Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "Justin" <jcom10@y...> wrote:
> Firstly hello to the group - first time poster here :-)
> 
> Currently I produce my own PCB's using the UV/dev/etch method.
> (homebrew UV box using insect killer lamps, etch tank is a cereal
> container and fish tank pump)
> This works well but is messy and time consuming (at least it is 
when I
> do it!).
> 
> I would prefer a CNC milling solution and having searched around,
> found what looks to be a promising 'off the shelf' solution:
> http://www.milinst.com/robotics/robotics.htm#axis. At £189 for the 
kit
> it would seem quite affordable, but is it up to the job?
> 
> I don't know much about this sort of thing, so wondered if anyone
> could speculate on its suitability for prototype PCB work.
> 
> Thoughts?
> 
> Cheers,
> Justin.

Interesting design.

I would assume that it will be able to do what you ask, but you need 
to also understand the tradeoffs.

I think the calculation is ....
( lead screw threads per inch times motor power times lead screw 
efficiency ) / 16 = pounds of force.

First, the stepper motors in a kit of that cost are most likely 
pretty small.  I would assume under the 50oz inch of a single stack 
NEMA23 stepper.  And more likly a pressed can stepper like found on a 
printer or fax machine.

That said, a pressed can stepper will be lucky to offer 15 oz-in of 
power.

a 1/4-20 screw is often the basis of these small machines, and 
threded rod has a generous efficiency of 20%.  That resolves to 

(15 x 20 x .2) / 16 = 3.75 pounds of force.   This is VERY light.

Therefore to get any work done, the machine either has to have a more 
fine screw, or use pullies to obtain a reduction in speed for an 
increase in power.

This results in a SLOW for said machine.

On the mechanical side, the frame may or may not be able to handle 
larger motors.   assuming it can, or you support it to do so, you can 
use larger motors.

NEMA23 single stack motors are not too uncommon so that would be the 
first up-grade.

Then a higher amp stepping motor controller would be a second upgrade.

This would then offer
50x20x.2/16 = 12.5 pounds of force.  This is still very light, but 
will probably have enought umph to push a dull cutter thru copper.

If I were in the market for a PCB machine, I would think long and 
hard about this, and probably buy it.    I am sure it can be 
strenghtened so it most likly can be upgraded.

I would considder this as a PCB-driller and etch boards by chemical, 
but of course try some mechanically etched boards.

I don't see this as a be all machine, but more as a first step into 
the wonderful world of CNC control.

Dave