knob woes...

[mordechai]

I've just purchased a bunch of knobs from Pedal Parts Plus...these ones:

http://www.pedalpartsplus.com/mm5/merchant.mvc?Screen=PROD&Store_Code=PPP&Product_Code=10021&Category_Code=KNB

They look good but some of them won't fasten to the smooth shaft of the pot (the set screw is defective and won't tighten).  And when they DO fasten, the mounted knob makes it hard to adjust the pot.  It gets "stuck" during part of the turn, making it difficult to adjust the pots.

Anybody have a solution?  Or can anybody recommend a different knob type that is about the same size but which performs better?  The small MXR fluted knobs are a little too bulky so I'm looking for something with a slimmer profile...

[davent]

The turning problem sounds like the knob is catching on the threaded bushing of the pot. You could ream the first 1/16" of the  knob hole with a bit slightly bigger then 1/4" or you could raise the knob so it doesn't grab the bushing or lower the pot with washers on the inside of the enclosure so it sits lower and there's no exposed threaded bushing above the nut.

dave

[Kipper4]

This isnt helpful at all but i've got so many knob gags going through my head right now i could write an episode of celebrity juice.

[mordechai]

Dave, thanks for those suggestions.  I'll use the extra washer option and hopefully that will do the trick.

[Jdansti]

Knob jokes aside, and inline with Dave's suggestions, is the bottom of the knob dragging on the surface of the enclosure?  If it is, turn the pot shaft fully counter-clockwise , place a temporary spacer on the enclosure surface next to the shaft (such as a piece of paper folded once or twice), and then mount the knob flush with the spacer. Remove the spacer.  When you turn the knob clockwise, it should rise a bit higher, and then return to the original height when you rotate it fully counter-clockwise. Hopefully I remembered the directions correctly, but if it still drags (assuming that's your problem) reverse the directions above.

As for the set screws, are the threads stripped or does the tip of the screw just not apply enough friction to stay in place?  If it's the latter, you might be able to do something to the screw tips or the shaft to make it hold better.

[Gurner]

This isnt helpful at all but i've got so many knob gags going through my head right now i could write an episode of celebrity juice.

Now that made me laugh.....the subject title was well honed & the above response was the perfect follow up.

Now then [wipes a laughter tear from the corner of his eye] ...what was the problem again?

[mordechai]

Jeez.  We are so juvenile.

Anyway -- I tried some of the tips...er, SUGGESTIONS...offered above, but they're not working.  When the set screw fastens tightly, the pot still gets "stuck' in a certain spot and won't rotate smoothly.  I checked and it's not catching on the bushing at the base of the shaft.  So I still don't know what to do here.  I'm not getting this problem with the small MXR type knobs, but they're too bulky for the project I'm working on.  And this still doesn't include the problem of the set screw simply not fastening at all in some cases...I keep turning it and it just rotates in its little niche.

[davent]

Hi Mordechai

The pot shaft turns no problems when naked or wearing an MXR knob, the MXR is hollowed out underneath so there's an apron around the edges that come down and will hide the pot nuts, correct?  The MXR is designed to sit low on the shaft and avoid coming into contact with the hardware or top.

Often times the shaft of the pot and knob hole is a pretty sloppy fit so when you tighten the set screw the knob is tilted over to one side and not fully erect so will rub against the nut or if it's a big knob, against the top of the enclosure giving you a spot where things bind. If you try to put a set screw knob on a splined shaft pot this tilt is really exaggerated and a major pain. Still sounds to me as if the knob is catching somehow, pictures?

For the set screws you could try retapping the knobs for a larger set  screw, checked a Small Bear Davies and the thread is 4/48 so might try a 5/40, 5/48, 6/32, i would think finding the 6/32 drill/tap/set screw would be easiest to source.

Contact PPP and let them know they shipped defective parts, they should pop replacements in the mail.

dave

edit; typo, grammar, etc....

[R O Tiree]

Well, your knob is rubbing against something... I'm blaming Dave for lowering the tone.

I use a similar technique to Jon - I use a piece of plastic card with a cutout in it large enough for the nut. Rest the knob on it and tighten the set screw. Slide the card out and I have ample clearance between the knob, nut and enclosure without the knob being too proud.

Dammit, this subject is too hard to discuss without getting smutty.

[John Lyons]

+1, those knobs are small and will hit the nut when pushed all the way down.
Get a credit card (etc) and put it between the enclosure and the bottom of the knob.
This way all the knobs will sit at the same height above the nut. If it still hits the nut
then use two thicknesses.

[Jdansti]

Do you guys find that the knob rises and falls (resist joke) as you turn the shaft (resist another joke)?  When you mount the knob (ditto), you want to make sure that the shaft is turned counter-clockwise. Correct?

[bluebunny]

Do you guys find that the knob rises and falls (resist joke) as you turn the shaft (resist another joke)?  When you mount the knob (ditto), you want to make sure that the shaft is turned counter-clockwise. Correct?

Sorry John, what was the question?   

[duck_arse]

- I got nothing -

does the set screw leave a mark on the shaft, and if so, where? right on the tip?

[bluebunny]

Seriously, I'm with John and John on this one.  I fairly often find that I have to raise the knob slightly to avoid it becoming impossible to turn at some point along its travel.  I think John is right: there must be some vertical travel in the pot somewhere, since it's usually free-running at the beginning and end of its journey, but must snag against the bushing at some point.  But easily solved with one of the temporary paper/card/whatever spacing methods mentioned.

[davent]

As far as the shaft up & down... measured with a depth gauge and shaft was a constant  0.335" tip to nut throughout the rotation.

dave

[markeebee]

+1 on the credit card trick to prevent the flange rubbing when you twiddle your knob (bonus points to me).

If you graunch the set screw up good and tight it'll leave a little imprint on the shaft.  If you carefully whack a centre punch (or a nail) where the imprint is, it'll make an indent for the tip of the screw to sit in.  Sometimes friction is not enough (bonus points & gold coin).

[davent]

I think he's either received the wrong size of set screw or the hole is stripped, wouldn't take much to strip the threads in the soft plastic of the knob.

[greaser_au]

+1 on the credit card trick to prevent the flange rubbing when you twiddle your knob (bonus points to me).

If you graunch the set screw up good and tight it'll leave a little imprint on the shaft.  If you carefully whack a centre punch (or a nail) where the imprint is, it'll make an indent for the tip of the screw to sit in.  Sometimes friction is not enough (bonus points & gold coin).

this is why I dislike setscrew knobs (and cogs - e.g. arcade driving games) on pots.  
Where I've had to use smooth shaft pots  in the past, I file a narrow flat where the screw bites to create an overhang, so that when the screw inevitably comes loose it doesn't just drop off...

david

[MartyMart]

I'm just giggling like a schoolkid reading the replies :-)

Knobs with just one setscrew are a PITA, you need at least two to get them on properly and stay seated level.

Either that or use D shaft pots with corresponding knob OR "knurled" pot & matching knob - ALA Boss.

Most every other combo / mismatch causes problems IMHO.

I have some expensive Aluminium ( UK ) knobs from RS that have 2 x set screws - all metal - and they will attach and sit "right"
on any type of pot there is .... shame they are about £3 a piece !

Marty.

[Perrow]

Let me recap this thread to see if I got it right.

The knob should be screwed but when it's all the way down to the nut the action is interrupted, and when using a credit card to solve the problem the friction is not enough.

Did I miss anything?