Homebrew PCBs

Stefan Trethan wrote:
> 20.05.2003 16:00:06, "Steve" <alienrelics@...> wrote:
> 

> 
> thanks for the pictures. now it is much clearer how you operate it.
> 
> @steve:
> in my browser the apostrophe was no problem.
> but tinyurl takes a lot time to redirect. ;-)
> 
> @markus:
> ok, i will regard this request.
> i didn't think about it a lot.
> normally i answer all emails on top.
> 
> i find it a little strange to have to scroll down and search the whole email for the reply (which is in 
> between and not at the bottom because of all of the sponsor advertising etc..
> 
> but i understand with mailgroups it is then easyer to read old postings because the text is in the right 
> order. anyways i personally find it more comfortable to write/read the latest thing on top of a mail. 
> (the lower part only being for reference if anyone is not familiar with it).
> 
> but of course i will join the majority and from now on write on the bottom.
> 
> 
> 
> i have tested the drill i wanted to put on the new press.
> it is scrap.
> the carbide bits will never withstand this.
> it is out of center....
> 
> 
> i will go to the tool shop tomorrow, see their minidrill products.
> the proxxon drill presses are very nice (and ready made) but also much more expensive than the hand 
> tools and making the press your own.
> i also have a second (dremel-like) minidrill at home which is much better centered..
> i will maybe use this after closer inspection.
> 


The small drill presses I've seen for a few hundred dollars have 
not been very stable compared to the thing I made. As I said, its 
a first design and there are much better ways do go about 
building a pivoting type drill press. I haven't seen a proxxon 
drill spindle but from the web page you gave they look better 
made than a Dremal. You have to check roundout.

The arc radius can be made smaller than 680 mm as I have done. 
I'd say a radius of 400 mm would be ok for drilling few mm deep.

A bit of math's shows the amount the drill moves out of position 
due to the arc is equal to  r - sqrt(r^2 - h^2)
Where r is arc radius and h is the depth the drill enters the 
PCB. So if r = 400 and h = 5 you get 0.031 mm or 1.2 mils.

I'm sure carbide drill bits can survive 0.03mm of movement.

A simpler approach for a pivot is to use two "rod end" bearings 
at the rear of the base. A 16 mm piece of threaded bar can be 
bent into a V or U shape to make up the main arm. Each end of the 
threaded bar is screwed to a female rod end bearing. Two vertical 
posts made from 16 mm bolts are mounted at the rear of the base. 
The opening of each rod end bearing go on these posts, and 
tightened up with nuts on either side. The advantage of using rod 
ends is they do not have to be aligned and you get perfect stable 
rotation along the axis between the two centers of each rod end 
sphere. You can also adjust the height of each rod end which 
allows easy alignment of the drill in that axis.

  |---------------------|
  |  O              O <-|-- 16 mm threaded posts
  |   \\           // <-|-- 16 mm female rod ends
  |    \          /     |
  |     \        / <----|-- 16 mm threaded bar
  |      \      /       |
  |       \____/        |
  |       |/  \|        |
  |       |\__/|  <-----|-- drill spindle
  |        ----         |   mounted to bar
  |                     |
  |                     |
  |                     |<- machine base
  |---------------------|


For drawings of rod ends see http://www.skf.com
Rod ends are relativly cheap and should be available from any 
bearing supplier.


Adam