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Old 21st Oct 2017, 7:00 pm   #23
David G4EBT
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Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,540
Default 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:

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):

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.
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