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Old 03-26-2019, 12:05 AM
Chris Lowry Chris Lowry is offline
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Flat lap polishing

For those that use your flat grinder and a felt pad to polish I have some questions.

Does slowing down the grinder help? I would imagine that it would help with the grabbing but does it help with polishing faster?

Anyone try the LP66 polishing pad?

Anyone do a prepolish on the Polpur pads?

I need to invest in some new equipment but first hand knowledge is great. Thanks
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Old 03-26-2019, 08:43 AM
Shawn Everette Shawn Everette is offline
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I've used the LP66 polish pads for some time. They're pretty good for a private studio, but I'd rather have napped felt or polpur style if your letting beginners near it; the LP66 can get gouged easily if not treated gently. That being said once it gets impregnated with cerium it stays there, can take a while to build up though.

The only time I slow it down is if I feel it's getting too hot. Once the cerium is on there it tends to shed the water right off the pad, so I have a tendency to run wet and slow.

Pre polish wise I just started using the diamond smoothing pads, those are a dream. Pricey, but do an excellent job. I'll post pics when I get a chance.
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Old 03-26-2019, 10:19 AM
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Pete VanderLaan Pete VanderLaan is offline
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I'm a polishing junkie and have a different machine for each grit (60, 120, 400 or 27mu) Then the pumice machine with a rodel GPX .125 pad and 0-3/4 pumice followed by a Universal photonics felt from Boston Felt at 1/2 inch thick.
All of those machines are a minimum 24 inch with the grinders being 30 inch. Wheelhead speed does matter. Diamonds want more water and more Surface feet per minute. Cerium will simply crack your work if you run too fast so, best to have more than one machine.

I think the first question you really want to ask is whether the glass you are using is receptive to a good polish. Sp87 is OK sort of. All the current cullets are marginal and unless you are melting a custom glass with high potassium, the concern over tooling may be a waste of your time. Surface feet per minute determine stock removal but getting greedy will rip the workpiece from your hand. By the time you are getting to 400 grit or finer, you have a real risk regarding suctioning down diamonds or grit. Cerium does not want those speeds and will overheat if pushed.

When we ran a lot of Schott optical as well as my high potash glasses, it simply was the case that silicon carbide was the way to get the best surface. Aluminum oxide optically graded at 27.5 mu followed the SIC and the rodel pad with the 0-3/4 pumice prepped a piece for a serious grade of Cerium Superox PMD or my chinese all time favorite Panda Brand cerium on the Universal photonics felt were best, unless one was polishing in a reciprolap and there we reverted to Rodel again. Rodel became unbelievably expensive some time back so I bought a fifty yard roll 54 inches wide and am still cutting pads from that. That was also true of the Universal photonics felt. In both I have a lifetime supply if I don't live too long.

So that was us in obsessive compulsion land.

These days, I don't do big slabs and mary beth just wants to shape jewelry so we use a 60 grit diamond from David Patchen and I can't say enough how superior those pads are. More diamonds, rigid, just perfect long lasting little buggers. I continue to use a 38 inch 120 grit machine for my work and then go to the optical grade 400.
The pads in Roberts video look exactly like Rodel pads but have gone up about ten times in price. I used to pay $20 bucks a pad and bought long rolls of it. Thickness is important and if you get thinner than a .125 They tear easily. I kept mine on a timer and when it reached 40 hours, it was replaced since the speed began to slow down quite noticeably. Similar things are true about the Photonics cerium pad and they do get lumpy bumpy if not dried well between sessions. Another annoyance with those pads is if you get 1/2 inch as opposed to 1.4 inch pads, the cerium tends to ride up on the edge of your workpiece, which if you are fuming is quite noticeable.

