Re: [CAD_CAM_EDM_DRO] Sorting out the options for a CNC mill system

Just about everybody uses Mach3 to control a stepper driver (such as a
Gecko 540) through the parallel port. Mach3's primary mode is to read
G-code, but there are a few wizards in Mach3 to make G-code
instructions. It's not much of a CAD package though.

Typically the design software is "CAD". The software to make G-code is
"CAM", which may or may not be a separate package. Mach3 is, well,
Mach3. You might call it the "driver software", not to be confused with
the actual hardware driver out there it's talking to.

Mach3 pulls some somewhat-beyond-normal-spec "stunt" use of the parallel
port. It usually works quite well though, provided:
1. it's not a laptop (some work, some don't)
2. it's not a USB-to-parallel port cable
3. the motherboard isn't using on-board video (you can add a video card
onto such a system and use that)

You can add a parallel port with a PCI card if your machine does not
have one. This usually works.

The computer does not need to be especially powerful (read up on
recommendations). But you've got to turn off Windows Update and
auto-updates for the software and auto-virus scan. If this crap
launches while it's trying to control the machine, it could ruin the
work, maybe break your bit or send the tool diving into the table. I
know this sounds scary but it's not hard to avoid. Probably best to
just unhook the network connection actually. It's not a bad idea to
have 2 Windows installations set up as dual-boot, one for
design/internet viewing/etc and one which runs Mach3 and nothing else
installed but the motherboard/video drivers, Windows Update turned off,
etc. You'll have to reboot to switch installations.

It's possible to get a motion controller that works through USB or
ethernet, but generally it's not necessary. It'll get around the
limitations of the parallel port and allow you to use a laptop, but
might cost more than a cheap desktop PC anyways. The use of a motion
controller may not make it immune to tool crashing if Windows goes
looking for updates or whatever during a run.

A G540 has 4 motor drivers. You only need one G540 for a 3-axis. The
4th axis is handy, and may be essential later for more advanced
projects, but don't worry you can just get one and add it on whenever
you need it.

Limit switches are not mandatory, but nice. There are things to learn
about limit/home switches you'll need to read up on.

You left out the motor relay. It's not a big deal but without it, you
may not want to leave the mill for long because the motor won't stop
running when it's done. Which is not a specific problem, just... maybe
not a good idea. Once I have seen the machine do a run OK I generally
feel comfortable setting it up, see it's started ok, and go shopping or
whatever. But if the motor's gonna be running indefinitely after it's
done then I just don't feel comfortable leaving it running for some reason.

Ah yeah. A big button for the E-stop. This is generally only used when
something's going wrong but you want to have it there to stop the
machine unconditionally. Look up the electrical requirements, it needs
to be a normally-closed and IIRC they're saying it really should be one
that has to be pulled out to reset or something.

Servos can go faster than steppers, but they need special drivers and
encoders (which count rotations so it knows position)- encoders
electrically and logically compatible with the system. This is more
expensive and tricky to get the right hardware. But the Taig's
leadscrew CAN'T really be driven faster anyways. Nor can many materials
be run much faster. So it probably won't make a lick of difference in
the end.

See there are many stepper drivers which suffer from mid-range stability
problems which prevents them from operating at high speeds. They may
stall, so the machine's intended position is lost, but without encoders
the computer won't know that, and may do awful things like driving the
tool into the table because it thinks the Z axis is higher than it is.
BUT, the G540 has a lot of compensation for steppers and is generally
completely immune to this problem. Physically it can easily drive the
steppers 60IPM or higher, no problem! But we're not sure how fast that
leadscrew can go before experiencing an elevated wear rate. And note
you can't usually send a tool through aluminum at 60IPM. 10IPM might be
reasonable but there are a lot of details on the cutter type, depth of
cut, whether you've got flood coolant to both cool it and wash all these
metal chips out of the cut it's making, lots of stuff. I don't know
much yet about how to select the ideal speed.

Danny


Douglas Vogt wrote:

> Thanks for the information and that from Wildhorsesoftware even though you guys differ on the electronics. The mill, chuck and collets as you describe is the way I'm headed.
>
> So what would a generic system include: PC, Taig CNC ready mill, motors, drive (=controller cards for each motor?), software to convert a DFX drawing to G code, software (maybe in the same package) to convert G code to motor commands, power supply for the motors, and power supply for the Drive? Anything left out? I've built Heathkit stuff decades ago so can probably handle the electronics as long as I know more or less what components are required.
>
> What about servos instead of steppers or do servos require a completely different setup?
> Are limit switches mandatory?
> In your particular case, what software package(s) do you use to get a drawing from the PC to the mill?
>
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