Engine Turning or "Jewelling

Plenty of info on the web about this but no threads on here that I can see. If you're a beginner you may not have heard of it but old hands surely will. There are many ways and tools that can be used to achieve this traditional attractive finish to smooth steel but I thought I would just describe the tools and method I use.

A jewelled finish looks like this:

Essentially a series of overlapping circles in a regular pattern. A photograph fails to capture the dynamics of the beautiful finish which moves and shimmers as it is turned in the light.

The pattern is ground into the surface of the metal using some sort of flexible head (rubber, synthetic, nylon, metallic brush..) as a rotating tool and some carborundum (valve) grinding paste. It is the grinding paste that does the work, whilst the head dimensions govern the size of the pattern. Naturally you will need some method of indexing the workpiece so it is moved in precise steps in X-Y axis (for flat surfaces) or x-rotation (for cylindrical surfaces).

The rotating tool I've found which works best is a small (5mm diameter) wire brush contained within a home-made holder which constrains the brush filaments and stops them splaying outward.

Only about 1/16" length of the filaments are allowed to extend beyond the end of the holder - and you will need to keep checking as work progresses because they will wear away fairly quickly.

This was my setup on my mill for the job shown above, with the workpiece held in a 3-jaw chuck attached to my HV6 rotating table. The mill bed takes care of the X-axis steps by way of the handwheel markings, whilst the rotational steps are achieved with the HV6 handwheel. It is an extraordinarily boring job to be sure, and one that could readily be done on some CNC machinery. However, need must... and the results are worth the effort.

In the picture above you can see the workpiece is coated in a generous amount of grinding paste (180-grit in this example), and the end of the brush is brought into gentle contact with it. Don't press hard! - it is not necessary and will achieve nothing other than premature wear of the brush head. Only a light contact is required, and In this particular job I counted for 15 seconds then released. (Did I mention this was boring...?). If you press too hard you can also end up with deeper scoring than expected and possibly a raised blob in the middle of the circle, either of which will ruin the finish.

Aim for an overlap of about 50% of the circle diameter in both axes, there is no hard and fast rule about this but that is a good starting point. Don't forget to keep checking on wear of the head, I had to re-set the depth once part way through this job. Oh, and make sure you cover all machine beds with rags or paper towels to keep the grinding paste off them - slideways and grinding paste don't mix well.

I suppose the difficulty of attempting this using a CNC setup is the loss of 'feel' which will normally compensates for any gradual wear in the brush head. A fixed depth setting simply won't work. I guess you would have to use a tool modified so it is weighted and able to slide freely (vertically) on a shaft - the CNC spindle will take care of the indexing just fine, the weighted head producing a nice even pressure (with exaggerated Z-movements when moving to the next step). Wish I had some CNC kit to experiment with

Thanks John, I had to Google 'Cratex bobs' described as 'rubberised abrasive wheels', can you say how soft they are? How long do they hold their shape/pattern? I've tried many things like this - but not those actual parts. For the ones that I used I found as they wear the pattern they produce 'softens' overall and this was noticeable as the work progressed, so later parts were less distinct than earlier ones. I also tried shaped pieces of hard rubber in combination with grinding paste, but the rubber invariably breaks down leading to an indistinct edge. One advantage of the brush is that it can cope with uneven or spherical/cylindrical work (provided the radius is not too tight) because it can flex a little. Also, the method is not reliant on abrasive integral in the rotating head so new sharp grit is always available to it.

Another consideration is the material that is being worked on - soft aluminium will respond to nylon blocks quite well, steel brush and abrasive being a bit harsh for this. Hard steel really does need the carborundum paste though (in my experience).

I must say your workpiece looks beautiful, so clearly your method is working well.

Edited By Chris Heapy on 29/04/2013 00:19:03

Edited By Chris Heapy on 29/04/2013 00:31:09

Hi Chris and John

that looks very nice indeed. I have seen something similar to the photo you are showing John, not seen it on round objects before.

Thor

My two 'pennorth - when ever I've done this I always use a piece a of wood doweling with a squared of end dipped in valve grinding past. Held in the drill chuck it is a simple process that makes a nice piece of tooling look a bit more special I think I have heard of this process being called "engine turning". Am I right or wrong? ---- Rik

Absolutely right Rik - like the thread title says! In fact there are many other names too but I'm not sure if any particular one is 'right'

I've seen this on vintage car dashboards. personally i think it's a bit OTT as it highlights the background, rather than the detail. Rather like the 'Duplex' boring bar holder that was scraped all over!

Joey the spoilsport

I think it better to avoid using the term "engine turning" as that is a subset of ornamental turning and using that term will debase proper ET. It is typical modern marketing to try and adopt terms from a top line product like that.
I think it was invented to be a poor man's substitute for proper ET and unless done with the precision of Bog's work above can look a bit naff like fake scraping on far eastern machine tools.

