Knobs and shafts

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cygmu
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Knobs and shafts

Post by cygmu » Fri Apr 15, 2016 11:03 am

I'm a more or less total n00b who has never seen a "real" module, only the tangles of wires and solder on my stripboards and breadboard. I'm starting to try to finish some of my builds with panels before mounting them in some kind of housing and I have a possibly dumb question:

All my potentiometers have shafts of around 15mm. I've bought a few knobs from various places, and so far never found any that are deep enough to sit flush against a panel.

What do you all do for knobs and pots? Pots with shorter shafts? Thicker panels? Or some knobs I just haven't found? Help!!

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ersatzplanet
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Post by ersatzplanet » Fri Apr 15, 2016 1:33 pm

Knobs are basically a nightmare to do correctly. When I worked for a large pro-audio company, spec'ing knobs to match pots was always a hassle. Typically you had pots made to match the knobs you planned on using and of course had to buy lots of them to make it worth the expense.

Here are some tips I learned about the different knob/pot shaft combinations:

Round shafts are the most universal for different uses. There is no horizontal vs. vertical mounting considerations. You just put the knob on and tighten the screws. Typically the cheaper knobs have set screws and the more expensive ones have collet mechanisms. The set screw ones come in versions that are all plastic, and ones that have metal inserts. The metal inset variety cost more but will not strip out easily. The trick here is to match the shaft size as closely as possible to the knob to avoid wobble. The second, as with all shaft versions is to match shaft height to knob hole depth. The advantage of set screw or collet knobs is that if the shaft is short, you can set the knob in a place where it won't bottom out on the panel or bushing.

The second kind is the "D" shaft. This might seem like an easy choice but D shaft pots and knobs come in different dimensions beyond just the shaft diameter. The orientation of the flat can be on the side of the pointer or the opposite side. The flat width (how deep it is cut into the shaft) come in a few different standard sizes. A knob meant for a shallower flat will work on a shaft with a deeper flat, but will slip at the ends of the rotation. The length of the flat (how far down the shaft the flat is cut) is also typically spec'd and varies per maker. This will make the knob not go on far enough if it is too short.

The third type is the 18-tooth knurl shaft. One might think this is universal as the plain round but you would be wrong. The teeth are such that when the pot is turned in fully clockwise or counter clockwise direction (usually 300 degrees of turn), there will either be a "peak" or a "valley" in the knurl at the top of the shaft. This means a 10 degree difference if you get the wrong matchup. This is apparent with makers that buy the same knobs for both horizontally and vertically mounted pots with the same knurl profile. Doepfer is a good example. Most Doepfer modules are vertically mounted - that is the PCB is vertical behind the panel. In bigger, and typically quad modules, like the A-143-1 and A143-2, the PCBs are horizontally mounted. If you turn the knobs on this modules full CW or CCW, you will see they are different from the other modules with vertical PCBs. The difference is little and if the graphics are adjusted, most people will seldom notice. If your pot has a center detent, it will become a problem.

The alignment problems can all be overcome with a knob like the Selco/Sifam style of knobs. They have a knob cap with the pointer on it that is put on after the knob is set and is aligned to the graphics then. It doesn't matter what the shaft is pointing to.

So, if you want to match the most pots and knobs together, you can't buy in quantities to custom order either, the best solution is a knob with set screws or a collet mechanism. These may take longer to install but will work with round shafts, shafts with flats (best when the setscrew lines up with the flat) and with knurled shafts too (they may be a slight non-centering if the setscrew compresses the split knurled shaft too much).

As far as length of the shaft getting involved - get short enough shafts so you don't have the knob floating too much, with the shaft still long enough to have something the setscrews can reach, and make a jig or some mechanism to make the installation easier.
-James

James Husted - Synthwerks, LLC - www.synthwerks.com - info@synthwerks.com - james@synthwerks.com
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Post by Reality Checkpoint » Fri Apr 15, 2016 1:55 pm

ersatzplanet wrote:Knobs are basically a nightmare to do correctly. When I worked for a large pro-audio company, spec'ing knobs to match pots was always a hassle. Typically you had pots made to match the knobs you planned on using and of course had to buy lots of them to make it worth the expense.

