Static electricity

[Keato]

Hey all,

I recently got a Proxxon DB 250 lathe for Xmas & the 3 Jaw Chuck that goes with it.

I’ve had a little play around with it with no problems though my expanding ring mandrel arrived and when I loaded it up in the Chuck it started making electrical arcs between the mandrel & the tool rest.

I couldn’t get a decent sized beginners lathe because I don’t have the space plus I only really want to make small things anyway.

on the ring mandrel I have a wood ring with stainless steel core. Everything seemed to run fine except for the static build up.

I’ve called Axminster & their suggestion was to find a way of grounding the mandrel with copper tape. The tech support there said it’s the mandrel generating the electricity. I thought maybe it was the machine because it’s German made so has a 2 pin to 3 pin adapter plug which means no earth pin. The lathe bed is aluminium & the Chuck is zinc alloy. I was told the combo of these with the stainless steel expanding ring mandrel can cause static because it’s only happening between the ring mandrel & tool rest

Anyone got any suggestion to grounding the mandrel? I’m not sure whether I should buy & wrap a small amount of copper tape around the shaft of the mandrel and then tighten it in the Chuck.


Looking forward to some advice on this.
Jamie

i
I’ve attached a short vid showing the static.

 

[minilathe22]

Do you have a tailstock? Perhaps if you add an earth to the lathe, and push a (metal) tailstock against the mandrel it might take the static away. I would want to be sure its genuinely static and not an electrical fault though first.

 

[Keato]

Ah yeah I’ve got a tailstock. I didn’t think it’d be needed if it’s an expanding ring mandrel & clamped into the Chuck.

I’ll give it a try later in the morning & see if that makes a difference.
How would I add an earth to the lathe though? Safely I might add.

 

[clogs]

keato
clicked on the link...it didn't work.....

 

[Phil Pascoe]

I can't comment on the static but its running off centre would worry me. Is there a coutersink on the end of the mandrell for a tail centre?

 

[minilathe22]

I agree the tailstock is not really needed as a tailstock support, but it might just conduct the static to the toolrest without sparks. Maybe earthing through the plug is not really needed to fix it.

 

[flh801978]

I would chop the fitted plug off and then wire on a uk 3 pin plug and if the original cable is only 2 core run a seperate earth wire ( tape it to original cable) from the earth pin in the plug and then bolt the other end to any metal part of the lathe

 

[porker]

Please DON'T add an earth wire as described above. I checked the manual for this lathe and it indicates it is class 2 double insulated. By adding an earth, you may be introducing a potential hazard that does not exist.

 

[flh801978]

I do realise that its double insulated but how can adding an earth possibly add a hazard?

 

[minilathe22]

I don't think you need to ground it to the earth pin in your electrics, although that might work. You only need to create a path for the static to get from the mandrel to the toolrest without having to jump across (eg hopefully the tailstock can do it).

As to why adding an earth would be bad/less safe, I am not sure but modern electrics do seem to be moving towards double insulated instead of earthed. You may also find that sending static down the earth lead would mess with the breaker RCD, so perhaps try the tailstock idea first.

 

[porker]

I do realise that its double insulated but how can adding an earth possibly add a hazard?

Some equipment that is double insulated carries a warning specifically not to earth and the usual reason is that the earth in the plug is part of the electrical supply itself, therefore a potential difference (voltage drop) could be created that otherwise wouldn't exist causing a hazard.
It used to be generally agreed that double insulating a product was safer than providing an earthed solution but like all protection methods there are cases which can be dangerous. If you mix the systems you are also going against the manufacturers design who has specifically provided a double insulated solution. This would not be good news if it caused an incident.

Incidently sending static down the earth lead should not cause an issue to the RCD as they are not connected to the earth. They detect an inbalance between live and neutral to work so this shouldn't be a problem.

 

[guineafowl21]

+1 for @porker ’s comments.

If the static voltage is developing between mandrel and frame, then those are the things you need to electrically bond together. Your copper tape idea should work.

 

[Keato]

Hi all, ive been testing it out & meant to reply earlier than today. As seen in the video I wasn't using the tailstock since I figured the ring mandrel would be secure enough to hold the wood ring. I know there was a wobble too, it wasn't running fully true.

Ive since used the tailstock & no more electrical arcs from mandrel to tool rest & also it runs true now.

Thanks for the replies, I didn't expect all these replies

Im guessing because I'm now using the tailstock I don't need to use the copper tape idea. I assume by using the tailstock its now grounding itself?

 

[minilathe22]

I believe the tailstock is a route for the static to go through instead, so it no longer builds up and jumps across to the toolrest. However static electricity is a bit fiendish so I make no promises about your problem coming back! But yes I don't think you will need the copper tape now.