Introduction: Fix a Power Tool

if you ever come in touch with an old power tool don't trash it, also if it's not working anymore.

Old tools were very simple in construction, but they also were built to last long. Since you will not find complicated electronics in them, you can disassemble them and look how they work. In most cases you will find out what is wrong, and fix it or ask to someone to do that.

In this specific case I found an old Italian brand electric sewing machine. Construction quality is great, very heavy and solid. At first sight it has a problem in electric wiring, let's see how to make a good repairing job.

Then we'll see that it also need some work on the motor.

Step 1: Fix the Wires

Wires are badly repaired and wrapped with package tape. When you see something like that don't try to connect the tool to the wall plug, if a shortcut will happen it can damage the tool and also your house network.

One way to fix it is cut the wires, and solder them together inserting them previously in shrinking tubes as isolation. but the best solution is to short the cable of all the damaged length, and make new connections inside the tool.

Step 2: Open the Case

This solution obviously obligates you to open the tool case, but this could be a good chance to look if everything seems ok before turning it on. You can also add oil or grease on all the mechanical gearing.

Usually you only need some types of screwdrivers, pay attention to use the right one, since you will be in bad troubles in case you strip the screw head.

At some stage of the disassembly you should reach the cables extremities. Stop here, don't open the contact screws before looking at the wire colours!

Step 3: Check the Connectivity

After writing a schematic with wires colours and corresponding plugs, you can open the contacts and extract the wires. In my case I need now to remove the clips, and I see that the wire is not the original one, so I have to write down a second diagram with the correspondence between two colour sets.

Finally you can cut the wires some inches before the clips, or you also can change the entire cable.

Step 4: Connect the New Cable

Now you can insert the shorted/new cable in the case hole.

You can be surprised but this is a critical stage... indeed I forgot to insert the shrinking tube! So remember that you can't do that in a second time, insert one or more shrinking tube pieces before inserting the wire.

Then you can connect all three wires to the correspondent screws. Close also a plastic cover if present.

Step 5: Assembling

After assembling all the covers, and tightening all the screws, is time to shrink your isolation tubes, which here are used to strengthen the wire and avoid it will wreck again in a short time.

I don't have the shrinking tube in the pictures, but I should have had it.

Step 6: Motor Turn

After fixing the power cable I turned the sewing machine on, and it worked. But pushing the pedal to obtain low speeds the machine didn't work, and some smoke came out.

With a further inspection I discovered that the commutator of the motor was not in good shape, and when powered, a lot of sparks were generated in that point.

Step 7: Repair the Commutator

So I had to open all the motor gauge to reach easily the commutator.

In the pictures you also see the motor brushes which are in most cases the reason that why old power tools doesn't work anymore. You can easily extract consumed brushes without dismantling too much, and you can find new brushes for cheap. Brushes are good in my case.

As you can see from the detailed pictures the commutator is a bit consumed, but not enough to need a complete rebuilding (see this instructable if you need to do that). I think that copper was spreaded from contacts to the adjacent ones, and electricity passes through the isolation.

I decided to scratch the isolation stripes with a thin screwdriver and then to polish all the contacts with sand-paper, and I obtained the result you see in second picture.

Step 8: Assemble the Motor

Before assembling the motor, check it and clean all the parts which are probably filled with dust and dirty, as the bush you see in the picture, which had the old exhausted filler in the cavity.

Assemble all the pieces back together, in the reversed order you dismantled them. Tighten all the screws, and add oil if you see rusted parts.

The sewing machine (and I hope every power tool you fixed in this way) is nor running great and I'm ready to make awesome project with leather and fabric!


Phil B (author)2014-10-23

In step 8 there is an old paper capacitor on the motor. My mother had a kitchen food mixer that would not run. It also had a capacitor and was almost as many decades old as I was at the time. That capacitor had failed, but there was no visual indicator. Capacitors do dry out and fail in time. Even though the machine is working, a new capacitor could not hurt. Just match the voltage rating and the capacitance amount. The new capacitor will not be paper, but could be mylar or something else. It will also likely be a bit smaller physically, which is a good thing.

andrea biffi (author)Phil B2014-10-23

Thanks Phil, that's very useful, I will probably add it to the description!

Phil B (author)andrea biffi2014-10-24

Low voltage capacitors are easy to find at Radio Shack, but capacitors for line voltage applications are not so easy to find there. You may find a good electronics parts store in your area, but, since there are fewer consumer electronics devices repaired rather than replaced and fewer home hobbyists building devices, those are more difficult to find, too. However, there are on-line suppliers who can provide what you would need. Still, in the old days you could take the defective item to a sales counter and the clerk knew how to read obscure codes to make certain you got the right replacement, in case the information was not straightforward.
You can always use a capacitor rated at a higher than needed voltage, but not one rated at a lower voltage. The capacitance value should be fairly close to that of the old capacitor. A different capacitance value can sometimes change the way the device functions, depending on the needs in the application.

seamster (author)2014-10-23

Nice work, my friend!

Way to tear into that sewing machine and fix it up. Can't wait to see what you're going to make with it!

andrea biffi (author)seamster2014-10-23

Ah, I wondered if you were the first to post a comment on this my last ible! ;-)

About This Instructable




Bio: I'm an Italian freelance structural engineer, graphic designer and photographer. I'm also investigating electronics, robotics and science in general. I enjoy hacking and ... More »
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