Shaft size adjustment
 

I have just bought the 'perfect' control knob for a project of mine, or so I thought, only to find it has a 1/4" shaft mount where my shaft is actually 6mm - grrrrr (and d'oh).

Is there a simple method to 'gap' the difference? I reckon - tell me if I'm wrong - that a small piece of 0.125mm thick metal would wrap around the 6mm shaft to take up the slack?

Is there an 'industry standard' shim (like slivers of coke tin!) that fits the bill or is there something actually made for the task?

I'll be more careful to check sizes next time of course.

Re: Shaft size adjustment
 

The flat springy bronze "door weatherstrip" stuff works well in this sort of application.

Re: Shaft size adjustment
 

A strip from a roll of aluminium foil works well (the sticky tape stuff, not the Baking foil) Just wrap a couple of turns or so around the shaft. It wouldn't be for a Pye Seafarer would it?


John.

Re: Shaft size adjustment
 

To put 0.175mm into perspective, a piece of 80GSM copier paper is 0.1mm thick (or should I say 'thin'), so a piece of shim cut from an aluminium drinks can would probably be about right. It's remarkable that the eye can detect that a 1/4" knob on a 6mm shaft isn't concentric, but whether that would keep us awake at night, I guess it depends on how fussy we are! Even if it wasn't noticeable, just knowing that it wasn't quite right would probably be a source of irritation to me, which suggests that I have some - as yet - undiagnosed condition. :-)

I'd most likely be rummaging through the re-cycling bin with tinsnips to hand.

Re: Shaft size adjustment
 

I wrap 38 swg enameled copper wire round the shaft with a spot of superglue to hold it.

Re: Shaft size adjustment
 

David - little things that catch the eye become 'big' things that annoy! I already have such an arrangement on another piece of equipment but that particular one uses a continuous rotating digital encoder with the knob having a finger recess for speedy turning and the eccentricity bugs the heck out of me....

This latest project - a variable isolated AC power supply - has a variac that only rotates 270 degrees but even that is enough to tick me off if it isn't concentric!

Sam - now that sounds like an idea I'd like to try.... nice one!

Thanks for all the other ideas.

Re: Shaft size adjustment
 

I don't think it's undiagnosed-it just goes with the territory of being an "Engineer"!

Re: Shaft size adjustment
 

I have never tried this but if you filled the hole in the knob with araldite and then ( In a lathe ) drill it out to the correct diameter. Experiment with unwanted items first though!

Re: Shaft size adjustment
 

Shim worked for me.

Re: Shaft size adjustment
 

I've done that with two-part epoxy 'Super Steel' by Plastic Padding. It sets far harder than Araldite and despite its name, isn't electrically conductive, which can be advantageous in all sorts of applications. I restored a Unitra 'Figaro Special' which uses an auto-transformer so the chassis can be live depending on the polarity of the mains lead. It had push-on knobs retained by as clip and the knobs were quite loose. Hence, were a knob to fall off and the metal shaft be live, it posed a hazard. I therefore filled the knobs with 'Super Steel' the milled them out on the lathe with a 6mm end mill, drilled and tapped through the side of the knob and fitted a 4BA grub screw, the head of which could be filled with wax.

A bit fussy some may say, but for me, it's always safety first, functionality second, originality a poor third.

As to drilling out knobs, it's a bit more problematical if you have a 6mm knob to fit on a 1/4" shaft. Trying to enlarge a 6mm diameter brass ferrule with a 1/4" twist drill is bound to end it tears, so I thought I'd gently try a 1/4" diam end mill in the tailstock of the lathe. It didn't end well, so I had to resort to using a boring bar in the tool-post, gingerly take off a thou or so at a time. Easy enough to remove metal, but you can't put it back!

Re: Shaft size adjustment
 

Solutions that require a lathe are usually beyond the capabilities of most amateurs (much as I'd love to own one!) so shimming is going to have to be the route forward on this occasion.

I'm wondering if the brass insert itself (in the knob) could be wholly removed (?) and potentially replaced with one of the same outer diameter but correct shaft hole?

