MB concave build

[MakkyBrown]

I'll enter aswell Giel. Just build it is the best approach, as you'll probably find unexpected issues you will need to change.

Yeah I know that I will probably run into unexpected issues, I already am while building it: I need to find a metal worker in the area for some parts, need to find a nerd to help me with the dc motor and driver, because stepper online will not answer my emails.
slowly but surely I am getting there.

I might be able to help with the motor.

[Giel]

I might be able to help with the motor.

I finally have an email from stepper online and I just ordered the cables to hook it up to the computer.
I think I will manage in the end, if I dont I will let you know. thanx for the offer!

First my idea was to use a brushless dc and threaded rod for both motions (swivel and positioning). But I cannot make it myself as I dont know much about electronics and programming.
Brushless dc mode 1: for swivel action, needs a speed control and  a circuit for polarity change every second or two. The time of
                                polarity change needs to be adjustable also.
                   mode 2: for positioning, needs a very slow and precise rotation so I can position the mandrel and lock it down.
So that would mean two motors, and circuits, one for each slide table. This way I could also use a V-wheel.
I really like the idea of a V-wheel for cutting large stones that are relatively flat, with a few V-grooves on the pavilion you can still have a great lively stone. (great when you have big but flat rough)

If I cannot find someone in town who can help me with the above, I think I am going the easy way on the machine.
I have a "12V DC 100 RPM High Torque Gear Box Electric Motor for Speed Control" that I will use for the swivel action.
I will use a threaded rod for the other slide table to adjust the position of the mandrel by hand. But that means I can only use cylindrical mandrels for now. So it will only swivel in one direction instead of two, and positioning will also be in one direction instead of two.

Hope this makes sense.

[MakkyBrown]

Hi Giel,
You are welcome to my code and wiring diagram for my controller. I am using the key pad to stop/start/directions/ and speed for the dc motor(with collet holder)
The oscillation motor where I was planning to use the stepper. I'm changing to a worm drive using a dc motor with an encoder on it. This will be controlled from the same control box as the main dc motor. Key pad will be able to stop/start oscialtion, and control oscillation speed, start position and stroke length.If you have not used arduino before it is great and lots of sample code out there to steal etc.
But didn't you purchase a driver box for the bldc motor?? You should be able to just wire a pot to it for speed control if it is like some of the others I've seen.
CheersMB

[Giel]

But didn't you purchase a driver box for the bldc motor?? You should be able to just wire a pot to it for speed control if it is like some of the others I've seen.

Yes I did, and I will be using a pot for speed control as you describe.
I think I did the wiring correctly, but apparently I have to set the whole thing up connected to a computer using brushless dc software to get it going. And to modify it with the softare so it can be used with a pot.
I have all the parts but I did not order the cables needed, as it was not mentioned on the website, I ordered those this morning so I have to wait for those to arrive.
I think I will be able to get the motor for the collet holder going.

[FlashGP]

Hi Giel,

I just used a small 30rpm 12v motor from Banggood.  It is tiny and looks like a motor from a model, but it is geared with a worm drive and  works better than a 2w turntable motor from a microwave oven, safer too.

I made an arm that fits on the worm drive  out of some 10mm square rod drilled and tapped with my bench drill.  The taps are 5mm threaded holes and I cut and filed that part of the  arm o 5mm thick using a hacksaw and file.  The holes are offset and spaced at 15, 20 and 25mm from the centre giving me adjustments for the length of travel.

I then bought a male and female tie rod ends from Banggoood and connected them, one end to the arm on the motor, the other to a post on my base plate of my concave cutter.  Polarity isn't important for the oscillator,  the rotary motion of the arm pushes and pulls the cutter head equally well in CW or CCW rotation.  It looks a bit like a steam engine crank.

I just use a 12 to 36v 775 motor from banggood.  It does 3500rpm at 12v, 10,000 rpm at 36v.  With small diameter cutters, 3500 rmp is about OK.  I wouldnt use a slower motor, it takes too long to cut.

Switch mode power supply is the way to go.  They are cheap and have 110/220v terminals and 12v and ground terminals on the 12v side, plus an earth terminal.  They are about 1/4 the cost of a traditional supply and pack more punch.  I bought a 25amp supply for about $35 Australian.  It would have cost me about $300 for the 2 transformers needed for the same current  for a traditional supply.  I went big as the price difference between a 10A and 25A supplý was only $10.  I figured if I needed bigger motors, I would already have the power supply.

The basic circuit is, mains in to the switch mode supply, with the Active Brown wire, rumming via a switch.  Two 12v wires 10A to from the power supply, one each to a pulse width modulator (dc speed controller). One set of wires from each pulse width modulator to a 4 pin plug, both motors are fed via this plug so I cant mix them up.