Here are some tips I learned about the different knob/pot shaft combinations:

Round shafts are the most universal for different uses. There is no horizontal vs. vertical mounting considerations. You just put the knob on and tighten the screws. Typically the cheaper knobs have set screws and the more expensive ones have collet mechanisms. The set screw ones come in versions that are all plastic, and ones that have metal inserts. The metal inset variety cost more but will not strip out easily. The trick here is to match the shaft size as closely as possible to the knob to avoid wobble. The second, as with all shaft versions is to match shaft height to knob hole depth. The advantage of set screw or collet knobs is that if the shaft is short, you can set the knob in a place where it won't bottom out on the panel or bushing.

The second kind is the "D" shaft. This might seem like an easy choice but D shaft pots and knobs come in different dimensions beyond just the shaft diameter. The orientation of the flat can be on the side of the pointer or the opposite side. The flat width (how deep it is cut into the shaft) come in a few different standard sizes. A knob meant for a shallower flat will work on a shaft with a deeper flat, but will slip at the ends of the rotation. The length of the flat (how far down the shaft the flat is cut) is also typically spec'd and varies per maker. This will make the knob not go on far enough if it is too short.

The third type is the 18-tooth knurl shaft. One might think this is universal as the plain round but you would be wrong. The teeth are such that when the pot is turned in fully clockwise or counter clockwise direction (usually 300 degrees of turn), there will either be a "peak" or a "valley" in the knurl at the top of the shaft. This means a 10 degree difference if you get the wrong matchup. This is apparent with makers that buy the same knobs for both horizontally and vertically mounted pots with the same knurl profile. Doepfer is a good example. Most Doepfer modules are vertically mounted - that is the PCB is vertical behind the panel. In bigger, and typically quad modules, like the A-143-1 and A143-2, the PCBs are horizontally mounted. If you turn the knobs on this modules full CW or CCW, you will see they are different from the other modules with vertical PCBs. The difference is little and if the graphics are adjusted, most people will seldom notice. If your pot has a center detent, it will become a problem.

The alignment problems can all be overcome with a knob like the Selco/Sifam style of knobs. They have a knob cap with the pointer on it that is put on after the knob is set and is aligned to the graphics then. It doesn't matter what the shaft is pointing to.

So, if you want to match the most pots and knobs together, you can't buy in quantities to custom order either, the best solution is a knob with set screws or a collet mechanism. These may take longer to install but will work with round shafts, shafts with flats (best when the setscrew lines up with the flat) and with knurled shafts too (they may be a slight non-centering if the setscrew compresses the split knurled shaft too much).

As far as length of the shaft getting involved - get short enough shafts so you don't have the knob floating too much, with the shaft still long enough to have something the setscrews can reach, and make a jig or some mechanism to make the installation easier.
Great reply!

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Re: Knobs and shafts

Post by batchas » Fri Apr 15, 2016 1:57 pm

cygmu wrote:All my potentiometers have shafts of around 15mm. I've bought a few knobs from various places, and so far never found any that are deep enough to sit flush against a panel.
Maybe you could lift the panel up. No idea what other panel components you have (LED and so on), but I thought I should mention until you find better fitting pot/knobs. Might help if the holes on your knobs are not high enough for the longer shafts.
You know whar I mean? Having the pot, than a nut (better than a few washers IMO), then the panel, then the nut. So the panel is lifted up, the shaft is shorter and the knob might fit.
Just an idea.


I'm having for the 1st issues ever with knobs and pots, like ersatzplanet mentionned because of knurled shafts, while the knob pointer does not align exactly in lowest or highest position compared to the panel marks.
Also had to adapt D-Shaft on knurled pot etc. Not ideal.
Though when I build buchla or serge modules, never had a problem.
Choosed Rogan or Davies knobs on Alpha 9mm Pots.
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Post by cygmu » Fri Apr 15, 2016 2:03 pm

That's a super detailed reply -- thank you.

