Startup "Bang" on Unisaw

[Bill Stephenson]

I thought I would post this for others who may have the same issue. My Unisaw is 7 years old and has required little attention. Feeling that it's about time to do some preventative maintenance I removed the side cover cleaned out the sawdust inspected the trunions and tilts. Everything checked out good and I tightened the belts. When I started the saw it started with a loud bang but ran fine. I then took the blade off and ran the saw & it started normally (quiet). I put the blade back on and again I had the "bang " on start up. I then thought it was the law of physics ( body at rest tends to stay at rest etc.) I then addressed the only variable I introduced tightening the belts, so I proceeded to loosen the belt and the "bang " became diminished. I then loosened the belts to what I would call "very loose" and started the saw. It started without any "bang" noise and was quiet and smooth. Thinking the belts now may slip I ripped some 4/4 oak and I could see no slippage. I believe loosening the belts allowed for some "give" during startup eliminating the jolting Bang. Hope this may help someone as it took me a few days to figure this out.

[Leo Graywacz]

Huh, interesting.

I don't have that problem with my saw, but I do have it with my planer. And I remember tightening up the belts a few years ago. I don't remember if that is when it started though. Maybe I'll check.

[Bill Geibe]

Bill,

I think you are right - I think the slightly loose belts create a bit of slippage that give a bit of shock absorbing effect to the drive train.

Sometimes the 'bang' (my Unisaw does it sometimes, too), can be attributed to a loose drive pulley. My theory is that it is often caused by motor's torque taking the slack out of the elevation mechanism. This is caused by too much clearance at the far end of the elevation shaft where the lock nut and fiber washers are. Or maybe it's too much slack between the elevation worm gear and the arbor bracket gear. But whatever it's from, it seems to be fairly common on Unisaws and loosening the belts seems to help.

Bill