Re: Making replica wooden knobs on a lathe
 

I'd say you were an amateur, David, and not a professional for the simple reason that I consider your skills superior to the many professionals I've met in my time. You are one of the relatively few highly skilled and talented people who set the bar for the rest of us to attempt to emulate.
I won't add 'well done' because it's been said by many on this thread and lots of others that feature your work. I will say 'keep up the good work', knowing you are sure to.
As Argus points out, very impressive. As always.
Regards
Tony

Re: Making replica wooden knobs on a lathe
 

Nicely done David, a dentist friend of mine used to make copies of knobs with plaster of Paris and cast replacements in what he called "Dental Acrylic" (Norwegian = Tannlegeakryl).
Cannot ask him these days because he died nearly ten years ago now, but I do have one or two of his repair jobs and attempts at creating CRT bases for WWII German radar equipment tubes. I think that it is a question of experimenting more than anything, the alternative would be what?

Re: Making replica wooden knobs on a lathe
 

Many thanks to those who have read this thread for their kind comments.

My purpose in starting the thread wasn’t so much to show off my handiwork, as to outline an approach and explain to others who may have small lathes but rarely use them, and who may not have considered their lathes to make replica knobs if needed. Though it’s flattering to receive so many kind comments, I'd like to emphasise that the level of expertise required to make replica knobs isn’t very high – just basic woodturning and metalworking skills, well within the scope of anyone who is of a practical bent and possesses lathes and a few turning tools.

Sometimes people ‘inherit’ a lathe, or might buy one on impulse but never use it. A small, simple metalworking lathe in particular is very useful in radio restoration for making things such as spacers and shaft couplers, and a woodturning lathe can be useful for turning plastics as well as wood. A lathe can also be useful for accurately tapping a thread on a rod or bar internally or externally, by either holding a die or a tap in the headstock or tailstock with the work-piece in the other end, and turning the chuck by hand. The thread will be far more accurate and concentric that it would if the tap and die were hand-held with the work-piece in a vice.

But to get back to making wooden knobs, if the knob is going to be sprayed - as the Ekco A22 knobs were, then kiln dried beech is ideal, being close grained and knot free. Luckily, beech in spindle form sufficient for several knobs is readily and cheaply available in the form of 35cms long x 2cms diameter pastry rolling pins from Wilko, currently for £1.25:

http://www.wilko.com/baking-utensils...m/invt/0078397

Alternative a search on e-bay for ‘English Beech wood-turning spindle blanks’ will find plenty of suppliers, then the square can be turned to round on the lathe to the desired diameter in a matter of minutes. Cross-grained beech say 40mm thick for larger diameter knobs such as the large A22 tuning knob that I turned can be had from hobbyist timber suppliers and sawmills.

As to the woodturning tools that I used to make the knobs, there were only three – a roughing gouge to turn the wood to the required diameter, a ‘parting tool’ with which I did most of the turning, and a round nosed ‘scraper’ to create the dome shapes. The tools are shown in the picture below.

To turn a length of square timber to round, the wood can be held ‘between centres’.

The easiest way to find the centre of the timber at each end of the blank is to use a ‘centre finder’ to mark the wood with as pencil, then prick the centre with scriber. Having mounted it between centres, with the tool-rest close to the timber, just below centre line with the roughing gouge angled upwards, the square blank can quickly be turned to round. (More experience turners may use a skew chisel, but lesser mortals such as me, steer clear of that!). Here’s a link to a centre finder, which can be used on square or round timber. (They can be found on e-bay):

http://www.axminster.co.uk/axminster...-finder-340146

Having turned the wood to a spindle of the desired diameter, a parting tool is used to slice off a knob blank of the required length into which a hole can be drilled on the lathe to accept the brass control shaft insert – in my case, the insert was 12mm diameter with a 6.4mm diameter hole through the centre. The blank is then fitted to a mandrel made to suit and mounted in the woodturning chuck to shape and finish the knob, as outlined in my earlier posts.

