Homebrew PCBs

On Sat, 12 Mar 2005 21:40:27 +1100, Tony Smith <ajsmith@...>  
wrote:

>
> You can get all sorts of non-metal bearing (ball), including ceramic,
> plastic & glass.
> From memory, you can get bearings that have glass balls with plastic  
> body,
> and are used in food preparation things.  No lubrication to prevent
> contamination, and can be washed clean with water.
> Look for 'food grade' bearings.  Very low RPM, maybe 200-300 RPM.
> Tony


Low rpm is a no-go and hard to get is a no-go too (which the  
above-mentioned is for me).
Thanks anyway.


I was doing a proof of concept the last hour from a piece of electrical  
tubing, 2 end-caps (spray-can caps), a 4mm steel shaft, a clear plastic  
bucket, a piece of wood, some water, a drill/grinder 100W.


The plastic tubing is maybe 3 to 4cm diameter, glued the endcaps on. made  
3 holes in the lower endcap to allow water in, put the steel shaft through  
the entire thing, glued the wood block in the bottom of the bucket after  
making a 5mm hole in it (not through) for bearing. made another hole in  
the lid of the bucket and attached drill/grinder to shaft.
Oh yes, made a single 1mm hole in the tubing as nozzle.

First results show that it definitely can work (as commercial products  
show).

The water rises easily, in fact i haven't got the top cap sealed all the  
way and it sqirts out there even at moderate RPM.

The single hole shows a spray "line" on the inside of the bucket.

What i want to do next is experiment with differnt nozzle holes (possibly  
with a water hose so i can watch the results in static conditions. I think  
if i use a small cutting disc in the grinder i might be able to create  
"fan" like nozzles.

I also had the idea to allow the whole assy to move up and down (via  
geared motor) to even out any effects from nozzle placement. would not be  
too hard to make but definitely better if not needed.

I further thought about making a triangular tank, with the sprayer in one  
corner and the PCB on the opposite wall. This should reduce ill-effects  
 from different distances/angles/sweep speeds compared to a rectangular  
setup of same volume.
It would be good to know all problems of the commercial units, and i will  
nag Markus off list about it some more.

I will also slowly try to find titanium rod somewhere from 6 to 10mm  and  
teflon plates/blocks.

As for the tubing, i think it might be a good idea to use thick-walled  
water tubing instead of electrical tubing?

Another thing i learnt from the experiment is that care must be taken to  
get things true and balanced.


After the results i have seen now i wonder why nobody seems to have built  
a rotary etcher so far. It shouldn't be hard at all to at least replicate  
the results of the cheap commercial units if not inproove them.

Well, i look forward to hearing about other ideas.

Anyone willing to work out formulas for the pressure at the nozzle per RPM  
(given tube diameter and assumed water "skin" thickness)?


ST