DIY CNC Update - frame, linear bearings, motors, electronics, mechanical drives...

Folks and interested parties...

I'd started my own lengthy project update last night, but just saw
Dave's post. Darn if he is not quick! I'll rejigger this to be a
general update to reflect his post. All are welcome to follow the
project progress and join, participate, or watch. It is a DO-OCRACY
as Chris says.

Frame = We will use the kit of extruded aluminum rails for the frame.
I've started the 2D and 3D assembly drawing and have been designing
corner brackets and piece-parts for the structure that can be made on
my home CNC. I'll figure out how to post some static images and can
probably export and post the as-is working 2D as a DXF file and the 3D
as a STEP file.

Linear Bearings = Since this is a "quick-and-dirty" CNC learning
experience we won't have fancy linear bearings on the X/Y/Z linear
axes. There has been project discussion, but Jim has prototyped a
sliding journal bearing that keys into the central grooves on the
extruded aluminum channels. It will be easy to make and hopefully
good enough not to bind-up and get clogged with machining chips. Stay
tuned for a week or two to see working parts.

Motors = We plan to start with NEMA 17 frame size steppers (rather
than larger NEMA 23). Dave's post said he's ordered a test set of
drivers and motors. Cash and parts do have a way of challenging a
project to move along further and faster.

Electronics = Dave's order includes the four Spark Fun EasyDrivers
http://www.sparkfun.com/commerce/product_info.php?products_id=9402
Each takes the two 5 VDC STEP and DIR signals and sequences the power
to the four stepper motor wires to increment the motor armiture 1/200
of a rev (1.8 degrees) with each STEP. TP is prototyping that up with
Jim's prior test EasyDriver and NEMA 17 motor. Next week's discussion
will be on other electroincs, break-out board, laptop vs. Arduino,
etc. I'll make another post on this topic later in the week.

Mechanical Drive = Since the NEMA 17 motor has a 5mm shaft, I
recommend to use 5mm all-thread threaded rod for the lead screw and
put a shaft coupling between motor and screw. We'll just use the
motor bearings as the axial thrust bearing for the lead screw at the
head end and float the tail end of the lead screw in a loose journal
bearing. This is not the most rigerous mechanical setup but keeps
with the quick-and-dirty theme to be good enough for now. The 5mm
diameter all-thread has a 0.8mm pitch (0.031") per revolution. Doing
the numbers, one STEP = 1/200 rev (1.8 deg) converts to a linear
distance of .004mm (0.000157") which is too small to see and that is
good. Six STEPS equals .024mm (or about 0.001") which is a good small
nominal working unit. Realistically we will have reversal (backlash)
errors and a general level of precision likely to be 5 to 10 time
bigger than that. This amount will be noticable, but not too bad for
such a simple beast. Based on the above the resolution should be OK
fine. The next trick is to mock it up and confirm that the torque and
speed capabilities are OK fine too. The threaded rod will increase
the motor's torque delivered to the moving carriage. Assuming it all
works out, we'll use the same general setup on X, Y, and Z.

We'll also restart the dormant EGGBOT project. It will use similar
motor/drive technology and be a quick follower to this first DIY CNC
undertaking. Stay tuned for further posts on that as it has special
additional needs.

More later, bye for now... Jim

So many toys, so little time!

I would also like to donate money to get some of the missing parts that we need for this project. I saw the list on the wiki of parts but not sure what the priority is on different things in order to start having a PoC.

I’m very excited about this project tho!

Jim, if you need a place to put images/files just send me an email and I’ll get you setup on our shell/web server (I assume you have SSH/SCP??) You can upload files and link to them via the wiki.

Craig

Craig wrote:

I would also like to donate money to get some of the missing parts
that we need for this project. I saw the list on the wiki of parts
but not sure what the priority is on different things in order to
start having a PoC.

I'm very excited about this project tho!

Jim, if you need a place to put images/files just send me an email and
I'll get you setup on our shell/web server (I assume you have
SSH/SCP??) You can upload files and link to them via the wiki.

Craig

    Folks and interested parties...

    I'd started my own lengthy project update last night, but just saw
    Dave's post. Darn if he is not quick! I'll rejigger this to be a
    general update to reflect his post. All are welcome to follow the
    project progress and join, participate, or watch. It is a DO-OCRACY
    as Chris says.

    Frame = We will use the kit of extruded aluminum rails for the frame.
    I've started the 2D and 3D assembly drawing and have been designing
    corner brackets and piece-parts for the structure that can be made on
    my home CNC. I'll figure out how to post some static images and can
    probably export and post the as-is working 2D as a DXF file and the 3D
    as a STEP file.

    Linear Bearings = Since this is a "quick-and-dirty" CNC learning
    experience we won't have fancy linear bearings on the X/Y/Z linear
    axes. There has been project discussion, but Jim has prototyped a
    sliding journal bearing that keys into the central grooves on the
    extruded aluminum channels. It will be easy to make and hopefully
    good enough not to bind-up and get clogged with machining chips. Stay
    tuned for a week or two to see working parts.

    Motors = We plan to start with NEMA 17 frame size steppers (rather
    than larger NEMA 23). Dave's post said he's ordered a test set of
    drivers and motors. Cash and parts do have a way of challenging a
    project to move along further and faster.