Pic 1: Centres marked on square spindle ends using ‘centre finder’
Pic 2: Roughing gouge, parting tool, round-nosed scraper.
Pic 3: A live centre and four pronged centre, which have 'Morse tapers' and fit into the headstock and tailstock of the lathe.
Pic 4: End of spindle marked for four-pronged centre.
Pic 5: Beech square blank held between centres, ready for the toughing gouge to turn the square blank to round.

A bit more info and a few more pics to follow.

Re: Making replica wooden knobs on a lathe
 

I'm very aware that this is a vintage radio forum - not about woodturning, which is well catered for on other forums. However, I hope this isn't too far off track and is sufficiently relevant to the hobby to be worth the space, given that most of us often find cabinetry restoration (veneering, re-finishing etc), and sourcing knobs is often problematical, which is where I came in with this thread.

A question that often crops up in woodturning, circles is ‘what speed should I run the lathe at?’ The answer is that the faster the turning speed, the cleaner will be the cut, and the smaller the diameter of the wood, the faster the lathe speed needs to be as there’s such a small amount of timber passing the tool with each rev when it’s of a small diameter. There’s a loose ‘rule of thumb’ formula for calculating the speed at which a woodturning lathe should ideally be run, and that is: ‘Diameter in inches x RPM = 6,000 to 9,000’. So for example, a 10 inch diameter bowl blank should be run at a speed of 600 – 900 RPM. Most turners will start off at a slower speed when the blank is first mounted as it will be out of balance until trued up with a roughing gouge.

Using this formula, it follows that a 2” diameter spindle would have a turning speed of 3,000 RPM, and a 1” one a theoretical speed of 6,000 RPM -, well beyond the capacity of the lathe, so most turners would run the lathe at perhaps 2,000 - 3,000 RPM.

At 3,000 RPM, a 1” diameter spindle would have about 3” of timber passing the tool for each rev, so that would be 9,000 inches of timber per minute passing the tool (about 750 feet). A 10” diameter bowl with the lathe running at 600 RPM will have 30 inches of timber per rev passing the tool - 18,000 inches (1,500 feet) per minute. Thus, the smaller the diameter of timber, the faster the lathe needs to spin at to get a good clean cut. At too slow a sped, instead of the tool cutting the fibres, it tears them, then it’s necessary to resort to sanding by working through the grits to perhaps 600 grit for a good finish. The sharper the tools, the faster the speed, the cleaner will be the result, and less sanding will be needed.

For sanding, the lathe speed needs to be reduced to 250 RPM or so and the sandpaper not held in one place or it will score rings around the timber.

Just to finish off, here are a few more pics regarding the process of creating a blank to make a knob:

Pic 1 Parting tool ready to part off a knob blank.
Pic2: Blank almost parted off.
Pic 3: 4-prong centre removed from headstock by tapping it out with a bar.
Pic 4: Chuck fitted to the lathe headstock, with blank in place ready to be trued up.
Pic 5: Using a 12mm end mill (not a drill) to mill the hole ready for a brass insert to be glued in.

I hope these notes will give an indication that no exceptional skills are called for.

There are countless woodturning videos on youtube showing spindle turning – some better than others.

Have fun!

Re: Making replica wooden knobs on a lathe
 

Hi David,

Only just noticed this thread today or I would have replied earlier.

All the knobs you have produced are superb but the A22 knobs are something else - not at all easy to get the tab on those correct, but yours are perfect!

Excellent David - a really first class result!

Kind regards

Re: Making replica wooden knobs on a lathe
 

Thanks for your kind word Robert, but as I've outlined in the last two posts, it's really quite basic turning for anyone with a modicum of woodturning and metalworking skills, given a bit of care and patience. If it doesn't work out first time, so what - the materials are very cheap and the pay-off is that we can make knobs that we'd otherwise stand little chance of finding at any cost. Being well thought of by our chums is an added bonus!

