Hello faithful readers.  In conjunction with woodworkers safety week, I am happy to present to you with an article I have been working on, and some of you have seen in rough form.  Many of us think about woodworkers safety as using the correct guards on our saws, using pushblocks when we cut or join, or using respirators when we sand.  One thing that is often overlooked is maintaining aging tools, whether they be ours, or bought second hand.  This is just as important as safety equipment itself.  A poorly maintained tool is an unsafe tool.

This time I am writing about an adventure of much peril and danger: I decided to rewire the miter saw.  Okay, maybe not THAT perilous and dangerous as I made it out to be.  The saw needed a lot of TLC, and was part of the long list of tools I inherited from my father in law.  I had been getting by using the old power cord, which, as you can see from the picture, had been taped with a different color of electrical tape every time a new crack in the insulation developed:

(Click image for full size)

Different projects around the house caused me to keep pushing back replacing the cord, because “It just worked good enough to get the job done”.  As all of you know, that’s not the mentality you should have around AC electricity and spinning blades, and I am ashamed that it crossed my mind that I was doing something that could be harmful.

Anyway, I pulled the saw apart (obviously, removing power from it first), and found this lovely Gem right inside of the casing for the handle:

(Click image for full size)

Yes, the insulation had dried, cracked, and completely removed itself from the conductive wire.  Leaving itself open to short to just about anything on the inside of the chassis.  Worse yet, this is an UNGROUNDED saw, so, the ground would have been, um, me.  Why didn’t this shock me, you ask?  The casing for the saw is plastic.  Nonetheless, if it found it’s way down to the base of the saw, the blade arbor, or anywhere else, I would have been in trouble.  Also, the insulation was cracked BEFORE the trigger on the saw, which means the saw would not have to have been in operation to electrocute me.

The fix:  I had some brand new REALLY thick computer server power cables at my disposal (These were rated higher in amperage than the saw was intended for, and came with a chemical and UV resistant outer insulation, that’s what the package said anyway).  It was a relatively minor effort to pull the old cable out and install the new one.  Here is the end result with it all closed up again:

(Click image for full size)

I think it turned out really well, and have no other hesitations about using the saw now.

Some side notes to remember when rewiring a saw (or anything motor driven):

1) Regardless of your relation to the blade where you are making the repair, remove it from the arbor.  There’s no telling how that saw might have been built, or if there are any fractured components due to stress that are willing to break at any moment.  Luckily, the motor windings were inside of the casing, and the armature unit was connected to the saw arbor.  They attached to each other by a bearing at the end of the assembly.

2) Remove the brushes that send current to the motor.  I neglected to do this before I pulled the casing off of the windings.  This caused the brushes to spring all of the way forward.  If I had not remembered they were there, I would have tried to reinstall the motor windings in the housing which would have led to  cracking them or breaking them.  Either way, they would have been ruined.  Motor brushes are generally always accessible from outside of the unit for easy replacement if they wear out.  They are always spring loaded to keep pressure on the windings.  In the past, I have broken more than my fair share of motor brushes as a welder repair technician.  I never take it easily.  We’re talking projectiles flung across the shop with choice words attached here folks.  For those of you who don’t actually know what electric motor brushes are, here’s a picture of what one looks like outside of the saw:

(Click image for full size)

Basically, they are spring loaded devices that transfer electricity from the power switch (or where ever) to the armature on the motor assembly, causing it to spin.

3) Always replace power cords with proper 3 prong cables where possible.  This was an all plastic case, so I didn’t have an option for grounding it, anywhere, but if you can, do it.  And on that note, make sure the cable is either rated for the same amperage, or higher than the cable you are replacing.  (If you suspect it was mis-wired in the past, take a gander at the motor specification plaque on the unit, and go from there)

4) This is perhaps one of the tips that goes in the book of DUH, but ALWAYS, check, and recheck, that there is no power going to the unit before servicing it.  Not only is there electrocution at risk, but spinning components that are just itching to deform something on you, or a near bystander’s body.

5) KNOW what you are doing, don’t just think you know.  If you haven’t ever worked with electricity before, or are uncomfortable around it, then don’t do it.  Have someone who is qualified do it for you, or supervise you if you are the learning type.

In conclusion, I am glad the saw is rewired properly, and, more importantly, I’m glad it didn’t injure me in the events leading up to the repair.

2 Comments »

1. 

   [...] The Ramblings of a Crazy Man - Rewiring a Saw….I Should Be Dead [...]

   Pingback by Tuesday’s Safety Week Links | The Wood Whisperer Woodworking Video Podcast and Blog — May 5, 2009 @ 11:55 am

2. 

   [...] Rewiring a Saw & I Should Be Dead [...]

   Pingback by Safety Week 2009 In Retrospect | Woodworker's Guide — May 10, 2009 @ 11:54 am

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