Huge numbers of sewing machines have been manufactured over the years. The older vintage machines are virtually indestructible, indeed one highly skilled and experienced seamstress told me that she still uses a 1929 treadle machine as her daily workhorse. Newer machines, especially the very cheap ones, have many more plastic parts and a much shorter life. Nevertheless, the life and effectiveness of any machine can be extended with simple maintenance, and my aim here is to show you how.
For demonstration purposes in this Instructable I will use a vintage machine probably dating from the 1950's or 60's because it's easier to show the mechanism, however, all machines work in the same way. If you can get hold of such a machine, so long as it's complete, you should be able to keep it running indefinitely and certainly much longer than a modern machine.
You can find an expanded version of this Instructable, including a description of sewing machine principles and common problems and their solutions in the Sewing Machines page on the Restart Project wiki.
Many spare parts, particularly for older machines, are readily available on eBay and probably elsewhere.
Step 1: Removing Fluff and Dust
The first thing to do is to remove all dust and fluff, wherever you can find it. Between the feed dogs is a favourite place for it to collect. Remove the needle, the foot and the needle plate to facilitate cleaning. The needle plate is a plate beneath the foot with cut-outs through which the feed dogs protrude, generally secured by one or two screws. Where the dust and fluff has become matted you can pick it out with a pin or a needle, otherwise use a brush and/or a vacuum cleaner crevice tool. You can use a can of compressed air or simply blow but there is a risk you might just blow the fluff further into the mechanism. Look out for any pieces of broken needle which might have come to rest here and could jam the mechanism.
Also, check for and remove any dust, fluff or pieces of broken thread where the thread passes between the discs of the upper tension adjuster, and at any other points in the threading path of the upper thread where it might have collected. Good quality thread sheds less fluff than cheaper brands and so is advised.
Replace the foot. Check the needle before refitting it. Run it between your fingers from the shank down to the tip. Any roughness can be carefully removed with fine emery, but it is better replaced if it has seen more than 6 - 8 hours' service. Always replace a bent needle as it will cause nothing but trouble.
Step 2: Checking the Bobbin
In a vintage machine the bobbin is often accessed by sliding away a plate next to the needle plate, as shown in the first photo. In modern front loading machines a very similar mechanism is accessed from the front of the machine. In modern top loading machines the bobbin is dropped horizontally into a mechanism in front of the needle plate.
Many very old (like pre-war) machines have a completely different bobbin fitting into a bullet-shaped shuttle which is thrown through a loop in the upper thread to make each stitch.
On a vintage machine as shown, the mechanism is hinged on a wooden base and can be lowered into a horizontal position and rested on a pile of fat books for easy access to the underneath. The remaining photos were taken with it in this position.
Remove the bobbin and bobbin case and remove the bobbin from its case. Blow out any dust.
The bobbin case fits into a bobbin case holder which rotates as the machine operates. It should be easily removed, for example by releasing a pair of clips on a retaining ring.
The bobbin case holder has a sharp point known as the hook (shown in the last photo), designed to catch the upper thread so as to engage it with the lower thread and make a stitch. Run your finger over this and if it feels rough (probably due to needle strikes) then smooth off any burrs with fine emery. Take care to reassemble it correctly.
In the case of a second hand machine, make sure that all the bobbins that came with it (and any extra ones that you buy) are of the right sort. There are several types, superficially similar, and the wrong ones will cause problems if they work at all.
Step 3: Lubrication
This is easy on a vintage machine. The bottom mechanism is accessed by tipping it on its side as in the previous step, and the top mechanism can generally be accessed by removing a couple of screws retaining the top cover.
On a modern plastic machine you will generally have to remove a number of screws, and you may then have to release a series of clips holding 2 halves of the plastic case together. Probe the crack between them with a thin spatula or blunt scalpel or thin knife in order to determine where the clips are. Take care not to insert it too far or to damage the plastic. Angling the spatula so as to lift one side of the case whilst depressing the other should release a nearby clip. Insert an old credit card, plastic prying tool, guitar plectrum or anything similar in the gap so created to prevent the clip re-engaging while you probe for the next one. Stubborn refusal of the case to come apart often means there's one more screw, possibly hidden under a label or a rubber foot.
Having gained access to the top and bottom mechanisms, gently turn the hand wheel to see which bits move. Anything that moves needs oiling on its bearings, joints or sliding surfaces, except for nylon gears, wheels or cams - these are generally greased for life.
