Re: [CAD_CAM_EDM_DRO] Newbie Question

On Wed, 21 Aug 2002, kimvellore wrote:

> I am planning on buying a Sherline with CNC option and convert it to
> CNC. I am trying to understand how the CNC process works, this is how
> I understand it works
>
> First you draw the parts you want made in .dwg or .dxf or other
> drawing format.

Or in some proprietary system like DanCAD. I don't use DanCAD, but
proprietary systems are certainly an option.

> Next you use another application and convert the drawing to g-code
> and use a g-code interpreter to convert the G-code to pulse and
> direction to the parallel port.

Right.

> The g-code interpreter works on DOS.

Not necessarily.

> If this is right why does the g-code interpreter work in DOS?

It works on some OS that lets you have real-time control over hardware.
And that's why DOS is so often used. DOS isn't multitasking or
multithreaded. So no other process will ever swap out the CNC control
software mid-stream and mess up your cut.

But it's by no means limited to DOS. Controller software exists for UNIX,
as well as for Windows, both of those using real-time hooks. You can also
get proprietary systems that run their own operating system.

> Is there one application that them all. I am will be using the
> mill/lathe for my hobby needs and I am looking for a cheap software.

Yes, there are. SuperCAM is one of these. It runs in DOS, and includes a
CAD package, g-code interpreter, and CNC controller in one program. I've
used it on a Taig, which is a setup that's sized similarly to the
Sherline.

I can definitely identify with the need for cheap software. I'm also
doing this for a hobby.

> Also can some one explain the options in hardware and software I have
> to convert the sherline to CNC.

In short you're gonna need:

1 - A machine tool with lead screws or ball screws

2 - Motors attached to the lead screws or ball screws with some way to
make sure you can positively move each axis to a particular location. In
all practicality, this limits you to servo motors and stepper motors.

3 - A motor controller that will make the motors positively move each axis
to a particular location. This will depend on your choice of motors.
Servos and steppers both work, but they work along different lines so
their controllers are wildly different.

4 - Something that will tell the motors where to go. This can be a
proprietary piece of hardware, or it can be a general purpose computer
running machine control software. Lots of choices here. Some are
expensive, some are cheap, some are free. There are tradeoffs with each.

5 - Something that will turn a drawing into a language the control
software understands. This is typically g-code, but other options are out
there (DanCAD and DanCAM being one of them.)

6 - Something that will make an electronic drawing. (A CAD package.)

7 - Time.

This last one is the sticking point. Getting all this working involves a
lot of time and effort on your part. Depending on your decisions, it may
take more or less of your time. Also depending on your decisions, your
cost may be high, middlin', or low. There are tradeoffs for everything.

Tom