My issue at the moment is entirely around shaft length. Searching on Mouser and Farnell for panel mount, 100k linear pots, the shortest shaft length is always 15mm which is what my pots have... and yet all the knobs I've got hold of (Davies 1900h, Re'An, some unnamed oddments) have a depth of about 11mm.

Some of the remaining 4mm is taken up with the panel but there's still a 2mm clearance between panel and knob.

Is that what "real" modules look like? I've never seen one... If not, how do you get the knob to sit flush (or at least close) to the panel?

Obviously I could mount an additional nut behind the panel to set the pot back
a bit further. Is that what people do?

I feel like I'm being really stupid. The practical part is always where I struggle. Ha.

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Re: Knobs and shafts

Post by batchas » Fri Apr 15, 2016 2:06 pm

batchas wrote:Choosed Rogan or Davies knobs on Alpha 9mm Pots.
I don't remember having issues with this combination.
These knobs have screws so you can fix them on the round shafts.
For instance these or these on these or these.
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Post by batchas » Fri Apr 15, 2016 2:16 pm

cygmu wrote:Some of the remaining 4mm is taken up with the panel but there's still a 2mm clearance between panel and knob.
Oh I see...
Yeah. Sometimes there coud be some tiny space like 2mm, depending on modules, who made them etc.
4 mm is too much indeed. Yeah you could lift it up with a nut behind the panel, that's what I meant in my previous post, why not...

Just as ex. where knob/pot fit well on the panel: on the bugbrand modules, there are REAN which exactly fit on the panel, cause they go around the nut.
This pot with this knob.

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Post by batchas » Fri Apr 15, 2016 2:23 pm

cygmu wrote:the shortest shaft length is always 15mm which is what my pots have... and yet all the knobs I've got hold of (Davies 1900h, Re'An, some unnamed oddments) have a depth of about 11mm.
This is what you'll find on the serge modules. Davies 1900h, then visible nut, then panel. There's always a tiny space then, yes.

Can't make pictures right now, but I'll check this thread tomorrow if you need photos.
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Post by batchas » Fri Apr 15, 2016 2:25 pm

batchas wrote:
cygmu wrote:the shortest shaft length is always 15mm which is what my pots have... and yet all the knobs I've got hold of (Davies 1900h, Re'An, some unnamed oddments) have a depth of about 11mm.
This is what you'll find on the serge modules. Davies 1900h, then visible nut, then panel. There's always a tiny space then, yes.
Maybe you talk about pcb mounted pots, so you omit the nut, which makes the difference. Maybe.
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Post by cygmu » Fri Apr 15, 2016 4:22 pm

Thanks for all the responses, batchas. Much appreciated.

I tried adding a nut behind the panel, with a 16mm panel mount pot, and then I can get the arrangement that you describe: Davies 1900h, nut, panel (then nut, then pot...) This looks quite good.

Now... where to get additional nuts? I don't know what the spec of the thread is. Hmmm. I might resort to washers for this, but I'm sure you're right that a nut is a more solid arrangement.

The bugbrand arrangement looks very good too. If I can find a source for pots like that I'll give it a try.

Thanks again.

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Post by momo » Sat Apr 16, 2016 4:38 am

Amazing reply from James! Great thread and thanks for sharing the knowledge.

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Post by batchas » Sat Apr 16, 2016 11:52 am

cygmu wrote:The bugbrand arrangement looks very good too. If I can find a source for pots like that I'll give it a try.
I can't help on the additional nuts, maybe you could ask in a new thread?