Would it be possible to drill a 1/4" brass rod with a 6mm hole? This could be cross-pinned/glued ovr a 6mm shaft and there's usually enough depth in a knob to allow the extra length to be absorbed....

Re: Shaft size adjustment
 

That bronze strip also works well as draught excluder, but where on earth do you get it?

AFAIK its no longer manufactured

Ian

Re: Shaft size adjustment
 

I doubt that an insert could be removed without wrecking the knob, and if it could, and another ferrule glued in with epoxy, you'd need the ferrule to be mounted on a shaft in the tailstock of a lathe with the knob in the headstock so that when the ferrule is inserted, it would be concentric and true when the adhesive has set.

It wouldn't be possible to drill a 6mm hole in a 1/4" brass rod because 1/4" is 6.35mm, so the wall thickness you'd be left with would only be 0.175mm - about 6 thou of an inch - so the wall would simply collapse. You could drill say a 10mm diam rod 6mm diameter on the lathe then turn the wall thickness down to 6.35mm diameter but again, the wall would be so thin that it would collapse.

As you say, few have a lathe, and those that do have one would, I'm sure in this instance, use metal shim. As I mentioned elsewhere, to put 0.175mm into perspective, it's slightly less than 2 thicknesses of 80gsm photocopy paper that most of us use in our printers.

You can buy phosphor bronze shim but I don't think you'd want to at the price:

https://maccmodels.co.uk/materials-m...150-pb102.html

Cheaper to buy a can of Coke, pour the contents down the gurgler and get out a pair of tinsnips - scissors even!

Re: Shaft size adjustment
 

My stash of the stuff is from when I reworked my front door to use Neoprene draught/water-excluders.

Phosphor-bronze or Copper/Beryllium "finger stock" is still very much available - it's pretty much the standard way to RF/EMI-seal around panels and access-covers on high-power transmitters etc.

Re: Shaft size adjustment
 

To drill brass back off the rake to 90 degrees, no grab then.

Re: Shaft size adjustment
 

The original Phosphor bronze draught excluder strip (and the cheaper nylon substitute) would still be useful products for older doors and windows that were not designed to be sealed. With your mention of this product I thought you might know of a source.

Getting back to the subject of this thread, although I have a lathe and am probably capable of making a tubular sleeve I think a shim made from sheet material is far more appropriate for a control knob.

Ian

Re: Shaft size adjustment
 

A bit off topic but for anyone who acquires a lathe, the following book is a mine of information.

"The Amateur's Lathe" L.H. Sparey. My copy is seventh impression 1983

Publisher ARGUS BOOKS LTD. Model & Allied Pubblications, Wolsey Road, Hemel Hempstead, Herts. HP2 4SS

ISBN 0 85242 288 1

When I googled the title it seems to be readily available.

Re: Shaft size adjustment
 

Out of interest, I cut a piece out of an empty Coca cola tin and measured its thickness: ordinary scissors worked fine. I made it about 0.1mm, not quite thick enough for a close fit, but I suppose making a few indentations would close the gap.

Re: Shaft size adjustment
 

When replacing knobs on old 6mm split shaft pots on guitars etc., brass 'pot sleeeves' are commonly used to solve the problem:-

e.g. Allparts EP-0220-008

https://www.allparts.uk.com/products...lit-shaft-pots

i.d. 0.238" (6.05mm)
o.d. 0.25""
length 0.375"

(Sold as 'for split shaft pots', but should also be good for solid shafts.)

Rebadged (?) as 'WD' here:-

https://www.ebay.co.uk/itm/WD-Music-...4383.l4275.c10

Cheers

Re: Shaft size adjustment
 

Presumably by 'split shaft pots' they mean the splined ones as shown below.

Sliding a sleeve over the shaft would enable a normal unsplined knob to fit the shaft and would also enable a 1/4" knob to fit a 6mm shaft and to be concentric - not offset.

Neat sleeves and not expensive.

Well spotted!