    Electronics = Dave's order includes the four Spark Fun EasyDrivers
    http://www.sparkfun.com/commerce/product_info.php?products_id=9402
    Each takes the two 5 VDC STEP and DIR signals and sequences the power
    to the four stepper motor wires to increment the motor armiture 1/200
    of a rev (1.8 degrees) with each STEP. TP is prototyping that up with
    Jim's prior test EasyDriver and NEMA 17 motor. Next week's discussion
    will be on other electroincs, break-out board, laptop vs. Arduino,
    etc. I'll make another post on this topic later in the week.

    Mechanical Drive = Since the NEMA 17 motor has a 5mm shaft, I
    recommend to use 5mm all-thread threaded rod for the lead screw and
    put a shaft coupling between motor and screw. We'll just use the
    motor bearings as the axial thrust bearing for the lead screw at the
    head end and float the tail end of the lead screw in a loose journal
    bearing. This is not the most rigerous mechanical setup but keeps
    with the quick-and-dirty theme to be good enough for now. The 5mm
    diameter all-thread has a 0.8mm pitch (0.031") per revolution. Doing
    the numbers, one STEP = 1/200 rev (1.8 deg) converts to a linear
    distance of .004mm (0.000157") which is too small to see and that is
    good. Six STEPS equals .024mm (or about 0.001") which is a good small
    nominal working unit. Realistically we will have reversal (backlash)
    errors and a general level of precision likely to be 5 to 10 time
    bigger than that. This amount will be noticable, but not too bad for
    such a simple beast. Based on the above the resolution should be OK
    fine. The next trick is to mock it up and confirm that the torque and
    speed capabilities are OK fine too. The threaded rod will increase
    the motor's torque delivered to the moving carriage. Assuming it all
    works out, we'll use the same general setup on X, Y, and Z.

    We'll also restart the dormant EGGBOT project. It will use similar
    motor/drive technology and be a quick follower to this first DIY CNC
    undertaking. Stay tuned for further posts on that as it has special
    additional needs.

    More later, bye for now... Jim

    So many toys, so little time!

>

Hmm, maybe have some way that people can log donations to different
projects? Maybe have something like a pledgie for large group projects?

- Paul

pledgie has served us well in the past :slight_smile:

Team,

Here is an update on the CNC project:

The parts I ordered came in. I received 4 Sparkfun EasyDriver boards
and 4 24v 2A NEMA17 stepper motors. I soldered some header pins onto
the boards and tested them out. I also soldered an end onto one of
the motors' wires and tested it out. I was able to successfully drive
the motor with a test program on my Arduino. I plugged all four
boards onto a big breadboard and wired them up so they are ready to
receive commands. I ran the motors using a couple different power
sources I found around the Hive, the highest one being a 19v laptop
adapter. We will have to hunt down or purchase a 24v power supply to
run them at full strength.

http://www.flickr.com/photos/dave_menninger/sets/72157622457271173/

I also went ahead and burned a copy of the EMC2 LiveCD (
http://linuxcnc.org/ ) so we can evaluate whether it will work for us.
If we don't use that, we can use Mach 3 which requires Windows XP.
We will need to find a PC to set aside for this use.

I've been trying to keep the wiki page up to date with progress so
check there for more details:
http://wiki.hive13.org/index.php?title=DIY_CNC_Router

I think the next big steps are getting the frame built and learning
how to use EMC2.

~Dave

Dave, thanks for the update on your great progress. I've got some
links to 24 VDC power supplies. How many amps do you think we'll draw
with all four running.

I'm glad your looking into EMC2. That is a popular alternative to
MACH3 but I'm not enough of a Linux guy yet to have tried it myself.
Let's try it together and see.

Jim

Jim, I am not an expert with electronics, but there are 4 stepper motors, each one is 24v and each one uses 2A. It has been a while since I had any electronics classes, is current cumulative? So if you have 4 motors, each one drawing their max 2A, is that 8 amps?

Yes - if the steppers are rated to draw a MAX of 2A, then thats

2A * 4 = 8A
8A * 24V = 192W

I would assume there is some loss through the stepper controllers as well, though I don’t know how much.

It may be possible to hack an ATX power supply to do this, but I just
don't know enough about them.

If not, we will probably want something similar to this:

http://cgi.ebay.ca/DC-Power-Supply-24V-8-5AMP-200W-CNC-Servo-Stepper-Motor_W0QQitemZ150336585599QQcmdZViewItemQQptZLH_DefaultDomain_2?hash=item2300c23f7f

~Dave

I'm no expert either, but the math by Chris looked right for amps and
watts. We typically won't run all four motors full out at the same
time. Another way to go is piece-parts (a big iron transformer,
bridge rectifier, and capacitor) but I'm not comfortable with those
design calculations and that's what's probably in Dave's e-bay one. I
do recall some prior forum discussion on another site about regulated
and unregulated power supplies. I think it was the regulated ones
that caused problems. Since Dave's e-bay one looks to be from a servo-
stepper source it is probably a good bet. The price doesn't seem too
bad. I'd say let's get it if someone wants to pull the trigger and
get it.

Jim

If your stepper controller does half steps then it will energize both
coils, thus a full load.