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What is — or was — "Frenc" metric?

99Panhard

Stainless
Joined
Feb 22, 2006
Location
Smithfield, Rhode Island
I was reading the 1919 Hendey manual and, where it mentions metric calibrated machines, it specifies that Hendey lathes could cut both "French" and "International" metric threads. I'm wondering what was different about the French threads. Thus far, the internet has been useless in deciphering this...which doesn't surprise me.

How do you edit a title? That is supposed to be "French" metric!
 
Not sure about French specifically, but there seem to be a variety of standards even now. There is regular european.
There is Japanese, which has differences.
And there is chinese, which seems to be a hodge-podge, although they will do any thread you want as long as it is "metric", and sometimes they actually do what you put on the print.......
 
I've also heard of Swiss metric. My question is the result of being asked to do some work on a 1904 French car. I don't know that I will but in thinking about it this questions came up. The Swiss metric screw - it was a left-handed screw — was on a very early motorcycle that belonged to a friend. I'm guessing c.1904 or 1905 so we are dealing with a metric system in use before any international standards were set. Obviously, Hendey saw them as being different, albeit similar.
 
I didn't look it up but I think an older Machinery's Hand Book may have some information on the different Metric threads .
By what I can see in this table from a search I tried some older French screw threads had thread angles different from the current I.S.O. or International Standards as well as different pitches for a given diameter .
They appear to be obsolete now.
System Francaise system of screw threads

Metric Screw Threads
So the gearing on the lathe may have needed to cut pitches not normally found on an I.S.O. only quick change box.
Perhaps a few extra change gears were added to a set or included with the lathe to make it compatible with both systems.

Jim
 
American Machinist's Handbook, 2nd Ed. 1914 has information and tables for French (Metric) screw threads and for International Standard screw threads (dimensions in mm). The International Standard was created at a meeting in Zurich in 1898. I note that the French had two standard pitches for 8, 9 and 12 mm threads, but the International eliminated one of each of those pitches. Both systems have 60 degree threads.

There was a German Lowenherz metric thread with an odd angle said to be invented in 1894 and found on German measuring instruments.

Larry
 
The French metric , Systeme Francaise, differed in profile from the modern DIN/ISO/JIS threads only in requiring a radius on crest and gullet. Modern metric threads are the same as UN, calling out a flat and allowing a radius due to tool wear. Pitches tended to be 1.0 in all small sizes. They will interchange with modern metric threads of the same pitch in all sizes as far as I know.
 
Most, if not all, industrialized "metric countries" had their own national-standard threadforms, which differed -- some more, some less -- from each other. Following WWII, the International Standards Organization developed an ISO-Metric threadform (based on the fundamental geometry of the Unified threadform that was developed by Canada, Great Britain, and the USA in 1949), in 1959 (IIRC). The ISO's intent was to replace the varying national-standard threadforms of the individual "metric countries" with one common standard.

That a 1919 lathe manual would mention national-standard threadforms is quite reasonable; it is the mention of an international-standard threadform that intrigues me.
 
The oldest copy of Machinery's Handbook I have is the 1939 edition but it describes both the French and German standards as well as the "International" standard (I should have looked here first!)The International form is described as having been agreed upon by a Zurich conference in 1898 so I have to assume that is what the Hendey manual was referring to rather than the ISO standards.
 
The oldest copy of Machinery's Handbook I have is the 1939 edition but it describes both the French and German standards as well as the "International" standard (I should have looked here first!)The International form is described as having been agreed upon by a Zurich conference in 1898 so I have to assume that is what the Hendey manual was referring to rather than the ISO standards.

Comparing the 1914 handbook French and International tables of metric diameters and pitches, the only difference I see that explains the Hendey statement is that the French table has some smaller diameters and finer pitches, namely 3, 4 and 5 mm diameters and .50 and .75 mm pitches. Pitches of 1.0 mm and larger are used in both systems. I suppose the Hendey lathe would cut .50 and .75 mm pitches in addition to the other coarser pitches.

Larry
 
It may be obvious,
but diameter is irrelevant.
Pitch spacing is what matters with threads.
Inch or metric, it does not matter.
It is a thing with inch or metric lead screws
as to what divides evenly into whatever gear ratio
to get the pitch spacing that you want.
So for threads per inch, just divide the inch by the pitch
to get the actual pitch measurement from thread to thread.
Metric is customarily stated that way.
So French or Swiss or bicycle or sewing machine thread,
it really only matters the pitch spacing. That being said
history is cool, and I love knowing where different standards
came from. All being said, an electronic resolution lead
screw gearing or a cnc lathe for threads is looking more
attractive to me in my shop to deal with any thread pitch
that is going to come through the door.

-Doozer
 








 
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