I bought a rotational axis ( 4th axis or A axis call it whatever you
like) for my CNC with a 4 jaws chuck. I intend to use this as both a 4th
axis on my CNC, or as an independent "poor man's lathe". I know, it
will be a very primitive lathe with a lot of limitations, but I intend
to try it out anyway to toy with and to learn. Maybe later on I'll buy a
real lathe as well, but for now this will do. I am sure I can use it
for some sort of work, but I will see that later.
To get the lathe function I had to design a control box. This is based
on an Arduino Uno module with a 2x16 lines LCD. It is a very simple
design, using only three buttons, one for clockwise rotation start, one
for counter clockwise rotation start and of course, one for stop.
Stepper acceleration and deceleration is also implemented, with a
possibility to select acceleration in 7 steps. The chuck rotation can be
adjusted between zero and 380 RPM, which is the maximum. This
corresponds to 2280 RPM on the stepper, due to the 1/6 reduction pulley
the stepper drives the chuck with. So it is a respectable rotation speed
for being a stepper. The rotation speed is set using a rotary encoder
and that speed is saved in the EEPROM, so after a power off, the last
used rotation speed is restored. The rotary encoder push button is
connected to the Arduino reset and acts as an emergency stop, in case
there is a need for stopping as fast as possible. Of course, this means
no deceleration, just an abrupt instant stop.
For powering and control I also built a separate PSU, which provides 48V
7A DC through four individual 12V power supplies connected in series.
Three of these are 9A supplies, the fourth is though only 7A, which is
why the maximum is limited to 7A, but considering that the stepper is
only 3A, I figure that the PSU will be good enough for the purpose.
The PSU box also contains a DM542 stepper driver, which is configured to
the maximum current and 2x micro stepping, which results in 400 steps
per rev.
There is also a relay inside the box. This relay decides if the 4th axis
is to be driven as A axis by my CNC using UCCNC software, or
independently run as a "lathe", controlled from my control box and
rotated non-stop until i press the stop button. The relay can be
switched from the control box and the default setting (with the relay
off) is that the rotational axis is controlled by UCCNC.
Yesterday I made a short video about testing the control box functions
and showing the rotations. I have not used it yet as a lathe, still
waiting for some necessary tools before I can do any real tests, but I
thought this can be interesting to show as well. Maybe it will give
other people some ideas as well.
I intend to share the Arduino code here as well. It is well commented,
so based on the code, the simple box can easily be built by anyone
understanding the basics of Arduino. I will need to add some file header
information before I post it here, but it will be posted soon.
I hope you will enjoy watching this video. I will make a new one once I start using it as well.