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Decorative Scraping


Sep 22, 2006
Stillwater, Oklahoma
I friend, now deceased, said that at one time he had watched a man put the decorative scraped finish on the castings of a Bugatti engine. He described that guy holding the scraper almost vertically and bumping it with his fist. He apparently had the layout marked in pencil so was filling it in with scraping.

So just recently a ran into a photo of what he must have been talking about. Still scraping, and still a machine, if not exactly a machine tool. Machi9ne porn category maybe.

Bugatti 57SC Engine.jpg
Pretty. Looks like standard bump flaking. Easy to learn, not so easy to get as consistent as that example.
Kinda reminds me of a butterfly scraping pattern that was discussed on here a little while back. It was used on a small lathe (something in the vein of Cataract or Barns?) and for that one I think they held a vertical scraper and twisted it to get the design.
Used to call both the bump "crescent" & wiggle "butterfly patterns" frosting. Mostly for light defraction and a little for lubrication. Haven't been to the RI arsenal for a long time but they did it on sliding surfaces on the big rifles (think 155 & such) years back.
Last thing artillery needs is a shiny reflection from the forrest...

Good luck, Matt
The manifold marks look like 1/2 mooning or that hit with fist with a flat blade not a 60 radius that we use to get a more circular technique. The fire wall does look like the butterfly or 1/2 of a butterfly shown on page 171 of the Connelly book, Machine Tool Reconditioning.
Mons. Bugatti had all the engine flat surfaces frosted - he thought that the engine should blend in as an element of the architectural visual composition, and not obvious in the motive power sense. Reason all the components including the block, look like a stack of blocks. But that frosting looks a bit more perfect than even ol' Ettore generally supplied..
Actually, that finish is fairly common and it's called "engine turned". It's not unique to bugatti. The most common way to create it is not by scraping, but by using a wooden dowel in a drill press, with grinding paste on the end of the dowel. It's easy and fast to do.
"To a man with a scraper". As EG said engine turning. It was always the shitty job given to the apprentice to neaten up the job. I do it on the CNC if I am working on thin plate jobs and the material is scratched. I use a scotch brite disc in the drill chuck and coolant, Z down and a short dwell and up. Great for hiding imperfections. If you zoom in you can see it.IMG_20230709_154730_HDR.jpg
Actually, that finish is fairly common and it's called "engine turned". It's not unique to bugatti.

The finish on the engine is frosting, done with a scraper.
Bump scrape in the olden daze.
Possibly a biax on the shown example.

They also did butterfly frosting (with a scraper) on some blocks and other mechanical components.
The firewall does appear to be engine turned on the OP restored model.

Here are some other versions, some original, some possibly "enhanced"

The one that does not look frosted, actually still has vestiges of the original, somewhat more open, and a bit more "curlique" version.

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The finish on the engine is frosting, done with a scraper.
I say potato, you say potahto but either way, it looks like shit. If you'll notice, the original bugatti finish is not done this way.

Bugatti did have a lot of quirky ideas; unless you are french I can't see going all ga-ga over them, but even they did not go for the crappy glitz look like in the original photo. They were not the Arlen Ness of the car world.