This script has a lot of variables you can tweak. Research continues, but there's a lot to work with now.
Version 1.1 now lets you adjust the arrow indicator with more parameters.
One of the most stressful things about making multiple copies of an electronics project is reliably locating interface controls that you like. Maybe you can locate them one time, but can you locate them a year from now? two years from now? And how much do they cost?
For example, I found some slide potentiometer knobs at Mouser.com for about $0.50 apiece two years ago, and they ran out of them... forever. I tried sourcing them elsewhere, and the best I could find was a seller that had them for $4.00 apiece (!!wtf!!). So that really sucks.
One strategy is to buy in bulk. But, buy too few and you may run out and pay twice for shipping. Buy too many and you end up with unused knobs sitting around not making your money back. That also sucks.
Round potentiometer knobs are somewhat readily available. But still, they can be from $0.80 to $5.00 each, and if you can't find enough for your project, that can be problematic. Mostly I'm tired of paying multiple dollars for things that should basically cost $0.25 apiece. Aesthetics are important too, so having options beyond what's out there is nice.
A different strategy is to print them yourself as you need them. No shipping, no running out, and you get to call the shots on how it looks and how it fits. Now, I like this way. Plus, for my project, making the knobs just goes along with the rest of the stuff I've done myself.
download the openscad script and take a look at the first oh, hundred lines or so. These are the parameters.
An incomplete list of parameters you can adjust:
shaft hole radius
shaft hole height
flatness of shaft hole
rounding on top (thanks very much to http://iheartrobotics.com for the articles on edge rounding!)
plus a lot more!
I've posted a bunch of info and screenshots at my blog: http://bit.ly/HGB3h0