# Pot and Knob shafts, Ds and Flats

Is it a standard in D-shaft, right-angle potentiometers for one endpoint to point the flat face of the shaft to the right of noon, sweep clockwise, and have the other endpoint to the left of noon? And for the corresponding knobs to align the flat face of the shaft with the indicator line?

I'm looking for the right combination of knob and potentiometer for my application. From the user perspective I want a front-panel knob that indicates low at 7:30, mid at noon, and high at 4:30. The board is perpendicular to the front-panel so the pot needs pins perpendicular to the shaft. Before noticing the note "shaft shown in CCW position", I bought this pot (https://www.bourns.com/data/global/pdfs/PTV09.pdf) and this knob (http://www.newark.com/pdfs/datasheets/spc/TA-790.pdf). They look and feel great except for this one problem: the angles are wrong by 180degrees.

I looked around a bit more for alternatives: Either a knob with the indicator line opposite the flatted side of the shaft, or a potentiometer with opposite endpoints (and keep in mind the knob needs to point parallel to the board, not orthogonal to it). So far this seems impossible. Everyone I've looked at seems to be in agreement that this is the standard.

Some alternatives I would like to avoid:

• mounting the pot on the other side of the board (there's no space)
• using a round shaft with a set-screw knob (it needs to be fairly precise and not change with time)
• panel-mount pots

The best alternative I can think of is to use a knurled knob/shaft but I really like the D shaft because it's so hard to screw up alignment.

• I take it the board is already done; are cuts and jumpers out of the question? – EM Fields Oct 13 '14 at 23:19
• Nah, still designing the board. Trying to choose components. – Dave Oct 14 '14 at 0:31
• Mill (or file) a second flat on the pot shaft. For quantities below the hundreds this may be the simplest solution. – Brian Drummond Oct 14 '14 at 10:30

It does look like some potentiometers are offered with options of where the full CCW position is. But anything other than the standard (30deg right of up, or about 1:30) is a special order part, or at least I couldn't find any in stock anywhere.

Here's an example: http://www.mouser.com/ds/2/414/p160-20748.pdf

• In the end, the solution I chose was to use a knurled shaft with 18 teeth and a corresponding knob. This way maybe it can be put on incorrectly but at least it will be obvious, 20degrees off. – Dave Oct 17 '14 at 22:26

We use spendy Selco collect knobs. You can set them where ever you want. (Well and then you need another ~$1 per instrument to include the (cheap) selco spanner tool for your customer.) You could also use a knob with a movable pointer on the face. ($1 is cheap compared to the cost of the knob.)

Do you have any possibility to think about orienting your circuit board parallel to the back of the panel? Or at least making a separate parallel circuit board to accomodate the pot?

If you could engineer either of those concepts into your packaging you could easily use the straight up style of the Bourns pot (PTV09A-1) and orient it as needed to make your chosen knobs work.

On the other hand if you must stay with the right angle

• Unfortunately that's too much of a complication to solve this relatively unimportant issue. It would complicate manufacturing and add another board to the design. – Dave Oct 14 '14 at 17:15