Drain Plug solved!!

[Wallace White]

I'll throw in what I know from my work as a mechanical engineer:

Huw Powell wrote:
>>>Sounds like it would have spend time in two different machines, probably
>>>some sort of cnc lathe/screw machine for the round part and threading,
>>>and some sort of milling setup for the tool faces.

Yes. Some screw machines have milling heads too. Or you could use hex
bar stock, so that you'd only need to do the turning operations.

>>It's possible to mold threads into a plastic part rather than cutting them as a
>>separate step.
>
> So that means finding a machine shop with the equipment to mold the
> right threads on the right kind of plastic, right?

You _can_ make threads by having a screw slide: that part of the tool
unscrews after the plastic is shot, to separate the tool and the screw.

But for a part like a drain plug, you can just split the tool along the
length of the screw. (If you want an Allen recess, the tooling does need
a slide somewhere, since that shape needs to be pulled from another
direction.) Makes for a much cheaper tool.

That said, I regularly get small, prototype tools made for the purpose
of shooting <20 parts, and I'd bet a simple tool like this would be
$500~$1000, with piece parts a dollar or two a piece.

I would guess machined parts, at qty 20, at $20~$40 each, but I work
mostly with prototype shops that do even lower quantities; a good screw
machine shop might go lower. I know of a couple, in case anyone's
interested.

For material, you don't have to brew up your own polymer--GE, Dupont,
and others are busy doing that--but you do need to choose an appropriate
one. I'm usually doing so for folding keyboards (see
www.thinkoutside.com), so I'm not familiar with the right plastic for
the chemical resistance, flammability, hardness, impact strength, etc.
that this app requires. Maybe a nylon or PC/ABS; probably not Delrin
(aka POM or acetal), which is pretty soft and slick.

> It's also possible to buy the finished part from the dealer... which I
> would call coming full circle...

Yep! That's bound to be better here. Cost _should_ be much cheaper, and
you get a product that has been engineered and tested. I'd be pretty
bummed if my custom drain plug melted, sheared, rounded, cracked, or
otherwise contaminated the system or let all the oil out.

- Wallace
   '87 5kcstq 192k