A Disclaimer!
Firstly, (and I should have thought of this myself before it was pointed out by a fellow member! and many thanks for that! ) You should ONLY attempt the procedures in this workshop if you are sure you can do the following:
1) Ensure that the electrical tool is completely disconnected from its power supply (that should be easy enough!)
2) Remove the two halves of the plastic body without having to use a large hammer! (You'd be surprised!)
3) Are confident enough to use a soldering iron. (Having worked for a while in the electronics industry I sometimes forget that not everyone has ever needed to melt solder!)
For those of you adding lighting to their models, there is nothing in this workshop that is beyond your capabilities. This IS an electrical apparatus though, albeit a low voltage one (12v) but if you are unsure about ANY part of this, take your broken rotary to a professional to get it fixed - far better safe than sorry!

Ok, safety lecture over (and there's no harm in reading it, although, has anyone else heard rumours of exploding computer VDUs? )

How to repair a broken power cable on a Dremel type Rotary Tool.

This little workshop was an idea which was forced upon me today as I went to use my Rotary tool to shape a piece of wood for the Victory. (Which I still haven’t done!)
Turning on my rotary produced – absolutely nothing. The only other time this had happened was when the silly thing wasn’t plugged in. My rotary is part of a lovely tool set made by a company called Rotacraft that I bought from Maplins a few years ago, it comprised of three separate tools, a mini jigsaw, a mini orbital sander and the rotary. All three of them use identical bodies and motors, with a different ‘head’ to each one and all use the same power supply transformer which means you have to plug in whichever one you want to use of course. Those of you lucky enough to possess cordless Dremels needn’t bother going any further – those who have wires sticking out their um’ ends, read on.
Checking the end of the rotary’s lead I could see that is was in fact plugged in to the transformer and the transformer itself was plugged into the main (this was also obvious from the fact it was warm to the touch). I twiddled the tool lead plug around a bit (as we do) just to make sure it was in tight and tried again – success! Off I went, ready to begin making sawdust and the little blighter cut out again.
By now it was obvious that something wasn’t right so I tried twiddling the lead again but the end up by the tool itself. It started up again and promptly died a sudden death. A close inspection revealed what I had suspected, the twin lead cable was damaged right up beside the rubbery moulding that is supposed to protect the cable from damaging the inside components if it was pulled too harshly. One of the two wires was partially broken giving an intermittent connection. As I tested its condition it broke completely as you will see below.
A rotary with no power is pretty useless so a repair was the next step, since I had to do this anyway I thought I’d make a record of it in case anyone else finds themselves in the same boat!
The first step (after removing the chuck and any tools from the front AND unplugging from the transformer) is to remove the outer casing of the tool to have a look at the innards. As I said, this is a cheaper ‘clone’ of the Dremel, the real thing, being far more expensive may have more bells and whistles and may be more difficult to get inside of. If anyone has a Dremel (sick or dead or you have taken it apart, please post a photo of how you get it apart on this thread for others to see!)
As far as the Rotacraft is concerned, there are six self tapping screws as indicated on the first picture, each one has a tiny washer, some come out with the screw, some stay put so be careful when you turn the body half over. Use a fairly small Phillips screwdriver to remove all six and then, instead of trying to figure out why it still won’t come apart like I did, simply unscrew the black plastic head from the front of the tool and then gently prise the left hand half of the casing off using a flat screwdriver head or similar.
You should now have something like in the first photo. The interior is quite simple to look at, the wires come in through the rubber block with the marked one of the pair (white dashes in this case) going to the on/off switch contact and the other going to the PCB. The PCB houses the speed control circuit consisting of a rotary potentiometer (a variable resistor in other words) and a few other components. This is wired to the motor and the only other moving part is a little brass knob and spring which engages into a hole on the motor shaft to tighten and loosen the chuck.
The next set of photos begins with the cause of the problem, a broken wire on the power lead just beyond the rubber strain relief. The first task is to pull the switch out from the plastic body and to de-solder and remove the two wires from the contacts. The best way to achieve this is with a useful little tool commonly known as a “Solder Sucker” or “De-Soldering Tool”. These can be obtained from any good tool supplier, the one featured here came from Maplins again. Not too expensive, expect to pay from £5 to £10 depending on the source. The suckers work just like a surgical syringe in reverse, pushing down on the black knob sets a powerful spring ( I first typed in the correct phrase for setting a spring but then thought FILTER! That word definitely won’t get through!) Once ‘set’ pushing in the black button on the side of the tool releases the spring backwards and instead of injecting, the tool sucks the molten solder back up its nozzle.
So, applying the tip of the soldering iron to the switch contacts, the solder was removed and the wires pulled out of the contact holes. Note: if the wires won’t come right out once the solder is removed, just re-heat the contacts again until the remains of the solder melts and gently pull the wires free, there is usually no need to re-suck the joint. You might ask at this point why both wires were removed when only one of them was connected to the broken cable – well, you can ask!
Anyway, on to the next part! Once I’d removed the correct wire at the second attempt, the switch was free of the body and PCB and easier to work on (And that’s what I’m sticking to!)
After the switch was removed I then removed the other wire from the PCB. This one you have to be a little more careful with, applying just enough heat to melt and de-solder the joint but not so much that the copper track and pad (the circular disk that the wire or component leg is soldered to) comes away from the PCB surface. Largish pads like this one aren’t usually too much trouble, but if it’s a tiny little one for IC’s (chips) or very small components its very easy with too much heat to melt the varnish which seals the copper down and they can lift off. No problems here however and both wires came out cleanly.
The next step is to cut off the damaged cable and then to try and pull the de-soldered wires out from the rubber moulding. Sometimes, the wires are simply passed through the rubber block and they will come out complete with their insulation but in most cases as here, the rubber block is formed over the wires, effectively welding it to the PVC sheath. In that case you will end up with the situation as seen below, the wires will pull out, but the insulation was left inside the block. This is no problem however, simply hold the rubber block in a suitable vice (horizontally is best) and use a succession of drill bits in a hand drill to drill a hole through the block where the cable used to be until the previously cut cable end will ‘just’ pass back though the block as seen in the next photo. Pull the cable through until you have approximately the same length sticking out the inside end as the original cable had, this makes fitting it all back into the body a little easier when it all goes back together at the end.
Unfortunately, I didn’t take any pictures of the re-assembly as I needed both hands to do the work! But its essentially just a reversal of the stripping down procedure. The new ends of the wires were stripped of their insulation (the one going to the switch being shorter than the one to the PCB as before) and both wires were soldered back in place. The second wire from the PCB to the other switch contact (YES, THAT one!) was also replaced (By the way, if you do possess a digital camera I would highly recommend taking a series of photos as you go, when re-assembling, I just couldn’t remember if that second wire went into the contact from front or back, in this case it probably wouldn’t matter either way but sometimes wiring routes are very tight for space, a quick check back on the camera and there it was – simples!)
With all wires back in position and soldered on, the two halves of the case went back together, the black plastic nose cap was screwed on and the six screws went back in (noting which ones still had their washers on!)
All finished, power lead plugged back in, flick the switch and one perfectly good rotary tool again! Total time to repair (including taking the photos for this workshop) about 35mins.
So if you do get a dose of the fraying cables, don’t just junk it and don’t pay through the nose for ‘professional repairs’ in many cases, doing it yourself is far cheaper and doesn’t require a qualification in electronic repair (actually I do have one but that’s beside the point!)
I hope you will find this little tutorial of some use, maybe in the future !!

Happy building to all

Robin