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My design - Concept, theory, background

Before we get too far into this I thought I should explain some of my thinking on this whole deal.  As I said I have looked at MANY  home made CNC machines over the past couple years. 

There seems to be 3 basic categories of machine. 

  • 1.  Ultra cheap -  These are great and some very interesting ideas for a basic get your feet wet deal. 
  • 2.  Middle of the road  -  Where I fall.  The catch is I was never happy with the pipe ideas and some of the other concepts. 
  • 3.  "Expensive" - Not in my budget as the slides alone can easily cost several hundred dollars then add ball screws and you still haven't made a frame or have any way to control the thing.  You quickly find yourself well over $1000 and more. 

My idea is to build a reasonably priced machine with good accuracy and simple techniques.  First we need to explain reasonably priced.   If you are looking for a sub $100 CNC machine you are a much better scrounger than I am or you only need to do business card sized machining.  :)   I hope to spend less than $1000.  This will include all the materials to build the machine as well as the hardware to make things move and even the software to run it all.   It is VERY possible to do this for a LOT less if you take your time and scrounge the parts.  The motors and controllers are the most expensive part of the whole build.  You will notice I am using commercial drivers and pretty heavy duty motors.  This is because I want some flexibility in my design and I want to be able to move most of this to a larger machine should I find the "need". 

I had originally planned on using Aluminum extrusions like 80/20.  These things come in many shapes and sizes, are pretty in expensive from the short cut pile (off Ebay) and easy for any one to work with.  The catch comes in when you want to make things move.  The bearings they use get expensive even off Ebay.  This brings the basic cost up fast and almost comparable to real linear slides which would be better in the long run.  My thinking on this was to save money by building a simple frame and using that frame to run the bearings.  So many designs build a basic frame and then complicate it by adding something else to run the bearings one.  This just seemed crazy for me to do what I thought could be done in 1 step. 

When I ran across the Build Your Own CNC Router Machine web site the whole thing fell right into place.  Its so simple I couldn't see what was right in front of me.  :) 

Using MDF as a base is a very good idea.  Its common to many Home CNC machines.  MDF is cheap, stable and easy to work.  It also adds some weight which will help dampen vibrations.  The Aluminum angle is also cheap, actually less expensive than good water pipe or nice solid shafting.  Plus you mount it directly to the machine removing countless hours of making some kind of alignment blocks and then mounting and adjusting everything. 

So what do I want from this machine? 

  • A 2' x 4' (24" x 48") working area.  X,Y axis
  • A 4" Z axis.  Now this is actually overkill for many "routers"  But you will see I have included the cost of a 4th axis in my build price.  This will drive a simple lathe function I will sit on the bed of the machine to make things like table legs and stair balusters.
  • I want a reasonable accurate machine.  Now that's an interesting statement.  I have NO intention of making parts for NASA and most of my parts will be in wood   I figure If I can get 0.050 accuracy out of this thing Its one great machine.   :)
  • I do want the ability to machine some Aluminum.

Again I want to stress that my machine will be somewhat different than Patrick's.  I have access to a complete wood working shop and have plenty of experience making things from wood.   Some of the parts will have a different design and many will use different joining techniques.  Yes this will add to the complexity of the build.  Some of the design I feel will be improvements for long term use of the machine .  Others will simply be additions some may feel are not needed.  Other changes will be experiments that may not work.  :) 

As of October 3 2007 I have started building the machine and have several parts cut and some assembled.  I am hoping to get some pics during the build to highlight things and eventually provide some basic drawings.


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