Homebrew PCBs

> Allthread quite accurate enough for drilling and PCB milling. If 
you use two
> preloaded nuts then backlash should not be a problem. For the 
larger sizes
> of allthread you can buy extra long nuts that are used as couplers. 
They
> seem to have less backlash then ordinary nuts.
> 
> Les


I use long threads and find that the typical play between a screw and 
nut is about 5thou (0.133mm) and that is pretty sloppy.

with a coupling, that cuts down to much less, but if you can tap your 
own part, the threads become even tighter.

The HUGE problem is the material that the screw is made from.

I took my threaded rod and chased it with a die that was adjusted so 
that it was not cutting, only cleaning the threads. lots of oil.

Then I took a rag with my thumbnail and proceeded to clean the 
threads.  every few turns the rag would catch or I could feel a lump 
in the metal.  A small file got rid of the lump.  By the time I was 
done, I could run the thread from end to end with no roughness.

Personally, I don't like all-thread, but I use it because it does the 
job.

While I am talking about it, do not expect heavy machining with it.  
The losses from friction are just too great.  A heavy motor and/or 
belt reduction is needed for that.  It can be done if you need to get 
by on a budget, but don't stop looking for ballscrews or an ACME rod.

Dave