Bazyle: The finish described above is just that - a decorative finish applied to an existing metal surface, and has been called Engine Turning for donkey's years. Ornamental turning generally employs a cutter to produce a new surface, often in 3D, using complex geometric chucks or machinery offering similar funtionality. I don't know where you get 'Modern Marketing' from given its history, and it isn't a poor substitute for anything - it is what it is. Used appropriately and executed well it can enhance appearance (dependent on the eyes of the beholder of course). As mentioned above, it also has a practical application in improving lubrication of sliding surfaces.

Chris, the "complex geometric chucks or machinery" on an ornamental lathe are known as an "engine" this is where the term Engine Turning originates from.

J

I know, but the key word is 'finish' - the appearance of an engine-turned finish, which is quite different from using a cutter to form complex surface geometry which has actually been 'engine turned'. However, we are splitting hairs and the name is not mine in any case.

Chris, John - What sort of rotational speed do you run the tool at and doesn't it fling grinding paste everywhere ? Thanks

Andrew: I keep speed down for that reason, although the grinding paste I use is quite viscous and doesn't tend to get thrown around much anway. Can't tell you the RPM as I adjust it on the fly (3-phase/speed controler) but I would guess 800-1000 -ish.

I used a far cruder system , a piece of dowel with a vertical split it its end with a piece of emery paper, stuck axially in the split, so it goes over the end of the dowel. The dowel went in a drill press and it was used for tarting up (hiding the scratches   on ali front panels of electronic kit.

Frank

there is another technique also known as 'engine turning'. Possibly this polishing technique was an attempt to reproduce without the expensive machinery...

**LINK** is a reference i could find quickly.

-russell

When listing the terms John has quoted above Eamonn Keogh (who's a professor of computing) does qualify them with the phrase "with various degrees of appropriateness". While the term 'damascening' may have been loosely applied to 'engine turning' that doesn't make it right.

'Damascening' (traditionally supposed to have originated in Damascus) probably arrived in Europe via Spain which for a period was under Moorish domination. The technique involves engraving designs in a base metal (commonly steel) and infilling the incised lines with precious metals — gold/silver — for decorative effect. Acid etching might also be used to add colour effects. It was commonly employed on swords (e,g, Toledo steel) and suits of armour. It was also revived and used for presentation swords given to notable naval/military figures in the Napoleonic period.

'Engine turning' is the generation of decorative regular or geometric patterns on metalwork using machine techniques. The 'machine' involved might only be a hand drill and abrasive bobs at its simplest but it's nonetheless a machine technique that's quite different from the hand engraving/infilling technique employed in damascening. Using the same term for what are quite different techniques only leads to confusion.

Joe

This page gives some interesting history of how the various terms have come to be used and what their original meanings were.

J

Hi Chris (Heapy) or Bogstandard2,

I've just come across this topic/site and joined up in the hope that you can help me out.I have just retired and sunk the savings into a Morgan (!!).

The dashboard has a beautiful engine turned alloy finish and the armrest /centre tunnel has a matching finish.

Sadly,the car is several years old and the finish on the centre tunnel is scratched and worn in several places.Morgan can no longer supply a replacement and whilst I have read up on the 'jewelling' technique ,I don't feel confident enough to try it myself.Would either of you be prepared to re-engine turn the piece in question for me (obviously for suitable recompense )?!

I recognise this is a bit cheeky and I don't want to break any forum rules but I truly am desperate to get the item re-finished and have so far drawn a blank....

Any help would be greatly appreciated;many thanks,James

We used to call it Jewelling and the pads Chris used were sold as Jewelling by Edgar Bros same as Brownells in US. Loads of stuff done with it usually bolts for rim and centrefires. Personally not worth the effort for what people will pay.

Which leads me on to Edgars brushes last hell of a lot longer than anything else, though used to buy in 10's personally for aluminium work up to about 2003. At work used on steel for lock plates and went through three brushes in 7 years, looked tacky like inferior Spanish stuff but saved time polishing.

The Morgans are spotted, whatever is done to the console would have to match the original unless dash done as well. Can anodise if a decent grade. Johns your man he has a long enough mill for centre console, I couldn't sniff for at least 4 months.

What looks naff is when the symmetrical look is not put on square to the edges or just 'one' out of place jewel standing out like a sore thumb. Used to cause grief on round objects where first and last meet.

Thought had replied two years ago, Chris front row of bearings too far back so not seen. Tx can go a front later called Venom Ultraglide in 94. Idea was the late Mick Dawes then Venom nicked early 80's.

Have had a go myself; I call it 'Jewelling' I used some 'Garryflex abrasive blocks' ... fine grade from Chronos (usual disclaimer ) I cut to suit some holders I made. It works well but doesn't last long so only very light pressure is needed... 1 fingertip pressure is quite sufficient. I have use other methods described on older stuff & they all work to a certain degree...

My attempt...

George.

Hi James, have you asked the same question on the T V R, Ginetta and Marcos forums? I'm sure they had models with these dashboards. Regards Alan