[sdiy] Pot mounting holes?

[Theo]

Ok here is a basic nuts & bolds lesson.
Probably more than you asked for,
but maybe some of it is useful for others.

M7 x0,75
M indicates metric tread.
7 means the outside diameter of the tread is 7 mm.
Depending on the tolerance you need your mounting hole should
be larger than 7 mm diameter.
7,50 mm is often used, if the pots are panel mount OR
if the pots are PCB mount with sufficient precision.
If your pots are on a home brew PCB a tolerance of 1,5 mm
may be more realistic.
In this case the hole size would be 7 + 1,5 = 8,5 mm

The 0.75 indicate the 'speed' of the tread,
every rotation the tread advances 0,75 mm.
So this number has nothing to-do with the hole size,
but indicate the nut type/counter tread  you need.

The height of nuts is also measured in M.
For M tread the standard nut type is 0,8M
so for M7 tread the standard nut is 0,8 * 7 = 5,6 mm high.
However nuts to mount pots are usually much flatter,
often only one speed high , in this case 0,75 mm.
Needless to say a one speed nut can easily be turned too
tight and damage the tread.

PP sometimes ask on this list for methods to avoid damaging the
front panel when mounting the pot nuts.
Well washers where invented for exactly that purpose.
The washer should be on the side where the bold / nut rotates
during mounting.
So when mounting a pot the washer should be under the nut,
and not on the side of the pot.

The washers protect the mounting surface (font panel) in two ways.
First off the washer prevents that the nut "eats" itself into the mounting
surface.

Second the spanner lays on top of the nut.
This creates a distance between the spanner and the mounting surface,
so scratches are avoided.
Some "socked" and "ring" type spanners fall over the washer,
making scratches after all. (note _some_ most are ok)
"Open" spanners don't have that problem.
But when you don't use them right the "open" may spring or the nut
and damage your front panel.


Class dismissed.

Cheers,
Theo



From: Jim Johnson <jamos at technotoys.com>

> Argh.. drivin' me crazy..
>
> Trying to lay out a front panel using the Schaeffer software.. What size
> hole does a pot with an  M7- 0.75 shaft need?
>
> Maybe I should just go to bed -
>
>
> Jim Johnson
> Metaphoric Software
> -------------------
> Makers of Techno Toys
> Software for Electronic Music
> http://www.technotoys.com
> info at technotoys.com
>
>
>