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 Post subject: Polishing requires the cheater?
PostPosted: Tue Dec 17, 2013 10:55 pm 
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I'm having a problem I need help with. I'm cutting and prepolishing a stone with horizontal step cuts with no problem, cheater at zero. When I polish, the surface looks as if I adjusted the cheater. The upper line slopes upward on the leading side. Is this normal? I'm having to crank over my cheater to compensate.


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 Post subject: Re: Polishing requires the cheater?
PostPosted: Wed Dec 18, 2013 12:07 am 
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I would suggest that your polishing lap has slightly different geometry than your pre-polishing lap. It may be slightly conical, dished, or may sag around the perimeter. Just go ahead and use your vernier adjustment so your polish matches the plane of the facet. That is not in any way "cheating" as it is just compensating for differences in your laps. It happens all the time. I have a solid tin lap that has undergone room-temperature creep to the extent that the rim is a good 3 mm lower than at the center hole! It's still reasonably flat over the platen, which helps.

Dick Davies


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 Post subject: Re: Polishing requires the cheater?
PostPosted: Wed Dec 18, 2013 1:55 am 
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Not normal. What is the brand, model, and age of your faceting machine?

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 Post subject: Re: Polishing requires the cheater?
PostPosted: Wed Dec 18, 2013 2:11 am 
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I beg to differ. I think it is normal and can be caused by frictional drag on long facets or non-parallelism of lap surfaces. No machine is absolutely stiff and no lap combination will stay in perfect alignment forever. Either way it is not a problem. Just use the vernier/cheater to make the necessary adjustment - and remember to dial it back to zero when you are done.


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 Post subject: Re: Polishing requires the cheater?
PostPosted: Wed Dec 18, 2013 3:31 am 
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I am wondering if this is a new problem you are having with this polishing lap and if it has been getting worse over time. Is it a pretty old lap and/or seen a lot of use?


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 Post subject: Re: Polishing requires the cheater?
PostPosted: Wed Dec 18, 2013 9:40 am 
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thomas.adamas wrote:
Not normal. What is the brand, model, and age of your faceting machine?

Agreed for the most part. There might be a machine or a lap isssue. Now...if you're cutting a 3.0 L/W stone...all bets are off.


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 Post subject: Re: Polishing requires the cheater?
PostPosted: Wed Dec 18, 2013 11:29 am 
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I think switching from one lap to another this can happen. I have a dual charge Ba5t lap, and after pre polishing on the outside, I need a slight amount of cheater to get the polish on the 100,000 on the inside. At fist I thought this could be an issue with the machine. But I have two machines, a GemMaster and UltraTec, and both require cheater in the same direction when using this lap.

I also have a pretty new Dominatrix lap, and when using this lap I don't have the same issue. The Ba5t lap has maybe 800 stones polished on it, so it could be that one section is worn differently than the other.

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 Post subject: Re: Polishing requires the cheater?
PostPosted: Wed Dec 18, 2013 11:37 am 
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Normal. No two laps are absolutely identical. Remember, we're talking about tenths of microns for polishing.


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 Post subject: Re: Polishing requires the cheater?
PostPosted: Wed Dec 18, 2013 1:02 pm 
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Thanks all for your comments. I have a Graves V 2009 model that I just bought used. Previous owner was a dust collector. Cutting Oregon sunstone. Polishing with cerium oxide film on a master lap I have a new master lap on order.

These are horizontal step cuts. I haven't had this problem with an SRB, for example.

Ps, I love this machine with the electronic indicator. The biggest thing I like about it is the ability to virtually match the previous cutting. And the Darkside? Wow!


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 Post subject: Re: Polishing requires the cheater?
PostPosted: Wed Dec 18, 2013 1:13 pm 
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SteveH,
I think a large part of your issue is polishing with a milar-backed powder-coated sheet. Those were designed to polish metallurgical and refractory specimens for microscopy. They work well for that, but the problem for faceting lies with the leading edge of the sheet bunching up, even a small amount, resulting in the leading edge of the facet polishing more than the rest of the facet. I suggest you give away or dispose of those milar sheets and use a proper polishing lap. You mentioned that you have a Darkside. Well, use that.