But I know that smallbear has the pots like bugbrand uses here.
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Post by batchas » Sat Apr 16, 2016 12:25 pm

cygmu wrote:Is that what "real" modules look like? I've never seen one... If not, how do you get the knob to sit flush (or at least close) to the panel?
Sorry the light in the studio is not optimal, but I hope you can see the spaces between knobs and panels depending on brands, systems, modules. These are only a few examples...
So you could ask for details here (what knob, what pot) if you see one which catch your attention, like previously with the bugbrand.

Buchla Verbos module
On Buchla 200e modules
On Buchla 200e modules
On Buchla 200 (dusty!) modules***
A module I made for Buchla system
Typical Doepfer modules
On my Serge STS modules

***Here it's a good example. I see there's a bigger distance on a few knobs only because I look at the photo and focus/concentrate now on the space inbetween. But when I play it, depending on the module and the kind of knob, I don't even remark.
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Post by batchas » Sat Apr 16, 2016 12:31 pm

cygmu wrote:I tried adding a nut behind the panel, with a 16mm panel mount pot, and then I can get the arrangement that you describe: Davies 1900h, nut, panel (then nut, then pot...) This looks quite good.
Glad it worked. Even if it's more a workaround and I hope you'll find the solution which fits your needs best.

I thought I'd post some pix from the studio (previous post), so you see that not all modules have the same space between pot and panel. And IMO, when you're patching on top, you don't really remark how big this space is, so it does not really matter anymore, that's my experience, even if I like when all details look good on a module.
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Post by jayhurst » Sat Apr 16, 2016 5:38 pm

momo wrote:Amazing reply from James! Great thread and thanks for sharing the knowledge.
+1. Yes, big thanks James. Exactly the info I've been look for, and all in one spot.
The 8 Steps:
(1) Figure out what it is you always wish you could do with your rig, that you currently can't.
(2) Figure out your maximum available budget.
(3) Look at and research all of the modular toys out there that will make Step#1 happen.
(4) Add an additional 25% to your Step#2 total.
(5) Buy the item(s) found during Step#3, repeating Step#4 as often as needed while completing the Step#5 buying process.
(6) Install newly purchased gear.
(7) Wiggle.
(8) Return to Step#1.

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Post by cygmu » Mon Apr 18, 2016 4:01 am

This thread turned out to be really helpful. Much thanks for the effort that went in to the responses! The photos posted by batchas are giving me Buchla envy apart from anything else...

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Post by batchas » Mon Apr 18, 2016 5:03 am

cygmu wrote:The photos posted by batchas are giving me Buchla envy apart from anything else...
Oops...
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Post by fattyparts » Sun Aug 13, 2017 11:49 am

i need a D-Shaft knob for my TR-09, i think it's roughly 6mm, but i'm not feeling confident as to what to buy here in the uk, if anyone as any advice i'm all ears! thanks
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Post by Synthiq » Sun Aug 13, 2017 1:05 pm

I have used an extra nut behind the panel and it works well. Smallbear sells extra washers and nuts fitting Alpha 16mm pots which have M7 x 0.75 bushings.

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Post by Laughing » Wed Aug 16, 2017 1:50 am

Wow, old thread, but to my experience, there's nothing a Dremel and an Emery Disc can't fix in this situation. I have somewhat cursed myself into using 1/8" shafts for nearly all of my panels, and all the shafts are clearly much too long.

So, once I'm ready to put knobs on (Which are set screw style), I go around and make a good guess or mark all the shafts on the panel, and get to cutting. Ends up with a whole bunch of nice little dowels that have found use in some odd places.

I've seen older versions of pots or rotary switches meant for electronics hobbying, and most of them are -incredibly- long. Like, 4 inches sometimes. That's because they expected you to cut off what you didn't need. Sometimes they even had grooves cut into the super long shaft to mark out common lengths as well.

Regardless, I've been quite happy, and here's an example of one of my panels with it's knobs nice and just about flush with the panel.

Image

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Post by Paul Perry » Thu Aug 17, 2017 5:20 am

I have shortened pot shafts using a pair of boltcutters.
Several thousand times.
Yes, thousands.

I am not proud of this.

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