Another Frustration – Quill Runout

Posted on October 17, 2008 by allan

As many of you who’ve managed to wade through all the text on this site know, my main frustration with the Omni faceting machine is that I can’t cut rectangular stones or step cuts without extreme aggravation. Meet points just don’t meet, and I seem to have to do a lot of fiddling with the cheater and mast height just to get things to come close.

I identified the mast as not being vertical as one of the problems – and because of the mechanics of the swing arm, moving the arm means that the angle and direction of the mast mis-alignment changes continuously. To remedy that I aligned the mast as best I could and now cut stones trying to avoid moving the swing arm. I also mark the swing arm so I know where I had it adjusted originally when I come back with a different grit after moving the arm.

That seemed to reduce some of the problem, but it still has been frustating me. So the next obvious thing was to replace the sloppy transfer fixture. I ended up buying a Polymetric transfer jig on the recommendation of a couple other faceters and indeed it’s a much more solid and accurate device (you can get one from the Polymetric website). But much to my dismay I still experienced difficulties getting meet points and facets to align when cutting a square tourmaline this past couple of weeks.

I then checked my dops to make sure they’re not bent – which they are not. So then a horrible thought passed through my head: what if the problem is in the Omni faceting head itself? It’s the only part of the Omni I haven’t yet taken apart.

So… I put the head in the 90 degree position and stuck a dop in it. I set up my dial indicator to rest on the top of the dop, and I put the quill into free-wheel mode. Then I held my breath and rotated the quill while watching the dial indicator.

Bingo! I measured a total wobble of 0.003″ to 0.0035″ in the quill. I couldn’t believe it! To ensure I wasn’t using a bent dop, I tried 3 different dops in the quill. All produced 0.003″ to 0.0035″ total runout. So I then tested the quill barrel itself – and I got about the same amount of runout.

To put this in perspective – on a 10 mm stone with pavilion and crown angles at 40 degrees (for simplicity), that’s about 1/2 a standard 0.3 mm girdle width of wobble. And to compare with other manufacturers the Polymetric website (the only manufacturer I could find that publishes their stats) states their machines have a an adjustable quill to reduce dop total indicated runout to under 0.0002″. That’s less than 1/10th the runout I measured on my quill!

So now my task is to take apart my Omni faceting head and try to figure out how to adjust/repair this. This is becoming a very tiresome exercise as the one place I would have expected precision machining and construction does not have it.

I’ll be posting photos and commentary about this little adventure shortly.

-Allan

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New Polymetric Transfer Jig

Posted on September 15, 2008 by allan

Updated Feb 7, 2010 – added photos of the Polymetric Transfer Jig.

On a tip from a reader I ordered a transfer jig from Polymetric. I finally have given it a try and it works much better than the stock Omni-e jig – much better stability and hence alignment.

It’s not specifically-designed for the slightly-larger diameter 0.300″ dops of the Omni (Polymetric and almost every other manufacturer except Jersey Instruments standardized on 0.25″ dops decades ago) but that poses no problems. As well the jig does not have any provision for aligning the keying system of the Omni dops (a 45 degree angle cut from the back of the dops) but after a call to Polymetric they are willing to make a modification to the transfer jig for a nominal fee that will accomplish this.

Overall I’m very happy with the quality and function of the Polymetric transfer jig and recommend it to anyone who’s looking for an alternative to the Omni jig. If you decide to order one, please be sure to ask them if they can modify it so it will work with the Omni keyed dops.

The page for Polymetric’s jig is http://www.polymetricinc.com/accessories.htm. Their link to a photo of the jig is broken but I’ll post a pic here later.

Polymetric Transfer Jig - Front View

Polymetric Transfer Jig - Oblique View Showing Block Details

Polymetric Transfer Jig - Rear View Showing Block Details

Polymetric Transfer Jig - End View with Locking Mechanism Detail-Allan

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New Spindle Has Arrived!

Posted on August 12, 2008 by allan

As I wrote about in my New Spindle Design post, I have designed what I think is a better Spindle and Platen for my Omni faceting machine. And it’s just arrived today!

I’ll write more later, but here are a couple of pics to compare with my original (modified) Omni Spindle and Platen.

I haven’t tested the vertical runout myself yet, but from the guy who machined it:

o.d runout : .0002 face runout: .0004

Compare that to my 0.007″ current runout! The new one has 17.5x less hop than the original!

-Allan

Custom Spindle and Platen Design for the Omni Faceting Machine

Current and New Spindle

Custom Spindle Installed

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2 Hours + $5 = New Splash Bowl

Posted on July 16, 2008 by allan

I’ve been trying to find some time to put up a full post on this, but I just haven’t been able to.

A couple of weeks ago I finally ran to the Dollar Store and picked up a bunch of plastic things, then to the medical shop to pick up some exercise elastic. Add in a bit of silicon sealer and the barrel of a pen and a few staples and… voila! A new larger splash pan that can hold the whole 16 oz of water in the drip tank plus more. Higher sides so it doesn’t spray the walls as much.

