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Thread: Potentiometer Bushing Material

  1. #1
    Old Timer defaced's Avatar
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    Potentiometer Bushing Material

    I'm wondering if anyone has a source for the raw stock that is used to make split shaft to 1/4" shaft pot adapters similar to these: Guitar & Bass Control Pot Adapter Bushings (2)
    By my measurements, it needs to be 0.250" diameter with a 0.007" wall. I'm not picky about material provided it's stainless or non-ferrous. So far my searches for this size in stainless, brass, copper, and aluminum haven't yielded anything.
    -Mike

  2. #2
    Old Timer
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    Iīd get a couple feet (or yards) of proper sized thin walled brass tube and have my friendly Machinist cut a lot of them (43 per foot).
    After setting the Lathe up, you can make 200 in 10 minutes, for a very low per-piece cost.
    For less than 10 or 20 units, pay through the nose for the ready made ones.
    As with everything else, actual part cost is cheap, if you make enough, but setup fees or just "getting into it" set a "floor" below which you canīt go.

    As an example, a customer ordered one of my 4 channel 100W mini Club Mixers, which I havenīt made for a few months now, and for which I have no front panels not PCBs left (Cabinet, PSU and Power Amp are "universal")
    I cut, folded and painted 10 blank 2U high aluminum front panels (they can be used elsewhere), silkscreened 3 of them and 3 PCBs , the minimum justified because although actual screening takes less than 60 seconds each, the screens have to be properly washed later, which takes almost 20 minutes.
    I will actually build 3 Mixer/Preamps anyway, even if only one was asked for.
    (My "now that Iīm into it" Theory)
    1 for immediate use, and about the 2 extra ones, I know that *if I have them*, Iīll sell them in a jiffy.
    Worst case, I publish them in "Mercado Libre", our local branch of EBay.

    Itīs good being able to make a lot of things "in house", without depending on external suppliers.

  3. #3
    Old Timer tedmich's Avatar
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    heat shrink tubing can work for this, or maybe this ultra thin wall SS from McMaster Carr
    12" 6100K221 $12.91

    .250" OD
    0.240" ID
    0.005" wall

    or you could hone down some smaller ID tubing with this tiny flexi-hone:
    4424A256 Flexible Cylinder Hone 6.4mm (1/4") Cylinder ID, 240 Grit, 8" O'all Length $12.31

    maybe this .01 wall tubing (0.230" ID)
    89895K221 Type 304 SS Smooth-Bore Seamless Tubing 1/4" OD, .23" ID, .01" Wall, 12" Length $9.02

    my experience is that splined shafts are pretty loose in their tolerances, maybe some RTV would snug things up a bit, and a bit of petroleum jelly on the shaft will be sure nothing is too permanent.

    life is harder for people who like things JUST so....

  4. #4
    Old Timer defaced's Avatar
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    Iīd get a couple feet (or yards) of proper sized thin walled brass tube and have my friendly Machinist cut a lot of them (43 per foot).
    That's what I'm trying to do, I have access to a lathe though work, but I'm not having success finding raw stock.

    ---

    I've considered the heat shrink tubing, but haven't seen if it'll work or not. Thanks for reminding me to try it.

    life is harder for people who like things JUST so....
    Thanks for the editorial. I'll keep that in mind.
    -Mike

  5. #5
    Old Timer
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    heat shrink tubing can work for this
    This is good!
    Why didnīt I think of it? ["slapping my forehead" smilie]
    Or: the actual problem is that the split shaft is *almost* 1/4" diameter, not that bad; the main problem is that unless by sheer chance the screw head gets exactly in the middle of the slot, it will crush the shaft which will become irregularly "thinner", making the rotation wobbly.
    *Maybe* if you can insert a proper thickness shim in the slot (it might even be pick-thickness plastic, cut with a scissor) you get "90% of the result with 10% the effort".
    Try it, itīs so simple.

