An odd callout

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.
Reply to
Tim Wescott
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You could add a cross-section drawing, open up the hole and use a thin washer, or "see sample for detail".
The chassis casting drawing for a [mumble] is like the latter and I had quite a hard time reconstructing the geometry of the battery mounting bosses.
Reply to
Jim Wilkins
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)
Reply to
Steve W.
Just be honest and note "crappy hackjob design, you have to wedge this shit together, so flare the holes on one side."
Put that on the outside too, as a favor to anybody that might have to service it later.
Using really short 9 volt battery leads with no strain relief would really polish this thing off too. Slather it with hot glue or foil security labels.
Reply to
Cydrome Leader
Would it hurt to chamfer the inside all the way around?
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Or have the assembler file it as little as they have to?
Reply to
Jim Wilkins
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.
Reply to
Tim Wescott
Cross-section of the wall will show the angle.. Same "detail" cross-section can be used for all holes with same dimensions.
It might be easier to make the hole 40 degrees chamber to all directions - at least, allow that.. I would CNC machine it that way with a circular cut of a 40 degrees cutter.. If they are cutting it instead of punching it or such..
Reply to
Kristian Ukkonen
I designed the box with the line drawing feature of the PC board program, as extra layers on the board artwork
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. That guaranteed a perfect match between them, which was important for RF-tight microwave enclosures with many SMA connectors placed wherever the electronic design rules forced them to be.
This Segway Balance Sensor Assembly was probably the hardest board I did with the package represented by carefully placed line elements, because of the angled, sloped daughter boards and poorly defined three-dimensional clearance restrictions.
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It would have been easier if PADS could correctly import .dxfs from Solidworks.
Reply to
Jim Wilkins
How thick is the wall these holes are going threw?
It seems to me that you should be doing one or more of the following: 1. Specifying the holes drilled at the 40 degree angle. 2. Increasing the diameter. 3. Raise the location of the holes a tiny bit
Stephen B
Reply to
StephenB
I think one can generate a plan view of any 3-D object with two rotations. Back before solid modeling this was accomplished by constructing projecti on views. I designed a gimbal system with a similar geometry specifying the cut out f or a connector in the round housing. I specified it by constructing a vie w parallel to the plan view of the connector defied by the angle the view w as offset from the part front and top views. One can do the same thing wi th 2-D cad.
Engineering schools don?t teach 2-D drawing anymore so a lot of the new e ngineers lack geometric agility
Reply to
d32

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