Use only sewing machine oil. Never use bicycle oil, or motor oil, or grease, or olive oil, or Vaseline, or anything else. None of these are sewing machine friendly.
Apply no more than a drop of oil to each bearing or connection. Wipe away any excess before it has a chance to drip.
In the case of a vintage machine that has been out of use for a long time, the mechanism may be very stiff or have seized up completely. Oil it thoroughly (but wiping away any excess) and leave it for a while for the oil to penetrate. Repeat as necessary until it operates smoothly.
Step 4: Checking the Tension
It's important to check the bobbin tension as you will get poor results and possibly broken or snagging thread if it's wrong. Fit a bobbin of thread to the bobbin case and thread it under the tension spring. Suspend it by the thread. The tension is correct if it is just sufficient to support the weight of the bobbin and case. Shaking it gently should unwind just a little more thread. Adjust with the screw in the tension spring. If you have any difficulty, make sure there isn't any fluff or pieces of broken thread under the tension spring.
Step 5: Checking the Bobbin Winder
Examine the bobbin winder. This often engages with the hand wheel by means of a wheel with a rubber tyre. If the tyre is worn or cracked or perished, replace it. Spares are generally easy to obtain.
Try winding a bobbin. The thread tension should be sufficient to produce a neat and tight (but not excessively tight) pile. Badly wound bobbins can cause trouble.
(I don't have any pictures of a bobbin winder as it's missing on my machine. I wind my bobbins on a piece of dowel fitted to the chuck of an electric drill.)
Step 6: Checking the Electrics
Before touching any of the electrics, double check that your machine isn't still plugged in.
Smooth operation of the foot pedal is essential otherwise it will be very hard to sew successfully. It may simply need lubricating. On older machines it will contain a rheostat, which is a variable resistance wired in series with the motor. Newer machines will more likely have an electronic speed control similar to a dimmer switch.
You will need to examine the foot pedal to determine how to disassemble it. Do not use sewing machine oil, but rather any light lubricating oil, or grease on sliding parts, and keep oil and grease away from all electrical contacts.
Also, check the motor belt tension. You should be able to adjust it by loosening the screws or nuts on its bracket. If the motor is sparking excessively or doesn't appear to be working well, check out the Electric Motors page on the Restart Project wiki. Replacing the brushes or cleaning the commutator might be necessary. If the motor bearings seem to need lubrication you should use grease specially intended for electric motors, preferably as recommended by the manufacturer.
A replacement bulb is easily fitted on older machines but may be wired-in and not so easily changed on newer ones. Consider replacing a filament bulb with a more modern LED equivalent, which will run much cooler. However, if the bulb needs to shine mainly downwards but the LEDs in a LED bulb appear to face sideways it may be less suitable. Take the old one with you to make sure you get a new one with the same sort of base.
Step 7: Checking the Timing
If you are getting unexplained broken threads, it could be that the timing needs adjustment. This is beyond what can be covered in an Instructable at this level and may be best left to a professional with the appropriate service manual, but it's not too difficult to see whether this is indeed the problem.
You need to be able to see the needle and the hook at the point where the hook catches the top thread. In the photo, I've turned my machine on its side so I can see the underneath, and I've removed the bobbin and and the plate which holds the bobbin carrier in place. I had to hold it to stop it dropping out as I turned the handwheel.
With the needle threaded, turn the handwheel until the hook passes the needle, whilst holding the free end of the thread taught, but without pulling on it. The photo shows the thread having been securely caught after the handwheel has been turned a little further.
The tip of the hook should pass the needle just after it has reached its lowest point. Typically, the needle should have risen 3/16 of an inch (1/10 of an inch, or 2.5mm). At this point, the rising needle causes the thread to go slack and form a loop which is caught by the hook.
Turning the handwheel still further, you should see the thread drawn around the bobbin (if you have it in place) so as to make a stitch.
If having come this far you've got the bug, and if the alternative is to scrap the machine, by all means search online for your make and model of machine with the key words "timing adjustment" appended, and you should at least be able to see what is involved in adjusting the timing. You need to ensure both that the lowest point of the needle brings the eye to the right level beneath the hook, and also that the hook passes the needle after it has risen by the prescribed amount. These settings and how to adjust them should be given in the machine's service manual, if you can get hold of it.
Step 8: And Finally ...
I hope you have enjoyed getting to know your machine better and overcome the fear of looking into quite an intricate and a very ingenious mechanism. If you have a good quality machine, hopefully it will now be purring away contentedly like a cat that's had the cream.