And — there’s no chance of the bearings ever touching water! Imagine that!

Here’s a pic of the partially-completed splash pan. Note that this slides over my smaller Platen and the collar prevents any water from getting hear the Spindle Housing and Bearings.

Omni Faceting Machine - New Splash Pan in Progress

So, until I get some time to write up the whole step-by-step process of making this thing, here are a couple shots of what it looks like.

Omni Faceting Machine New Splash Bowl

Here’s a pic with the girdle cutout splash shield in place. Note the rubber top.

Omni Faceting Machine New Splash Bowl with Girdle Shield

And here’s a close-up of how the Girdle Shield can slide down so you can cut a bit higher-angle on the laps without the Omni Faceting Head hitting the edge of the Splash Pan. The exercise rubber is to provide a nice soft lip that will conform to the shape of the Faceting Head to allow it to still stop a bit of spray and give a gentle warning when you’re getting close to hitting the pan.

Omni Faceting Machine New Splash Bowl with Faceting Head

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Replace Your Omni Bearings with Proper Ones

Posted on July 4, 2008 by allan

My Omni Faceting Machine shipped with NSK 6202VV bearings. These bearings are deep-groove ball bearings with double rubber seals – one on each side. However they are “non-contact” seals, meaning that the rubber does not touch the inner ring of the bearing.

What this means is that when the Splash Pan floods (remember, you’ve got less than 1/8″ of clearance from the drain hole to the top of your bearings) water can flow between the seal and the inner ring. This water will be carrying all sorts of diamond and gem dust into the bearing, which will quickly reduce it to junk and start vibrating and making noise.

Non-contact sealed bearings are used to prevent dust from entering the bearing, not liquids. In this case the wrong type of sealed bearing was used.

A proper bearing would be the NSK 6202DDU – it’s the same bearing with double CONTACT seals. These seals touch both the inner and outer rings, providing an effective barrier to liquids. This will prevent the bearings from getting junked if they get a bit of swarf and water splashed onto them.

Using proper bearings would reduce the likelihood of bearing damage due to accidental flooding. But the real problem is that the Omni Faceting Machine has a serious design flaw with its Splash Pan and Spindle Housing encourages flooding, and until that is resolved there will probably continue to be problems with swarf destroying bearings.

A set of 2 NSK 6202DDU bearings should not cost you more than $10 and likely much less. When you consider how little money could prevent such serious problems, you wonder why it wasn’t done properly in the first place.

If you can’t find the exact NSK 6202DDU bearing, ask for 35 OD x 15 ID x 11 H metric bearings with double contact seals.

I have not had to change my bearings, but if anyone has done this and can supply pictures, I’d be happy to post the process.

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Omni Faceting Machine Can’t Use Topper Laps

Posted on July 4, 2008 by allan

Further to my complaint about the Spindle Hold-down Screw being inadequate and the Spindle itself not being the correct diameter so the laps slop around, I’ve now discovered that the Omni Faceting Machine can’t handle using cheap “topper” laps.

Topper laps are those low-priced laps with diamond bonded to a thin metal disk about 1/16″ thick. They are designed to be put on top of a master lap (or old worn-out lap) to provide backing so they don’t warp when used.

The design of the Omni Faceting Machine Spindle is once again poor. The Omni Spindle ends in a little nub that sticks up out of the Platen – on my Omni it’s only 3/16″ tall. You can see in my photos that with a brand-new Crystalite Aluminum Master Lap on the Platen, the Spindle does not extend through the Master Lap. This means that any Topper lap you put on does not have anything centering it… which means you’re going to have it slopping around causing damaging vibrations.

This is just one more design flaw in the Omni Faceting Machine that limits your choice of supplies and causes frustrations.

Omni Faceting Machine Can't Use Topper Laps

Omni Faceting Machine Can't Use Topper Laps

The bottom photo shows the Spindle Hold-down Screw without either the factory-supplied brass washer or my plastic faucet washer in place. This is to give you a clearer view of how the lap sits.

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Omni Faceting Machine Head Design Flaw

Posted on July 4, 2008 by allan

I’ve written on a bit about the Omni Faceting Machine head design in my GemologyOnline post.

One thing that I noted was the Omni Facet Head has the index pin on the bottom of the head. At the time I wrote the article I noted that I didn’t like it because you have to life the head up to see what index you’re on. Since then I’ve realized that there are other drawbacks to having this located on the bottom of the faceting head.

Have a look at this photo. You can see that I have a stone that I wanted to preform on the dop, and the head is set to 59.5 degrees. The lap on the machine is an old Crystalite 600 plated lap, about 1/2″ thick. I’ve lowered the Omni Facet Head so the stone is almost touching the lap.

Omni Faceting Machine Head Design Flaw

Now look at the close-up photo. Notice that the metal parts that house the Cheater and Index Pin are bulky and now contact the edge of the Splash Pan. This severely limits the movement of the stone across the lap.

Omni Faceting Machine Head Hitting Splash Pan

Here are two photos showing a top view. Notice that you only have about 1″ of travel across the lap before the stone either hits the lap screw or the Facet Head hits the edge of the Splash Pan.

