Belt Tension on Moulder

Pros troubleshoot a belt-slippage problem during a new moulder's break-in period. August 31, 2005

I'm running a Leadermac moulder. Recently, the last bottom head belt slipped. I assume it needs to be re-tensioned. What is the rule of thumb for how tight to make the belt? The moulder is still in its break-in phase. Is it likely that all the belts will need to be re-tensioned?

Forum Responses
(Solid Wood Machining Forum)
From contributor R:
I think the rule of thumb of belt tension on most machines is just tight enough to do the job without slipping. If you over-tighten belts, it can shorten the life of bearings. I doubt if all the machine's belts need to be re-tensioned. Probably a fluke.

From contributor C:
Leadermac should be able to provide their specs for your machine. Follow their guidelines. As a general rule, check tension on new belts weekly as they stretch. After that, check belt tension monthly. Also check the belts for proper tracking, as mis-tracking belts wear out faster.

From Dave Rankin, forum technical advisor:
Depending on the type of belt that you are using, the tension can vary. Most belts that slip are either v-belts or flat belts. With v-belts, check alignment first and then adjust the belt until you have about 1/32" pull together. This means lock out the machine, then grab the belt in the middle (between the pulleys). If the belt has more than about 1/32" of squeeze, tension it.

On flat belts, you can follow close to the same rule. The problem is with some of the thicker belts. They have to be tighter to work well. This can cause possible bearing problems and in some cases, chatter.

From the original questioner:
I had already checked the belt (flat) on the offending spindle; it seemed tight to my unfeeling hands. Haven't checked since your email, will do so tomorrow. 1/32" squeeze seems very little. Just to make sure, is the squeeze the inward deflection the belt should have with medium squeeze pressure?

From Dave Rankin, forum technical advisor:
The way that you described it sounds about right. Avoid overtightening, as this can damage the bearings. Also, do not use belt dressing, as this does not work in this application. If the belt still seems to slip, go a little tighter or try a different brand of belt.

From the original questioner:
I tightened the belt on the offending spindle, restarted, tightened another horizontal belt, restarted and tightened the third horizontal belt. Spindles come to speed immediately, rather than ramping up, as before.

I ran about 500 lineal feet of six inch flooring, uneventfully. Switched to eight inch, and the first piece came out with a .110 inch difference in thickness, from side to side (.750-.640"). I don't know what could have caused this. I checked the top head for parallel to the bed, and also the pressure shoe, but everything seemed fine. Fiddled with the last head, etc. Next ran a piece through and it came out perfectly! Go figure!? Went home.