gEDA-user: Fitting a hobbyist design into someone else's form factor

[Mike Hansen]

Most bent sheet metal enclosures are toleranced to +/-0.015 inches.  So 
anything on a face of the enclosure at worst case will be +/-0.015 inches 
off from the expected dimension.  If there are bends between the mounting 
holes then the tolerances will be greater(it's difficult to hold the 
tolerances around a bend).  However since you have to measure the part to 
get the dimensions I would guess you will need at least twice the slop to 
get everything to fit.

Generally molded pieces will have higher tolerances, perhaps to 0.005 
inches.

As a for instance for mounting holes for a #6 screw the mounting hole on the 
PCB will be 0.156 inches in diameter.  I believe a #4 is 0.120 inches.  
Again, since you are measuring this by hand you will need much larger 
clearance holes.

Since you don't have a drawing on the part I suggest using a 
calipers(they're available for <$30 from places like Sears) to measure 
inside edge to inside edge of holes, then measure the diameter of the holes 
and subtract the difference to get the correct dimension.  Of course this 
will be difficult if the holes are lined up.

Don't forget the keepout areas around the mounting holes, otherwise you run 
the risk of shorting traces to the enclosure.

Good luck!


>From: msokolov at ivan.Harhan.ORG (Michael Sokolov)
>Reply-To: gEDA user mailing list <geda-user at moria.seul.org>
>To: geda-user at moria.seul.org
>Subject: gEDA-user: Fitting a hobbyist design into someone else's form 
>factor
>Date: Mon, 29 Jan 2007 04:46:32 GMT
>
>Hello fellow gEDA/PCB users,
>
>I would like to fit my design into the form factor from an existing
>gadget so that I don't have to invent my own mechanical design and can
>utilise a ready-made enclosure.  This means that I need to carefully
>measure out the existing board in order to reproduce its mechanical form
>factor.  Here is my question to the list: what level of measurement
>precision is required to make a generally acceptable fit of the form
>factor?  Will a metric ruler with mm ticks be sufficient, or would I
>need something finer?  I don't know if the form factor I'm trying to
>copy was originally designed as metric or inch-based.
>
>The mechanical aspects that I need to measure and reproduce in my design
>are:
>
>* Board dimensions and shape.  It is shaped like this (read in a fixed
>   width font):
>
>   +----------------------------------------------------------+
>   | RJ45                      RJ45        AC mains           |
>   |                                       connector          |
>   |                                                          |
>   |                                                          |
>   |                                   +----------------------+
>   |                                   |
>   |                                   |
>   |                                   |
>   |                                   |
>   |                                   |
>   |                                   |
>   |                                   |
>   |                                   |
>   |                                   |
>   |                                   |
>   | LEDs                              |
>   +-----------------------------------+
>
>   I guess such a board is fabbed as rectangular, then a corner is cut
>   away, right?
>
>* Location and drill diameter of mounting holes.
>
>* Location of some connectors along the back side.  The existing board
>   has two RJ45-style jacks and a "kettle plug" AC mains connector, and
>   mine will have identical connectors in the same locations.  The
>   existing board also has a block of 4 RJ45s stuck together (Ethernet
>   hub), but mine will have a DB25 in its place.  The DB25 is smaller
>   than the 4 RJ45s, so I'll have a little bit of wiggle room for it.
>
>* My board will have some surface mount LEDs on it, and I want to put
>   them exactly where the existing board has its LEDs so that they are
>   visible when my board is put into the existing enclosure.
>
>I would appreciate any advice on how much precision is required to
>achieve what I've just described.
>
>TIA,
>MS
>
>
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>geda-user mailing list
>geda-user at moria.seul.org
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