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Old 10th Feb 2019, 11:49 pm   #1
Peter.N.
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Default Cloning vintage knobs

I found this on Youtube, thought it might be of interest.

Peter

https://www.youtube.com/watch?v=aNBHtlhlHF4&t=15s
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Old 11th Feb 2019, 8:30 am   #2
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Default Re: Cloning vintage knobs

That's really helpful. I guess there is an initial expense in the moulding chemicals and the glue gun but if you've got one very rare knob and you need two then it's a great solution.

Thanks for the link.
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Old 11th Feb 2019, 9:32 am   #3
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Default Re: Cloning vintage knobs

You might contact David Pirkle. He is on Etsy under Pirkleations Productions.
He made some fantastic Philco "Bullet"knobs for me. Matched the color exactly too. He was even able to mold the slot in for the knob spring! That's real skill.
If nothing else, he should be able to give you some hints.
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Old 11th Feb 2019, 2:23 pm   #4
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Default Re: Cloning vintage knobs

Quote:
Originally Posted by Peter.N. View Post
I found this on Youtube, thought it might be of interest.
Good video

A nice old method and they look better than 3D printed ones
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Old 11th Feb 2019, 2:30 pm   #5
mark_in_manc
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Default Re: Cloning vintage knobs

What a great result. The chemicals are a little pricey, but OK, if the forum fails to find the knob you've always needed...
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Old 11th Feb 2019, 3:40 pm   #6
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Default Re: Cloning vintage knobs

I uploaded a video in 2012 on this topic:

https://www.youtube.com/watch?v=SIdYBPQsjxk

I used Alginate as a moulding compound. Its cheap and clean working, ideal for one or two good copies before it deteriorates.

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Old 11th Feb 2019, 4:39 pm   #7
nebogipfel
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Default Re: Cloning vintage knobs

This chap has achieved good results too...

https://www.youtube.com/watch?v=sHH6WHNoLoI

https://www.youtube.com/watch?v=YdMKQuYXuOw

I suspect the quality of the resin used has a big part in the appearance of the final result.
I note some on YT use a vacuum chamber to ensure all the bubbles are out of the resin.
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Old 11th Feb 2019, 5:39 pm   #8
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Default Re: Cloning vintage knobs

Certainly a good result, John, but at a cost. Up to the individual to decide. My method was 'cheap and cheerful'. Alginate is completely harmless, doesn't require a two-part approach, works with normal tap water and doesn't tend to cause air bubbles. As for resin, I used Auto body (for fibreglassing) liquid resin, bought from auto accessory shops.

Not too many of us have access to a vacuum chamber but one is essential to be certain to prevent air bubbles. They are used commercially.

For the tinting, as I suggested in the video, a very small quantity of ordinary paint - or aerosol paint, added quickly - served me well enough.
I have used other methods over the years but all were more expensive and/or trickier to do than the simple Alginate.

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Old 11th Feb 2019, 5:58 pm   #9
nebogipfel
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Default Re: Cloning vintage knobs

Not too many of us have access to a vacuum chamber...

Hello Tony,

Yes, there are some nice little units available (Ebay) for around 140, which probably isn't too bad if you make good use of it.

One alternative method, 3D printing, very much in vogue at present, looks like quite an expensive hobby. That said, with a printer you don't need a physical item to take a copy from, just a good 3D drawing.
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Old 11th Feb 2019, 8:04 pm   #10
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Default Re: Cloning vintage knobs

I've looked into this many times as the thought of the end of worrying about that missing knob intrigues me.
One of the 'online' moulding supplies companies I looked at showed a replica backnut for a sanitary fitting being made from resin, strong and accurate enough to work like the original.
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Old 11th Feb 2019, 8:44 pm   #11
Aerodyne
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Default Re: Cloning vintage knobs

It is even possible to mould 'one off'* using plaster of Paris, provided you are moulding an item with a positive taper throughout its length (no negative shapes or undercuts) and with a flat back! Such a mould will not take resin unless it is thoroughly sealed, however and the item to be moulded must have a thoroughly applied release polish.

Another method is to mould with liquid rubber. This is a slow job as it is built up in layers, each needing to dry before the next is applied. Then there's Gelflex, a hot melt rubbery compound which is excellent but again tends to 'aerate' rather, and it stinks if you overheat it, something that is all too easy to do. Resultant moulds are very tough and long lasting, though.

I have cast resin into moulds and added a moderating compound such as French chalk or very fine wood flour to soften the hard gloss of pure resin. Along with colouring matter, cast knobs can be made to look and feel perfect.

*Removing the cast resin will almost always shatter the plaster mould.

