Hole Spacing on Rack Rails?

[bongolation]

Anyone know what the standard center-to-center distance on the device mounting holes in rack rails? I'm setting up a jig on the drill press and want to get them more or less right. 8-)

Thanks...

[MISTERQCUE]

Yeah I know, but 1st you need to change that avatar!

[skippy]

What seems really simple actually isn't, thanks to Our Friends The Military. There is one basic spacing, but different rack size panels use it differently- which is why EIA rails appear to have 3 different drillings.

Ready for this?

The basic 1-slot panel is 1.75" high. The holes (or more correctly slots, so that you can change the shot-up radio in your B-17 quickly, and get back to bombing Germany) are inset from the edges 1/4" on center: so their spacing is 1.25" OC.

The basic 2-slot panel is like a 1-slot, twice as high (3.5"), but rather than having 4 slots per edge it omits the innermost two. The outers are still inset 1/4" OC from the edge, so you have a spacing of 3" OC.

With the 3-, 4-, and 5-slot panels, we get wierd. The inset changes to 1.5". So for those we have 2.25", 4", and 5.75" spacing OC, respectively. This is the second set of drillings you see on the rails. 3, 4, and 5-slot panels still have only 4 slots.

The 6-slot gets even wierder: it mounts on 8 screws (4 per side). The outer two are inset 1.5", but the next two are then inset 2.25" (leaving the spacing between the middle two 3").

But wait, there's more: the 7-slot is the wierdest of all. This monster mounts with 12 screws, six per side. The outer two are inset 1.5", and the next two are 1.75". This leaves the spacing between the middle two as 2.25". Unfortunately, because of the pair of 1.75"s previously, this leaves you out in the middle of nowhere... This is where that odd single hole comes from, forming that 5-hole repeating pattern in the rail. You know, the one you never use...

And no, I'm not making this up. Aren't you _glad_ you asked? (;-)

[bongolation]

Originally posted by MISTERQCUE
Yeah I know, but 1st you need to change that avatar!

There aren't enough to go around, they're not unique, others use the same one and now that you mention it, YOU'RE the one who's supposed to change his avatar; these dumb pre-chosen ones are for those of us without enough posts for a custom one. You have plenty more posts than you need to supply your own. So, if this bugs you, I suggest you look into that.

Stylin' guy like you should have his own special avatar, don't you think? I have mine already to substitute when I have enough posts. It's a doozy.

Have a nice day...

[bongolation]

# And no, I'm not making this up. Aren't you _glad_ you asked?

Dang. I can't get a simple answer these days on anything! 8-)

Funny, those pricey pre-drilled rails at GC looked so simple, too.

My thoughts were that if I just eyeballed the first spacing to fit one device and extrapolated from there, the cumulative error from a jig drilling would probably have them unusably off by the time I got to the bottom.

Could be wrong about all this, I dunno.

Discouraging.

[regebro]

And then, of course you have metric rails. Happily they are EXTREMELY unusual. What not so unusual is using metric screws. Which is why, in most rails, you don't have threading in the rail, but just holes (at least if you buy them in Europe), so that you have to insert a small square nut at the back. Of course, holding a nut, a screw and a rack at the same time is hard, so you have a tendency to drop them inside the rack, behind the other rack units. So, you have nuts with springs on their side to keep them in place, and small holes on the back where they should fit. The practical thing with this is that now suddenly you have to buy special nuts that only fit in your brand of rack. And therefore, these nuts are hugely expensive. And the racks are now so complicated to make, that the are hugely expensive too.

I suddenyl remembered why I haven't got a rack...

[MISTERQCUE]

But-But-But, I like my avatar!!!

[bongolation]

Originally posted by MISTERQCUE
But-But-But, I like my avatar!!!

This raggedy-ass Seen-on-TV not adequately stylin'. You need something fancy. Express yourself!

I have three picked out for myself already for when I get the posts.