knob for rotary switch?

[MrStab]

hi,

sorry if i'm asking the obvious here, but as i can't find a cheap source of on-on-on 3 or 4PDT toggle switches, i'm going to have to settle on a rotary switch for an upcoming project. i'm looking at one like this:

, but i'm wondering how i would secure the average pot knob to that, or if i need something more specific? i'm unsure as the shaft is smooth. no euphemisms.

cheers!

[defaced]

Those are D shaft switches - D shaft knobs are very common in other segments of the electronics industry.  You may also be able to use a set screw knob on them as well. 

[joegagan]

setscrew is very helpful for this type of switch  ^^, as is the anti-rotate nib at the bushing base. worth the time it takes to locate and drill the extra hole.

if you really must have a 4pdt, and like the look of a sexy chrome rocker, i have these for $9 shipped.

[MrStab]

just googled "set screw", and had an "aaaaah!" moment - i currently have 2 guitars with such a system on the knobs. don't know why i didn't think of that. thanks, guys! now i know what to look for.

that switch looks awesome - the kinda thing i'd expect to find at a nuclear launch silo - but budget-wise it'd be a tiny bit overkill i guess. cheers, though!

[joegagan]

yes, it is a remnant from our local nuke industry.

[Mark Hammer]

That's a dead sexy switch, although the machining required can be a deterrent to some who may have all the tools they think they need except for the ones required for installing rocker switches.

For rotary switches, there are a couple of things to keep in mind, I suppose.  One is that switching takes a little more torque than adjusting a pot, so you want as much "mechanical advantage" as you can fit in there.  That's one of the reasons why folks like chicken-head knobs - the parts that poke out give you a place to apply leverage with thumb and index.  At the very least - and because sometimes spacing does not permit otherwise - fluted knobs give a little bit more grip, and wider diameters do as well.  Bigger switches also permit a little more leeway, I find, when legending a chassis for the switch positions.

BTW, if anybody has any suggestions for foolproof strategies, when it comes to easily and reliably marking off switch positions on the chassis, I'm all ears.  I tend to install the switch, mark off where the pointer on a chickenhead points to, using a marker, remove the switch/knob, apply some rub-on dots, and then spray laquer over top.  But I find I'm frequently a few degrees off, such that the pointer knob overshoots or undershoots.

Finally, if you have to use set screw knobs, try to apply the set screw tip to the "belly" of the D, and not the flat part.  And if you can get them, knobs that have two set screws, instead of one, can provide more secure positioning of the knob.  In those cases, the scres would likely be tightened against the last portion of the curved part just before you reach the flat side.

[davent]

Mark I posted this at madbean a while back regarding labeling rotary switches.

The switches i have are all 12 position based, whether 1 x 12 or 4 x 3, a tabbed washer acts as a position stop preventing it from switching to too many positions. So... 360°/12= 30° between stops.

To create a label using simple CAD software,

Draw a circle slightly greater in diameter then the switch's mounting hole. Based on the same center point draw a second slightly larger in diameter then the knob you want to use.

Draw a ray from the circle center to the 9 o'clock position extend it to just past the outer circle and stop it at the point where you want your legending word to end.

Highlight the ray, the software will have provisions for radially copying the ray around the center point of your circles. You'll end up with 12 same length rays emanating from the center of your circle 30° apart, your position markers.

For, 4 positions, oriented to the side, you'll probably want to rotate the whole deal 15°.



Label your four rays. Dress it up however you want.

Delete everything you don't want to be seen but not the small circle and crosshairs as you'll need them to position the label/decal.







dave

... and i'm puzzled by your recommendation for the set screw.

[Mark Hammer]

You mean where to put the screw?  In theory pushing the screw up against the flat part of the shaftshould sort of mimic the round part being pressed flush against the knob, the way it would if you had a knob for a D-type shaft.  But that presumes the set screw will be long enough to do the job, and it may not.  IN which casepushing the screw tip against the apex of the D (here: D <- ) may get you a more solid knob placement.  Of course, if the set screw IS long enough, go for it.

Having removed some 2-screw knobs to find a D-shaft inside, I've been impressed with how secure a knob placement they make.

[haveyouseenhim]

I have some small d shaft chicken heads if you want a couple.

[haveyouseenhim]

[armdnrdy]

BTW, if anybody has any suggestions for foolproof strategies, when it comes to easily and reliably marking off switch positions on the chassis, I'm all ears.  I tend to install the switch, mark off where the pointer on a chickenhead points to, using a marker, remove the switch/knob, apply some rub-on dots, and then spray laquer over top.  But I find I'm frequently a few degrees off, such that the pointer knob overshoots or undershoots.

I think I mentioned this in another post. I create my box artwork in Office Visio. For "tick" marks I use a free add on program for Visio called Radial Elements Tool.
http://www.visguy.com/2009/11/05/radial-elements-tool/

Here's an example of artwork for a resistance test box:

[MrStab]

by sheer chance, i was gonna go with a chicken-head knob anyway, but i didn't realise the leverage advantage. i'm having flashbacks to physics class at school.

i'm glad this thread has become useful beyond my naivete!

[duck_arse]

mrstab, there is a lugged-washer under the star washer on those rotarys. you may need to lift and rotate it to make it stop at 3 positions, as the same switch body is used for 12 position and 2 position configs. and the hole for the anti-rotation pip is a MUST.

[deadastronaut]

I used a davies on my space patrol fuzz on the rotary...no problem.

[candidate]

BTW, if anybody has any suggestions for foolproof strategies, when it comes to easily and reliably marking off switch positions on the chassis, I'm all ears. 

Don't feel bad.  I find that is the case on production units of everything everywhere; whether it be vehicles, pre amps, or other appliances.