I did have a go at casting knobs in a range of materials but with limited success. Basically, because I was trying to use a 'home-brew' casting jig to accurately locate the brass insert in the centre of the knob and couldn't do that to my satisfaction. I'm going to revisit it and try just using the jig to make the alginate mould into which to pour the casting medium, then when it's set, I'll drill the cast knob in a 'jam chuck' on the lathe, made to suit each knob to enable the brass insert to be fitted concentrically, as with wooden knobs.

Not every knob will lend itself to a cast replica, (or a wooden one, come to that), but many will. I've spent more hours fruitlessly searching for knobs at the NVCF etc, than I ever would in gearing myself up to cast one, or even a set so they all match each other and look as original as possible within the limitations of what we have at our disposal. If the outcome is successful, I'll start another thread on that.

Re: Making replica wooden knobs on a lathe
 

Excellent work. I would love to have a decent sized workshop to accomodate the necessary machine tools. I used to really enjoy my time at college using the various lathes and milling machines. Very inspiring work David and thanks for the helpful advice.

Regards
Symon

Re: Making replica wooden knobs on a lathe
 

Like others, I'm late in coming to this thread but am struck by the excellent results. Really impressive work David. I'm very jealous of your skills.

Well done!

Peter

Re: Making replica wooden knobs on a lathe
 

Excellent work David .

Re: Making replica wooden knobs on a lathe
 

I had the pleasure of seeing the Ekco knobs in the flesh last week. They look even better than the photos here show. A truly excellent job and a work of art! Well done David.

Peter

PS: the Pye PE94MBQ works fine.

Re: Making replica wooden knobs on a lathe
 

Well done David , looks very impressive...it's all about the passion isn't it not the money...great work

Re: Making replica wooden knobs on a lathe
 

It's really kind of fellow forum members to make such encouraging and flattering comments, which it's nice to be on the receiving end of. But without wishing to sound falsely modest, I can only reiterate that anyone who has a basic woodturning and metalworking lathe and a few tools, together with an average level of skill could attain the same results. Obviously you have to be fairly accurate to get the dimensions correct, for which a cheap pair of digital calipers is useful, but it's hardly precision engineering. I'm sure that anyone who does possess and use a lathe would agree with those comments.

To my mind, in all that we do in life, for us to make much of a success of anything, we need to be 'pernickety' - a word sometimes used as a term of derision - 'excessively precise, fussy, overly attentive to detail', obsessive even. But if we're not all of those things, I think we're on a slippery slope, in the wrong hobby and it becomes a chore - not a pleasure.

Of course you do ideally need an original knob as a pattern - if only a damaged one, and it may be that if replicas of Bakelite knobs are required, especially if the knob has features that aren't easily reproduced in wood, such as milled edges, then casting would most likely produce a better result. I'm going to have a go at that and if the results are worth sharing, I'll post a thread on it.

In some instance, depending on the colour and texture, maybe 3-D printing would be a good option, but that requires considerable investment in equipment and expertise.

At risk of turning the forum into a back-slapping 'mutual admiration society', 'high-fiving' each other, the level of resourcefulness, skill and investment it time to achieve the accomplishments is the posts below is way up in the stratosphere, far out of sight of my replica knobs!

http://www.vintage-radio.net/forum/s...d.php?t=111951

https://www.vintage-radio.net/forum/...ad.php?t=47965

http://www.vintage-radio.net/forum/s...d.php?t=114857

http://www.vintage-radio.net/forum/s...d.php?t=138304

That's where 'pernickety' - in the nicest sense of the term - gets you!

Re: Making replica wooden knobs on a lathe
 

Thanks Peter - glad the knobs passed their quality control inspection!

The Pye was my first radio, bought in 1958 as I recall when I was 19, and a Short Wave Listener. I've still got some broadcast station QSL cards that I received!

Re: Making replica wooden knobs on a lathe
 

I am in awe of anyone who can create such precise replicas.

Maximum respect!

I've seen websites of people using 3D printers to make figurines and they lament the rather coarse finish.

One person found a solution - he suspended his printed items in acetone vapour (no direct liquid contact or the item melts!)

Timing is important but get it right and the figurines acquired a glossy finish.