[David G4EBT]

There was an article In the Spring 2017 BVWS Bulletin on an American 'Bestone' radio by Stef Niewiadomski (known on this forum as 'Saddlestone Man'). If not rare, the radio is certainly uncommon. Unfortunately, one of the three original wooden knobs was damaged, so Stef had fitted a set of three alternative wooden knobs, it being unlikely that an original knob would ever materialise.

Over the years, Stef has been a prolific writer (still is!) in the Bulletin and other magazines such as Radio Bygones. I’ve enjoyed reading his articles and built a capacitor reformer that he designed, so as a small gesture of appreciation for his efforts I got in touch to say that if he sent me the damaged knob, I'd have a go at making him a set of three replicas.

I'll say right away that the process is time consuming and a labour of love, involving a number of processes over a period of several hours, so I'm not in a position to make knobs to order, but given that quite a lot of forum members seem to have lathes, yet might not have considered using them to turn replica knobs, I thought it might be helpful for me to explain how I went about it.

Accurate measurements are called for, involving lots of stopping and starting of the lathe as the work progresses. As the knobs are sited close together on a radio, any slight differences will be immediately apparent. If knobs are in natural wood rather than painted, due to variations in timber grain and colouring, there's little prospect of just making one replica to exactly match the original, so really, a full set needs to be made.

The processes involved are:

• Turn a wooden square to a round spindle, 5mm larger in diameter than the knob.
• Part off a wooden blank from the spindle for each knob.
• Make a brass insert on a metalworking lathe for each knob, drilled out to the diameter of the radio control shafts. In my case, the insert needed to be 12mm outside diameter, drilled ¼” bore.
• Mount a wooden blank in the woodturning lathe and use either a 12mm Forstner bit, or end mill in the tailstock, rotating the chuck by hand while advancing the bit into the blank, not going any further into the blank than necessary. Don’t use an engineering drill as it may penetrate too far into the blank, being pointed at the tip.
• Coat the brass insert with two-part epoxy cement and with the wooden blank still in the lathe chuck, force the brass insert into the wooden blank with the tailstock.
• Make a metal mandrel on which to mount the blank when turning the blank to shape on the lathe.
• Drill and tap the blank and the mandrel 4BA and use a 4BA brass grub screw to mount the blank on the mandrel, placing the mandrel in the chuck.
• Turn, sand and finish the replica knob.
• Remove the knob from the mandrel and fit the knob on the radio control shaft using the 4BA grub-screw.

I had the damaged original knob from Stef to hand so was able to compare various hardwoods to try to get a reasonable match. Iroko and mahogany were not a good match, but English walnut seemed quite close, so I went with that. I drew a sketch of the knob with the critical dimensions and given that the largest diameter was 30mm and the height was 25mm, I turned a spindle 35mm diameter from which I parted off three blanks 30mm long.

The knobs required a 12mm diam brass insert drilled 1/4" for the control shafts of the radio, 16mm long and tapped 4BA for mounting the knobs on the shafts. To ensure that when mounted on the shafts of the radio the knobs would be exactly concentric and true, I turned mandrel on my metalworking lathe with 1/4" shaft for each knob, on which to mount the wooden blank in the lathe chuck for turning.

I turned the brass inserts, roughing the outsides with a junior hacksaw while the inserts were on the lathe, so as to provide a good key for the two-part epoxy adhesive when the brass inserts were glued into the wooden blanks.

The only complication in completing the knobs was that eight notches had to be milled out around the perimeter and I don't have a milling machine. I tried a number of techniques using a router jig and a Dremel in a jig, but not to my satisfaction, so in the end I had to get a chum to mill the notches for me on his monster Bridgeport.

It occurred to me that replica wooden knobs could be turned to mimic Bakelite for some radios, so I later made two replica black knobs for an Ekco A22 - the larger being the tuning knob, the other - with a 'tab' on it - being the volume control on/off knob, (identical to the wave-change switch knob). I'll cover that in another post.

The aim in woodturning is to ‘sand the shape of the wood’ – not to ‘sand the wood to shape’ or sharpness of detail can be lost, so it’s important to keep the turning gouges sharp and to get a good finish ‘off the tool’ to minimise sanding. I gave the knobs a coat of shellac sanding sealer to seal the grain, then a light sanding, firstly with 220 grit, then 320, 400 and 600. (There’s no possibility of skipping and grades - say going from 220 to 600). I finished them on the lathe using shellac 'friction polish'

Not all knobs will lend themselves to wooden replicas, especially if they’re engraved with lettering or have intricate designs and fancy milled edges, and admittedly it’s quite a palaver. It takes hours rather than minutes to create a knob, involving the use of a metalworking lathe as well as woodturning. But that said, if a replacement knob can’t be sourced, for those with the equipment, skill and time, it provides a solution – in my case at minimal cost as the materials were all to hand. True, it’s time consuming, but we’re hobbyists doing what we do for fun and a sense of achievement, using our leisure time for enjoyment – not to make a living. What’s more, here in Yorkshire, ‘summat for nowt’ has a certain appeal!

As I said earlier, I’m unable to make replica knobs as a service to others, but I hope this rather lengthy post and the pictures might be of interest, use and even inspiration, to those who are equipped with lathes, but perhaps hadn’t considered using them for this sort of application.

Hopefully, the pictures might make things a bit clearer.

Pic 1 is the damaged original knob.
Pic 2 is a sketch I drew to show the critical dimensions.
Pic three, a couple of brass inserts turned and roughened up.
Pic 4, three walnut blanks with inserts fitted, and three mandrels turned from scrap alloy bar on which to mount the blanks for turning.
Pic 5, one knob turned and sanded, ready for the perimeter grooves to be milled.

Some more pics in the next post.