Harvey Pascoe
10-20-2011, 7:01 AM
My 1994 Unisaw started to make some noise, not much but then I am very attuned to changes in machine sounds. Plus I noticed vibration was increasing, so I check arbor bearings and motor shaft bearings as best I can in place. Putting a large screwdriver against the motor pulley and prying gently, I seemed to get about 1/16” play in the shaft, forward and back. Arbor bearings have no runout and are quiet. So I pull the motor – not a fun job – and when I get it out I can find nothing wrong with it. Dial the pulley and I get -/+ .002” runout and that's fine. Apparently my screwdriver test was moving the motor on its mounts and we misread that as shaft movement.
In the meantime, I had ordered a new motor which I no longer need from Grainger at $461.00, a good price for a new Leeson 3 hp 230V motor. The 54 lb. Motor arrives the next day (their service is great) but it turns out to be the wrong one – no mount brackets so I have to crate it up and send it back. Grainger is not arguing about who made the mistake, they'll ship me the right one but I go to pay the return.
After pulling the arbor, I still cannot detect any problem with the bearings until I get them off the arbor. Then I detect noise in the bearing race and its got very substantial runout laterally. This is not the load carrying bearing next to the blade but the opposite end which I thought surprising. But I'm told by an engineer friend that it is almost always the non load bearing end of a shaft where the bearing fails due to oscillation and an uneven load. What I should have done, he said, was to use a large screwdriver or hammer handle as a stethoscope putting one end on the bearing and my ear on the other while rotating the arbor. “You would have heard that bad bearing,” he said. He is right, of course, but I just didn't think of it at the time.
After ordering new bearings from Sawparts at $22 each, I later find that Grainger has them for $7.68. So goes my comedy of errors which has gotten rather expensive. I make this post so that others might not make the same mistakes that I did.
First, if your saw is making unusual noise or vibration is increasing, diagnose where the problem is by first removing the drive belts and then use the stethoscope trick with a large screwdriver on the arbor while rotating by hand. Then check the motor by the same means, noting that the first bearing to go is opposite the pulley end of the shafts. Bearings that are press fitted onto shafts can be very difficult to get off and can easily be damaged in the process so be sure to determine bearing condition before trying to remove them.
In fact, since the saw blade mount flange is press fitted onto the shaft and is not intended to be removed, its guaranteed that you'll ruin that bearing getting it off. I had to use a cold chisel as wedge to drive it off.
In the meantime, I had ordered a new motor which I no longer need from Grainger at $461.00, a good price for a new Leeson 3 hp 230V motor. The 54 lb. Motor arrives the next day (their service is great) but it turns out to be the wrong one – no mount brackets so I have to crate it up and send it back. Grainger is not arguing about who made the mistake, they'll ship me the right one but I go to pay the return.
After pulling the arbor, I still cannot detect any problem with the bearings until I get them off the arbor. Then I detect noise in the bearing race and its got very substantial runout laterally. This is not the load carrying bearing next to the blade but the opposite end which I thought surprising. But I'm told by an engineer friend that it is almost always the non load bearing end of a shaft where the bearing fails due to oscillation and an uneven load. What I should have done, he said, was to use a large screwdriver or hammer handle as a stethoscope putting one end on the bearing and my ear on the other while rotating the arbor. “You would have heard that bad bearing,” he said. He is right, of course, but I just didn't think of it at the time.
After ordering new bearings from Sawparts at $22 each, I later find that Grainger has them for $7.68. So goes my comedy of errors which has gotten rather expensive. I make this post so that others might not make the same mistakes that I did.
First, if your saw is making unusual noise or vibration is increasing, diagnose where the problem is by first removing the drive belts and then use the stethoscope trick with a large screwdriver on the arbor while rotating by hand. Then check the motor by the same means, noting that the first bearing to go is opposite the pulley end of the shafts. Bearings that are press fitted onto shafts can be very difficult to get off and can easily be damaged in the process so be sure to determine bearing condition before trying to remove them.
In fact, since the saw blade mount flange is press fitted onto the shaft and is not intended to be removed, its guaranteed that you'll ruin that bearing getting it off. I had to use a cold chisel as wedge to drive it off.