Q: minimum case hole size for row of 8 x 6mm diameter rotary encoders

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Q: minimum case hole size for row of 8 x 6mm diameter rotary encoders

Post by Nonchai » Tue Sep 15, 2020 10:23 am

For those who are electronics engineers or makers who've messed midi projects involving a row of rotary encoders:

Given encoder shaft of 6mm diameter, and a row of say 8 of them... what is the minimum diameter of hole in the case faceplate in order to cover tolerance issues with the PCB containing the encoders in a row? is 8mm too small? I'd prefer that for my needs - rather than goto 10mmm.

The PCB will be made and populated with components by contract PCB manufacturers.


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Re: Q: minimum case hole size for row of 8 x 6mm diameter rotary encoders

Post by KSS » Wed Sep 16, 2020 7:07 am

Depends on the bushing size, if they're panel mounted. If not, let the knob's diameter be your guide. There's no benefit to having the holes too small. Crap is going to get in a 1mm gap too. Besides which putting a dust shield 'washer' -or eight- on rotary is a no-brainer, unlike sliders.

What you can get away with for a single SDIY build can be much different than what you'd spec for a production item. If you're doing the assembly and you prefer 8mm, the PCB shouldn't make that impossible. But if you're gonna put knobs on anyways, bump it up. Better safe than sorry.

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Re: Q: minimum case hole size for row of 8 x 6mm diameter rotary encoders

Post by jorg » Wed Sep 16, 2020 1:23 pm

Here's a trick to get them centered in the holes: Slip a piece of soda straw or a layer or two of heat shrink over each shaft, before you solder them into the PCB. Place the encoders on the PCB (do not solder yet), then slip the panel over them. Hold it all together and flip it over onto a surface with a gap big enough to accommodate all the shafts. For example, a couple of pieces of equal-thickness scrap wood on your table, with a gap between them. Jiggle gently to make sure all the encoders are sitting straight. Now solder them in. Flip it right-side up and remove all the sleeves on your shafts. Voilà, guaranteed clearance.

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Re: Q: minimum case hole size for row of 8 x 6mm diameter rotary encoders

Post by MikeDB » Wed Sep 16, 2020 2:19 pm

Are these encoder with nuts, or are you trying to avoid using nuts. When I was involved in mixers we used to align around 100 pots into the panel without nuts on low cost mixers. But you couldn't have the holes too large or otherwise you'd get slop in the pot shafts. Key thing was very accurate jigs to hold the pots in place during soldering.
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Re: Q: minimum case hole size for row of 8 x 6mm diameter rotary encoders

Post by Flounderguts » Wed Sep 16, 2020 2:30 pm

Some of the encoder companies offer a neoprene dust guard that goes under the panel. They look and work great if your holes are a bit big...which is usually easier to build and fit.

Generally, though, I like a little bit of room on the panel cutout, usually 10% of shaft diameter is minimum...in your case 0.6mm on a 6 mm shaft. That's the absolute tightest you should go for a pcb mount encoder or pot.
For panel mount, I like to go a bit bigger. I usually measure the nut, and use half of that over bushing size (measured, not spec'd) So if your nut works on a 12mm socket, and the bushing is 9.8 mm on your caliper, then half of 2.2 is 1.1...hole size 10.9 ish. That gives lots of extra room, but ensures you have good bearing from the nut, if it is used alone.

That's not a hard and fast rule, but it tends to work, and no one has complained when I've used that...as opposed to the tight tight holes I use on my personal builds (a reamer helps tremendously)

As everyone else has pointed out, mounting the encoders is 75% of the challenge...and there are lots of strategies for that.


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Re: Q: minimum case hole size for row of 8 x 6mm diameter rotary encoders

Post by Rex Coil 7 » Wed Sep 16, 2020 3:29 pm

I add <0.010" to whatever I measure the component to be. For example;

Pot (ALPHA 16mm) threaded barrel OD = 0.268".

16mm Pot hole = 0.275".

In this case I added 0.007" to the measured threaded barrel diameter, essentially just rounding the hole size up from the barrel size. It fits wonderfully.

I created a word file that contains the actual measured diameters of various components that I typically use, along with the hole sizes I've chosen to mount those components. I refer to that file often, most especially when designing a panel that will be manufactured by Front Panel Express since they are so accurate (more so than I). I tell them I want a 0.275" hole ~here~ ...and that is precisely what I get. Here's a copy/paste example from that file I made up, this is just a very small piece of the information I've gathered and created. This word file is pretty large, what I've pasted here is a small portion of it all. Any time I design a panel intended for Front Panel Express I use these "standards" I've worked out ... it lends itself well to design continuity and consistency and also makes designing a panel far easier for me.

It serves to observe the fact that several brand name components are specified in this list. It's important to note that many of the "same" components have different dimensions. Look closely at the "Mini toggle switch barrel OD" numbers, more specifically how different they are from manufacturer to manufacturer. See my point?

Component Actual Barrel Sizes:

LED Holder "Tandy" barrel OD = 0.308".
Pot (ALPHA 16mm) barrel OD = 0.268".
Pot (ALPHA 25mm) barrel OD = 0.308".
Rotary Switch barrel OD = 0.363".
Large "MPJA" toggle switch barrel OD = 0.460".
Mini toggle switch barrel OD (Taiway) = 0.240".
Mini toggle switch barrel OD (Mountain) = 0.230".
Mini toggle switch barrel OD (No-Name-Red) = 0.227".
1/4" jack barrel OD (Switchcraft 112A) = 0.369".
1/4" x 28tpi Button Head Bolt (Technical Earth) = 0.246".
3.5mm jacks barrel OD = 0.230".
3.5mm jacks Shoulder OD = 0.304".

