CNC faceting and engraving bit machine idea.

[twistedfuse]

Hello All,

Well now that ive completed my first machine i am looking to build another 2 machines for diferent purposes and was looking for help etc.

My very next machine will be a smaller cnc router used for engraving and lithophanes and such so that i dont have to power up the big one to do really small jobs. The other machine was to be a small engraver of about 100mm x 100mm to allow me to engrave rings in wax and maybe dog tags. The second really small one was because my better half would like to have somehting small to play with as well and i thought it would be a good idea for something different.

While i started designing this one she also had an idea of getting into faceting after my father showed her what it was. He doesn't have one and is looking to retire soon and i thought that it would be good since he is already talking about buying one to get into it and i'd love to do something for him after everything he has done for me.

So to get to the point of this thread, i have changed my mind to start thinking about a way to build a cnc faceting machine. To make it worth my while in building(well not really as i enjoy building stuff, more like extra incentive) i thought i might be able to add in an extra feature of replacing the lap with a grinding stone and allow myself to be able to grind my own engraving cutters(the half round engraving cutters).

My problem is that i know what faceting is and get a general gist but don't know 100% and was looking for some help while im designing it.
My first question would be wether or not this would work as an idea? Also i was curious as to wether or not i would need 3 or 4 Axis controller? Since they won't be doing dimonds anytime soon, lol, i thought i would only need to use small stepper motors maybe the NEMA 8, 11 or steppers from a floppy drive depending on how much torque i would need. The other thing would be in regards to the cutter grinding, would this work?

I saw a manual faceting machine on ebay and thought maybe i could use 3 axis one for height control, one for tilt(up and down) and one for twist. If it needs to be able to move forwards/backwards/left/right during the process i would think i would add an extra axis but feel that it shouldn't need to so i would just make them manually adjustable.

As for software i would probably need to code something to work with it. I will need help with that for sure but will cross that when its time. For the software i would have the faceting automated with a dwell time to make sure the face is complete before moving on to the next rotation/face. As for the cutter grinder i would have that as a stepped software that waits for a response from the user before continuing. That way i can make sure its complete before moving on. Having never ground any tools and being told its hard by hand i thought that this would be a better option since its hard to source these cutter at a reasonable price is australia and would just enjoy doing it also. SO depending on how quick the grinder can grind away the blank and the total pocess the software might be similar to the faceting with a dwell time instead.

I will draft up my idea soon to see what people think and then go on from there. Any help/ideas etc would be greatly appreciated.

Daniel

[twistedfuse]

Gee we are blessed to live in such an age. Just browsing youtube and the net and can't see too many CNC faceting machine(enough to get some ideas) but i did find a couple vids on you tube and the process with the spring arm made me realise if i can't add the cutter grinder i maybe able to get away with 2 axis and have the software step processed so whoevers using it can look at it and then decide to re-do that cut or to move on.

Just a thought as im typing maybe i could end up making the controller PIC programmed. That way i could have the controls on a pad and display which would rid the need of a pc to be close. Less electronics around water/lubricant.

Daniel

[epineh]

Hey Daniel, this is something I have kicked around myself as well, in fact I am sure there is a thread or two on the Zone I have contributed to about a CNC faceting machine. (couldn't find any in a hurry).

What I think would be the way to go is a 4 axis machine, the 4th could be mechanical but probably easier in the long run to have an actual axis. You need to be able to index the stone (1st axis - rotary), then set the angle (2nd axis - angular from 0-90deg) also adjust the cut height (3rd axis - linear) and the last is to "wipe" the stone across the surface of the lap so as not to cut in one place all the time. A mechanical wiping action could be used but if this was an axis it would be easier IMO.

My plan was to have the post in the centre of three laps, this way you could rough in the stone on the first lap, swing the head around, smooth off and touch up the facets on a finer lap, move to the polishing lap then polish, same as doing it manually, but with the post in the middle you just swing it around to the lap you want to use, this is where the 4th axis would simplify things greatly. Of course you would need cleaning stations in between laps to avoid grit contamination.

I think the cutting would be reasonably straightforward, the polishing is the bit that I think would give the headache's. I have done a reasonable amount of faceting manually when time permits and individual stones can have soft or hard spots that require care when cutting/polishing. I have a few ideas on that as well but they would require a working machine to test them.

I think it could be done, but you would have to transfer the stones manually as far as I am concerned, I can't see how you could automate that process, but it is not too time consuming once you get some practice. Also I would gear this towards cutting small stones, around the 5mm dia finished size and smaller, mainly as the polishing phase will be easier on smaller stones, and I think I would like to cut any bigger rough manually, it isn't very cheap to buy or even find quality rough anymore.

Just my thoughts though, I would be willing to combine "talents" on a machine design of some sort

Russell.

[epineh]

Oh yeah, with normal CNC control, the G code would be pretty simple, around a couple dozen lines of code per side of stone, I would just do this by hand, it is easy enough for this, it is just the height/depth of cut that would require some MDI experimentation. I would just do seperate programs for different dia finished stones.

