Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "hjf2k2" <drgenio@h...> wrote:
> > Bad idea,
> > 
> > You will have no control over the force - with a spring, you 
would 
> > simply get a single feedrate for everything.  Believe me, 
a .010" 
> > diameter drill requires a much different feedrate than a .125" 
> > diameter drill.
> 
> Why? If I compress the spring a little more, I'll have more 
strength.
> Or so I think. So I can put a screw to adjust the spring tension 
for
> the different bits (I use .75 and 1mm bits anyway...)
> 
> > There is no quick and easy answer on motor sizing,  
> Well, I'll be making my machine with whatever I have handy. I can't
> seem to find a supplier of ball screws for my country (I'm sure 
there
> are, but anyway the price will be too high), so I'd have to build 
it
> with a regular threaded and nuts. I don't mind the efficiency 
either,
> I don't care if it's a little oversized. I ask this as I have
> absolutely no idea about stepper motors.
> 
> hjf


While similar methods have been used on drilling machines WAY BACK 
in time, they too suffered from the lack of control.  You would not 
have any way of knowing if it's too fast till you break the tools.  
With a controlled axis, you simply tell it how fast to feed in 
inches per minute.  For small drills, the difference between 1 IPM 
and 2 IPM will be the difference between a broken tool and a tool 
that will drill all the holes.

For a stepper size reference, my CNC router uses 160 oz-in motors - 
direct drive to ball screws running dry.  The way system is very 
basic, UHMW plastic against aluminum.  It developes around 50 pounds 
of cutting force - very approximate value.

These 160 oz-in motors are running at 44 volts and 1.5 amps through 
a unipolar chopper driver.  I can get rapid speeds up to 150 IPM but 
only with some pretty slow accell/decell ramps.

That should give you some parameters to start with.