herb
spending too much on rocks
Member since November 2011
Posts: 470
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Post by herb on Jan 10, 2022 16:56:53 GMT -5
I have a Beacon Star 15 inch vibratory flat lap. Over the last couple of years it has been getting A LOT of use polishing thunder egg halves. When I first got it, it ran fairly quietly, but over the years it slowly became more noisy. The issue is that the motor is slowly destroying itself due to the stress of the offset weight. When I first started using it, the shaft didn't jiggle at all if you tried moving it back and forth. As the jiggle got worse, I decided to give the motor shaft some support by mounting an aluminum bar with a 7/8 inch bearing that has a 3/8 inch bore. The setup worked pretty well, but the bearing and motor shaft are only connected by friction and over time the vibrations loosen things up. Now I have to pack teflon tape around the shaft after every 3 weeks or so of use because the shaft and bearing bore wear down. The bearing was just something something I had laying around. I don't know if it is even designed for this level of abuse. I destroyed the 1st bearing after about 1 year of almost continuous use and am now on a 2nd bearing. Also the motor shaft is slowing getting ground thinner due to the slack between the bearing and the shaft. I was wondering if anyone has any ideas of how this setup could be improved. The motor shaft has a flat side so a bearing with a setscrew would be a great solution but there is at most only about 18mm of space between the bottom of the offset weight and the top of the plate the motor is mounted to. Last year, I saw online some bearings where the inner bore is "D" shaped instead of round which I guess would also work, but I think the ones I saw were in the $40 to $50 range which seems like a lot for a tiny bearing. Plus I didn't know how heavy duty they were and didn't want to spend the $ only to have the bearing get destroyed in a month or 2. Also, now that the motor shaft is worn I don't know if a "D" shaped bearing would fit tight without there being some play. I guess I could put a sleeve on the shaft to fix that, or maybe just get a new motor. Hear are some pictures to show the current setup: Bearing_main by Shiny Objects, on Flickr Bearing_top by Shiny Objects, on Flickr Bearing_side by Shiny Objects, on Flickr
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nik
spending too much on rocks
Member since May 2019
Posts: 315
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Post by nik on Jan 10, 2022 20:16:54 GMT -5
I would say that about the best thing you could do without serious modification would be to come up with a bearing mount plate that is thick enough for two bearings. they do not need to be keyed to the shaft, so that should save a bit of money. If I were to build one from scratch, I would isolate the motor from the oscillating portion of the lap, a belt drive and separate shaft for the eccentric weight.
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herb
spending too much on rocks
Member since November 2011
Posts: 470
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Post by herb on Jan 11, 2022 10:18:32 GMT -5
I would say that about the best thing you could do without serious modification would be to come up with a bearing mount plate that is thick enough for two bearings. they do not need to be keyed to the shaft, so that should save a bit of money. If I were to build one from scratch, I would isolate the motor from the oscillating portion of the lap, a belt drive and separate shaft for the eccentric weight. Hmmm... I'm not sure adding a 2nd bearing would help much. I think I'd still have the same problem with the contact between the shaft and the bearing not being tight enough to prevent them from slowly grinding themselves down. Maybe with 2 bearings the overall friction would be more so as to keep the bearings and shaft moving as one? I though about trying some epoxy to glue the pieces together but I'm not sure the epoxy would handle the vibrations very long. The gap between the bearing and shaft isn't much so not alot of epoxy would be there. Also worried that it holds too well and I can't get it apart if I need to replace the motor or bearing! Switching to a belt drive setup would be great! It would take most of the stress off the motor shaft. Unfortunately, I dont known if I have the skills or tools for that kind of a project from scratch. Maybe I can think of a simple way to modify the existing lap without destroying it.
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Post by Rockoonz on Jan 11, 2022 12:06:15 GMT -5
I would call the local bearing place, give them your dimensions, and ask for low RPM and the highest side load available. Your alignment to the motor may also be an issue. I rebuilt an old Lortone vibe unit years ago, and the motor had to be perfectly centered while fighting the permanent magnets trying to pull it to the side, I have never touched one since and their new ones are belt drive.
