Turning oval knobs/handles

[RichardG]

I want to make a couple of replacement knobs for an Ercol dresser we have. Trouble is they’re oval in shape.

So my initial thoughts was to turn between centres and then offset but having drawn it up I don’t think that’s going to work.

I know you can get fancy ellipse chucks or indeed make one but is there any other way of achieving this shape? The fall back is to turn a round knob and and then use the disc sander to manually shape it, may well be the easiest option

 

[SVB]

I’d turn it round, then shape as you say. Could turn it with multiple centres but likely to need some hand finishing anyway and probably easiest to get closest match by disc sander anyway. If you had 100s to do then maybe different story but for a couple I’d accept the hand work path.

 

[Richard_C]

Perhaps start by turning a rectangular blank then finish by hand. Less to remove from the sides than if you start with a square.

 

[Jacob]

Shape the workpiece to the oval finish size/shape first and simply turn the knobs - but without touching the edges of course.
Don't know if this would work, might be simpler to turn them round and then shape the edges.

 

[RichardG]

Thanks for the ideas, I‘d convinced myself that I was missing a way of doing this but obviously not. Just need to find an Elm offcut, I’ve got this horrible feeling that I turned the last piece I had into a bowl….

 

[Alpha-Dave]

Looks to me like the dished-out front has 2 different curves in the short and long directions, therefore there that will require significant work off the lathe to the point where turning the rough shape would only be a small part of the work.

I suspect that these were made by the thousands on a machine that partly worked like a shaper, but also its cutter was fed in & out as the wooden rod was rotated to create the oval shape.

There are a few options to make more: 1) by hand; 2) with a CNC machine (2 side milliing); 3) or a router-in-a-pantograph (use the originals as a template).

 

[RichardG]

Looks to me like the dished-out front has 2 different curves in the short snd long directions, therefore there that will require significant work off the lathe to the point where turning the rough shape would only be a small part of the work.

I suspect that these were made by the thousands on a machine that partly worked like a shaper, but also its cutter was fed in & out as the wooden rod was rotated to create the oval shape.

There are a few options to make more: 1) by hand; 2) with a CNC machine (2 side milliing); 3) or a router-in-a-pantograph (use the originals as a template).

Sound like you’re right, they used it as a selling point in the their 1985 brochure. No less than 15 separate operations!

 

[Droogs]

You need an eliptical chuck. If I remember rightly one of the better known woody books for turning has a design in it

 

[J-G]

You need an eliptical chuck. If I remember rightly one of the better known woody books for turning has a design in it

David Springett's book is what you need - that is if you want to make your own elliptical chuck.

I didn't know about him when I designed mine a few years ago - working from first principles it took me two years - and I've hardly used it since

As Alpha-Dave has pointed out, the 'dish' in the front would be very difficult to achieve without resorting to a proper elliptical turning chuck. Turning a round knob and then making the outside elliptical would leave the 'dish' still spherical and therefore less than ideal but may well be a good compromise.

 

[Droogs]

If you don't want to make the chuck then you could possibly make a small Archimedes Trammel, but probably not on a small enough scale to be practical for your purpose. Other than that a CNC lathe

 

[RichardG]

David Springett's book is what you need - that is if you want to make your own elliptical chuck.

I didn't know about him when I designed mine a few years ago - working from first principles it took me two years - and I've hardly used it since

Sounds like it needs the cobwebs blown off by making a couple of knobs.

As Alpha-Dave has pointed out, the 'dish' in the front would be very difficult to achieve without resorting to a proper elliptical turning chuck. Turning a round knob and then making the outside elliptical would leave the 'dish' still spherical and therefore less than ideal but may well be a good compromise.

Yes I can see that, I’m hoping to have a go today, once I’ve cleared my todo list…

I’m also thinking that perhaps smoothing the edges of the existing ones may disguise the damage enough to look OK. On trying to remove one this morning I also discovered they’ve been attached using glue and tapered wedge so going to be a destructive process getting them off….

 

[J-G]

Sounds like it needs the cobwebs blown off by making a couple of knobs.

I initially resisted the temptation to respond for that very reason and I did consider looking to see if I had a piece of Elm on hand but I'm busy with a clock project and setting up the Elliptical chuck would mean I'd become very distracted and the clock might join the pile of unfinished items that litter my workshop!

The new pictures show a better view and it looks to me as though (unusually for Ercol) those knobs are incorrectly cut into end-grain which I would consider quite wrong and prone to such damage purely due to 'wear & tear'. ie. they are made as though they are 'spindles' rather than 'bowls' if you see what I mean.

 

[stuartpaul]

Just a thought but have you tried contacting Ercol to see if they can supply?

 

[RichardG]

I initially resisted the temptation to respond for that very reason and I did consider looking to see if I had a piece of Elm on hand but I'm busy with a clock project and setting up the Elliptical chuck would mean I'd become very distracted and the clock might join the pile of unfinished items that litter my workshop!

The new pictures show a better view and it looks to me as though (unusually for Ercol) those knobs are incorrectly cut into end-grain which I would consider quite
wrong and prone to such damage purely due to 'wear & tear'. ie. they are made as though they are 'spindles' rather than 'bowls' if you see what I mean.

I was only jesting but I do have got a copy of the book you mentioned on the way as I‘m intrigued by the concept.

I’ve looked carefully at the knobs and I can’t work out whether it’s end grain or not as some of the Elm does have a grain that looks very much like end grain. I can’t believe Ercol would make such a mistake…but perhaps in was Friday…

 

[RichardG]

Just a thought but have you tried contacting Ercol to see if they can supply?

I have contacted them but not heard anything so far.

I have since found someone on eBay selling spares made of Beech. Trouble is even if I could get the staining right to match I think they’ll still look very different? Perhaps a fallback option.

 

[J-G]

I was only jesting

I knew that

...but I do have got a copy of the book you mentioned on the way as I‘m intrigued by the concept.

You may like to see both the 'concept' drawing that I found during my research :

and photo's of my attempt :​

Made from Plywood, Tufnol, Burbinga, Oak This was my 'Mark 1' - the large circular piece of Oak in the cenrte is in fact a ball-race with 100 - 3.5mm st-steel balls. My 'Mark 2' still uses most of these components but I added a self-centring 2 jaw chuck :

The Mark 3 added a means by which I could adjust the eccentricity.