Homebrew PCBs

Hi Guys

I am going to start building a small CNC milling machine (X = 7", Y = 
7", Z = 6") for machining PCB's and I am wondering what I should be 
using for the Feed Screws?  I am not sure if a small machine like this 
warrants installing Ball Screws?  What about using a good stainless 
threaded rod and a split nut to adjust the backlash?  I have a Sherline 
Mill with Stepper mounted directly onto the screws and I find the travel 
speeds to be very slow.  Sherline use 18 threads per inch on their Feed 
Screws.
What are you guys using for your feed screws?  When using directly 
mounted Stepper Motors, what would be a good thread pitch for reasonable 
travel speeds?
Thanks for the help.

Bill

Bill Blackburn wrote:
> What are you guys using for your feed screws?  When using directly 
> mounted Stepper Motors, what would be a good thread pitch for reasonable 
> travel speeds?
> Thanks for the help.
> 
> Bill 
> 

   Thinking 'linear motion products' but can't remember for sure if that's the 
right company name.  They have 1/4" lead screw, and plastic anti-backlash nuts. 
  A friend got some and 3 four foot sections plus screws was around $100 or a 
little over, which isn't too bad really.

   Most notable, pretty sure they had some that was 2 start.  As in still 20 
groves per inch, but 2 helix both at 10 pitch so you only had 10 turns to the 
inch.  Something like that is what you want if you can get it, still reasonable 
from the smaller size but faster travel.

Alan

On Mon, 16 May 2005 19:43:49 -0400, Bill Blackburn  
<billblackburn@...> wrote:

> Hi Guys
> I am going to start building a small CNC milling machine (X = 7", Y =
> 7", Z = 6") for machining PCB's and I am wondering what I should be
> using for the Feed Screws?  I am not sure if a small machine like this
> warrants installing Ball Screws?  What about using a good stainless
> threaded rod and a split nut to adjust the backlash?  I have a Sherline
> Mill with Stepper mounted directly onto the screws and I find the travel
> speeds to be very slow.  Sherline use 18 threads per inch on their Feed
> Screws.
> What are you guys using for your feed screws?  When using directly
> mounted Stepper Motors, what would be a good thread pitch for reasonable
> travel speeds?
> Thanks for the help.
> Bill


I will use M8 stainless on my machine. I think the pitch is too small but  
it will only travel slower, i can live with that.
Don't have the money for fancy screws.

ST