[sdiy] embarrassing noob needs to mount some pots

[peter edwards]

I think Laurie's answer is a good one, but I strongly disagree with  
his casual stance on the anti-rotation tab. :-)
I do a lot of repair and salvage and I have seen plenty of problems  
stem from the lack of proper utilization of the anti-rotation  
tabs....really. People very commonly cut the tab off and I always  
recommend that they do not. Using the tab makes for a more solid  
interface. And think about it, the knobs are your connection between  
you and the functions of the device you're tweaking. This interface  
should be as reliable as you can make it with a reasonable amount of  
work.

  The quickest way to drill the hole for the tab is to A) measure how  
far the tab is from the center of the pot shaft and mark a hole that  
far from the main shaft hole on your faceplate.
  or B) First drill a hole for the main shaft of the pot. Then press  
the pot through the hole so that that tab is pressed against the face  
plate and turn the pot back and forth a few degrees. This should make  
a little mark showing you where to drill the hole.
The tabs are usually flat on smaller and/or cheaper pots. I used to  
try to make rectangular holes for the tabs to stick through which was  
really silly and time consuming. Now I just measure across the width  
of the tab and drill a hole that size. They're usually around an 1/8"  
wide.
if the hole is a little too small, you can usually force it through  
anyway, especially if you are using a plastic faceplate, that ensures  
that you get a nice tight fit.

As far as grounding the pots goes, Laurie's suggestion of eyelet  
washers is the best approach. IF you are desperate and you NEED to  
ground the pot and you don't have any eyelets, you can solder a  
ground wire to the body of the pot. But be aware that the pot will  
get very hot! This could damage the plastic elements of certain pots,  
like the back cover or the shuttle which holds the center lug wiper.  
You will need to abrade a small area on the side of the pot where you  
will be soldering your ground wire. I use a dremel with a cutting  
wheel to do this. Don't cut into the pot! you just want to rough up  
the surface. Then you will probably need some flux to help solder to  
the surface. Flux is a toxic pasty material that helps prepare the  
surface of dirty metals for soldering. Just put a little dab on the  
area you are going to solder to. Another thing to be aware of is that  
soldering to large metal surfaces is much more difficult than  
soldering to the little lugs on a pot or leads on a circuit board.  
Metal dissipates heat very quickly through it's mass... so as you are  
heating up the areas to solder to, the heat is being pulled away..  
you will need to turn your iron up higher than usual or if you have a  
set temperature iron, you will need to hold it there longer than  
usual. Melt a big blob of solder onto the tip of your iron as you are  
heating the ground spot. This will help spread the point of contact  
between the iron and pot surface which will allow for a quicker  
transfer of heat.
Despite my little rant above about the importance of reliable pot  
behavior, I have used this grounding technique more than once.  
Luckily I have not had any problems with melting parts or  
malfunctioning pots. If anyone thinks this a totally wacko  
suggestion, don't hesitate to say so!
-pete

On Mar 9, 2009, at 7:23 PM, Elby Designs - Laurie Biddulph wrote:
> I am happy to try and answer any questions you may have.
>
> With regards the pots.
> the tab is an anti-rotation device. It fits in to a mating hole or  
> recess on the
> panel and stops the pot from trying to spin in the hole should you  
> try and ram
> the control past its end stops. If youu have a sufficiently large  
> knob that will
> cover the hole, then I would include this. It is, however, a lot of  
> extra work
> and if you intend to treat your controls with some respect then you  
> can forget
> them. On pots that have the tab phsyiclly aprt of the pot body,  
> simply get a pair
> of heavy-duty pliers and snap it off (this is usually just a matter  
> of wiggling
> it back and forth a few times) - it is unlikely that you will do  
> any damage to
> the pot unless you are ridiculously clumsy. Some pots have a tab on  
> a separate
> washer (much like many switches have) and you can discard the  
> washer or sometimes
> just flip it over so the tab points towards the pot body.
>
> If you are using plastic/rubber/wooden or other similar non- 
> conductive knobs then
> there is no real need to ground the pots. Once the panel has a  
> ground connection,
> you can usually rely on the metal bush of the pot making the  
> electrical
> connection to do this for you. If you WANT to ground the pots then  
> you need what
> are commonly called eyelets or lugs. These are like a washer with a  
> tag sticking
> out one side. Fit the washer over the bush before mounting the pot  
> to the panel.
> You can then attach a ground wire to the tab.
>
> Hole size is dictated by the pot. You should have a datasheet for  
> the pot or the
> catalogue where you got them from should at least mention the panel  
> hole size
> needed. if you can't find that then just grab one of the pot  
> washers and measure
> the inside gap at the widest point or just get a box of drill bits  
> and find the
> bit that just fits in the washer.
>
> Best regards
> Laurie Biddulph
> www.elby-designs.com
>
> On Tue Mar 10  9:15 , Horton  sent:
>
>> There are so many basic knowledge things out there that are just  
>> taken
>> for granted by the computer-brain electronics wizards, so for a new
>> hobbyist there are no real guides or 101-style information.
>>
>> I'm in the middle of a project and suddenly I need to mount a  
>> punch of
>> pots and switches into a typical plastic project enclosure. I have no
>> idea where to begin! What's up with the nuts, and that little tab
>> sticking out of the pot body? Should I ground each pot to the  
>> metal in
>> the case in addition to the ground bus on the PCB? How? What size
>> drill bit do I use to make the holes, and how do I secure the pot  
>> body
>> against the frame of the enclosure anyway? I need all this basic  
>> info.
>>
>> Ideas? Tutorials? Instructables?
>>
>> AH
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>
>
>
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