Couple of thoughts Jorge. First is how to manage building the machine base. I'm sure that you know that the parts of the machine that hold it together and allow it to move are what absorb the cutting forces and harmonics and allow it to cut accurately. The K&T company built quite a business with large machines using welded bases rather than cast. You might look at some of their designs. The concrete floor provided quite a bit of the rigidity of the assembled machine. You might also consider concrete castings for some of the base. Portable concrete step manufacturing companies do some great work with small aggregates and fiber mixes.
The second thought is EMC2 related. The linear scales, while very accurate in themselves have not proven to be very good for use with EMC2 control. The problem has to do with backlash in the drive components. Our backlash compensation counts encoder pulses to find the other edge of the lash whenever the direction reverses. Since the linear scale is connected on the work piece side of the lash EMC will not see pulses until the lash has been taken up. Even small amounts of lash will cause a well controlled servo system to hunt and overshoot. We've talked about using a motor driven encoder connected to one PID loop in our software to handle this lash problem and another PID connected to the linear scale to handle final positioning. I don't know that any real tests of such a system have been reported.
HTH
Rayh
--- [EMAIL PROTECTED] wrote:
From: Jorge Barrera <[EMAIL PROTECTED]>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Subject: Re: [Emc-users] home-mad CNC machine project.
Date: Fri, 14 Mar 2008 20:09:24 -0700 (PDT)
I would love to connect with anybody that has relevant experience
Jorge
From: Doug Metzler <[EMAIL PROTECTED]>
To: Enhanced Machine Controller (EMC) <emc-users@lists.sourceforge.net>; [EMAIL PROTECTED]
Sent: Friday, March 14, 2008 1:35:27 AM
Subject: Re: [Emc-users] home-mad CNC machine project.
I’m on my third rev of my home-built CNC project. My best advice is to make it much more rigid than you think you need to. I started out with small slider shafts and now I’m up to 7/8” (which you can get surprisingly cheap at speedymetals). But in my case every rev got considerably bigger. The first rev was a little 8*11 PCB cutter and it had ¼” sliders, the second rev grew to 11*17 with 3/8’s and the latest rev will be a whopping 20*34”, thus the need for the huge sliders. But definitely err on the side of over-engineering for rigidity.
The other part that I couldn’t afford that I wish I could have was good linear bearings. I tried many times to come up with my own linear bearing surface but in the end most of the available torque was spent trying to overcome the sliders. I still can’t afford good linear bearings but my latest home-brew setup uses small standard bearings (some of which are spring-loaded). These are a bear to manufacture but will dramatically increase the quality of the machine.
I am using threaded rod but it makes for a very slow machine. If anyone here has a line on good inexpensive ballscrews please let me know.
As for electronics I am doing it all myself because I want smart nodes. But I think the consensus here is probably right – spend the money to save the time.
Drop me a note if you have specific questions.
DougM
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of seth wiley
Sent: Sunday, March 02, 2008 1:10
PM
To: [EMAIL PROTECTED];
Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] home-mad
CNC machine project.
sean,
i'm slowly (in my very spare sparetime) working up a small
(12"x12"x3") low tolerance cnc machine for light wood and
plastics. it is also serving as a general teach-myself-cnc project. i chose to
go with a pre-config'd electronics / servos package from keling inc. (http://www.kelinginc.net/ThreeXCNCPackage2.html).
after reading lots of cnczone entries and doing lots of chipset / board /
wiring research, i figured it's 329$ well spent by saving me time, and it's a
pretty complete set of items for a good price. also, this site has some helpful
info on wiring (http://www.robertguyser.com/).
i am next building up the machine using basic 8020 or minitec extrusions and
linear accessories. lovejoy couplings will round out the basic bom. i'll use
whatever i have as a cutter head - dremel, trim router, etc. it should turn out
to be a fairly cheap machine without eating up too much time reinventing the
wheel. cam environment: emc2 packaged with ubuntu. it was a smooth install and
the forums are great. so, i cannot say that this route is flawless and worked
out yet since i'm still in the process, but i can say that i've spent a bunch
of time running cnc machines, spent lots of time reading everything i could
find on the internet and printed about various diy cnc options. i think this
route seems like a pretty efficient and solid starting point. i'll let you know
how it comes out - if i ever get the time to complete it!
have fun regardless of which direction you choose. good luck.
-seth
On Fri, Feb 29, 2008 at 10:59 PM, <[EMAIL PROTECTED]> wrote:
I was wondering if anyone
has ever tried a do-it-yourself CNC project like this. http://www.instructables.com/id/Easy-to-build-CNC-Mill-Stepper-Motor-and-Driver-ci/
and this http://www.instructables.com/id/Easy-to-Build-Desk-Top-3-Axis-CNC-Milling-Machine/
. If so, any pointers or words of knowledge before I dive in?
Also, I'm still looking for some stepper motors to use if anyone has a good
source.. I'm a college student, so I'm obviously broke and
starving. So, inexpensive would be good. Thanks guys.
Sean
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