The posters to this topic have all identified factors that could cause a facet to not polish flat-on. One thing we disagree on here is what is "normal" behavior for polishing, indicating we have some different expectations in going from pre-polish to polish. What constitutes normalcy is what we believe is normal.

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 Post subject: Re: Polishing requires the cheater?
PostPosted: Wed Dec 18, 2013 1:24 pm 
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Interesting first paragraph. I think you are right.


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 Post subject: Re: Polishing requires the cheater?
PostPosted: Wed Dec 18, 2013 7:24 pm 
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thomas.adamas wrote:
One thing we disagree on here is what is "normal" behavior for polishing, indicating we have some different expectations in going from pre-polish to polish. What constitutes normalcy is what we believe is normal.


Definitely, and it's bound to happen when we have a mix of pros and hobbyists (as well as liberal artists and engineers, lol), and thus an inherent range of demand for accuracy and repeatability in our equipment.

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 Post subject: Re: Polishing requires the cheater?
PostPosted: Wed Dec 18, 2013 10:07 pm 
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upcyclist wrote:
thomas.adamas wrote:
One thing we disagree on here is what is "normal" behavior for polishing, indicating we have some different expectations in going from pre-polish to polish. What constitutes normalcy is what we believe is normal.


Definitely, and it's bound to happen when we have a mix of pros and hobbyists (as well as liberal artists and engineers, lol), and thus an inherent range of demand for accuracy and repeatability in our equipment.


Eric -

I think you and Thomas both hit the nail on the head. With the spectrum of folks here, our expectations can be wildly different. As a learning hobbyist, my initial response to the original question was "Yeah, absolutely normal - that's what the cheater is there for', due to the inaccuracy in my 40 year old machine.

However, for a professional cutter where time is money and deadlines loom, he/she needs the utmost accuracy so that fiddling around with cheater/angle adjustment is kept to zero, or a very minimum. I can mess with settings and spend a couple days polishing a stone, just because it's fun (OK, so I'm a little eccentric). The pro can't waste time with that.

Greg


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 Post subject: Re: Polishing requires the cheater?
PostPosted: Thu Dec 19, 2013 1:38 pm 
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redmond wrote:
Eric -
I think you and Thomas both hit the nail on the head. With the spectrum of folks here, our expectations can be wildly different. As a learning hobbyist, my initial response to the original question was "Yeah, absolutely normal - that's what the cheater is there for', due to the inaccuracy in my 40 year old machine.
However, for a professional cutter where time is money and deadlines loom, he/she needs the utmost accuracy so that fiddling around with cheater/angle adjustment is kept to zero, or a very minimum. I can mess with settings and spend a couple days polishing a stone, just because it's fun (OK, so I'm a little eccentric). The pro can't waste time with that.
Greg

Yes. When laps or a faceting machine have issues, corrective actions equate with spent money.
Dedicated hobbyists and professionals require their laps to be flat with parallel top and bottom surfaces, machine platens with no significant vertical runout, secure quill and mast components, accurate and repeatable angle and index readouts, and ergonomic machine layouts.

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 Post subject: Follow-up: Polishing requires the cheater?
PostPosted: Fri Dec 20, 2013 8:43 pm 
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I've learned a lot about horizontal cuts with this one. I also learned that the phenomenon I was concerned about shouldn't have been a concern to start with. The upward slope worked itself out.

To explain, as a review, looking at the pavilion with the culet pointing upward, the bottom line (closest to the girdle) was straight and the upper line was sloping upward. I found that the cheater was not required and was catastrophic to use it. The reason is because the cheater would put a slope on the bottom line to straighten out the top line.

By not using the cheater, on the next set of horizontal cuts (closer to the culet), the upper line would eventually fall off of the culet on the last set of cuts.

Problem solved.


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