[sdiy] Learned something today...

[Batz Goodfortune]

Y-ellow Jim, Harry, 'n' all.

At 10:21 PM 6/7/03 -0400, harrybissell wrote:
>You could try using a PCB as a drilling guide directly... or getting a lazer
>plotted
>film as a full size guide. If you tried to lat out the panel on the metal, I
>can see
>that not working for you.
>
>I should talk... since I don't even HAVE a drill press (though I did look at
>one today...)
>
>H^) harry

I'm no expert but I do make a habit of using boards on front panels. If not 
boards then at least a sub panel to avoid mounting hardware tightening down 
on the actual front panel surface.

There are probably no strict rules at the one-off level but a technique 
which I believe Cynthia uses is to make an accurate template first, clamp 
all her front panels together, and using a drill press, drill a stack of 
panels all at one time. But the template is the key.

You could, as Harry suggested, use the PCB it self as your template but 
what happens if the PCB doesn't actually have the mounting centres on it? 
Well you could put them on in the master I guess but the key is to start 
from your PCB as the master guide. This assumes you're using a PCB but I'll 
get to another method shortly.

When you lay out your PCB in whatever program you use. Include the mounting 
centres of the entire front panel. This might not be convenient or 
intrusive on the PCB it self for whatever reason but when you're all laid 
out, convert the board to a DXF file (Or whatever's convenient) and export 
that into the CAD package of your choice. You can then pretty up the dial 
markings and so fourth and produce your actual panel design. Nothing 
unusual here but this by default has your mounting centres on it. As well 
as any other holes for mounting the front panel it self.

The next trick is to get back to the way Cynthia does it. By making a 
drilling template first. You can print out, and glue down your front panel, 
then use a punch of some kind to indent all the places you're going to 
drill. This is fairly important even if you ARE using a drill press. These 
dents will naturally guide the drill centre. The next trick is to drill 
pilot holes. A 2 or 3mm drill at most. Because these will guide your 
subsequent larger drills.

At this point you have 2 choices. You can leave your template with just the 
pilot holes. (Recommended for a template) or you can begin the process of 
drilling larger holes out to the actual required size. Never go straight to 
a whopping great 1/4" drill or something. Work up to it in 2 or 3 stages. 
If you're drilling aluminium, use a slow speed. Aluminium tears, and 
over-sizes. This is especially true if you're subsequently going to tap the 
hole for a screw.

If your front panel requires square holes, then make hole guides along the 
inside perimeter of the hole. You can then drill these out to make room for 
another tool such as a saw, file or even a nibbling tool.

But suppose you have already got a front panel. Or worse still, you're 
front panel is a one-off or prototype on vero board. The trick here is to 
simply allow for tolerance. An engineer that worked for the airforce once 
told me that there are always tolerances. No matter how accurate your 
design is, nothing ever fits exactly. So the trick is to know (Or guess) 
how inaccurate your design is going to be and allow for it. But in this 
case you do it in such a way that it looks consistent.

Usually my front panels aren't simple flat pieces of metal these days. More 
often than not I find myself working with some kind of extrusion. A piece 
of angled or boxed aluminium of some kind. Or simply a piece with varying 
thickness or one that is particularly thick and hard to work. Try nibbling 
a piece of 5mm thick aluminium extrusion for example. This is where things 
get really tricky. But one thing you can do is allow the main piece to be 
rough as guts. But apply a thinner sheet with more accuracy over the top. I 
have experimented using aluminium cladding for this even. Although that has 
it's problems too, it can be useful in certain situations. (It's like a 
thick foil used for cladding roofs these days.)

And don't underestimate using plastic. Sure you might want the panel 
underneath to be metal for shielding and strength but plastic can be dead 
easy to work and you can make some interesting 3-dimentional shapes with 
it. You could make all your sections on raised pedestals and look like it 
was a windows program with knobs. Err. On second thoughts...

Finally, there's one other thing you could do if you really want to be 
kinky, and I've not actually done this but I've always been toying with the 
idea. And that is to make your front panel out of actual PC board. Just 
have your dial markings as the etched in bits. Spray paint the whole thing 
white, then spread a bit of mat black paint onto a surface and sort of roll 
the board onto it. White dial markings on black. And indented no less. 
Worth a shot.

Hope this helps.

Be absolutely Icebox.

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