Gauging Moulder Belt Tension
Different manufactures of flat belts will have their own tensioning recommendations, which are normally described as being a percentage of the length of the belt. For example, if the correct flat belt tension is to be 1%, then a 900mm (35.43") long belt has to be tensioned until the “stretched" length of the belt is 909mm (35.79").
If your moulder has "V" belts driving the cutterhead spindles then the belts are correctly tensioned if they can be deflected no more than 1/2" by average thumb pressure.
From Dave Rankin, forum technical advisor:
For different belts you can purchase belt tensioning tools. As a tech for over 20 years, I do not use them. I have found that most people can adjust the belts with some basic guidelines.
1. Make sure that pulleys are in line with each other.
2. Make sure belts are tracking straight and not walking up or down on the pulleys.
3. For V-belts, adjust to about 1/32" pull together at the center of the belt. Do not over tighten as this can damage the bearings in the spindle.
4. For flat belts, adjust to about 1/32" pinching the belt at the center of the belt. Most good quality flat belts will need to be tensioned at least once a week for the first couple of weeks and then once a month after that. Be aware that there are some flat belts that are thick and can cause problems. The thicker belts can hold a memory which can cause chatter, and can de-laminate causing finish problems.
5. For timing belts, tension to no more than 1/32" tension.
6. Check belt tension once a week for the first couple of weeks and then once a month after that.
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