Irregular rack thickness???

[Magnus Danielson]

>>>>> "PS" == Paul Schreiber <synth1 at airmail.net> writes:

Hi Paul!

 PS> While looking at the deep mechanicals of the MOTM front panels, I
 PS> decided to measure the thicknesses of the front panels of the
 PS> stuff in my rack. It's important to note that there is a 1U space
 PS> between each unit, 

 PS> Much to my surprise, no two matched! Here's what I measured:

 PS> DP/4: 0.125"
 PS> Mixer: 0.100"
 PS> D*****L sound module: 0.070" <figures!>
 PS> Midi interface: 0.092"

 PS> So, if all of these were placed side-by-side there would be a
 PS> noticeable 'ripple'. I then for reference looked in 
 PS> the Allied catalog and the standard Bud rack panel thickness is 0.125"

 PS> Anybody else noticed this variance in equipment??

Sure. This is old news to me.

First one should know that all this 19" rack buissness is a bit of
hasty-work to start of with and people and buissness hasn't helped
along the way.

The international standard (can't recall it's name) is a mix of metric
and imperial measures and measurement faults was discovered too late
for being brougth into the standard. Standards is good but may be
inaccurate to what was intended.

To no supprise has effort gone into the new metric rack standard where
all measures are based on mm and the only old measure kept is the
width (19 inch) but now measured in mm.

That the thickness of front panels differ should be quite apparent for
anyone who has assembled some racks for PA/live gigs or studios. The
main reason for having thinner pannels could probably be traced in
economics, let's save some money on the casing and let it go into our
own pockets instead... that kind of thing. I would guess that quite
few equipment manufactors even bother to accuire the standard(s) that
they are suppose to follow, and even fewer really follows them while
making the design.

A common fault is that many does is a round off error in the heigth of
units.
If you measure the height in inches you get that 1 U = 1.75 Inches.
If you measure the heigth in meter you get that 1 U = 44.5 mm.

But, hey! This is wrong!

1 Inch = 25.4 mm so...

1.75 Inch = 1.75 * 25.4 = 44.45 mm

So, how does this little roundoff error show up in real life?

If you mount a number of 44.5 mm boxes in a 44.45 mm rack will some of
them not fit!
A 44.45 box will fit thougth....

Therefore shall the rack itself use 44.5 mm (which is NOT standard)
while the boxes preferably should be 44.45 mm (which is standard).
This will be safe but may not allways be easy to do.

This is one of the quite irritating things about the 19" rack system
in the real world usage.

As for variating thinckness of front plate, this should not be a big
trouble if you use propper screws (and propper screwdriver! more on
that in a diffrent mail) and not these snap-screws (which I happend to
be using at home, stuipidly enougth... ah well, I am not touring so it
is not critical) which assumes the correct thickness.

Too thin front plate can be a real burden since this also makes the
front less rigid, and the more the box weigths and the longer away
from the frontplate that the center of gravity is from the front
plate, the higher importance since it can cause severe deformation
while bumping around on the road or in extreme cases by just sitting
still in the rack with only the gravity as the main force.

A real carefull truck-packer will even consider how the rack-fronts
are oriented while packing the truck. This to reduce the damages
caused by transport. Do you do this when touring?

It seems like basic mechanical knowledge is a really dark field in
music/PA electronics. I have seen several cases of good boxes which
have good electrical functionallity but their mechanics (or a lot of
their electrical design for that matter) cause it to "not work" in a
real situation. It is apparent that few firms really knows how their
equipment is being used in the field and therefore does not shape them
properly. It is also common that diffrent firm shape their stuff
diffrently according to diffrent thougths and that this cause
incompability... this is a minor minefield!!!

I am sure that people on the lists have more experience on this, and
that some has the experience but didn't know why...

Cheers,
Magnus