[time-nuts] TAPR Oncore M12+ kit

Bob kb8tq kb8tq at n1k.org
Fri Apr 28 16:09:20 EDT 2017


If you ever get a chance to visit a PCB fab it’s an interesting sort of process. No 
two of them are quite the same. The gear they have does impact what they can 
or can’t do. Every one I have ever visited has done routing on the boards. That
may be because it is a very common requirement on industrial boards. Essentially
they just swap out he drill bit for a routing bit and go with it. It’s not quite that simple, 
but almost. The big reason you don’t see it done on the low end boards is that it takes
time. The machine isn’t a cheap item so in this case time is money. It’s the same 
reason a “real” fab will hit you with a charge for the number of holes you want on the
board. Same basic issue - time on the machine. 


> On Apr 28, 2017, at 2:31 PM, Bob Stewart <bob at evoria.net> wrote:
> Hi Bob,
> It may be because the process of cutting the boards apart is not part of the board milling process.  Yes, cutting holes in boards for through-hole parts is part of the business - round holes.  The fab house for OSHPark won't make oval holes.  They won't overlap two holes, either, nor make square notches.  This is only a guess, but I'd say that this is because they use actual drill bits to make those holes, rather than a laser.  Drill bits are expensive, and it takes a lot of time to change a drill bit when you've got hundreds of boards to mill.  It's not something I would want to do, either, without a serious penalty for the customer for a broken bit due to odd shaped holes and missed deadlines.
> And OSHPark seems to use different fab houses for the small runs vs the large (10+) runs.  With the small runs, the boards are connected to each other by small tabs.  Often small boards arrive still tabbed together.  I don't know whether they route the distance between these tabs, or use a laser.  On the larger runs, there are no tabs, and the board edges are smooth, as if they were cut apart in one single operation not part of the milling process.
> NB, I don't work for a fab house, nor have I ever toured one.
> Bob 
>      From: Bob kb8tq <kb8tq at n1k.org>
> To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
> Sent: Friday, April 28, 2017 1:06 PM
> Subject: Re: [time-nuts] TAPR Oncore M12+ kit
> Hi
> If you go with the PCB approach, the nice thing is getting stuff like
> the slot for the D connector done at the PCB fab. That way you 
> have something that drops right in and works. The downside is that 
> not every pcb house is happy doing that sort of “CNC work”.  I 
> have absolutely no idea why. They all have to run some sort of gear
> to cut the boards apart. Cutting slots or weird holes with it is pretty
> trivial. 
> Bob
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