Russell.

[twistedfuse]

Russell,

Thanks for the reply, i did see a couple posts but there wasn't too much in them as they didn't have too much of a following so i presume went dead. I would love to be able to work together and build such a machine. As an extra what do you think about the station being able to grind cutters. I don't see the problem since it is just simple flat grinding. As for the forth axis i was thinking along that line so as not to wear out one part of the pad and waste the rest. Also for cutter grinders i would imagine the back relief of the cutter, the bit would need to move back to just do the tapered section. My idea for the laps were to be interchangable on the motor spindle. I Guess the spindle would be belt driven from the spindle and the motor kept out of the way anyway.

I also had an idea watching that video on youtube too. If you needed to check out the gemstone between cuts you could have a software button(similar to a height setter etc) that movs the gem into a light and have one of the usb cameras that rodm etc use to align their routers to check the gemstone up close, this of course would only be applicable if we use a computer.

Daniel

[epineh]

I am not too sure about grinding cutter, only as in I haven't done anything like it before, it sounds feasible. I have tried grinding metal (stainless) on the diamond laps and it doesn't work all that well, I was quite surprised, I think as it is so soft compared to gemstone it tends to clog up the lap, maybe a more suited wheel would fix that.

I agree that a button would be nice to check progress, I imagine once the heights are sorted this wouldn't get used much but it would be good to have at the testing phase.

I think using a PC would be the way to go, after all, the hard work is already done, run Mach, Turbo, Desk whatever and it is good to go, once all the mechanicals are done of course...If you have to start from scratch and build a complete motion controller then it could bog down progress.

Another way to go could be to use EMC as the motion controller, use discrete H Bridges (which I already have designed and using for my router) and you have a fully functioning servo system. I have been playing around with servo's lately as you may know and they are very sweet, I don't want to go into a servo vs stepper debate here but EMC would provide quite a cheap entry to the world of servo's, especially if we just use the parallel port for the I/O instead of an I/O card (MESA or Pluto-P)

If your father gets a machine, have a look at it for design tips, the grit from cutting a gemstone does evil things to bearings, just have to watch that. I think you can still buy Hall machines new, that is what I have, it cost around the $1500.00 mark, not bad for what it is.

Cheers.

Russell.

[twistedfuse]

Russell,

Yeah may think about leaving the cutter grinder off...maybe... if i was/am going to do it the surface lap would be replaced by a grinding disk. Either way ill see where the machine gets to and decide later.

I agree with the fact that pc would be the best way to go. Maybe a future project if i learn enough PIC programming to make a comletely enclosed system.

The servo system sounds great since i have been following your experimentation. Either way.

As for my father getting one soon i doubt it. Hence why i decided to go with the idea of building. lol. Starting to design up some simple ideas in cad from good old google images of faceting machines. Should be simple enough to replicate with minimal parts. The rotary indexer will be the hardest.

Im really looking forward to this since it seems very simple to do and the result could be great. Something you don't see very often.

[twistedfuse]

p.s i'm just 1 ic socket off and 1 9 pin female off finishing the programmer at last. Just thought you'd like to know. Hopefully ill have a pendant for my other machine soon.

[wjfiles]

Hi All,
Just my 2c worth. Having done faceting and built a number of manual machines.
The height control would need a a light spring load to allow for the varying hardness of different stones . it would be almost impossible to calculate a feed rate. So the control of the height (X-Axis) would control the limit of depth.The spring tension would allow the hardness to determine the rate of material removal. Hope this makes sense.
WJF

[twistedfuse]

WJF,

Thanks for the reply. Im not 100% clear on hat you meant by that so im just trying to cear it up. Im thinking what you mean is an idea like having a floating spindle on an engraver? Axis jogs down, spring takes the compression when jogged too far before rock surface? Doesn't seem to make sense but im sure i get what you mean, its a good idea to compensate for that. Thanks for the tips. Anything else we may have overlooked?

Daniel

[epineh]

Yup, that makes sense, when faceting manually you do this automatically (does that make sense ?) you bring the height down and apply pressure to the stone on the lap, and it cuts down until the stop, too much pressure and the stone can dig in and fly away, WJF is right, if the thing is too rigid it would be easy for this to happen, a simple spring pressure system would eliminate this. A limit switch on the hard stop would be enough to tell the PC the depth has been achieved, like a variable homing switch.

Cheers.

Russell.

P.S. Daniel, any chance you can make the BBQ ?

[twistedfuse]

Russell,

I would kill to get there but unfortunately too busy to do so. I will make sure i make the enxt one. Might try to bring a mate too he is interested and thought if there was another it would be the perfect thing to push him to build. My conselation prize for missing out is a trip to the manufacturing expo i sydney next week on the way to newcastle. Should be great to see some pro machines and get some ideas. IM hoping im allowed to take a camera and video to capture ideas.

You'll have to tell me how the BBQ went. Maybe the next BBQ could be in Sydney or at least NSW.

Daniel