Quote Originally Posted by dnmilikan
If the frame that Lynn has developed is locked by the lock lever and the negative holder is removed and reinserted the very fact that is removable is indicative of greater the .005 available spacing since a "machinists press fit" is .005. The term "machinists press fit" means that with .005 a human being could not physically insert one piece into another without the use of mechanical aid in the form of a hydraulic or mechanical press. It is at this point when one would remove the negative holder to change masks that the negative holder registration would move. In moving the negative stage, it would throw the "whole shebang" out of registration. Even taking the fact that greater then .005 spacing exists (it must if one is physically inserting and removing the negative holder), when one enlarges that by a factor 800% (16X20 enlargement from 4X5 camera negative) the .005 becomes .040. This is a highly noticeable lack of registration. In fact, I imagine even a neophyte would notice that in a print.
You have lost me entirely here. A "Machinist's press fit..." is what? The idea of a "press fit" is that one part will *require* force of some level to be assembled into another, due to the fact that the internal part will be physically *larger* than the external. The greatest interference in use is provided by a "Shrink fit" where the internal part is cooled to shrink it, and the external heated to expand it. That is rarely as much as a difference of .001 inch - or .025 mm. Press fits are from about .0002 inch to .0005 (.005 - .012mm.).

It is entirely possible to have a "line-to-line" (zero clearance) fit - where the internal part is extremely close in size to the external - that will result in a "wring" fit ... (we had a number of display examples for this in the aerospace guidance system - and optical systems - business).

Very close tolerances are difficult and *expensive* to manufacture - so a lot of equipment is designed on "Kinematic" principles. I don't have enough time or space to go further...