Making Replacement Knob Brights.

[igranic]

Having spent far too much time fruitlessly looking for knobs to replace those missing their brass trims, I decided to make my own. Here is how I did it.

Raw material. 0.5mm thick brass strip, obtainable from model shops.
Rough blanks, cut from strip with tin snips, ready for pressing.


Convex press tool, made on lathe to be the same outside diameter as the finished item. Concave press tool. Made larger than finished item in order to ensure even curvature at the edges.


Pressing blank between convex and concave tools using 6" bench vise. This would be better done in a hand press or fly press but, as I don't have either to hand, careful alignment by eye allows an acceptable result.


Concave lathe arbor. Same outside diameter as finished part.


Trimming the part in the lathe. The pressed part is held between the concave arbor and the convex tool under pressure from the the ball-bearing 'live' tailstock centre. Double-sided adhesive fixes the part to the convex tool and helps prevent slipping and consequent scoring. The surplus material is trimmed off and the part finished to the correct diameter.


MORE TO FOLLOW IN PART 2

[Robert Darwent]

Hello Edward,

I see you've be busy! That looks to be an excellent way of turning out replacement brights, well done.

Do you think this method could be modified slightly to make acceptable brass brights of the type used on the Bush TR82B/MB60 models?

Regards

[igranic]

Skimming the part to the correct diameter. Note the trimmed-off waste to the left of the cutting tool.


Before removing the finished trim from the convex tool, it is placed in the chuck and polished under power using very fine emery cloth and metal pollish. Alternatively, if a 'spun' satin finish is required, then fine or medium emery paper can be used, omitting the metal polish.



After removal, the inside of the trim is cleaned and roughened with coarse emery paper to provide a 'key' for the adhesive. The completed knob-bright is then coated with Rustins Clear Metal Lacquer in order to preserve the shine and prevent tarnishing.


Finished bright fixed to knobs with urethane adhesive.


Although not quite of production quality I am pleased with the result, and I will certainly use the method again. The shallow concave dome stye favoured by Grundig and Philips may prove more challenging, and would certainly require a special spherical cutting attachment to make the tools.

Edward

[igranic]

Robert,

Thank you for your kind comments.

This method could be used for most knob brights formed from sheet brass or aluminum unless they have a swaged-over or roll-formed edge. These, and other more complex types could be probably be turned from solid bar using a form tool or CNC control.

As I do not possess a TR82/MB60, and can't readily find any really good close-up pictures of their dial brights, it is difficult for me to express an opinion. If you could post pictures of the front and rear of a typical bright I will try to be more specific.

Edward

[howard]

Hello Edward,

I have a spare TR82 chrome trim here, pics below. If you think you could make these I'll send it to you.

Regards ...... Howard

[igranic]

Howard,

I can probably make a set of tools to produce a passable replacement in either brass or copper. However, as I don't have plating equipment, chrome would be difficult, and stainless steel would need proper tool steel dies and a fairly heavy press to produce an acceptable result

Please go ahead and send me the spare you have, and I will see what I can do.

Edward

[howard]

Hello Edward,

OK it's on its way. The chrome plated trims are identical in size and shape to the brass ones but it's the brass ones that are hard to find.

Howard

[Brian R Pateman]

I've altered the title as there isn't a part 2.

I'll also stick the thread as it seems to be of great interest.

Regards,

[Brian R Pateman]

After some discussion in the moderators' area I've moved this thread here as it seems the most appropriate place for it.

Regards,

[ajs37]

Originally Posted by howard

it's the brass ones that are hard to find.)

Certainly is hard to find these - I wonder why there appear to be proportionately more brass brights missing from TR82s than chrome ones?

If anyone can turn these out, I'd be willing to pay for a few! (and there would be a small market for Roberts knob brights as well!)

Cheers
Andy

[Robert Darwent]

Originally Posted by ajs37

Certainly is hard to find these - I wonder why there appear to be proportionately more brass brights missing from TR82s than chrome ones?

My theory is that the glue Bush used all those years ago doesn't for some reason adhere to brass as well as it does to chrome, hence its not often you find a MB60/TR82B now with its original brass bright still intact!

Regards

[Mike Phelan]

Or they changed the adhesive?

That is a great idea, Edward; full marks for that!

We'll be interested to see how you go on with turning the edge over for the TR82; you might have to anneal it as doming will have work-hardened the brass.

[60 oldjohn]

Hi Edward, The brights look great. There used to be a platers in Hull minimun charge was £5 a few years back I could find out todays situation if needed. I would agree it seems a big proportion of missing brights are brass. Could it be the brass reacting over the years with the Glue? John.

[igranic]

I must admit that I do like a challenge, and this certainly has been one. After a deal of head scratching, quite a bit of trial, many errors, and some not insignificant costs in terms of material, equipment, and (that most valuable of all commodities) time, I think I may have achieved an acceptable and reproducible result.



As I don't own an MB60/TR82 I made these out of sheer curiosity, just to see if I could do it. However, if there is sufficient demand at a realistic price, I may offer them for sale. Considering the rarity of the original item, and bearing in mind that any profits would go to a worthy cause, what would forum members consider to be a reasonable price for one of these? Answers by private email please - I would not want this thread to turn into some form of Dutch Auction!

My grateful thanks and a free sample to Howard for providing original parts as patterns, and to Robert (rrdmpb) for posing the stimulating question.

Edward

[Robert Darwent]

Originally Posted by igranic

My grateful thanks and a free sample to Howard for providing original parts as patterns, and to Robert (rrdmpb) for posing the stimulating question.

Hello Edward,

They look to be just perfect!

If the photo is anything to go by you appear to have done a really excellent job of reproducing the brass Bush brights. They certainly look authentic to my eye!

I'm sure you'll get quite a response from forum members regarding them for purchase. Also many thanks for your very kind gesture of offering me a free sample, it is most welcome and appreciated!

Kind regards

[howard]

Well done Edward

They do look authentic and you have accomplished what others have attempted to do and have failed or given up ! And many thanks for a sample.

Howard

[igranic]

I finally found time to work on the Roberts knob brights that many people suggested or requested, and have made a set of prototype tools that will successfully produce these.

It was possible to produce about 12 brights with the soft proof-of-concept tooling, but I expect hardened tooling to be capable of meeting all likely demand.

Edward

[batterymaker1]

Cool!

Now if you do some Hacker brights, I'm THERE!

[ajs37]

nice one Edward! If these are half as good as the TR82B brights, they will be excellent (and I'll buy some)
Cheers
Andy

[howard]

Well done Edward

Howard