P3D Re: Spicer vs. RBT

[john bercovitz <bercov@xxxxxxxxxxx>]

>The Spicer mounts definitely have their place, 
>but that place is not in the projector, IMO.
>Paul Talbot

Having looked at your subsequent posts, it appears you're talking 
about variations in the mounts' apertures' dimensions.  In my 
experience, all mounts have aperture variations; it's just a matter of 
degree.  It's really a materials and fabrication methods problem.  
Metal masks have little variation because metal tends to be more 
stable than many other materials and because it is sheared (punched) 
with precision dies.  Plastic is difficult to mold accurately because 
of residual stresses from cooling quickly in the mold even though the 
mold might be very precise.  Paper is more difficult yet because it 
moves around with moisture and because it is fabricated with an 
inherently less precise process than either shearing or molding.  
Usually it is done with a "shoe die" which is a block with replaceable 
razor strip material (purchased in long rolls) wrapped around it.  
These are all appropriate fab methods for the particular materials and 
I wouldn't want to switch them around.  8-)

I'm going to go measure some mounts.  I have an Albion 5P, an RBT 5P, 
and a Spicer 5P and a Spicer 7P since Spicers are the emphasis today.  
The extreme range of variation for the Albion is < .001" (< .025 mm), 
for the RBT it is .004" (0.1 mm), the Spicer 5P it is .004" (0.1 mm) 
and the Spicer 7P is .005" (.0125 mm).  Frankly I would have expected 
more variation in the paper but it seems about the same as the plastic.  
I guess I could grab fifty of each type and measure them but I'm not so 
excited about doing that.  8-)

If you have any mechanical problems with Spicer mounts running through 
projectors (I haven't) then try gluing the mounts shut.  It makes them 
a whole lot stiffer.  I do this as a matter of course but I'm probably 
the only one nutty enough to do it.

John B

Orthostereoskopie ueber alles!
(Is ortho spelled correctly?  I'm just guessing.)


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