Re: Relation of a DRO to a CNC modification of a machine?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Joe Albeanese" <jda3@c...>
wrote:

> Tom,
> I have a question for you if you don't mind. I am so new to this I

am not

> sure if I am born yet!! I want to set up one of the small lathes I

have. I

> had purchased some step motors to try and do this. I would be glad

to give

> you thew particulars on them if you need it. Anyway I don't

necessary want

> to use it as cnc but more to use it as a left and right movement

for the

> longitudinal feed. What do I need in the way of hardware to make

these

> motors move the way I want them to. I don't have a lot of money to

spend on

> this project right now. I have been looking on ebay and have found

some

> electronic parts that I think my work but I am not sure. If I

would send you

> the site would you be willing to go look and tell me if it would

work. It

> would be greatly appreciated. If you can't just let me know I will
> understand.
> Thank you,
> Joe
>
>

Joe, checkout the low cost stepper drivers at www.hobbycnc.com (the
$79 three axis kit is a good deal if you know how to solder PC
boards). Also there is the Xylotex cards. Try to stay with bipolar
(although not absolutely essential on a small machine) chopper type
drives, at least half-stepping. There are several other cards for
twisting a stepper. Somebody help us out here.....

For bigger steppers you need (obviously) motor drivers that will
handle higher voltages and currents. Microstepping drives are a
vast improvement. Steppers are current driven devices that require
you limit the current. The rotational speed is determined by how
fast you can charge and discharge the coils in the stepper. The
only way to do this is to raise the voltage then cut the waveform
off when you hit the current spec. Typical target values for
voltage are anywhere from 10 to 20 times nameplate voltage spec.
The chopper type drives use a method called PWM (pulse width
modulation) to drive the motor. The DC is "chopped" at a set
frequency and the duty cycle of each pulse is a function of the
sensed current. No current limit resistors are needed.

Sounds like what you are need is more of a power feed for your lathe
but once you have the motors mounted and running you have the
makings of a CNC machine.

You will need a source of step and direction pulses to run the
motors. The most common way is to use one of the low cost PC based
software controller applications like TurboCNC, MACH2 or if you are
comfortable with Linux, EMC. I don't know if TurboCNC has a lathe
piece but it could be used to manually jog the motors for manual
feed. There have been discussions about a manual Pulse generator
(MPG) device so you can sit and "dial" in a position. Check the
MACH1MACH2CNC list for some of the MPG threads as well as this list.

If you pay attention to building a minumum backlash design then you
also have a built-in DRO for your lathe.

If you want to get deeper into CNC and do things like threading and
complex shoulder cuts and tapered surfaces then you need to consider
the CNC "trio" of CAD, CAM and Controller. MACH2 has a lathe
component and is the Controller piece. Others can advise you on CAM
for lathe (Vector and Dolphin come to mind) and the CAD side has a
wide range of options as well.

I have a 12 X 36 lathe that mostly sits compared to my other
machines. Someday I want to CNC it just because I can! Once I have
completed my conversion of my big mill to full CNC I am going to
move the current DRO over to my lathe. That is one feature that
will be real nice on a lathe.

Don't worry about being a newbe. We all started out that way at
some point. Don't worry about asking what you think are dumb
questions. There are probably hundreds of "lurkers" that too shy to
ask the questions. The reason we all hang around these groups is
that we like to help propagate the hobby and newbes are the
lifeblood of the "sport".