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Old 11-23-2018, 12:25 PM
Marcel Braun Marcel Braun is offline
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Question 18" lap polishing station

Hey guys and especially Pete,
Im putting together a dedicated cerium polishing station and considering the merits of direct drive vfd vs a belt drive/gear box reduction and single speed motor control or if theres a reason still vfd.

Scenario 1, 2hp 1800rpm motor on VFD no reduction direct drive target rpm about 1000 to 1100 at the wheel. Would be slowed to 70% or so with the vfd
Im worried about starting torque in this configuration.
Scenario 2, 2hp 1800 rpm motor on vfd with 2:1 belt reduction. Is the reduction needed to get our starting torque? the reduction would allow almost 1800 rpm if needed with the VFD and at 120% be about 1000 rpm with a nice adjustment range.

Scenario 3 and 4, 1.5Hp motor same as above but this could run on 120V. Do you think id have the torque?

NON VFD options

1800 rpm non vfd motor belted to run about 1000 rpm. (insert rpm reccomendations here)

3600 rpm motor with higher reduction factor. From what I can understand the 1800 rpm motors get more torque and use slightly more energy on either drive type, even after compensating for rpm and hp. It seems to be the number of magnets that makes the difference but it is pretty confusing still im definitely open to experiences that can be shared.



About my application: I start the polisher with the load on the wheel. My asw with a 3/4 hp non vfd 3600 rpm and around 3 to 1 reduction is anemic at best and usually requires a bit of a push to start spinning. The glass pieces are mounted in weighted holders that rotate while applying pressure. I want to increase the load as well because I have only used about half the wheel area at this point. Do you think this can be pulled off in direct drive and would it be worth it?

Another question: Additives or techniques to keep the cerium in suspension while using a recirculating slurry system? Home made or industry supplied equipment is of interest.

Thanks in advance for your thoughts,


Marcel
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Old 11-23-2018, 03:28 PM
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Pete VanderLaan Pete VanderLaan is offline
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You have a number of abbreviations in there I'm not familiar with. VFD and asw. Please forgive my ignorance there.

I look mainly to surface feet per minute in polishing and subsequently preventing overheating at the polish surface. About 300 SFM always worked best for me. I do like a slurry in an ideal world to be around 100F and I do consider the quality of the cerium to be really important. The photo mask division (PMD) ceriums are the best American quality. I continue to use my trusty Panda Brand Cerium out of China but I don't believe it's imported here. Happily, Eveline keeps me in a lifetime supply but we're quite cautious about trying to bring too much here. Chinese customs are actually tightening up and the tariffs will make things far worse. 10KG at a time is our max.

What I can't quite tell is whether you are asking how much pressure you can bring to bear on your polish surface based on motor Horse power and I think that's a touchy-feely sort of thing. You don't want the work getting either hot or dry. I suspect David would be a better resource on that than me and I haven't been in contact with him for some time. I do think the prep prior to the cerium to be key and I would want a 1500 grit prep to be efficient. That's a whole different can of worms. Type of glass also really matters.

I do think you should make a way to hang onto the slurry and to recycle it constantly or it will get really pricey in a hurry. I do add sodium tri phosphate to my cerium and it does help keep solution constant. Stirring helps. A somewhat alkaline PH is commonly used although I don't do that. Keep it out of the drains or you will eventually have a major headache.

I love the idea of a radial polisher but it would take serious bearings to keep it on a flat. Even a moving table on a milling machine gets a small amount of sag out at the end of the table run. I doubt I'm much help here since my glory polishing days are over and I now sail inland waterways.
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Old 11-23-2018, 05:16 PM
Rick Kellner Rick Kellner is offline
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Wink

VFD= variable frequency drive (for motor speed control, etc.)

