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 Post subject: Fine adjustment dop anyone?
PostPosted: Mon Sep 04, 2017 10:24 pm 
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I've thought about this many times. Again I've just cut a fairly expensive stone on my set and would have loved to have been able to adjust the stone alignment by a fraction.

As it was I had to adjust the mast height for each and every facet. Well, sometimes I don't bother and will live with opposing facets at slightly different angles.

I would like to add a means to minutely adjust the center of the stone once its on the dop. I've never seen diamond being cut on a modern machine but think they may have something that does this.

Many years ago, I bought a "guei aligner" (spelling) which would have been useful if I had been blind. Point is, I need very fine adjustment (probably less than 1/4 mm).

I don't often cut to competition tolerances but it would be nice to have the option without having to sacrifice weight.

Anyone else think this would be useful?


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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Tue Sep 05, 2017 2:00 am 
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Richard Burton wrote:
I would like to add a means to minutely adjust the center of the stone once its on the dop.

Wax dopping and small butane torch. Indispensible for adjusting an off-centre stone, especially one that needs a crown repolished, and for eliminating late-revealing flaws. I have also considered a mechanically adjustable dop, but it just isn't necessary.


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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Tue Sep 05, 2017 2:06 am 
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How do you avoid tilting it at the same time?


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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Tue Sep 05, 2017 2:39 am 
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Stephen Challener wrote:
How do you avoid tilting it at the same time?
I position the quill vertically with the stone on top, heat the dop just enough to soften the wax without melting it, and nudge the stone with a fingernail in the desired direction horizontally. With a little practice you can do this successfully. Another wax adjustment trick I use is with rectangular stones. When dopping I find it difficult to centre rough for rectangles by eye, but initially do the best I can. Then when two long girdle facets have been cut at 90 degrees, at different mast heights to preserve material, I measure the difference in height on the calibrated mast, adjust the mast to halve the difference, allow the high side of the stone to rest on the lap and heat the dop to allow it to 'sag' into position. One can do that on the short sides too, and then the stone will be centred with minimum loss of material. The Guiu dops are supposed to help with initial centering. A 'target dop' is also helpful. I understand the urge to have a micrometer adjustment on the dop (or quill), but I can't think of a way of making one that isn't unwieldy. Off-set dop holders exist for preforming curved girdles; but for centering you need X and Y adjustment. Rotation can be taken care of with the cheater. And what happens when you transfer?


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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Tue Sep 05, 2017 9:38 pm 
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Wax and butane, mast at 90 degrees - sure this works to some extent. But as Stephen mentions the table alignment will suffer and this method is not very precise.

I would like an inch long (as short as possible) adapter to put between the dop and the quill. Transfer will have to be different but I'm not too concerned. Either the adapter plus dop can fit into a longer modified jig or you could use the adapter on the other side of the stone.

Anyone with the skills and machinery willing to make me one? I would be happy to pay for it. :)


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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Wed Sep 06, 2017 3:44 pm 
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I'm interested to see what anyone comes up with for a design. I have a similar need but I deal with it by careful re-dopping when rough cutting the pavilion. This doesn't work all the time depending on the degree of shift required, but usually gets me within 0.2mm or so of the desired result.

My concern about it would be additional mechanical slippage and cumulative error by introducing an additional piece into the dop/quill chain.

-Allan

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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Thu Sep 07, 2017 9:18 am 
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You could build a guiu dop that takes a screw with a much smaller lead and lower run-out, like those used in adjusting optics. Here and here are my suggestions, with the threaded bush it shouldn't be too hard to find a compatible hole for them, and the sprung ball bearing tip should take care of any lack of parallelism in the holes.

Sometimes the solution is simply using finer parts, though I would keep any diamond paste well away from these in case it seizes the thread!


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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Wed Sep 13, 2017 11:44 pm 
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That's along the right lines Shifter.

The guii I bought was not a precise bit of equipment so I'm sure it could be improved on. Also inherent in its design is that the force on the stone only comes from one side during adjustment and is therefore liable to scew the table alignment. A more accurate scenario would be to clamped/lock the stone in (table alignment) position and then the whole gubbings moved for central alignment.

