New to CNC - HELP choose milling machine!

[Faszero]

Can someone please help me with some advice on what to look for in choosing a used CNC milling machine.
I design parts in CAD, but what software is needed to send it to the milling machine?
I have space for a medium size floor standing vertical turret mill and am thinking of one which already has motors built into the XYZ axis.
What changes would I have to make to such a mill, if any, to operate it with a computer and touch screen?
Also, is there such a thing as a complete CNC kit for a older manual Bridgeport mill as I have been offered one from a college, a nice tight machine with a modern dro.
Thanks

[AndyUK]

Hi Faszero,

Welcome to the forums.

To convert a CAD model into something for the machine to create, you need a CAM package, such as Vectric Aspire (or one of their simpler and cheaper other products) or Fusion 360 (free for hobbyists, very capable, slightly bigger learning curve). There are millions of videos on this topic on the old youtube - go have a search for tutorials to get the idea.

Very envious of your space! I've got access to an old BP, but no space to bring it home with me unfortunately... :(

You can get turret mills which already have CNC capability, and buying used is probably the cheapest and most sensible solution. Having said that, we're not on this forum because we like taking the sensible option, so there is plenty of information about conversions in both the milling machines area of the forum (http://www.mycncuk.com/forums/33-Milling-Machines-Builds-Conversions), and the bridgeport forum (http://www.mycncuk.com/forums/299-Bridgeport-Milling-Machines) in particular.

Happy milling :)

[magicniner]

If the mill you buy second hand has axis motors but isn't already CNC then they will be Power Feed and not suitable for CNC use.
I know this sounds obvious but the question posed doesn't make clear that knowledge as ALL second hand CNC machines have motors coupled to the axes an this should therefore have gone without saying ;-)

[Faszero]

The S/H CNC turret machine I was looking at I was told 'has ballscrews on all axis that are driven by DC servo motors.'
Also, 'the control is very easy to program you can also run it with a cad cam program or the offline software.'
Sounds OK does it not for working with Fusion 360 but the Anilam 3300 control panel DRO has an old cathode screen would it be easy to replace?

[AndyUK]

Very generally speaking, all CNC machines should use GCode - which are literal instructions to the machine about where to move in sequence, for example:

Move quickly to X=10, Y=0, Z=10
Turn on the spindle
Move at this feed rate to Z = 0

This is the set of instructions which the CAM program makes. The controller on the CNC is responsible for enacting those instructions precisely.

If you buy a used CNC, it should be able to take these instructions from any CAD program. It may also have some manual offline functions as you mentioned, but they will be machine specific.

Now, replacing the cathode screen. This is likely to be a can of worms; it probably won't be just a standard interface to swap out (it might be, but certainly don't bank on it). Often, if there is any problems with the machine controller it's worth considering ripping it out and rewiring the entire thing with a more modern controller - but this gets very complex and expensive very quickly.

[JAZZCNC]

The S/H CNC turret machine I was looking at I was told 'has ballscrews on all axis that are driven by DC servo motors.'
Also, 'the control is very easy to program you can also run it with a cad cam program or the offline software.'
Sounds OK does it not for working with Fusion 360 but the Anilam 3300 control panel DRO has an old cathode screen would it be easy to replace?

Unfortunately, It's a little more complex than just selecting a Cam program.
First, the Cam software you use must have a post-processor that suits the controller your using and doubt Vectric or F360 will have a Post for these old Anilim controllers as often they are programmed at the controller or by hand and imported which leads to next issue..

Second, these Old Controllers are often limited on memory and modern Cam programs writers are lazy so they spit out large file sizes for even the simplist tool-paths. This means you have to drip feed them code and this leads to all sorts of issues with drop outs etc.

Third, retrofitting isn't a simple affair either. DC Servo drives on these older machines nearly always require Analog signals so require an expensive analog controller.
The DC Motors can be re-used with modern DC drives but even this isn't a simple switch as they tend to use Single-ended encoders and/or tacho's which need to be replaced or bypassed with modern differential encoders which modern drives will require.

All these things become expensive really quickly and are why often they get ripped out and replaced with modern controllers and motors/drives etc
That said if the machine really does have ballscrews fitted already then it's a good head start as often fitting ball-screws isn't a cheap or simple swap and requires a lot of work in many cases.

[Faszero]

Thanks for all of your replies, looks like the S/H cnc market is a bit of a minefield.
Would someone have a look at the specs of the new milling machines at www.skyfirecnc.com and let me know if they are of a good standard?

[Doddy]

Google the reviews from people that have them - actual experience would trump any review of sales literature.