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One of the first things I realized when I started working with all the different sewing machines was the differences in drive belts. Some of the differences are easy to account for and accept as historical evolution of the sewing machine. During this evolution, a person might expect that belts would slowly follow a pattern and eventually a single design would stand out. This doesn’t appear to be the case. The first successful belts were simply round rubber rings. The rubber compounds used at the time were the biggest demise to this design of belt. The rubber was simply too pliable and it stretched and flexed so much it had a short life expectancy or it was too hard and stiff that it would not consistently grip the motor pulleys and it would slip whenever it was under a load. If tightened down tight enough not to slip then motor couldn’t spin freely and it would burn up motors.
The next innovation in belts came in the shape of the belt itself. It was the commonly recognized V-belt design. Using a v shape would allow for more surface contact which would keep the belt from slipping as easily without having to tighten it so tight the motor couldn’t pull the load. By laminating the center of the belts with cloth, the flex and stretch could be controlled. The downfall of these belts came in the form of life expectancy. They were a bit temperamental to climate change and they would start delaminating after a couple years use. These belts were also expensive to build and this would lead to their being replaced by the next generation of a V style belt.
The second generation of the V-belt used a neoprene type of rubber that was stronger than the rubber belts. They were also grooved on the bottom side of the belt to help the grip of the belt on the motor pulley. This belt has proven to very reliable under all circumstances and because of its performance in the line of duty, it remains one of the industry leaders still today. The only improvements I can think of with this belt was the addition of cogs or grooves on the top side of the belt that helps the belt to stay flexible and maintain contact better on smaller diameter pulleys. Although in my opinion, they are inherently noisier than their counterparts.
Keeping in mind we are only covering the Vintage sewing machines I am going to stop here because although I know there are newer machines using a variety of different belt configurations I don’t have enough experience with them to formulate an opinion or recommendation.
When it becomes necessary to replace a worn belt or to adjust the tension on an existing belt. There are a couple simple rules that need to be followed. When adjusting a round rubber belt it needs to be adjusted just tight enough to drive the machine. It should slip slightly if you hold the hand wheel of the machine and apply full power to the motor if it doesn’t slip using this test then it is too tight and motor power is being sacrificed by pulling the shaft against the side of the bearing. This causes bearing damage after a period of time and it also causes the motor brushes to overheat and will shorten the life expectancy of the motor.
When adjusting a V-belt the same is true with the exception of the slip test. Instead of holding the hand wheel and checking for slippage I like to measure the belt deflection to establish a base point from which I will fine tune to suit my needs. Deflection is the amount of flex that can be obtained when the middle of the back of the belt is pushed towards the gap between the two pulleys when the belt is fully installed. This deflection should be approximately 3/16 of an inch. If it is less, then it is too tight, If more then it may be too loose. Too loose is always better than too tight. Adjust your belts always leaning towards the too loose end of the spectrum and your machine will love you back for a long time.
These are the techniques I use and have found will yield decent results for me. There is always room for other techniques but once I found some I was happy with I stopped looking. If you find this works for you then I am happy to help. If not, at least now you know how not to do it. And I am still happy to help.
Until next time, enjoy your machines your way and may your stray pins be found with the vacuum and not with bare feet.
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