Curious about creation of a custom filter adapter, what it would take

As one whose knowledge of practical machining would fit on the point-end of fine needle, I am asking an idle question. What would it take to measure and create a quality custom adapter filter ring in black at around 39mm? Cost and time. Could a qualified home machinist make, say 20 or 50 and offer at a reasonable cost (i.e., modest profit margin on a competitively-priced item)?

My curiosity was recently peaked by acquisition of a limited-production Leitz lens (made for the Leica CL but fitting the M line), the 90mm f/4 Elmar-C. The filter ring was made with an evidently unique, or at least very esoteric, diameter and/or thread-pitch, so that a special adapter is needed, which, for similarly bizarre-seeming reasons, holds unthreaded Series 5.5 filters. (Why not just adapt to hold 39 or 40.5 mm filters?)

After much back and forth over on the RangeFinder Forum and reviewing alternatives for this oddity, I chose to take the path of an experienced user who has used a 39mm filter for years with no ill effects. The filter threads in about a quarter turn, just enough to keep it in place (burden-free) and not push the mismatched threading into trouble. Works for me.

In any case, having read one post by someone years ago who made his own adapter to a common threaded size, I wonder if one (meaning home machininst) buys a length (say, two feet?) of aluminum tubing that's close enough not to require thinning on a lathe, then slices individual rings from, then cuts the internal and external threads, and finishes them, or something like that.

Gee, way back when High Schools offered Vocational Ed classes, you could have asked the machine shop teacher.
How about "printing?"

I just had SK Grimes make a custom adapter for me. It works perfectly.

Heliopan makes an extremely large range of brass adapter rings. Check this page:

http://www.heliopan.de/wp-content/up...Preisliste.pdf

Pages 12 to 16

"Reasonable cost" is the project killer of the home machinist's time is worth more than pennies per hour. Semi-skilled workers in basic machine shops overseas can afford to sell them postpaid anywhere in the World for a very few dollars if they know there is a market.

I think Peter had the right idea-call SK Grimes.

I think they are 39mm, but the 'pitch' is different than regular filters. Tiffen used to make a whole slew of series filter adapters that 'pushed on' to the outside of the lens front.. maybe you can find one that will work in series 6

Thanks.
As it turns out, the filter I ordered, a Himatt Fire-something, is internally threaded in front for 39mm, i.e., it's a regular 39/39 filter, which I mention because the ad indicated that there was no internal threading.

It will do fine for now, though I probably will check with Grimes, just out of curiosity. Maybe they know the secret thread on this lens.

The bean counters at Leica made the company make odd size filters so they could sell overpriced specific filters for individual lenses presumably to sell at top dollar prices... Some were threaded, some were series, but expensive...

If you can find a scratched junk filter that size, you can probably remove the glass, screw the ring to the lens with maybe an old glassless 39mm filter ring bonded to it so you can screw a 39mm filter into that...

This is the cheap, mad scientist way to do it...

Steve K