Do these control knob scales have a proper name and how were they used ?

[GrimJosef]

I have a few of these engraved acrylic objects, which look like they were used to provide regular scale marks behind a control knob. I'd like to know a bit more about them, but without knowing what their proper name is I can't easily search for more information.

The central circular boss is hollow, so it could sit on top of the nut which secures a control pot to a panel. But I'm not sure how the scale was meant to be fixed in place - maybe using the four prongs, which stick up out of the boss, in some way ? Presumably these would then be hidden under a hollow knob ? The scale marks are engraved on the surface opposite the boss projection, which would place them directly against the front panel, thereby protecting them from damage. Presumably numbers corresponding to the major divisions (of which there were 10 spaced avoer 240 degrees) would be marked directly onto the panel.

Of course it's possible they were specific to a very particular piece of equipment - a scope perhaps ?

Any info much appreciated .

Cheers

GJ

[Alistair D]

RS Components still do similar for indexing rotary switches
https://uk.rs-online.com/web/p/poten...-knobs/0581969

The search term I used was knob skirts.

The ones in your picture were probably made for a specific piece of equipment.

Al

[GrimJosef]

Thanks Al. I hadn't heard of knob skirts. I guess they are supposed to rotate with the knob, so at any time the relevant number aligns with a fixed cursor mark on the panel. Since there are multiple marks but no numbers on whatever mine are, I think they have to stay fixed and have the knob (probably some sort of pointer ?) rotate past them. Does that sound right ?

Cheers,

GJ

[Radio Wrangler]

Rendar or Sifam make?

Odd to see a scale with no numbers.

David

[Alistair D]

The only advantage over a marked panel and a pointer knob is that the markings will not be disappear after a lot of use.

Looking closely at picture 2 above there is a slightly raised ring of plastic round the centre of the skirt. That will prevent the markings rubbing on the panel and being worn off.

I have no idea what it would be used for. Perhaps another forum member will recognise it and solve the mystery.

Al

[Refugee]

Whatever side the printing is on would face the panel surely.

[GrimJosef]

I suspect so too. That's the opposite side to the four prongs and the circular indent which might cover the pot nut.

Cheers,

GJ

[Alistair D]

Originally Posted by Refugee

Whatever side the printing is on would face the panel surely.

It does. What I am saying is that the raised lip prevents the skirt being pressed hard against the the panel so the markings cannot be rubbed off that way.

Al

[Terry_VK5TM]

It looks like a "nut cover".

The four 'prongs' fit up in to the knob.

Similar items here - see bottom line of pics - http://knobshop.com/Knobs_s6

[ms660]

Mods permitting....Similar here:

https://www.ebid.net/uk/for-sale/fig...iABEgIHTPD_BwE

Lawrence.

[McMurdo]

ISTR Radiatron-Elma made this sort of thing

[emeritus]

Beat me to it. I have some similarly-shaped skirts but with black numbers for use with 12-position switches, that were made by Elma in the early 1970's. They have the four pips that engage corresponding recesses in Elma collet knobs and were used with circular fixed black plastic discs that have one white sector to make visible the number of the selected position.

[GrimJosef]

Originally Posted by Terry_VK5TM

It looks like a "nut cover".

The four 'prongs' fit up in to the knob.

Similar items here - see bottom line of pics - http://knobshop.com/Knobs_s6

Originally Posted by ms660

Mods permitting....Similar here:

https://www.ebid.net/uk/for-sale/fig...iABEgIHTPD_BwE

Lawrence.

Ah. So this scale does rotate with the knob then (that's not what I was thinking).

Without numbers on the scale, how does that work ? Presumably if you want to know where the control is set you have to count round manually from zero to whichever (moving) scale mark is opposite the (fixed) mark on the panel ?

Cheers,

GJ

[mole42uk]

Perhaps the skirts are 'unfinished' and should have had another process to put numbers or some sort of scale on?

[pmmunro]

I would suggest that they could be described as "graduated" knob skirts. Another reason for having the graduations on the panel side would be to reduce parallex error with reference to the panel markings.

It could be that the corresponding knob, or an intermediate accessory carried the numerical markings.

PMM

[GrimJosef]

Thanks Richard and PMM, that kind of thing sounds like it would work.

Cheers,

GJ

[factory]

Originally Posted by emeritus

Beat me to it. I have some similarly-shaped skirts but with black numbers for use with 12-position switches, that were made by Elma in the early 1970's. They have the four pips that engage corresponding recesses in Elma collet knobs and were used with circular fixed black plastic discs that have one white sector to make visible the number of the selected position.

Yes Elma used to offer them as a figure dial (custom ones were are available), unfortunately they seem to have discontinued making them sometime in the last five or ten years.
Here is an old pdf I downloaded years ago with them in; Elma Knobs 26963.pdf

David

[emeritus]

Thanks for the Elma PDF, it covers the knobs and accessories that I have. I couldn't find any on-line data for them when I looked about 10 years ago.

[Graham G3ZVT]

I'm not sure if these acrylic scales have a proper name but back in the day these vernier reduction drives were very common
https://www.ebay.co.uk/itm/Small-Cal...BoCbSQQAvD_BwE
And we called them verniers even if they didn't have the secondary scale.

[factory]

Originally Posted by emeritus

Thanks for the Elma PDF, it covers the knobs and accessories that I have. I couldn't find any on-line data for them when I looked about 10 years ago.

I can't remember where it came from, must have been the Elma website or an archived version.
We couldn't get the small figure dials directly from Elma though, I think work had to pay a daft amount to get them from another supplier, as they were already obsolete at the time.

David