Prototype #2: Building

(My main hard drive crashed in Summer 2009, so most of my process pictures are gone).

So after the incomplete 1st attempt, I decided to make my own CNC design with improvements I find fit.  Because I am working in my backyard with minimal tools and no welder, I decided to choose wood as the main material again.  Wood is a common material for DIY CNCs, it can create highly accurate CNCs when properly built.  I do not have any plans for prototype #2, sorry.  I designed and fabricated it as I went along.

For prototype #2, I decided to use Baltic Birch instead of MDF as per prototype #1 plans.  I did not like MDF as it does not handle screws that well.  I discarded the homebuilt bearings and slides (using skateboard bearings and aluminum angle bars) as it was not up to par for my expectations.  I went on eBay and found used high precision bearings and slides.  The 1st picture shows the back of the Z axis using fully supported slides and Thompson bearings, really nice stuff!

The X and Y axis (shown in picture #2) I used precision slides and bearings (forgot which brand) but not fully supported.  They work great but found that aligning them during assembly is much harder than fully supported bearings.

I used the Acme 1/2" 20tpi lead screw from prototype #1, as the anti-backlash lead nut.  TPI is teeth per inch, so 20tpi means it has to spin 20x to move 1 inch.  The result of this combo is dirt slow!!  It crawls about 1" per second movement.  I recommend anyone in using a multi-start Acme screw (as I have done on my newest CNC) as it will speed up movement tremendously.  More TPI means more precision, but who really needs to be accurate 0.0001" increments?  Your backlash tolerance will be more than that so in reality your precision is only as good as your backlash movement.