[Leica] M-6 Pressure Plate Scratches

[DonjR43198@aol.com]

LEICA PRESSURE PLATE REVIEW

Please bear with me as I have not mastered the art of communicating on the 
LUG net.

A number of persons on the Internet have reported their film being scratched 
by their Leica M-6 cameras.

I purchased a new one in October 1998 but had not put more than one roll of 
film through it, and had not viewed it, as it was Kodachrome in a single 
strip since I intend to make color prints. I put a fresh roll of Kodachrome 
film in the M-6 and cranked off a few frames. I opened the back and there 
were scratches beginning at the cassette end of the pressure plate right on 
to the take-up spool end.  With the back open, I then cranked a few more 
frames to see if the scratches were being caused by the felt lip in the 
cassette or something else and there were NO scratches on the film.  The 
camera was closed up and a few more frames cranked through and the back 
opened again.  The scratch marks returned.  This indicates the pressure plate 
was the culprit. 

I examined the surface finish of the flat surface of the M-6 pressure plate.  
It appears to be approximately the same finish as the flat surface of the 
pressure plate of my 1966 vintage M-3.  I would like to check the surface 
finish of each with my Bendix Profilometer (an instrument designed to 
determine surface finish measured in one-millionths of one inch) but the 
diamond stylus would damage the surface.  To the eye and fingernail, the 
surface finish of the radius at each end of the M-6 pressure plate is many 
time rougher than that of the M-3 pressure plate ends.  Further, the "lay" or 
direction of the finish is perpendicular to the direction of film travel, 
which creates an additional source for scratching.

Two brand new pressure plates that I had ordered from Leica in 1988 but 
unused were also examined.  The radiused ends of the two new pressure plates 
were much nearer to the surface finish of the M-3 pressure plate radiused 
ends than is the M-6 pressure plate.

The cause of the film scratches may lie with the comparatively rough radiused 
ends of the M-6 pressure plate since the radius blends into the flat surface 
and at that junction, the rough finish of the radius may come into contact 
with the film.  

If I were to resort to self-help, I would remove the pressure plate from the 
back plate, and carefully stoke each end of the pressure plate on a piece of 
crocus cloth glued to a sheet of glass so the factory rough finishing marks 
are removed.  Just pulling the pressure plate toward you should do the job.  
Carefully clean the debris away with an ultra sonic cleaner if possible. If 
the marks have been removed, use some very fine polish to put a nice polish 
on the ends.  Clean again.  Reassemble the back plate and run a roll of film 
through to see if there are any scratches.  If none, have a plating company 
anodize the plate. Reassemble and see how it works for a while.  If there are 
scratches on the plate, you may wish to "lap" the flat section of the 
pressure plate on the crocus cloth but it is likely this will create even 
more problems.  If you are game and wish to risk more problems, place some 
double sided tape on the back of the pressure plate and cut a piece of wood 
about 1 ½ X 1 so it will serve as a handle for lapping the plate.  Then move 
the pressure plate in an arc across the lap but use very little pressure.  A 
few passes and the high spots should be knocked down.  The work accomplished 
should be seen in the removal of the black anodized finish.  Once satisfied 
with the finish, the pressure plate should be anodized.  The plating company 
may even be able to run the pressure plate though a chemical process that 
will remove even more of the rough spots before anodizing the part.

This is an involved process and it is the reason why I suggest Leica provide 
the solution.