Tony
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Old 14th Feb 2019, 4:49 pm   #12
David G4EBT
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Default Re: Cloning vintage knobs

A couple of years or so ago, I spent a lot of time and effort in knob casting exeriments, and soon discovered that it's one thing casting the knobs - it's quite another devising a method of mounting them which is robust and is absolutely concentric, so that when mounted on the control shaft, there's no sign of eccentricity. If the mounting hole in the knob is just 1mm off centre (not a large error), that will give 2mm of eccentrity as the knob is rotated. Also, the hole must be perfectly vertical or the knob will be wonky. By no means an easy task if relying on a pillar drill say.

Based on Tony's experience, I used alginate to make the moulds. It's cheap, safe, flexible and not unpleasant to use. (For reasons that elude me, a popular use is to make moulds to cast replicas of new-born babies feet). The only downside - which Tony mentioned - is that when you've made your mould, you need to use it right away as alginate shrinks as it dries out.

To ensure that the means of fixing was robust, I made brass 'ferrules' on my lathe, 12mm O.D. drilled either 6mm or 1/4", roughened the outside to give them a good key to fix into the knobs with epoxy cement, then to drill and tap the side 4BA for a grub screw. I made a 'knob casting jig' to mount the original knob on a shaft to lower the knob down into the alginate to make the mould. The jig ensured that the knob was perfectly aligned and not wonky in any way as it could be if lowered into the alginate by hand. So far so good.

My intention was to then fix the brass ferrule onto the shaft that the original knob was on, to fill the mould with casting medium and to lower the ferrule into the casting medium, figuring that in theory at least, the ferrule would be exactly central. But the difference between theory and practice in practice, is greater than the difference in theory. This technique did not as I'd hoped, result in the ferrule being exactly concentric.

I decided that the only way of ensuring that the ferrule could be perfectly concentric would be to mount the knob is what's known as a 'jam chuck'. That's a piece of wood mounted on a woodturning lathe, with a hole the same shape as the knob, with the knob pushed into the hole protected from damage by a piece of kitchen roll. I then mounted a 12mm 'end mill' in the tailstock (rather than a drill as an end mill creates a hole with a flat bottom). I rotated the chuck by hand while gently advancing the end mill into the knob. Then I slid the ferrule onto a 1/4" or 6mm diam rod mounted in the tailstock to make sure it was exactly concentric with the knob, coated the ferrule with epoxy, and advanced it into the knob allowing the epoxy to set.

The knobs I made were perfectly concentric.

It's ludicrously time-consuming of course, but that's irrelevant in hobbies, which are about the 'low tech/high skill' enjoyable use of leisure time.

I'm sure there will be those who don't have the luxury of a woodturning or metal turning lathes, who may have devised a means of accurately centring the mounting hole, or may perhaps accept the limitations of slightly wonky knobs as the best that can be done with their limited facilities. If the end result is knobs that are presentable and functional, then it's 'mission accomplished'.

As to casting materials, they're really quite expensive - even more so if there's a desire to colour the resin to get a good match with original knobs. I used materials that I had to hand - namely, Ronseal two-part wood-filler, which sets rock hard, and Plastic Padding 'Super Steel, (which - despite its name is not electrically conductive, which could be a consideration on knobs for live chassis sets.

I covered these experiments in the thread below and I've attached some pics of knobs that I cast.

https://www.vintage-radio.net/forum/...d.php?t=142098

Pic 1: Four Unitra 'Figaro Special' knobs cast in Ronseal Woodfiller.
Pic 2: An original Figaro Special knob in the centre, with two finished cast knobs either side.
Pic 3: A Portadine 'Princess' knob just cast using 'Super Steel' as the casting medium.
Pic 4: Two 'Princess' knobs, ether side of the original.

Not related to 'casting' but just to show that some shapes of knobs lend themselves to be turned in wood by anyone with a woodturning lathe and moderate turning skills. Pic 5 shows a small and a large Ekco A22 brown Bakelite knob on the left, alongside two that I turned in beech and sprayed with 'ebonising lacquer'. I did it as an exercise to see if passable results could be obtained. They could just as soon have been sprayed brown but I didn't have brown paint to hand. Someone had said it wouldn't be possible to make the smaller one on a lathe as it has a tab on it, but I didn't know that until after I'd made it. See:

https://www.vintage-radio.net/forum/...d.php?t=140529

Hope that's of interest.
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Old 14th Feb 2019, 5:42 pm   #13
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Default Re: Cloning vintage knobs

My own experience is that for smallish items, a metalworking lathe will easily cope with woodturning. It is certainly ok with hardwoods. I imagine very soft wood may need a much higher speed.
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Old 14th Feb 2019, 5:59 pm   #14
stevehertz
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Default Re: Cloning vintage knobs

