Where to get one??!!??

[jimbob]

I was just wondering where would be the best place to get a small CNC Machine, is ebay my best bet?

if i were to buy an older bbc controled machine, what would it take to get it up and running as a full 3axis machine??

James

[davidimurray]

Hi James

I bought a Denford Starturn (BBC version) from ebay. Almost completed the refit. If the machine had Parker Digiplan drives in them then I have a circuit that allows the 12V signals on the drivers to be controlled from 5V from the PC. My list of bits is as follows -

Breakout Board for PC isolation
Digispeed Spindle speed interface
2 Relays, for spindle and Estop circuits
Custom circuit for interfacing stepper drive signals
2 regulator/rectifiers to utilise old transformers

I chose to use the original stepper drivers as there is little performance increases to be gained with the motors I have. However, some other machines have 2A drivers and 3A motors.

You will also need a package such as Mach3 to control the machine (www.machsupport.com)

You may also need to rewire some of the wiring on your machine of choice. I had to cut into my wiring loom to seperate the limit switches from the estop circuit.

Cheers

Dave

[Denford Admin]

There is always a wealth of ex-educational machines on ebay, although some seem to go for more than they may be worth, considering that you end up binning all the electronics and control / computer, and have to work with the old plugs/sockets and guarding

Depending upon what working area you need you could go for a brand new small milling machine which is fairly easy to retrofit with something like MACH (others on here will tell you about that)
eg:
http://www.axminster.co.uk/product-Axmi ... -33370.htm looks good quality for £234
or
http://www.sherline.com/

Doing this would be a cleaner option as long as your not worried about guarding and safety interlocking.

[davidimurray]

Personally, unless you want this as a big project, I would stay away from the 'cnc conversion'. The reason is that if you buy a nice Triac or something like that, it has got the ballscrews in, pulleys one etc. Of course if you want bigger motors, then you can simply take the old ones off and put new ones of the same frame size on.

If you go the conversion route then you would probably need to strip out the Acme leadscrews and replace with ballscrews. You will probably find that there is very little room below the saddle and you will struggle to fit a ballscrew in without machining the saddle. Then of course you need to find a way to mount the motors, and you might have to make new end bearing carriers etc etc. How do I know - been there done it, still doing it. My mill seems to be undergoing a constant rebuild - I did run Acme screws but I picked up some cheap ballscrews so I will be machining my saddle to suit.

Cheers

Dave

[clarkea1]

I agree with what Dave says about trying to get an existing CNC machine and update the controller. I'm currently in the middle of an Orac conversion - however, try to get a machine with the original electrics intact. It's surprising how much of this you can re-use - my Orac was missing most of it's controller and it soon adds up when you have to replace stepper drivers, and add various power supplies, switches etc most of which could have been re-used from the original control system. It's also a lot quicker!!!

Cheers

Alastair

PS - once I get around to taking some, will upload some progress photos of the Orac onto the projects section in this site.

[Denford Admin]

Of course, I've never made my own CNC from either a manual desktop, or a second hand one.
I thought for personal use it would be fairly straight forward to get a machine like the Sherline, and buy a CNC kit which is made to bolt on.
I know DeskCNC do servo motor kits with the control card, drives and software for something like $600 to $800 US
If your quite happy to run a machine without guarding and interlocks, then this would seem the cheapest and cleanest way to get CNC into your shed / workshop.

I often think that Denford should be supplying CNC stepper kits as the VR software is really powerful yet easy to get into for beginners - it has to be used by school teachers - so it can't be too complicated - no offence