The only drawback on a guii redesign is that it is one step removed from the quill. If you could get something that fits in the quill itself then you wouldn't need to estimate how much the stone needs to be moved - you could immediately check it.

Still if you make a super smooth and accurate guii type thing - I'd probably buy it!


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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Tue Sep 19, 2017 12:01 pm 
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For fine adjustment & centering I use this transfer block that I built from scrap brass. It sits horizontally for transfer and upright for adjusting; the retractable needle in the post constitutes a centering gauge. Needless to say the stone itself must *be* adjustable. Dopping with wax permits this.

Cheers all
Hans Durstling
Moncton Canada

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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Tue Sep 19, 2017 8:20 pm 
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Nice homemade transfer jig Hans. I like the retractable needle idea.

Still would like something which allows for even finer adjustment.

Is anyone familiar with how a diamond is cut. Are all the facets centered by eye (adjusting the height of the mast to keep the angle the same) or is the diamond rough centered on a dop and cut like meet point faceting?


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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Tue Sep 26, 2017 7:20 pm 
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Richard Burton wrote:
Still if you make a super smooth and accurate guii type thing - I'd probably buy it!



I've been thinking about this for years and have actually made a 3D model of a device that does just what you want, (I've wanted to make one in order to change the centerline location slightly when cutting sapphires). The downside with this is that the requirements are pretty strict and this requires much more complexity than the GUIU device. My model has 11 parts that all have to be machined and it operates on internal cams which are at right angles and move the dop/stone about 1mm in any direction. The overall size of the main body of this unit is a little over 1 inch in diameter and a little under 1 inch long, having a dop end to fit into the existing quill and a quill of it's own to hold the users dop, (these two parts make the entire unit around 4 inches long in total). I'll drop an image back here once I finish and render the model and start making some parts.

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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Mon Oct 02, 2017 2:26 am 
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michael_e wrote:
Richard Burton wrote:
Still if you make a super smooth and accurate guii type thing - I'd probably buy it!



I've been thinking about this for years and have actually made a 3D model of a device that does just what you want, (I've wanted to make one in order to change the centerline location slightly when cutting sapphires). The downside with this is that the requirements are pretty strict and this requires much more complexity than the GUIU device. My model has 11 parts that all have to be machined and it operates on internal cams which are at right angles and move the dop/stone about 1mm in any direction. The overall size of the main body of this unit is a little over 1 inch in diameter and a little under 1 inch long, having a dop end to fit into the existing quill and a quill of it's own to hold the users dop, (these two parts make the entire unit around 4 inches long in total). I'll drop an image back here once I finish and render the model and start making some parts.



Haven't been here for a while and had pretty much given up on my post. Imagine my joy when I saw your post Michael - I am not alone!

Sure with expensive material (Burmese sapphire at "crazy prices" and up) and a desire to do the best job possible: this type of widget is needed.

I noticed from your older posts that you're building a faceting machine - how's that going?

I'd be keen to see the cad design, though I'm doubtful I can offer anything you've not already considered. Please pm me if I might be able to help


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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Mon Oct 02, 2017 10:46 pm 
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Hi Richard,
My existing faceting machine is an older Facetron, so the first dop centerline adjuster will be made to fit the quill on that machine. What sort of faceting machine do you have and what do the dops look like?


On the Faceting machine that I'm building... I was high centered on everything about 5 years ago and had to move numerous times. I'm in a more stable situation now, so full steam ahead! I've gotten most of the parts together and am now setting up my shop, (taking forever unfortunately), and my small Tormach milling machine. Once the mill is up and running I can get this project into high gear and get something done. Stay tuned.

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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Mon Oct 02, 2017 11:22 pm 
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In 1990 I purchased this jig from a gentleman in B.C., a double dovetail adjustable dop.

It came with a couple of 6 mm dops, 1" long. I cut the last 1" off a few other dops to get other sizes.

Don't know if he is still around, but the idea is.
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 Post subject: Re: Fine adjustment dop anyone?
PostPosted: Tue Oct 03, 2017 5:01 pm 
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It looks like a simplified version of a goniometer head... :)
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