I needed some ultra difficult to find knobs for a very ornate 1930s Crosley console set. I eventually found and used Larry Bordonaro. The results were amazing, just like new old ones. Ok, it's not moulding them yourself, but sometimes buying in a service is the best or even the only way. I couldn't have made them.

http://www.antiqueradioknobs.com/
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Old 14th Feb 2019, 6:16 pm   #15
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Default Re: Cloning vintage knobs

As always, David has set the standard here. His replicas are works of art. It is true that casting materials can be very expensive - at least the material used to make the mould with - which is why I try to find economic methods to produce things that are comparable in quality to those made using more costly products. Alginate makes the lowest cost moulds for me, so far.

It is indeed difficult to drill an accurate spindle hole and I haven't found a foolproof way of doing so. I've usually cast two or three copies in order to achieve just one adequately drilled. I do not possess a lathe so ferrules, though a great idea, are out, but at times damaged or unusable old knobs can be broken apart for their brass ferrules.

Not having an end mill, I tended to drill with a standard 'pointed' bit then re-drill with a matching size drill which had its point flattened on the grinder to offer just a little of the remaining angled flutes. This leaves a hole that is close to being flat-bottomed.

Tony
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Old 14th Feb 2019, 8:55 pm   #16
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Default Re: Cloning vintage knobs

As you say Tony David always sets the benchmark. The knob with the tab is very impressive
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Old 14th Feb 2019, 9:56 pm   #17
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Default Re: Cloning vintage knobs

I am surprised that no-one has come up with a method of 3D scanning and printing of knobs. Saying that you probably will still have the problem of mounting shafts etc as has been mentioned previously.
Alan.

Whoops, missed the 3D bit in post #9!

Last edited by Biggles; 14th Feb 2019 at 9:58 pm. Reason: extra info
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Old 24th Feb 2019, 8:16 pm   #18
David G4EBT
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Default Re: Cloning vintage knobs

Quote:
I am surprised that no-one has come up with a method of 3D scanning and printing of knobs. Saying that you probably will still have the problem of mounting shafts etc as has been mentioned previously.
Someone has. Forum member Jon, 'Ti Pwun', produces a small rane of 3-D printed replica items for Hacker & Roberts radios, such as these Roberts knobs (Sold out):

https://jonsprintshop.com/index.php?...hig3lgnut09d12

The original Roberts knob was a very poor design from an engineering point of view, as illustrated below with an original R200 broken knob, (still with it's knob 'bright!) alongside a replica I cast, but with a brass insert and grub screw. Tightening the grub screw into the captive nut on the original knob was destined to crack the fragile Bakelite off and that's what often happens, not to mention the knob 'brights' getting lost.

With any type of knob, if cosmetic appearance is of paramount importance rather than just functionality, generally (as with the Roberts knobs), if one is missing or damaged, you can't make an exact replacement, so would need a full set, the cost of which could well exceed what the set is worth. (I don't think I've ever paid more than a fiver for a Roberts set, nor would I).

It can end up being a lose-lose situation - not economically viable as a commercial proposition, yet too expensive to produce to be attractively priced for anything but the most expensive sets. (The same applies to other production methods of course, such as casting.

From what I've seen of 3-D printed items (not radio related), apart from the complexity for 'the lower orders' such as myself when it comes to the software aspects of scanning items for the 3-D items, there are two limitations: Firstly, you don't get a smooth finish as you would with cast items - there are tiny 'striations' from when the nozzle laid down the molten plastic filament. That might not matter with something like Roberts knobs, which have ribbed sides, and little else showing, but it would be very noticeable with others styles. Maybe the 'striations' can be smoothed out somehow - I've no idea.

Secondly, you can't easily replicate original colours, (as you can with cast materials). For example, at this link, there are 38 colours of PLA filament (Polylactic acid), but apart from black, white, grey, and maybe red, few other colours that could be used to replicate knobs for radios or test gear.

One thing that can certainly be said for PLA is that it's very tough stuff and has applications in the hobby that go beyond just replica knobs.
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Old 25th Feb 2019, 3:16 pm   #19
Mike. Watterson
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Default Re: Cloning vintage knobs

That knob is used on at least one Vidor and other sets. Almost all of that kind I've seen are damaged.
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Old 25th Feb 2019, 3:33 pm   #20
Aerodyne
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Default Re: Cloning vintage knobs

That broken knob isn't the first I've seed of its type, either. Not only is it a bad design, it is or was quite prolific. To think, someone was paid to design that. Makes you wonder... hardly seems like a saving in cost, as the nut had to be located in the Bakelite, just as David's concentric and far more durable brass insert is.

Tony
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