Damaged Power Cord Repaired With Shop-Made Mold

We’ve likely all seen a power tool with a less-than-functional strain relief at one end of the power cord or the other. Fixing the plug end is easy, but at the tool end things are a little harder and often not worth the effort compared to the price of just replacing the tool. There’s no obsolescence like built-in obsolescence.

But in the land of Festo, that high-quality but exorbitantly priced brand of premium tools, the normal cost-benefit relationship of repairs is skewed. That’s what led [Mark Presling] to custom mold a new strain relief for a broken Festool cord. The dodgy tool is an orbital sander with Festool’s interchangeable “Plug It” type power cord, which could have been replaced for the princely sum of $65. Rather than suffer that disgrace, [Mark] built a mold for a new strain relief from two pieces of aluminum. The mold fits around the cord once it has been slathered with Sugru, a moldable adhesive compound. The video below shows the mold build, which has some interesting tips for the lathe, and the molding process itself. The Sugru was a little touchy about curing, but in the end the new strain relief looks almost like an original part.

Hats off to [Presser] for not taking the easy way out, and for showing off some techniques that could really help around the shop. We suppose the mold could have been 3D-printed rather than machined; after all, we’ve seen such molds before, and that 3D-printed dies can be robust enough to punch metal parts.

25 thoughts on “Damaged Power Cord Repaired With Shop-Made Mold

  1. Hmm – it’s a nice experiment but …

    I would be concerned more about the safety of that lead after been pulled out like that the cable retention is now non existent and the cables have been stretched.

    The damage is more than just what you can see.

    What he did could have some use for the replacement of molded strain relief when replacing a cable. But appears a porous mold would be required to allow the sugru to set fully. Maybe a timber mold would work better or is there an activator for sugru?

    1. Yeah, without being able to inspect the buried part of the cord I’d worry about the safety. I suppose the current draw isn’t going to be very high, but I’ve seen enough failures in yanked cables to make me think the savings here may well be “false economy”.

      The repair is cool enough for the attention given to the mold-making process, and I learned not to make a (nearly) gas-tight mold for something that needs the outside environment for curing. I would have recommended cleaning and scoring the areas to adhere to the Sugru, but the repair sure looks nicer than a lot of mine!

  2. Sugru is good stuff. I think a 2x small pvc pipe halves used as a mold could have accomplished something similar without all of the lathe muss and fuss. That said, I did learn a few things, especially about adjusting a 4-chuck lathe for roundness.

    1. @Techknowledgist, because of your comment I watched the video, a video in which a man makes a die that is pointlessly perfectly concentric, and then proves to be just pointless, because on removing the die the man cleans up the finished product with soapy fingers, a task that could have been done 48 hours earlier and only taken 30 seconds, but yeah the jaw trueing thing will be good for irregular shapes.

  3. My biggest complaint about Sugru is that it expires like Milk or Eggs in about the same amount of time. I bought an 8 pack, used one and a year later went back to use more only to discover that the 7 remaining packets expired shortly after I bought them.

    That being said the product works beautifully and the one item I did repair looks great.

    It looks like this job could have been done with a couple layers of shrink tubing.

    1. The trick with storing Sugru is to keep it in a refrigerator. In my experience it can last for 18-24 months without going off. I use the black and white Sugru regularly but the coloured stuff only occasionally so fridge storage is very handy.

      I’ve repaired several power cords (and lots of other stuff) but have never needed anything but my fingers and a flat surface upon which to roll the finished repair in order to get a smooth finish.

    2. I’ve used long past expiration (refrigerated) Sugru to good result. One problem with long storage is that the emulsion of filler and binder starts to separate out.

      To mitigate that, I spent some extra time to mixing it in its wrapper. Then, once opened, I rolled it out, folded it over on itself, and rolled it out again to more evenly distribute things. While well distributed, there may still be layers, so I smush it up it up to scramble the layers before finally using it.

    1. Isn’t there potential corrosion problem using that type of silicone? They are usually air-hardening using acid catalysts AFAIK so there should be acid left to do some “work” right?

      1. It is not an acid catalyst, but the most common type chemically produces acetic acid as the byproduct of the curing reaction. But there is another type, suitable for acid sensitive surfaces like marble or electronics. Just choose that type.

    1. Pretty much most 2-part silicones will do. I would highly discourage from using anything that needs moisture or air to cure.
      Epoxy resin is hard and thus very unsuitable for strain reliving a flexible cable, also not suitable.

  4. Looks like the cord has been wrapped around the tool habitually. This is the way this happens, not from use. Don’t wrap cords around things. I would put contact cement or silicone on the exposed area, then milk the jacket towards the end, stretching it over the wires. It will close up to the plug neatly. Dope some more over, it will stay.

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