Gauging Moulder Belt Tension

Tips on how to set and maintain proper belt tension. October 30, 2005

I’m wondering what a good way to check for proper belt tension is. My book says 1/32" deflection. Is that in the center of the belt or near the edge? The belt is 55mm wide and the moulder is a bridgewood 757. I replaced the belt recently and tensioned to what I thought felt right, and so far so good. I checked it again and it doesn't seem to have changed. How often should I check the tension of this new belt and for that matter, all of the belts? Do they eventually get broken in to the point where they will stay at the same tension?

Forum Responses
(Solid Wood Machining Forum)
From contributor S:
Your description of the correct belt tension being "average thumb pressure of 5 to 7 lbs force" is in reference to spindles that are driven by "V" belts, and not "flat" belts. "V" belts should not be run extremely tight, whereas the "flat" belts that are used on later machines have to be tensioned to a precise amount in order to be able to transmit the horsepower from the motor to the cutterhead.

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.