The small motor is controlled with a 10A PWM, one direction only, that cost about $4.  The big PWM can handle up to 40A at up to 50v.  It cost about $12  from Banggood.

next supply I make, I'lllhouse in an old computer case or CD case from the recycling shop, the plastic electrical box I bought cost me abput $50 and everything was a tight fit.

lastly, put a 47ohm 5w resistor across one of the 12v outputs.  Thiskeeps the switch mode supply under load when the motors arenot turning.  It is supposed to make the switch mode supply run better.

Regards,
Flash

[Giel]

We think alike Flash, I have made something similar as you describe for the swivel action.
I have a 12 V 100 rpm motor with a speed control, with a "swivel block"
Made the black block on the 3d printer, It has a threaded rod running through, a square aluminium plate runs through the block connected to the arm. When I turn the two nuts the aluminium plate slides up and down, that way I can adjust the swivel length. (just need to print the turning knob and fit it over the two nuts.)



I also have DC motor for the mandrels, 3500 rpm, already have the speed control and power supply.
I have almost all the parts now, looking for a metal worker in the area to make the aluminium plates as I cannot do that myself.

[FlashGP]

Hi Giel,

Necessity is the mother of invention.  Yours looks a bit nicer than mine,  maybe I should buy a 3d printer.  Rej (Gem Cut Studio) Poirier madr his faceting machine using one.

The neatest oscillator I have seen is on the VJ, it is two disks with a ball bearing race and offset locators that screw to the machine's platten and the base of the cutter housing.  But this is way beyond my capability using silversmithing tools and a bench drill.

[MakkyBrown]

Back into the concave build just cut a few bits, a new motor mount and my alignment clamp/tool I'm going to use. I'm going to try direct driving the 2mm pitch feed screw. Motor has a 400cpr encoder on the back of it. I'm hopeful it works. Might have to buy a 1mm pitch screw.
More tomorrow.

[MakkyBrown]

Discovered my feed screw was 2mm pitch but 8mm lead, didn't know what lead was do now  . So I made a new a feedscrew and nut out of 10mm 1.5mm pitch stainless threaded rod i had laying about. The other choice would have been waiting 1-2 months from china.
Sleeved the motors shaft from 4mm to 5mm and screwed all the bits together. Bit of loctite 680 here and there. I think direct drive will work, motor is 3000rpm not loaded, so lets say 2500rpm loaded with carriage. 2500/60x1.5 = a max speed of 62.5mm per second, which will be slower as it will need to ramp down on the turns and accelerate. So maybe max speed will be 40-50mm a second.  Which should do as a maximum speed. Now to do the electrics/code.

[MakkyBrown]

Made an alignment tool, think it will work. it goes in the concave machine collet and aligns with a bit of 1/4inch brass in the faceting machine hand piece. I think this will work and gets around the limitation of using the gemmasta mast/faceting head.

[FlashGP]

Hi Geil,

I see you ate looking for an aluminium plate.  Is that for the base?

If so, have you thought of using plywood reinforced with aluminium angle to stop it warping.

I bought 4mm T nuts to use as mountings in the plywood.  It wor, is available at the hardware and cheap enough to reconfigure as often as you like.  It is also quicker to cut and shape than aluminium.

Regards
Gordon

[MakkyBrown]

[MakkyBrown]

Almost ready to cut a stone, a few bits left to do. It is A LOT quieter than the video. Plus I can't hear the PWM whine. BUT it goes but I think it would be better to build with standard ossilation set up. I was processor constrained so only using the index on the encoder.  It is running at 50% speed which will do, I've slowed the turns to try and stop the drive nut chopping out or the coupling slipping. The the linear bearings are probably the noisiest bit, I purchased plastic inserts but they didn't fit.I can adjust the oscillation stoke from 18-42mm, if I was using a better processor I would have got the full 50+mm but it will have to do as i can't be bothered rewiring.
https://www.youtube.com/watch?v=X01ntNngcVY

[FlashGP]

Crikey MB, anyone would think you played around with robotics.

I like the simpler worm drive with rotary cam and lever.  Polsively steampunk vs starwars.

Happy faceting.  Looking forward to seeing your entry in the annual faceting comp.

Regards
Flash

[MakkyBrown]

I'm trying Flash, hopefully I'll get a design in, but I certainly will not be winning just making up the numbers I'm planning to use 6.35mill mandrels so i don't have to make any  . Brass and aluminum can only try.  Cut on brass polish on the softer aluminum or wood.