On Mon, 18 Feb 2013 19:37:42 -0500, Steve W. wrote:
Tim Wescott wrote:
I'm in a bit of a quandary.
I know how to machine this, but I don't know how to call it out on a
drawing.
I'm working on the mechanical drawings for a small electronic
enclosure, to modify a purchased case by drilling some holes for some
connectors.
The holes are 1/2" diameter, and are on an end of the case that forms
one wall of a well: the other wall is formed by the molded-in battery
box about an inch away.
In order for the circuit board to fit, it must be tilted at about 40
degrees, the connectors that go through the above-mentioned holes are
inserted, pushed home as far as they'll go, then the whole shebang is
rotated into place.
In order for this to work, the top edges of the 1/2" holes need to be
cut at about a 40 degree angle. The end effect is that on the outside
of the case the holes are round, but on the inside they are oval.
Assuming that the above discussion makes sense, how would one call this
out on a drawing? Just draw the hole outlines, and leave it to the
machinist to figure out how to make it all work?
The case is ABS plastic, and the way that I'm making it is to machine
the holes on a mill, but make the 40 degree chamfer with an x-Acto
knife. But the case manufacturer is putting themselves forward to
machine the case for production. I'm going to send them a case with
all the bits installed, but I'd like to send them a drawing that could
at least be construed to be correct in some sense.
Suggestions welcome. Thanks.
Do the holes have to be machined? I would think they could mold that
into the box using a retractable piece on that area of the mold.
Or if you want to machine it use a ball shaped cutter to plunge mill out
the hole, then move cutter up and use the back half to mill the relief
area.
As for how to put that on the drawing. I would try.
Hole 1/2" bore located X / Y position. Inner edge of hole to have a 40
degree relief chamfer from 90 - 270 degrees. (the degrees will be
based on what you have to have. If you only need the top 1/4 of the hole
milled just call out the degrees needed)
Thanks Steve.
It's for very low quantity -- if the product was of sufficient volume to
have a custom-molded case, I'd be hiring real mechanical engineering
talent, not marking up the manufacturer's drawing with my mods.
What you suggest is more or less what I've done, plus Jim's "see sample
for detail". I am, quite frankly, going to send off a sample to them
with a note that says "This part has been machined not only by an
engineer, but by an Electronics engineer. I expect to get back pieces
that correct all my mistakes. Thank you".
I almost didn't bother with drawings at all, except they've been a help
for me to get the holes located correctly, and to prove to myself that
the part can be made to be solid and good looking without custom molding.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com