John in CR
100 TW
Tonight I was trying to check whether I should replace the bearings in my 9C covers before I close it up, so I stuck the end of my finger in the hole of the bearing and gave the first cover a spin. Instead of a smooth feeling I can feel the bearings rolling and almost a tick on each revolution. That answered that question in a hurry...new bearing for sure since this will run out of wheel at 147V off the charger, so probably 1krpm or more.
That's not the biggie though. As the cover slows I feel my finger forced back and forth by the spinning cover. Uh oh, so I turn the cover near vertical and spin again, and when it slowed to a stop, it turned back the other way before stopping. I do this a few times and it always came to rest at the same rotational position, sometimes it rotated back the other way nearly 180° to come to a rest with the heavy point down. I figured the hole for the bearings was off center, but nope the edges and lip that locks into the magnet retaining ring are nice and true.
Then I start thinking maybe I drilled my ventilation holes inconsistently, but I look closely and it appears that I actually took more material out of the side that's heavy and there's even a ridge that was cut when the machine cut the retaining lip that doesn't exist on the light side. I don't have the kind of caliper for measuring a thickness in the position, but from the best I can tell with the caliper I have, the aluminum at the curve in the cover is well over 1mm thicker at the heaviest point than it is at the lightest.
The cover for the other side has the same issue. I wonder if this could be part of the singing 9C covers issue.
Here's are pictures of the inside edges of the cover at the lightest point and then turned 180° to the heaviest point. Notice the edge cut where the material is thicker that occurred when the machine cut the retaining lip and axle hole in the cast blank motor side cover.
Now that I've identified that the cover is significantly out of balance, though the stator will still be centered for a consistent magnetic gap, what do I do to fix it? Could I get accurate enough for 1000-1200rpm by taking a grinding wheel to it and remove material from the heavy side, and then test for balance by clamping onto the inner race of the bearing with two nuts and a threaded rod clamped in a vice and spin the cover up using the wire brush wheel on my angle grinder?
I welcome any ideas for a fix.
John
That's not the biggie though. As the cover slows I feel my finger forced back and forth by the spinning cover. Uh oh, so I turn the cover near vertical and spin again, and when it slowed to a stop, it turned back the other way before stopping. I do this a few times and it always came to rest at the same rotational position, sometimes it rotated back the other way nearly 180° to come to a rest with the heavy point down. I figured the hole for the bearings was off center, but nope the edges and lip that locks into the magnet retaining ring are nice and true.
Then I start thinking maybe I drilled my ventilation holes inconsistently, but I look closely and it appears that I actually took more material out of the side that's heavy and there's even a ridge that was cut when the machine cut the retaining lip that doesn't exist on the light side. I don't have the kind of caliper for measuring a thickness in the position, but from the best I can tell with the caliper I have, the aluminum at the curve in the cover is well over 1mm thicker at the heaviest point than it is at the lightest.
The cover for the other side has the same issue. I wonder if this could be part of the singing 9C covers issue.
Here's are pictures of the inside edges of the cover at the lightest point and then turned 180° to the heaviest point. Notice the edge cut where the material is thicker that occurred when the machine cut the retaining lip and axle hole in the cast blank motor side cover.
Now that I've identified that the cover is significantly out of balance, though the stator will still be centered for a consistent magnetic gap, what do I do to fix it? Could I get accurate enough for 1000-1200rpm by taking a grinding wheel to it and remove material from the heavy side, and then test for balance by clamping onto the inner race of the bearing with two nuts and a threaded rod clamped in a vice and spin the cover up using the wire brush wheel on my angle grinder?
I welcome any ideas for a fix.
John