Millers Falls 806 bench grinder

[Mal-110]

I am repairing this grinder for several reasons, one being that they are more sturdy and reliable then what you can buy today. I need a little advice, the machine was plugged directly into a domestic wall socket and switched on using the socket switch. Having looked at the wiring when unbolted an turned over it is very tatty. I will try and add a photo. It was original fitted with a switch on the front panel and a cable entry at the rear. Both these were filled in and the cable entered from below. I want to reinstate the switch and feed new cable in from the rear. It is a UK model rated at 220volts and the motor is 1/3 hp. Some American literature indicates the switch is placed in the negative line, they don’t mention the Earth, which in this case is connected to the stand with a small grubscrew.
Hopefully I have explained my situation, in summary it appears from physical evidence and American literature that the switch is in the negative line is this correct?
Whilst I am asking for advice the decision will be all mine
Thanks
Malcolm

 

[Sideways]

I'll give my ten pennorth. Don't put the switch in the neutral. Regardless of whether it was or was not done that way originally it is a safety hazard to switch a neutral unless you switch the live at the same time using a double pole switch.

 

[Mal-110]

Thank you for your reply. It does make sense. I have added three photos (they had been to large) since your reply. They go some way in explaining the issue.
Regards
Malcolm

 

[Sideways]

Wow ! Solid piece of machinery Malcolm.
This looks pretty old as far as I can interpret the photos. I can sympathise wirh your wanting to resurrect this
From a purely safety point of view i'm going to offer some comments and suggestions.
The insulation looks like it may be rubber. Rubber is good and durable but it does age. A house with old rubber insulated wiring reaches a point where a rewire is needed for safety. Please look at the insulation and if it's showing signs of cracking, get proper advice. It is no longer safe. There may be options but an online forum isn't really a suitable source of advice.

Personally, I hate it when people use electrical tape to insulate joints. It doesn't take long before the adhesive goes slimy and it's not reliable so I don't trust it. Professionally I ban anyone from using it on sites that I run. When you make your repairs, I recommend looking at "wago" connectors or better still "hylec" style gel filled connections. These make a good connection and don't leave exposed terminals.
Heatshrink tube is good if you need to add insulation to any wire.

This grinder has a metal body so it's important to have the earth wire on the power cord well connected to that earth screw in the photo. Crimp a loop terminal onto the wire and use an anti vibration washer when you fasten it. That will help stop it shaking loose.

The last safety measure i'll recommend is to use this tool on a circuit that has an "30mA RCD" protecting it. If you have RCDs protecting your household sockets these will protect anything connected. If not, you can get an RCD adaptor or an RCD plug to use on the power cord. These will cut the power quickly if a harmful amount of electricity leaks to the metal body of the tool and anyone touching it.

I don't know your background or knowledge of electricity so excuse me if this is "teaching grandma to suck eggs". If in doubt it's always best to seek advice

One thought. I assume you're not going to use this for business so it's not required, but a PAT" or portable appliance test is specifically intended to tell you that a piece of equipment is safe to use. If it's done right and not by some monkey who doesn't know what he's doing, a PAT test will give you confidence that your machine is electrically safe.

 

[Rhyolith]

I sympathise! I have had a lot of difficulty trying to find out how to make my old metal bodied power tools safe and I still am not sure... No professionals I have talked to are willing to go near them for some reason, though I can’t claim to have found many (mostly PAT testing places).

I have restored and used a handful of 1950s-60s power tools and non of them have given me so much as a tingle so far.

I can tell you to ingore the American literature. They use 120V with no earth over there, I thinking the logic is that 120V is safe enough not to need as earth. Whether or not thats true you definatly want an earth on your grinder.

Few other relevent threads:
wolf-locomotive-belt-sander-t109555.html
wolf-bench-grinder-t106250.html
wolf-bench-grinder-restoration-help-t96290.html

These RCD things sound like a good idea.

Something I would check on an old bench grinder though is if the rods the wheels mount on are central, with the rpm these things do a slight miss alighment can make them quite unplesant to have on.

 

[Mal-110]

Thank you both
I could have saved myself some trouble and just retwired the grinder without reinstating the switch. As it is an American product most of the info I can find indicates American wiring techniques. I would have taken the old wiring back to good stuff or all the way to the motor if I had to. I know enough about electricity to ensure I found a good earth however the shakeproof washer is a neat idea I would have missed. I was hoping to have only two connections and if I have to go back to the motor none. These I would have soldered and covered with shrink sleeving but I will now look for the connectors mentioned.
As to the switch am I right in thinking I need a DPST in the jargon. It will be a toggle switch and I will tidy up the cable entry with a sleeve.

Regards
Malcolm

 

[Sideways]

That's great Malcolm.
Yes a Double Pole Single Throw (DPST) switch will be fine. Just make sure it's rated for 230V and not a "car" switch only meant for 12 or 24v
A sleeve, strain relief or a plastic cable gland is a really good idea to protect the flex where it passes through any hole in the metalwork.
You will find wago connectors and the hylec things in the screwfix catalogue. They are easy to use. The wago type with small levers are suitable for connecting the stranded wire (of the flex) as well as solid wire so they would be the ones to choose from that range.

 

[Mal-110]

Thanks again sideways.
I have found a switch which is for domestic voltage and rated for a 1/3 hp motor DPST so I will order it as well as a wago connector (may have to buy a few. Have now stripped back the cable from the motor some of the tape was the old cloth type. I have hit a bit of a snag in that the cables attached to the motor are black and an off white, the off white was attached to a red bit of cable and then to the brown live wire. The black is attached to the neutral. Now before I removed it I had checked it was working (considering the state of the connections) this is surprising but it did run well.
My research tells me that American cable code specifies white or grey for neutral in which case it was wired incorrectly when I tested it.
Now this may seem odd and indicate my lack of knowledge but if it was wired in reverse would the grinder work in the opposite direction.?

Regards
Malcolm

 

[AndyT]

Only on a DC motor. With AC the polarity is changing 50 times a second anyway.