How to make an old drill insulated

Discussion in 'General Electronics Chat' started by Gdrumm, Aug 26, 2013.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    I bought an old electric drill from Ebay, a '1/4" High Power, Model 77"
    , made by Portable Electric Tools Inc., Chicago 20 Illinois.

    Its a 2 wire set up, and when I tried to clean the rusty chuck by running it against a small wire brush mounted in my table vise, it shocked me.

    So now, with gloves on, it sparks at the point of contact each time I run it against any grounded metal.

    I can run it fine if its touching something ungrounded or non metalic.

    Inside, I found a thread or two of wire near the switch, touching the housing, and I cleaned that up, but no success.
    I re-wired the plug, but no success.

    I blew it all out around the brushes as best I could, without complete dissassembly.

    Can I put a 3 wire set up on it, would that work?
    Or does it sound like a more serious problem?

    I'm guessing this is a problem with old tools?

    Any advice would be appreciated.

    Thanks,
    Gary
     
    Last edited: Aug 26, 2013
  2. JohnInTX

    Moderator

    Jun 26, 2012
    2,347
    1,029
    Nope. If you are getting sparks, you have a short to the case, probably from somewhere in the the field windings to the metal case. Maybe an internal short to the stacked field cores coupling to the armature etc. A 3 wire cord would pop any GFCI and maybe the breaker too.

    This is what double-insulated tools are all about. The mfr's address is pre-zipcode so this is an OLD tool. Over the decades, we've gotten better about electrical safety - for a reason.

    If you want to play with it, take it apart and look for insulation scraped off where any winding is in contact with the case, or as you did, look for any frayed wiring etc.

    EDIT: Back in the day, you'd take a bad motor to a rewinding shop who would strip all the wire out of it and rewind the armature and stator with new lacquered wire. But these days, its not worth it.

    I'd toss it. Sorry.
     
    Last edited: Aug 26, 2013
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    My guess it pre-dates double insulated at a time when there were often only 2 wire sockets, and has a metalic case?
    It could be the carbon from the brushes has tracked down one of the brush holders, so unless you can find the ground leakage and repair it and fit a 3 wire cord, it might turn out to be a unusable antique.
    Max.
     
  4. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    Thanks alot,

    I'll break it down tomorrow and look for a visible short.

    Hopefully I'll find one I can fix.

    Gary
     
  5. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    I agree with the diagnosis but the symptoms still seem a bit curious to me. What could explain the fact that he only gets a jolt when he touches the drill to something that's grounded? It seems to me that a live case would shock you any time you drilled anything, regardless of if it's grounded. Actually I would think that you would be shocked LESS if you drilled something that's grounded, as it provides a lower resistance path to ground.
     
  6. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    strantor, I believe you have read the description too quickly.
     
    strantor likes this.
  7. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    So, the cure is to have it re-wound and attach a 3 prong cord with the case connected to the third wire. It's a decision about price vs desire. Take your pick.
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    If it has been stored somewhere moist the motor windings could be leaking a bit. If you don't have a megger to test the motor insulation you could try a simple test of drying the motor out by leaving it in the hot dry sun for a few days (just remeber to bring it in each day when the sun goes down!).

    In Australia all metal motorised equipment needs to be grounded to the 3rd prong on the power outlet, so it can't shock you. And if the motor leaks to ground, it just trips off the ground fault safety switch in the household fusebox.
     
  9. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    If you find the short and fix that, you should then definitely rewire with a 3-wire cord with ground. That way if it shorts again sometime in the future the current will have a path to ground other then through you. :rolleyes:
     
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,770
    970
    Its garbage.. throw it out.
    simply amazing what some people try to save around here.
     
  11. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    easy fix this-it works every time with this sort of fault and its so easy to do-follow these simple steps
    1 pick up drill in one hand make sure it is unplugged from your wall socket
    2 take drill outside -you may need good light to carry out the next few steps
    3 locate nearest dustbin and open lid
    4 throw drill in open dustbin,close lid and BUY A NEW DRILL.....
     
  12. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    Gotta ask... Are the original windings / armature lacquered or varnished ? are the bearings - ball or sleeve - sloppy enough to allow the armature to rub the field core, or is there metallic detritus / brush dust in the verge betweel field and armature ?
    I have resurrected some real crappy looking garage-sale-neglected power tools, so see some hope for even the worst looking ...
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    For me I would regard it as a bit of a challenge, and at least give it a shot, especially if I went to the trouble of purchasing off ebay.

    Which raises the question, what piqued your interest in the first place with this oldie?
    Max.
     
  14. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    It's a hobby of sorts, I just enjoy fixing up old things.
    In this case, it's a fairly small drill, and I had one similar years ago, with a stripped out gear. So, nostalgia was the primary reason I bought it.

    Like Packratking, I enjoy the challenge.

    I'll open the case this afternoon, and post back.
    Thanks all,
    Gary
     
    Metalmann likes this.
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    Is this one of the old ones with an shiny cast aluminum case?
    Max.
     
  16. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    Yes, it's an aluminum case.
    I took it apart, no big discoveries.

    How do I check it with a meter?

    The inside of the aluminum case was scratched up a bit, I honed it out.

    New problem, the brush caps self destructed upon disassembly.

    Now I'm looking for (2) 5/16" -24 plastic screws, or replacement covers.

    No luck with ebay or Google; any ideas where to look?

    Anyway, right now, it's in a box.......

    Thanks,
    Gary
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    If you can find some plastic rod, and can find a suitable die, you may be able to make them.
    Also check local motor repair/re-winders for parts.
    To test the leakage, Ideally what you need is a megger, high voltage insulation tester, if you know any electricians they may be able to help.
    Max.
     
  18. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    Those petrified brush caps could have been the culprit. One of many possibilities. I think I recognize your name from a machinist forum; am I right? Do you have a lathe?
     
  19. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    This is not very relevant to he discussion at hand, but I have an old aluminum case drill with a brass bushing at the rear of the armature. I drilled a .07" hole in the handle so I could oil that bushing. The front of the armature has a ball bearing in a grease cavity, so that one doesn't have problems with going dry.
     
  20. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    I'm not a Mechinist, but I am on a Machinists forum.
    I don't have a lathe, but I do have a set of button dies.

    I think I can make the caps, but I thought they might be easy to find on-line.
    With Google, who knows how deep they would be in a search (I did try).

    Where I work, we are always throwing away old motors, I'll ask the electricians about caps, and testing (although "Government Work" is frowned on.

    Thanks,
    I'll post back when I succeed.
    Gary
     
Loading...