[hpsdr] Pandora backplates for Ozy, Mercury, Penelope

[w3sz]

Thanks Graham, Lyle, Paul, and Dan for the helpful comments.  I will 
edit and post my answers in-line below.


> I would like you to consider doing one for Excalibur also.
> It would be two 0.45 inch holes, for two BNC connectors

Will do.

>
> Do you have an index point for where the lower right edge
> of the PCB falls on the cover plate? It should be in exactly
> the same place for each card, since it is indexed by the
> Harting connector.

The way I interpret the drawing for the Harting connector:
http://www.nitehawk.com/w3sz/TB_0903196x921_BL01_R34650.pdf

the dimension is 3.85 mm or 0.152 inches.  My measurements range from 
0.13 to 0.16 inch.  That variability of 0.03 inches is why I allow 0.03 
inches 'extra' in the dimensions along the line perpendicular to the 
centerline.  I have set the dimension to approx 0.145 inches, at the 
midpoint of the range I measured.

> Are you sure they can cut/stamp metal as thin as you have
> on the left edge of your plates. It seems that you are only
> dealing with 0.085 inch or slightly less thickness on the left.
> That seems thin for a stamping. Maybe OK for an NC
> cut.

You are correct, I have only 0.082 to 0.086 inches of metal along the 
'top' of the backplate.  I don't know if that is too thin or not, as I 
haven't submitted to vendor yet.  If it is too thin, the options are to 
shrink the hole, just leave it open at the top, or make backplates that 
are asymmetric with respect to the mounting notches.  I don't like the 
third option at all.

> I think you can get by with much narrower slots. Something
> around 0.45 inch for BNC connectors. 0.42 for the "D"
> connectors. No need to go all the way out to the metal
> edge of the "D" connectors.

You are right, Graham.  I made the holes larger than necessary to allow 
for dimensional errors.  If we can tighten up the dimensions then I can 
shrink them somewhat.  In part, though, I was trying to keep things 
simple.  Unfortunately, on my Ozys the "D" connectors stick up above the 
level of the backplate, and so the cutout does need to go all the way 
out to the edge of the metal connectors for Ozy.  For simplicity, I 
decided to do the same for the connectors on the other boards.  I don't 
need absolutely tight backplates.  They just need to be tight enough to 
keep out rodents.

> In fact, picking up the jackscrews on the D connectors would probably be a good idea.

This is more complicated than I want to get.

> Look at protocase designer (free download) it has standard cutouts included and they will manufacture direct (no connection to me)

Interesting!

> 1) Since the notches on the top and bottom are on the centerline of the part, just put a centerline style line down the middle of each plate.  (It is an alternating short dash and long dash.)  It isn't necessary to show a dimension for the location of the centerline.  Showing locations from the centerline should simplify the dimensioning you will have to put on the drawing.

I added a centerline ;)

> 2) It isn't necessary to show each and every dimension..  Those who interpret engineering drawings are used to doing some arithmetic.  In fact it is a bit of a game to see how much you can actually describe with minimal dimensional information.

QSL!  Most of the 'extra' dimensions are so I can check measurements on 
my actual Pandora/Board assembly.

> 3) Make the notches on each end of the plates as long and as wide as feasible.  The difference between the diameter of the attachment screw and the width and length of the slot are the primary adjustment to compensate for some of the not so precise alignment of the connectors on the PCB's.

OK!  The 4-40 screws supplied have a head diameter of 0.21 inches and 
shaft diameter of 0.112 inches, so I will play with these dimensions and 
the notch width and length.

>
> 4) Tighter tolerances always equate to more cost.  My guess is that some of the dimensions can be left at two decimal places.  Some place on the drawing you should note the tolerances for the two and three decimal dimensions.

I should be able to reduce all dimensions to hindredths only I think.
>
> 5) It is best to have as much material between the outside edge of the plate and the edge of the internal opening.  In other words, make the plates as wide as possible. Material is cheap.  Holes are expensive.

OK.  Based on the Pandora layout, the plate width is locked at 0.790 
inches.  If I can increase the confidence level of the dimensions 
perpendicular to the centerline, then the hole widths can be reduced 
somewhat, giving more metal around the edges.

This morning I went to Home Depot and got a digital calipers so that I 
can perhaps tighten up the confidence intervals of some of the 
dimensions I measured, to proceed as suggested.

I will send the drawing to a vendor or two to see if they think the 
project is do-able, and at what cost.

Thanks again all, and

73,

W3SZ
Roger Rehr
http://www.nitehawk.com/w3sz

 1248715845.0