Eveline's Panda Brand Cerium is the worlds best and costs very little but it isn't exported. Price is controlled by the government unless you are smuggling it out which I did. I came close to real trouble doing that. Most Cerium's are going to run you around 2K per pail and all cerium is definitely not created equal. There are slurry Cerium's that sound better on price but are remarkably ineffective in polishing. Politishing is expensive and involves a serious financial commitment.
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Old 03-26-2019, 01:23 PM
Chris Lowry Chris Lowry is offline
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Thanks Pete there is a lot to read there. I do use Spruce Pine and to my eye it gives a nice polish. I do order wheels like David for the rough. On a small surface the diamond pads work fine but for anything nice or big I hate the lines they leave. I guess loose grit is the way to go.

I just need to perfect my polish set up. Iíll try some of your suggestions. Iíve been debating buying a variable speed grinder but maybe just having a detracted slow one for cerium would work.

When on a rociprolap do you go straight from 400 to cerium?
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Old 03-26-2019, 02:50 PM
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Pete VanderLaan Pete VanderLaan is offline
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First, I do have six laps. That being said I now use just one. I go directly from a 120 grit rough to the lap. I use a 15T also called fifteen hundred microgrit in that lap and leave the piece(s) in for two hours. If it's a vessel, I put a few inches of water in to it for deadweight. Everything needs to be wrapped carefully to avoid destruction. You cannot use 1500 grit on a standard wheelhead. The work will instantly be ripped from your hands. It's actually frequently hard to get the piece off a reciprolap. Suction.

After two hours,it comes out and goes directly to the pumice with 0/3/4. Prep usually takes about 1.5 minutes. Then it goes to Cerium. Salt to taste.
There are interesting layers in the pumice/ cerium processes. In Pumice, if I really wanted a superb polish where I saw mirror reflections on facets, I'd drop to an "0" pumice. Canneto Lipari was the italian pumice of choice. The Navajo brand has some iron in it and needs magnets in the slurry tray. Then, going to cerium, polish occurs at two levels. You get one very quickly but if you look at it carefully, it resembles orange peel. That can indeed be polished through but it takes a while. At that level is when I was referring to how good your actual glass is. For Schott optical, it's important and it's important for my formulation as well. I would suspect you would not see major benefit in SP and any of the current cullet won't show well either.
With Mary Beth's work in Schott, we came out of the 1500 lap and went directly to a rodel pad with cerium in another rociprolap. Typically that took four hours.
Back when Jack Rose sold the business off, I formed a buying club with David Lindsay so we could get additional trays at a reasonable price- about $275.00. I ordered a lot. The new price was $700 dollars, a huge increase. His had a distributorship. I bought more than they did. Then HIS glassworks complained to the manufacturers about that deal and I was cut off. I never order another tray from anyone. That really pissed me off.

What I do is tried and true. There's no better machine that the Rose lap. It's just not cheap to do. I do tend to think that individual machines are the way to go. It indeed takes up space but you get great surfaces if your work demands it. If you get serious about it, you need a machine shop that can true the dishes. They don't have a very long lifespan before being worn too thin. I think I have something like 18 trays.
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Old 03-26-2019, 02:54 PM
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Pete VanderLaan Pete VanderLaan is offline
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Quote:
Originally Posted by Chris Lowry View Post
Thanks Pete there is a lot to read there. I do use Spruce Pine and to my eye it gives a nice polish. I do order wheels like David for the rough. On a small surface the diamond pads work fine but for anything nice or big I hate the lines they leave. I guess loose grit is the way to go.

I just need to perfect my polish set up. Iíll try some of your suggestions. Iíve been debating buying a variable speed grinder but maybe just having a detracted slow one for cerium would work.

When on a rociprolap do you go straight from 400 to cerium?
******
Indeed. Diamonds give a great surface with one long scratch- every damned time. Then you have to polish through the scratch.

You can go direct from the 1500T to Cerium but it takes its sweet time.
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Old 03-26-2019, 09:02 PM
Marty Kremer Marty Kremer is offline
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I'm usually liking diamonds to about 140 and then hand grinding on a glass plate with 220 SiCa slurry. Gets right past those big bling scratches.
But then I'm not looking for polish....

But- Bullseye set up that way and then fire polished at around 1350F is plenty good for my stuff. Pavel Novak polished some BE for me but complained the whole time. This stuff just isn't made for optical finishes.
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