Omni Faceting Machine Head Hitting Pan Top View 1

Omni Faceting Machine Head Hitting Pan Top View 2

What this means is if you are cutting a stone at an angle higher than about 50 degrees, you will have to cut the stone through the girdle cut-out in the Splash Pan. This means you will need to change the orientation of the Swing Arm (and consequently the stone’s orientation to the Platen and lap).

This is bad – in order to maintain the same alignment of the stone to the lap, you should be cutting swinging the stone from the 6 o’clock position to the center of the lap as much as possible. By forcing you to cut in the girdle-grinding position, you have much less travel (due to the limited size of the Splash Pan cut-out) and you are also not cutting on the optimum areas of the lap. It’s also one of the reasons I’ve been frustrated trying to cut rectangular and step-cut stones – moving the Swing Arm position changes the orientation of the stone to your lap.

A final gripe is that if you’re cutting a facet with the Facet Head low and then swing the Quill up to look at the stone, you run into the problem of knocking the Fine Adjustment Arm against the Splash Pan. Irritating and it will change the angle that the Facet Head is set to.

Omni Faceting Machine Head Angle Adjust Arm Hitting Splash Pan

BTW – the stone in the pic is a nice big piece of Afghan Aquamarine 17x9x10 mm, Internally Flawless. I can’t remember how many carats. It’s a beautifully-formed crystal with sharp edges and termination at one end. Pale, as all Afghan Aquamarine tends to be, but very very bright once cut. I’ll post a pic once I’m done.

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New Spindle Design

Posted on June 27, 2008 by allan

I’ve decided I want to have a new Spindle and Platen for my Omni, so I’ve drawn up a new design.

The basic design is the same as the original Spindle and Platen except that the Spindle will extend above what it now does and will be threaded. Getting left-hand threading is difficult, so I will stick with right-hand threading and find a quickie-nut instead of a normal threaded nut to hold the laps down.

Omni Faceting Machine - New Spindle Design

I’m in the process of getting a few quotes for costs to fabricate it, and I’ll post the results of my quest once I have it in my hot little hands.

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Lap Hold-down Screw

Posted on June 14, 2008 by allan

The Lap Hold-down Screw that came with my Omni Faceting Machine is a small knurled screw with a right-hand thread. The standard washer that comes with it is brass. The problem with this is that it would undo itself as the machine was running, possibly due to the vibration caused by a poorly-sized Spindle that the laps are centered by. This meant the laps would slowly loosen and then start sliding on the Platen. And the Hold-down Screw itself would come off and bounce around the lap and room like a crazy grasshopper.

The other problem is that the threaded hole in the Spindle that the Hold-down Screw fits into isn’t deep enough. When fully-tightened, my Hold-down Screw has about 7/16″ of space between it and the top of the Spindle.

I have some old steel Maja Manufacturing laps – about 5/16″ thick – which the Hold-down Screw could not be tightened down to reach.

My solution for this was to purchase some 11/16″ diameter plastic tap washers pictured below (note that this is before I had the Platen size reduced). The right package shows the thick plastic washers I found – just had to thread one onto the screw and use it instead of the brass washer. This now allows me to tighten the screw sufficiently without forcing anything and the plastic has enough grip to prevent the screw from coming undone by itself.

For my Maja laps I use 2 of these plastic washers stacked together.

Omni Hold-down Screw with Plastic Washers

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Spindle Diameter is Off

Posted on June 14, 2008 by allan

The Omni Faceting Machine I received has a Spindle diameter that is too small for my laps. Every lap I have – Crystallite plated, old Maja Mfg Steel, Ceramic, Batt, Lightning Lap with standard 1/2″ arbor holes – all slop a bit on the Spindle and do not sit centered.

This means that the Omni vibrates at varying frequencies depending on the speed the lap is set to. This is obviously not good for the Faceting Head and Mast which vibrate and resonate at certain frequencies, nor for the poor stone being cut, nor for the Spindle Bearings.

I was told by the well-known owner of Faceters.com (whom I bought the Omni from) that it was because my laps that were not standard. This after *every* lap I owned and had used for years on my old MDR without problem exhibited the same problem!

Anyhow, I found a simple solution you can view in the Lap Hold-down Screw and Spindle Bushing post.

In the photo below, you can see the left package for 9/16″ (outer diameter) x 7/16″ (inner diameter) x 1/16″ rubber o-rings. I put one of these o-rings on the spindle – it’s visible as the black ring on the spindle. They’re small enough at 1/16″ to not get in the way yet provide just enough to get my laps to center on the platen. Now the vibration problem is greatly reduced – but not eliminated.

Omni Platen and Spindle with O-ring to center laps

Strangely I’ve heard from another Omni Faceting Machine owner who sent his machine back to the factory for service, only to have it returned with the Spindle diameter being *too wide* to allow his laps to sit on the Platen. He too was told it was because his laps were not standard – though they worked on the machine before it was sent back for servicing.

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