choosing the right electromotor, please help.

[MakkyBrown]

I'm thinking I'll use a T8 1mm pitch feed screw to oscillate.  Figure I'd roughly need to attach  a 4000rpm motor with encoder to it or a stepper with a 2mm pitch screw.  1 osication (forward/back) per second at maximum speed. 35mm stroke max, 70mm return =70*60 = 4200rpm.
https://www.ebay.com.au/itm/T8-Pitch-1mm-2mm-Lead-1-2-4-8mm-Rod-Stainless-Lead-Screw-brass-color-nut/132381744971?hash=item1ed2911f4b:m:mDCgJZqzleCbGDJjXKZpunA:rk:1:pf:0

[FlashGP]

Hi Makky,

The length of your cutting mandrels determines the distance between the max fsd and max backward stroke on the oscillator.  I have 3 settings, 30, 40 and 50mm  achieved using threaded holes on my oscillator arm at 15, 20 and 25mm from the centre of rotation.

My darkside mandrel made by gearloose is 42mm long so I'll provably have to use the 30mm setting so the dop stays under the entire facet.  But if cutting a long facet, say 15mm long, I would need to make another arm with throws of say 15 and 25mm.

Clarry Trevena makes dops up to 60mm long so the 50mm setting would be fine for facets under say 8mm long.

Stop press, I made the arm from 10x10 mild steel rod with the end cut to 5mm thick to accomodate a lock nut on the retaining bolt for the agm that pushes and pulls the assembly back and forwards.  The 5mm tapped holes are 5mm apart but drilled in a zig zag patten.  If I add a tab to the other side of the motor shaft I can add 3 more adjustments at 1/2 distances giving 6 settings at 5mm increments starting at 15mm throws.

Oscillation speed control is an advantage.  Really slow settings give you time to position the mandrel for checking allignment, etc.

Regards
Gordon

[MakkyBrown]

Thanks Flash I'll design for 50mm max oscillation, then I can have variable oscillation distance and speed control. I think for bearings I might just use holes in some Acetal brackets. I was playing with some linear bearings today and they were getting a bit grippy oscillating the same amount constantly. So I might just cut holes in plastic as bearings.

[FlashGP]

Hi Makky,

Do you mean that you were using linear bearings on the oscillator threaded rod?  I didn't think they would work very well with a rotating shaft in them.

The 6mm pitch threaded rod assembly I bought as a kit from Banggood has pillow block bearings at each end.  The bearings are mounted in a ball like housing allowing the bearing to be off up to 5 to 10 degrees perpendicular to the mountings. 

The 2nd one I mounted wasn't true, but it was just a case of putting the rod into the bearing and twisting the bearing housing until it was properly aligned with the direction of the rod.


Regards
Flash

[MakkyBrown]

Hi Flash,
No I was going to use holes through plastic to act as bearings to slide on the smooth round linear rails. You can buy brass or plastic inserts, I may use those not sure yet.

To drive the oscillation I'm most likely going to use a stepper motor and 2mm pitch feed screw. I'll use small endstops for zeroing and an arduino to control stroke length and speed and smooth direction transitions. I'll also have a screen and control pad.

[Giel]

I like the idea of a stepper to drive the oscillation, figure they are more quit than a geared motor, but Im not familiar with the arduino or other ways of controlling the action of a stepper. That's why I bought a geared motor.

The way I am making it now it has a max oscillation of 55 mm. I think in "concave mode" using round mandrels, that is more than enough. But it also depends on how big your stones are.
I have two slide tables, the middle point of the cutting mandrel is the point where the two slide tables can rotate up to 90 degrees.
I want to make it so you can disengage the oscillation of both slide tables and also use them as a "microadjustable cross slide" (dunno what else to call it)
So in zero position you use concave mode, one table for oscillation, the other for moving the mandrel sideways. for cutting parallel facets on a tourmaline for example. (thats why I bought the digital sliders)
In 90 degree position you can use both directions of oscillation. One way for a round cutting mandrel and the other way for a V-wheel.
No matter what you are doing you always have measurement of where your mandrel is relative to your stone.

Ah, I also found some info on the lathe, http://www.lathes.co.uk/boleyF1/
There is no brand tag on mine but it has the exact same cross slide as the one in the link. (photo under the machine with the bright red belt)
Its an old machine, does not have bearings for the shaft, but it does feel very tight, no play in the parts.
I am taking it appart, cleaning it of all kinds of gunk, lubricating and putting it back together.

[MakkyBrown]

Giel, If your every wanting to do any arduino projects I don't mind helping. I'm also going to use the same processor that controls the stepper/oscillation to control the speed of the main rotating motor aswell.

