Homebrew PCBs

At 18:47 06/04/13, you wrote:
>Message: 8
>    Date: Thu, 13 Apr 2006 12:14:50 -0400
>    From: John Young <wa8kne@...>
>Subject: Re: Looking for a specialty bit / looking for a prototyping board.
>
>You may be thinking of the New Jersey Islander (NJQRP)
><http://www.njqrp.org/islanderpadcutter/index.html> that used a small
>diamond hole saw.
>Similar hole saws are available from Harbor Freight, but watch for half
>price sales.
>I just tried the 'brad point' wood working bits also from harbor freight
>- low cost and good results.
>The brad point bit does not walk the way the hole saw did.  I can even
>work without
>clamping the board to the drill press.
>
>As a bonus the brad point bits cut perfect holes in the thinest sheet metal.
>
>John
>WA8KNE
>
>
>George Lawrence Storm wrote:
> > A long time ago I once had a specialty bit which was used to create a
> > "donut" pad on a copper clad board, it had a pilot/drill and two
> > spurs which cut the pad.
> >
> > I forgot what it is called, can anyone identify it and where I can
> > obtain them (preferably in a few sizes)?
> >
> > -----
> >
> > I also am looking for a prototyping board for a MLF-56 (QLN-56)
> > package. I need a quick and dirty prototype and don't want to design
> > and etch a board until I know more about the part.
> >
> > My problem is that it has the ground pad underneath and I have not
> > been able to find an adaptor which has that feature, has anyone made
> > any for their own use and who might want to sell an extra or two?
> >
> > Specifically I will be working with a Cypress CY8C24794 chip.
> >
> >
> > Thanks,
> >
> > -  George
> >
> > -----
> >
> > George Lawrence Storm
> > Macintosh Applications Development
> > Edmonds (Seattle), Washington
> > E-mail: <keencoyote@...>
> >
> >
> >
> > [Non-text portions of this message have been removed]
> >
> >
> >
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> >
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Brad point bits can be made by regrinding HSS twist drills,
perhaps with a Dremel. (I find a cut-off disk can do very fine
work if not stressed sideways.) It's easier than getting the
usual conical tip angles right and a possible re-use of a
blunt or broken drill. Just remember to make the brad point
a wee bit longer than the two vestigial "ears" of the spiral
so the drill locates properly. For this application, the
leading edge of the ears should probably have a zero to
slight negative cutting angle to avoid the bit "digging in".
Everything between the brad point and inner edges of the ears
is relieved and doesn't cut, so no need for precision there.

Alternatively, this Japanese and English page
http://www.qsl.net/7n3wvm/easy-const.html "Easy Construction"
has a variation on the woodworker's flat or spade bit in a
hand tool called a "nezumi-ba kiri". It would be quite easy
to make this style of bit if you can crudely blacksmith a
piece of hardenable steel (not HSS), or you could regrind
a spade bit (they seem to start at 1/4", approx 6mm).
I did consider trying to regrind a ceramic tile drill which
had a flat triangular tungsten carbide bit insert, but I didn't
think a carborundum cut-off disk - or any other small wheel
I had - would touch it.

On Fri, 14 Apr 2006 00:09:34 +0200, Len Warner <yahoo@...>  
wrote:

> Brad point bits can be made by regrinding HSS twist drills,
>
> perhaps with a Dremel. (I find a cut-off disk can do very fine
>
> work if not stressed sideways.) It's easier than getting the
>
> usual conical tip angles right and a possible re-use of a
>
> blunt or broken drill. Just remember to make the brad point
>
> a wee bit longer than the two vestigial "ears" of the spiral
>
> so the drill locates properly. For this application, the
>
> leading edge of the ears should probably have a zero to
>
> slight negative cutting angle to avoid the bit "digging in".
>
> Everything between the brad point and inner edges of the ears
>
> is relieved and doesn't cut, so no need for precision there.

Yes, it seems not to hard, and i own a few large ones that were clearly  
hand ground from normal drills. I hadn't thought of the small cutoff  
wheels, those might work very well for the small sizes, i was not sure how  
i would grind them.

I can sharpen a normal conical tip adequately so i think i could do this.  
The most tricky part will be to get the two edges the same so both cut, i  
don't always manage that with the conical shape...

it seems the angle of the cutting tips is different for hard and soft  
woods, i would expect for sheetmetal work a angle similar to the cutting  
angle on a conical tip must be sufficient. Maybe if i am careful i can  
start with the conical shape and not actually take anything off the  
outermost edges.

>
>
> Alternatively, this Japanese and English page
>
> http://www.qsl.net/7n3wvm/easy-const.html "Easy Construction"
>
> has a variation on the woodworker's flat or spade bit in a
>
> hand tool called a "nezumi-ba kiri". It would be quite easy
>
> to make this style of bit if you can crudely blacksmith a
>
> piece of hardenable steel (not HSS), or you could regrind
>
> a spade bit (they seem to start at 1/4", approx 6mm).
>
> I did consider trying to regrind a ceramic tile drill which
>
> had a flat triangular tungsten carbide bit insert, but I didn't
>
> think a carborundum cut-off disk - or any other small wheel
>
> I had - would touch it.

Hmm that would indeed be even easier to do. could be ground out of almost  
anything i'd say.
You really don't have any use for the spiral flutes for PCB island making,  
but then you wouldn't need them for sheetmetal work either.

About the carbide tile bit, i think you'd need a diamond wheel. Not sure  
if the diamond wheels you get for mini grinders would be up to the job.

I think it would also be possible to make such a island creating drill out  
of something like 3 broken PCB drills with 1/8" shank. Just make the  
middle one to a point, and the outer ones to cutting edges, and shorter,  
and either braze together or epoxy with a few fibers of glass around the  
outside. I have never brazed tungsten carbide but i expect it must work  
fairly well since all those stone and glass drills are brazed it seems.  
The PCB drills would ensure it lasts long.


ST