Component Drill Hole Sizes ("Final" file):

LED holder hole = 0.3125".
Rotary Switch hole = 0.370".
16mm Pot hole = 0.275".
24mm Pot hole = 0.3125".
Large "MPJA" toggle switch hole = 0.465".
Large Carlisle type momentary push buttons - 0.468".
Mini toggle switch hole (MOUNTAIN or NO-NAME) = 0.235".
Mini toggle switch hole (TAIWAY) = 0.245".
Case screw hole = 0.170".
PCB screw hole = 0.125".
Option Panel border screw hole = 0.125".
1/4" x 28tpi Button Head screw (Technical Earth point) hole = 0.250".
3.5mm Jack BARREL hole = 0.240".
3.5mm Jack SHOULDER hole = 0.315".
1/4" Jack hole = 0.375".

Notice that included in those dimensions and data are 3.5mm shoulder and 3.5mm barrel dimensions. This is because in some cases the hole needs to be large enough for the "shoulder" to countersink into the panel, usually because either the panel is too thick, or the threaded portion of the jack is too short (can't start a nut since there's not enough threads showing). This is what I mean when I go on and on about fitment and workmanship. Like that old sign hanging up in some repair shops .. "why is there never enough time to do it right, but always enough time to do it over" ... yessir.

Look at the 1/4" jack dimensions vs hole size (1/4" jack barrel OD (Switchcraft 112A) = 0.369" .... 1/4" Jack hole = 0.375"). There's only six +/- thousandths of an inch of clearance. Did it work? Yes, absolutely and beautifully so. When there is a row of jacks 20 jacks wide, I like to be certain they align as well as possible to the observer's eye. Close clearances really help with that. Sure, you can drill larger sloppy holes and manually align them during the mechanical assembly phase, but that can take a lot of time, especially with panels having 28 jacks. Didn't need a reamer once, on all three of the panels I designed using this data I've compiled (one even uses 60mm sliding pots, using the same ~standards~ everything fell into place very nicely).

It won't surprise me if little (or none at all) of this information is useful to the OP, but I felt like this information may still be useful to other readers and lurkers. It took me months to work out and compile a lot of this, I had to make choices on various component selection commitments whilst on-the-fly designing the panels. Then the moment of truth was when the first panel arrived .... will everything fit? Yup ... right on the money! ... even with the tight clearances I went with on components and their placement. I reckon sharing my efforts is a good thing.

Alright then. I'm done rambling about nothing (again). Thanks for putting up with my chatter box post.

Have fun! :)

5U NORMALIZING PROJECT (for your entertainment) viewtopic.php?t=78836&highlight=


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Re: Q: minimum case hole size for row of 8 x 6mm diameter rotary encoders

Post by Rex Coil 7 » Wed Sep 16, 2020 3:48 pm

ON THE OTHER HAND (continuation from the post above) ;

If one wishes to manually drill their panels, if you take your time and use a few very basic tools your work can come out beautifully.

You'll need:
** Combination square.
** Sharpie.
** A good quality center punch that is sharp.
** A good hammer (I prefer to use a 3 pound brass mallet since the brass helps to mitigate ~bouncing~ of the hammer head when center punching a hole. If the hammer bounces, while it is in the air between the two strikes ("two" since the hammer bounced and hit the center punch twice) the punch can "bounce" out of position when the hammer bounced ... now you have two center punch marks. Shit.).
** Some type of "scratch awl" to mark the panel where you want the holes to be.

With the combination square, Sharpie, and awl, make your marks on the panel. Apply a bit of Sharpie ink around the area where the hole is to be drilled. Then, using the combination square and the scratch awl tool precisely make your drill marks by scratching off the Sharpie ink with the awl. I usually scribe a cross or X, with the intersecting lines of those symbols being exactly where the point of the punch needs to be. Carefully place the punch, and land ONE blow with the hammer. ONLY ONCE! Then check your work. If the punch mark needs to be deeper, reposition the punch and hit it ONLY ONCE and check your work again. Lather, rinse, repeat as needed for however many holes you're drilling.

Patience really pays off here.

Bus Bars Fab - 5.jpg
Bus Bars Fab - 1.jpg
Bus Bars Fab - 3.jpg
(below) these are not drilled holes in this picture, they are the center punched marks. I make them nice and deep so the drill bit has less chance of walking out of the mark and ruining the panel. That material is 6101 Aluminum alloy (very well suited for the particular application it's tasked with here).
Bus Bars Fab - 7.jpg
MAIN CAB - REAR VIEW - BUS BARS - Bottom - 2.jpg
Main Cab - Rear View - Bus Bars and Norm Rails - 1.jpg

All of the holes pictured here were drilled with a drill press .... however I used no clamps or workpiece holders to position the work on the drill press table. I just aligned the point of the drill with the marks, held the part down on to the table with one hand and operated the quill lever with the other hand. No tricky clamps or holders, nothing to undo/redo for each hole (loosen the vice, reposition the workpiece, drill the next hole .. none of that going on). I could have just as easily drilled them all using the tailgate of my pickup truck as a workbench and manually drilling all of those holes with a drill motor. I have actually done that in the past, more than once. DO NOT DO WHAT I'VE DESCRIBED HERE (no clamps on a drill press table) ... TOTAL SAFETY HAZARD ... DO NOT BE A DUMASS LIKE ME. I'm simply pointing out that precise work can be done with less precise tools if you put in the work and do proper layout before cutting/drilling anything. Patience.

Alrighty then. Time for my nap.

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