[Giel]

Giel, If your every wanting to do any arduino projects I don't mind helping. I'm also going to use the same processor that controls the stepper/oscillation to control the speed of the main rotating motor aswell.

That's very nice, someday I want to make some stuff with an arduino, but I will save that for later.
Thanx!!!

[FlashGP]

Hi Geil,

Sounds good.  I used a cross slide coupled to a thread so I can manually adjust the position of the cutting mandrel so it is centred on the axis running up the centre of the quill.

I think this is what you are talking about in  relation to the cross table allowing parrallel concave facets.

55mm maximum oscillation would require rather long cutting mandrels and runout could be a problem. 

If you can adjust the length if the oscillation, that would be good.

The length of oscillation should be a couple of mm shorter than the length of your cutting mandrel minus the maximum length of the facet you will be cutting, otherwise the edge of the mandrel may run on the face of the stone and mar it.

Regards Gordon

[Giel]

I think this is what you are talking about in  relation to the cross table allowing parrallel concave facets.

Yes, that is what I mean, Sometimes it's difficult for me to explain technical stuff in english.
You also want to be abe to cut parrallel "V-groove" facets.

55mm maximum oscillation would require rather long cutting mandrels and runout could be a problem. 

If you can adjust the length if the oscillation, that would be good.

Yes oscillation length will be adjustable up to 35-40mm. The 55 mm is for when it is not in oscillation mode, so I can cut parrallel facets on a stone up to 55 mm. (hope that makes sense and explains what I mean)

I used a cross slide coupled to a thread so I can manually adjust the position of the cutting mandrel so it is centred on the axis running up the centre of the quill.

Yes I am making something similar, "one mode for oscillation and one mode for manually adjusting the position" both tables can be used in both "modes"

[FlashGP]

It sounds like you are on the right track.

I have just ordered a dial indicator on a magnetic base like you would use on a lathe to centre the job.  It is so I can use it for trouble shooting and for checking the run out on my cutting mandrels.

[FlashGP]

Hi All,

I had a Zircon on the dop that had a crack in the crown.  I gave up trying to recut the crown and instead opted to concave cut the side facets on the Crown to cut away the fracture.  The stone was an Old Mine  cushion cut with facets at 95, 1, 23,25, etc.

It's the first run of my concave cutter.  I found the following. 

Allignment of the cutter to the centre of the mast was critical.  Next time I'll opt for micrometer screw gages for mast alignment and mast stop alignment.

I am still learning how to accurately allign my cutter.  It seems that with close indexes, imperceptable changes (less than 0.25mm) makes a big difference to the position of the facets.  My laser level is just too course for that job.

regards
Gordon

[Giel]

Allignment of the cutter to the centre of the mast was critical.  Next time I'll opt for micrometer screw gages for mast allignment and mast stop alignment.

What do you mean with "mast stop allignment?
I think the ultratech fantasy machine also has a cross table under the mast for alligning it with the mandrel.
Maybe I will try something with precision dowels (is that the correct term?) so I can always find "zero" on the cross table.
And so I can only put the mast on the machine the correct way. (holes in the mast base and dowels on the fantasy cutter.)

Its good for me that you allready finished your machine. your post makes me rethink "potential problems" and how to avoid them. 

[FlashGP]

Hi Giel,

All machines have a mechanism that alligned the dop with the centre of the cutter so you can allign the direction of the cut to the stone and lift and inspect the work then return it to the same allignment as cutting progresses.  The VJ has a micrometer screw guage that clamps onto the swivell for the quadrant mast.  Thes system wont work for a mast machine like a Facetron.

The Polymetric uses a quill stop to achieve allignment.  Ive used something similar. 

I tried to concave the mains on an SRB on a machine where the mast base was 3mm out if allignment with the cutter but the stone was centred on the cutter, the meets didn't line up.

If the cutter gets off centre to the stone, it is the same as rotating the stone on the dop.

This is why I set out to adjust the front/back positioning of the cutter.  But you also need a stop to ensure that the Quill stays in the same side to side plane as the cutter, albeit above the cutter.

[MakkyBrown]

Check this out, my cheap chinese collet/holder arrived. I stupidly tapped it on to the shaft of the printer motor I have. It was a tight fit will need a puller to remove. I should have perhaps cut a bit off the shaft first. Anyway it's on there. It's a 6mm shaft. So I put a bit of brass in the collet and measured the runout it was that good I even uploaded a vid. Run out is probably about 0.010-0.013mm, cheap chinese gauge is not that good.  Highly recommend the cheap chinese collet holder I got. The masking tape was to mark the side.
https://youtu.be/4T1Jas-lETk