  6. #6
    Noodle of Reality Steve Conner's Avatar
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    That's what I do, I jam a piece of an old credit card or plectrum into the slot, and then wrap copper tape around the shaft to fit a 1/4" knob.

    If it's a metric knob you just need the piece of plectrum. The pots on my old Westone bass were "converted" like this at the factory.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  7. #7
    Supporting Member Jazz P Bass's Avatar
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    The "jam a piece of plastic" in the slot is what is missing, when it comes to doing it right.
    Why the vendors of the sleeves do not offer something (a tech tip?) elludes me.

  8. #8
    Old Timer
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    It's not loose tolerances. That just doesn't happen in modern-day production manufacturing.

    The issue is the difference between 6mm and .250" pot knobs and shafts and realizing that they are not interchangeable. Metric vs. SAE is the "problem".
    John R. Frondelli
    dBm Pro Audio Services, New York, NY

    "Mediocre is the new 'Good' "

  9. #9
    Supporting Member Jazz P Bass's Avatar
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    Yup.
    1/4"= 6.35mm.

    Edit: What the heck ever happened to the "Metric Act"/ from the '70's.
    The most technologically advanced country (for now) on the planet & we still measure things by how long your foot is!

    Edit Again: I am refering to the USA.
    Last edited by Jazz P Bass; 12-28-2011 at 07:31 PM.

  10. #10
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    Quote Originally Posted by Jazz P Bass View Post
    Edit: What the heck ever happened to the "Metric Act"/ from the '70's.
    The most technologically advanced country (for now) on the planet & we still measure things by how long your foot is!
    Where's my silver one piece body suit, personal jetpack and flying car? The future looked awesome in old movies and TV shows. Now that it's here, it totally bites!

    The adapters in the OP are very likely the Allparts adapters which are just cut pieces of brass tubing like you get at the hardware store.

  11. #11
    Old Timer defaced's Avatar
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    We'll find out, I ordered 10 of them. If they work, great, I can take measurments and keep looking for raw stock. If not, then I'm out 10 bucks, big whoops.

    The adapters in the OP are very likely the Allparts adapters which are just cut pieces of brass tubing like you get at the hardware store.
    All of the 1/4" OD brass tubing I've come across is 0.014" wall or greater, so if these parts are really what they say they are, it's not made from stock off the shelf tubing. It's either drawn down for thinner wall, or bored out (which I can't see as being economical, so I don't think that's the case).
    -Mike

  12. #12
    Senior Member Enzo's Avatar
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    The general hobby store stuff appears to be .014 wall. Hobby stores and places like MicroMark sell tons of that.

    I can't imagine they are putting any labor into this at all other than chopping to length.


    Here are the guys who make the hobby store stuff. Perhaps contact them and ask if they make thinner walled stuff, or could refer you to who does.

    Home - K & S Engineering: Full Line Metal Specialists
    Education is what you're left with after you have forgotten what you have learned.

  13. #13
    Old Timer
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    Itīs drawn tubing.
    You can reliably get any wall thickness.
    Brass is a wonderful material.
    Itīs been with us for 2500 years yet you can do with it things that are impossible with other materials.

  14. #14
    Old Timer defaced's Avatar
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    Thanks for the link Enzo. I'll give those guys a call and see what they have/can do.
    -Mike

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    Quote Originally Posted by Jazz P Bass View Post
    Yup.
    1/4"= 6.35mm.

    Edit: What the heck ever happened to the "Metric Act"/ from the '70's.
    The most technologically advanced country (for now) on the planet & we still measure things by how long your foot is!

    Edit Again: I am refering to the USA.
    All systems of measure are arbitrary. There is nothing more or less proper about any of them.

    The length of some extinct monarch's member is as good as a fictional fraction of some portion of the planet.

    The one thing that is truly outdated about the inch / foot / miles system is that it was designed for the convenience of people conversant with fractions.

