Nervex probably started off with 3mm to 5mm thick steel plate which was run through a series of stamping and drawing dies much like those used in jewelry making but much heavier duty.
The last step in the stamping operation was rolling over the bottom part and welding the seam. After that several areas such as the bore for the steering tube and maybe the pockets for the fork blades were machined probably using semi automated machine tools (probably pre WWII vintage).
They were most likely manually finished on a belt sander or grinding wheel but this could have been automated too.
All of this was done before the days of CNC machine tools and much of the work could have been done manually instead of on semi automated machinery. Bike manufacturing was pretty crude in those days.
The steerer bore and fork blade pockets on the forged Wagner crowns were also machined to size.
Chas. Colerich Oakland, CA USA
Mark Bulgier wrote:
> Jay Dubiel wrote:
>
>> I'm confused. The statement that Nervex are made by wrapping
>> sheet metal and welding seems odd for what I have in hand and
>> pictured. Beneath the chrome there is evidence of a course
>> surface, pitting and heavy grinding marks which I would think
>> might indicate a cast or forged piece. The inner tangs are
>> 4mm thick, how does that get wrapped?
>
> I completely understand -- it does seem hard to imagine them wrapping
> such thick metal around, but they (Nervex/Dubois) were masters of it.
>
> I took some pictures of the raw crowns that make it clear that they are
> in fact hollow and made of sheet metal.
>
> The first pic is of the bottoms of the crowns, and shows off the Nervex
> hollowness well. The crown on the left is a Wagner, the other three
> Nervex. Look at the Nervex chevrons or "epaulets", clearly seen here on
> the _inside_ of the crown, showing that they are formed from sheet
> rather than machined in later, like Wagner chevrons.
> http://bulgier.net/
> (if the URL is too long and wraps, use http://tinyurl.com/
>
> This next photo shows the tops, showing what Chas. Colerich meant about
> the chevrons being pointed on the end with Wagner, but blunter or
> squared-off on the Nervex:
> http://bulgier.net/
> (or http://tinyurl.com/
>
> Two of the three Nervex crowns in my pictures have the feature cut that
> matches the classic Nervex Pro lugs. Feature cut on the third Nervex is
> plainer, looks better with Dubois or any regular non-curlicue lugs, and
> this is the cut on the orange fork in the photos Jay showed us earlier.
>
> Being hollow yet relatively large in their outside dimensions gives
> these crowns a very high strength-to-weight ratio. They are also
> relatively easy to heat up for brazing. I like 'em, but they were not
> popular with some framebuilders due to the relatively crude finish and
> the large amount of work required to make them look nice.
>
> Mark Bulgier
> Seattle WA USA