POLL: Where is the high spot on your faceting machine?

[Shifter55]

For a while now I've owned a used Gemmasta, and have done my own aligning. One of the things I had to do was alter the alignment of the lap spindle, so it had only one point of contact relative to the arc of the handpiece.

The reason for doing this is with one point of contact you can cut a flat facet regardless of the wear on a lap, and improve repeatability by hitting the same height every pass. If it's near the spindle you also take advantage of the reduced vibration nearer to the rotational axis.

I figured I'ld see who else has their machines set up for this, whether they are new or used.

[FlashGP]

I am not quite sure what you mean.  Is it that you platten is slightly rilted towards the mast so the edge is marginally lower than the middle?

I have noticed some of my laps seem slightly thicker at the edge, but have thought this is due to wear differences, or the centrifugal force causing the zinc to creep a bit.

[Rusted]

I'm glad someone else is scratching their head.
Talking Gemmasta here.
The surface where the lap spindle bolts should be perfectly level and aligned with the surface that the base of the mast clamps to. As far as I know they look like they would be machined at the same time. Severe wear on the mast clamping surface could eventually throw things out but I would look at having everything machined flat again if that was the case.
I have found the base of the mast on several machines including my own not being perpendicular to the mast. A slight cut off the mast base with the mast swung between centres remedied that.
One machine I checked someone had shimmed the platen spindle to compensate, but any change in the orientation of the mast base threw everything badly out of wack, this was the first machine I found the mast base needed machining.

[Faceting Frank]

I have used a couple of Gemmasta machines Shifter, but never done any maintenance on them so don’t know how the spindle bearings are fitted to the base. Or how they have provided for levelling the master lap.
As Rusted said the mast may not be square to the base and having it turned in a lathe to square it up will be a big help.
But you can compensate for that by moving the mast base as far back as it will go and drop the quill down as low as possible. Resting the dop on the table at two points near the front and back edges, take note of the differences with the dial gauge. You may have to remove the pan to do this. Gradually turn the base round till those measurements are the same.
What you have done here is have the quill swinging level with the table. Mark the base front and rear above the slot in the table. The mast base will now have to face the same way all the time.
 Set your quill at say 45deg, rest a dop on the edge of the master lap in four different places. Front, rear, left and right, adjust the spindle base till the dial gauge reads the same at the four places. What this has done is levelled the master lap up with the table in both axis.
If there is still some wobble in the master lap, then put the dop in the same place on the edge and rotate the master lap by hand till you find the high spot. Then adjust the shaft base to lower that point, keep doing that till it always reads the same. As I said before I have no idea on how Gemmasta have provided for those adjustments.
There will still be some wobble in individual laps, I don’t worry about it till I get down to 1200. I have to put a shim on the master lap for that and my 3000 Batt lap. Though I have got the dial gauge flutter down to 0.02mm.

A lot of stuffing about Shifter but once you have done it, it shouldn’t need doing again and make faceting a lot more fun.

[Dihusky]

First thing to check is the spindle bearings, they wear and a couple of thou wear translated to one heck of a lot on the edge of a lap.

The last 4 machines I have serviced (all our own) had worn bearings, they cost about $6-8 each so are a cheap primary fix before you play with alignment and you may well find this solves a lot of problems.

[Pro-oz]

First thing to check is the spindle bearings, they wear and a couple of thou wear translated to one heck of a lot on the edge of a lap.

The last 4 machines I have serviced (all our own) had worn bearings, they cost about $6-8 each so are a cheap primary fix before you play with alignment and you may well find this solves a lot of problems.

Yes have just put new bearings in mine.
Cheers Prooz.

[Dihusky]

Made a difference??

[Pro-oz]

The bearings that came out felt ok, being an old hall machine I was doing some maintenance and renewed any way. If there is any difference it would be very slight.

[Dihusky]

The difference will only ever be minor, but even minor can throw a run or girdle facets out

These discussions always open up some interesting comments, but the bottom line is a machine should not have any high spots, sure frisbys will have highs but once one hits pre-polish everything should run flat, if not then where is the problem?

Hollowed laps? Machine out of true, bearings, mast, facet head bushes on the mast, quill bearings, even the machine base... four contact points on a table and one is rocking slightly... these are just a few of the possible faults. I've even heard of new machines being out of wack, direct from the factory... not good

At the last AFG Muster, a few of the facetors were fascinated by the rubber dop guards my wife and I were using! Simple rubber suction cups with a small hole in the centre, but keeps the splash out of the quill and its bearings. Seems they had never considered how much damage water carrying fine grit can do to accurately machined surfaces.

A lot of old timers adapt to a machine as it wears and don't realise it's out of wack, but it's a killer for a new facetor when they pick up a second hand machine and can't make anything line up. They'll give up out of sheer frustration.

[Pro-oz]

While doing my checks I did find one of the little rubber cushions on the machine base legs was missing I always thought it was my bench and had it packed, have since sat the machine on 1/4in. rubber mat and now is running very smooth and quiet.

I have checked the quill is parallel with the table and with the master lap, since fitting the new bearings and happy with the alignment.

The only thing that I noticed with the spindle bearings with the old and the same with the new bearings there is the slightest bit of end float ( up and down movement) but no side to side movement.

[Dihusky]

Had the same quill problem with our 2000, got Horst Ricker to make a new quill, it's a dream now.

[Faceting Frank]

Love that dop guard idea Dihusky. Have been using that thin blue masking tape to protect the collet chuck from water entering, but will have to find some suitable rubber for the job.

[FlashGP]

Ill see if I can find some small rubber suction cups.  I have neen cutting washers  out of a rubberised Windex glass cleaning cloth usin a 1/4 inch and 3/4 inch disk cutters and holding them in place with a 1/4 inch O ring.

I also wrap a Veda cleaning cloth around my mast to keep it clean and cover my deck with 2 of those cleaning cloths to trap any particles before they get to tne  base of the mast.  The cloth can breathe so moisture  can evaporate and not corrode the seat for the mast.  They have a hole for the  mast cut in them.

regards
Flash

[Dihusky]

Love that dop guard idea Dihusky. Have been using that thin blue masking tape to protect the collet chuck from water entering, but will have to find some suitable rubber for the job.

Just look for some cheap silicone suction cups, around 20mm dia. I use a small wad punch to make the hole once I've cut the mounting button off the back. 6mm wad punch is perfect as the hole always ends up a bit smaller, fits snugly on any dop.