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Post by greig on Jan 11, 2022 12:10:52 GMT -5
I only have one thought if you stick with a direct drive: "big bearings". FYI -epoxy won't work (for long) - the machine vibrations will likely cause it to debond from the substrate or crack
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herb
spending too much on rocks
Member since November 2011
Posts: 470
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Post by herb on Jan 11, 2022 15:16:38 GMT -5
I would call the local bearing place, give them your dimensions, and ask for low RPM and the highest side load available. Your alignment to the motor may also be an issue. I rebuilt an old Lortone vibe unit years ago, and the motor had to be perfectly centered while fighting the permanent magnets trying to pull it to the side, I have never touched one since and their new ones are belt drive. Yeah, getting a bearing that I know is up to the task would be a great start. The bearing I had on hand was from a high volume laser printer that is designed to print millions of pages a month but wouldn't experience anywhere near the stresses it gets in the lap. I was worried about getting the aluminum plate with the mounted bearing properly placed. I made the holes in the plate a little bigger than the bolt and used grippy washers (the ones that have teeth that can dig into what they are holding) with the bolt to give me some better chance of aligning things, but I think I might still be off a little which would definitely take a toll on the motor and bearing.
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herb
spending too much on rocks
Member since November 2011
Posts: 470
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Post by herb on Jan 11, 2022 15:19:44 GMT -5
I only have one thought if you stick with a direct drive: "big bearings". FYI -epoxy won't work (for long) - the machine vibrations will likely cause it to debond from the substrate or crack Thanks for the confirmation that epoxy is a bad idea. I kind of figured it was. A bigger bearing is also a good idea. I assume a larger bearing is naturally stronger than a smaller one. A little extra strength can't hurt!
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nik
spending too much on rocks
Member since May 2019
Posts: 315
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Post by nik on Jan 12, 2022 0:54:17 GMT -5
If there is really any noticeable slop in the bearing to shaft interface, you will have problems in that setup. If you can find some brass or stainless shim stock to fill the gap, that may help. The bearings should be press fit on both the inner and outer bores.
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herb
spending too much on rocks
Member since November 2011
Posts: 470
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Post by herb on Jan 12, 2022 10:11:44 GMT -5
If there is really any noticeable slop in the bearing to shaft interface, you will have problems in that setup. If you can find some brass or stainless shim stock to fill the gap, that may help. The bearings should be press fit on both the inner and outer bores. It started out as a pretty tight fit. I had to push with a bit of force to get the bearing on the shaft initially. Since I could do it by hand, it obviously wasnt as tight as it should be for a long term secure fit. Some metal shims would be a good idea. The teflon tape that I periodically pack in really isn't up to the task. I was thinking of trying some tin foil since it is thin but I think something stiffer would work better
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herb
spending too much on rocks
Member since November 2011
Posts: 470
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Post by herb on Jan 24, 2022 15:40:51 GMT -5
Thought I'd give an update for those playing at home. While contemplating how to convert my lap to a belt drive, the motor suddenly starting getting much noisier. Even without the offset weight and my homemade bearing support the motor was still loud. I figured that meant it was time to start shopping for a new motor. Looking at the motor label I saw "shielded ball bearing" so I decided to open up the motor and investigate. Turns out there is a ball bearing at both ends of the shaft inside the casing. The bottom one came off fairly easily and it sounded like rocks grinding against each other when I spun it manually. I couldn't get the upper bearing off (I dont have a bearing puller) so I went to a nearby auto shop and they were able to pop it off in about 30 seconds. Talk about using the right tool for the job! The upper bearing didn't sound as bad but it definitely was past its prime. Picked up 2 new bearings from Grainger this morning. There are metal cups on the inside of the top and bottom halves of the motor case into which the bearings sit. The cup for the lower bearing was a snug fit, but the upper one was pretty loose. It looks like that is what caused a lot of the slop in the shaft that led me to install my homemade bearing support. Not having any better ideas, I wrapped some masking tape around the outer circumference of the bearing so it would fit snuggly in its cup. Hopefully the tape won't wear out too quickly. I put the motor back together and plugged it in before putting it back in the lap. You can hardly tell it is running it is so quiet now! I didn't bother reinstalling my homemade bearing support since there no longer is any slop on the shaft. Fired up a pan of thundereggs and was surprised at how much more actively the eggs are moving around. The only issue I've noticed is the new bearings turn a bit stiffer so the motor takes about 30 seconds to get up to full speed when the bearings are cold. But after it has been running for awhile and I turn it off for a bit, the motor spins up to full speed quickly when I turn it on again.
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