  16. #16
    Old Timer defaced's Avatar
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    So, heat shrink material does work, but requires some finagling to make it fit. This involves shirnking the tubing around the pot shaft (which results in a ~0.254" OD), allowing it to cool, removing it, inserting it into the knob, and then pressing the knob onto the shaft.

    I received the bushings from the guitar electronics site linked in the first post. I haven't measured all of them to see what kind of spread they have, but the one I measured was 0.249" OD, 0.005" wall; they looked about 5/16" long, but I didn't measure. These are extruded, not typical 0.014" wall and bored out. The edges aren't deburred which makes it kinda difficult to push them into a 0.250" hole, so some sanding is in order. I haven't got the magnifying glass out, but judging by the burr, they were parted on a lathe.
    -Mike

  17. #17
    Supporting Member Jazz P Bass's Avatar
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    "
    The one thing that is truly outdated about the inch / foot / miles system is that it was designed for the convenience of people conversant with fractions. "
    Fractions s*ck!

  18. #18
    Old Timer
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    So, heat shrink material does work, but requires some finagling to make it fit. This involves shirnking the tubing around the pot shaft (which results in a ~0.254" OD), allowing it to cool, removing it, inserting it into the knob, and then pressing the knob onto the shaft.
    Why?.
    Cut the heat shrink slightly longer, so when heated it tightens around the shaft, but also bends inwards at its unsupported end.
    That lip makes it easier for it being pushed into the knob.
    You still need to put some sheet material in the shaft slot, to avoid its deformation by the knob screw.

  19. #19
    Old Timer defaced's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Why?. Cut the heat shrink slightly longer, so when heated it tightens around the shaft, but also bends inwards at its unsupported end. That lip makes it easier for it being pushed into the knob. You still need to put some sheet material in the shaft slot, to avoid its deformation by the knob screw.
    I appreciate your contribution, but your approach sucks. I'm an engineer too; stop talking down to me. And please, read my posts before you reply (referring to your first reply in the thread where you clearly didn't read my OP).

    Now for your question as to "why":

    Because that's the process I came up with at 9PM last night. Further, when the heat shrink tubing is shrunk around the shaft, and in the case of the shaft/heat shrink/knob combination I have it creates an interference fit, when the knob is pushed onto the now heat shrink covered shaft, the heat shrink tubing is pushed downward covering the pot muting thread which requires trimming. While your approach of leaving the heat shrink tubing long reduces this problem (I just tried it), it is still a problem. Now, if the knob were say reamed out with a 6.5mm or F size drill bit, or I used a different knob which had a slightly larger ID, this would resolve the interference fit and eliminate all of this talk of different assembly order, but I digress.

    As for the shim, depending on relative location of the set screw to the indicator on the knob (if there is one), and the pots rotational position in the panel and any indicating marks on it, if the set screw aligns with the slot in the pot shaft, tightening the set screw will not damage the pot shaft. Now, if everything doesn't work out to those conditions (there's alot of "if's" in there), then yes a shim will be required. Now since shim stock is both readily available in a myriad of sizes and materials, and is inexpensive, I am focusing on finding material for adapting the diameters.

    -----------

    Quote Originally Posted by defaced
    the one I measured was 0.249" OD, 0.005" wall; they looked about 5/16" long
    The bushings are actually 1/4" in length. The OD and wall dimensions are within +/- 0.001" from those I reported.

    Also for anyone else looking for this same information, I'll save you the trouble of contacting the Micro Group. While they specialize in small diameter tubing, they are mainly a carrier of stainless tubing, and their price this material size (at the date of this post, SS prices fluctuate violently at times because of Chrome and Nickel prices) is about 17 bucks a foot. This was for quantities under 10 feet, the next price break was 16 bucks a foot. I forgot to call Enzo's source. I'll get to that tomorrow and report back tomorrow.
    -Mike

  20. #20
    Old Timer
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    Dear defaced.
    Really don't understand how can you feel
    stop talking down to me.
    definitely not my intention but just in case I gave you the slightest reason to think so, I offer my apologies in full.
    Happy 2012.

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