either system. The machine *must not*, under any circumstances, restart without manual operator control. 

This applies to all machines actually. What happens if one trips a breaker or otherwise loses power. When the power is restored, one would not want the machine to restart on  its' own. Something as simple as a lanyard on the switch would work. A foot pedal switch falls into this concept. by far not the best solution, but a start. If only to remind the operator to center up the switch.

A magnetic starter switch such as Grizzly's D-4159 is a good start. I happen to like the large paddle so my aim is not quite as important. Looking under "magnetic switches" will list also magnetic starters. Something, anything, to require operator input to restart the machine.

This is only an introduction to Estop and interlocks. It is a complex subject and requires considerable education.

Bill Hudson​


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## Bob Korves (Jun 8, 2018)

Think carefully about the location of an emergency off switch.  Supplementary to the idea of having it as convenient as possible so it is easy to turn off, the most important thing we need to do when epic stringy chips or loose parts are flying off is to FIRST get away from the danger.  On a lathe, the chuck area, especially in front and behind the chuck, and above the carriage, are the most dangerous places to be.  If your E-switch is in that area and the machine is about to crash, you will be torn between putting your hands in there to try to shut it off or getting away to watch the lathe self destruct.  Instead, move that E-switch to perhaps the left end of the headstock, so you can turn it off while getting clear of the carnage.  If you ever do need to use the E-switch in anger, do not stop there and watch the action, rather keep on going away until the action has stopped completely.  A good habit to get into with controls that are used in both emergencies and in daily use is to try to think about the emergency sequence before performing the ordinary sequence.  In an emergency, we tend to do things by habit even if they are not the correct moves.  We must train ourselves to perform safely all the time, and it does not take much effort.  My favorite mantra in the shop is "What could possibly go wrong?", and having the sober thought along with the chuckle.  Remember that we are the only safety department in our home shop, and act appropriately.


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## tweinke (Jun 8, 2018)

Safety, the first thing thought of after the accident! Kudos to anyone trying to make a situation safer. I always try to remember that I am not necessarily the master of the machine and if I think I am its time to step back and rethink things.


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## markba633csi (Jun 8, 2018)

Will: Here is a basic sketch of a latching relay circuit.  It's a 24 volt system which is safer than running 120 volts through the pushbuttons. I show just two stop buttons but you could add more
Mark


NO means normally open, NC means normally closed.


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## benmychree (Jun 8, 2018)

All this brings to mind some thing that the Yankee philosopher from Walden Pond, Henry David Thoreau, might have said "simplify, simplify, simplify".  I manage to run many machines without any of this "over complication" (my words) without any problems, all that is required is that you pay attention to what you are doing.  If you have a phase converter, when it is turned off, nothing will start up when restarted unless you leave a non magnetic switch in the (on) position.  As I said, pay attention!


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## JimDawson (Jun 9, 2018)

For an inexpensive setup, high current PRD relays fit the bill.  For a 120V system @markba633csi diagram above and relays like these https://www.automationdirect.com/ad...eries)#Contact_Configuration_s="DPST"&start=0

Plenty of current carrying capability and they give you a nice audible ''clunk'' when they pull in, and most importantly are reliable and inexpensive.

For a 240V system, since you need both contacts to switch the power, add a small ''ice cube'' relay to control the coil on the power relay.  I'm not aware of any of the PRD type power relays that are 3 pole, so you have to add the extra relay.


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## British Steel (Jun 9, 2018)

As Benny says, Pay Attention! 
But... all of us make stupid mistakes occasionally (or in my case, frequently), so making things safer is never a bad idea, and it's really no more complicated than running a drum switch rather than having to rewire the motor every time you want to reverse...

Way safer than the open-frame PRD relays (particularly when working live to diagnose...) and also on the Automation Direct site are "contactors" - A Few Dollars More (thanks, Clint), but less complicated - most listed are 3-pole so you can switch both lives (220v) or live and neutral (110v or rest-of-the-world 220), the third contact set can be used for the relay holding as part of a no-volt release.

Dave H. (the other one)


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## markba633csi (Jun 9, 2018)

Just don't get electrocuted building a safety system


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## tq60 (Jun 9, 2018)

Already posted are good suggestions 

We have VFD so controls are logic into VFD but controlling a motor or other loads is simple.

First avoid "going cheap", nothing wrong with saving money but given you are asking we are assuming limited skill set.

So forget about locating relays and contractors unless you get lucky like us and get a box full for 2 bucks.

Search for a "magnetic starter" for a motor same size as the one on your machine.

But wait...You need remote control (start and stop buttons) and you need to be able to upgrade to larger motor later.

These devices have current sensing in them and will protect the motor from over current and some are adjustable or have changeable parts for motor current.

Start and stop buttons are common items on ebay.

Your "e-stop" I'll not really be a stop but rather "off" as you likely do not have a motor that can have braking.

The "safety" or "multi - point stop" switches can be placed in many places.

We added a foot bar to ours that allows it to be shot off with tap of foot.

The stop switches are normally closed so all connected in series so any one pressed causes stop.

Someone else stated a shop master.

On our air compressor we were forgetting turn it off.

It is 7.5 hp with mag starter.

We added a toggle switch to the control line so easy to control 

Next added a relay with 120 vac coil and placed a standard cord on it.

We added an outlet wired to light switch that compressor control plugs into.

Lights on allows compressor to run.

Same can be done to anything with magnetic control.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk


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