ASW...the best I could come up with is anti-submarine warfare. Who knows?
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Old 11-23-2018, 05:17 PM
Marcel Braun Marcel Braun is offline
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Thanks Pete i will crunch through the advice you gave me. Rt now I'm just circulating the cerium bucket with the pump but its not helping enough. I'll incorporate something new starting with that chemical. The vfd is a variable frequency drive - magic black box speed controller for ac 3 phase motors to run on single phase up to 1.5hp on 120V 5hp on 240v. And ASW is a brand of lap wheel...i doubt youd like it much but it does better than a hobby wheel.
.
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Old 11-23-2018, 05:38 PM
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Greg Vriethoff Greg Vriethoff is offline
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I've put a lot of hours in on an ASW. It was a perfectly capable machine.
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Old 11-23-2018, 07:27 PM
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Pete VanderLaan Pete VanderLaan is offline
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I had most of my wheels made for me from bridge drops over 20 years back. The smallest is about 200 lbs. They have served me well. I suspected you were talking variable speed and it's really nice. You can't load a small wheel with much pressure, it just deforms, you just may not see it.

Don't skimp on your cerium. It's what polishes the glass.

Then: Don't skimp on the glass. bottle glass doesn't polish well ever, neither do most commercial cullets. You pay for luster.
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Old 11-24-2018, 07:57 AM
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Quote:
Originally Posted by Marcel Braun View Post
Thanks Pete i will crunch through the advice you gave me. Rt now I'm just circulating the cerium bucket with the pump but its not helping enough. I'll incorporate something new starting with that chemical. The vfd is a variable frequency drive - magic black box speed controller for ac 3 phase motors to run on single phase up to 1.5hp on 120V 5hp on 240v. And ASW is a brand of lap wheel...i doubt youd like it much but it does better than a hobby wheel.
.
*********
Well, what grit level are you starting the cerium at? I had said a 1500 grit but that's still pretty coarse. Cerium will eventually get through that but it takes time. Normally, on smaller work, I would run a 15T and then go to a 0/3/4
pumice and then the cerium. Automating changes a lot of approaches. The trouble with going past a 15T still using a microgrit would be having the head suction down to the workpieces which would break something.
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Old 11-24-2018, 08:16 AM
Marcel Braun Marcel Braun is offline
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Right now we cut our slices (coins) with a resin bond 220 or 150 grit wheel. Its not the most durable blade but it can make a very flat and smooth cut. Because of the way the polisher plates hold the coins I've found I need the cuts within 5 to 10 thousandths of thickness for best results. Then if needed a 220 smoothing pad or 325 metal if there are kerf marks or heavier chipping. 325 smoothing pad (brown) is pre polish and then we go straight to cerium. Seems to run about 15 minutes per cycle to get through each batch of 20 to 50 coins but there are some subtleties of my home made experimental equipment giving me a hard time. The current state is to take what has been learned and build a machine from the ground up. Accuracy and consistency at every stage is key as the saw gets better the coins polish better.
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Old 11-24-2018, 09:23 AM
Eben Horton Eben Horton is online now
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Quote:
Originally Posted by Marcel Braun View Post
Right now we cut our slices (coins) with a resin bond 220 or 150 grit wheel. Its not the most durable blade but it can make a very flat and smooth cut. Because of the way the polisher plates hold the coins I've found I need the cuts within 5 to 10 thousandths of thickness for best results. Then if needed a 220 smoothing pad or 325 metal if there are kerf marks or heavier chipping. 325 smoothing pad (brown) is pre polish and then we go straight to cerium. Seems to run about 15 minutes per cycle to get through each batch of 20 to 50 coins but there are some subtleties of my home made experimental equipment giving me a hard time. The current state is to take what has been learned and build a machine from the ground up. Accuracy and consistency at every stage is key as the saw gets better the coins polish better.
I would cut them on your saw and then throw them in a big rock tumbler with 450 grit alumina and walnut shells and then move them to cerium and walnut shells. Try it. Send me a coin when you smack your head and kick yourself for not trying this earlier.
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Last edited by Eben Horton; 11-24-2018 at 09:26 AM.
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Old 11-24-2018, 10:29 AM
Marcel Braun Marcel Braun is offline
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id like this to work for sure
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