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  1. #21

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    If I remember correctly, you have the 4550 XLG, which has the same negative stage as the 4500 II. Let me say that the negative carrier frame is locked quite securely in place when you flip the lever. In fact, once you lock the negative carrier 'frame' in place, it does not move. Yes, you can move it if you push hard enough, but if you're doing that sort of movement to the enlarger, you've got other things to worry about.

    That is the reason that I went to the system that I have and use. Unfortunately, I know of no way to remove the negative holder from the enlarger for mask changes without releasing the lock lever. 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.

    My registration system while more expensive and I believe more precise is still relatively crude in comparison to another photographer here in Kansas(Charles Phillips) who does tri tone separation masking through a $61,000 enlarging system. This allows a selection of higher contrast filtration through the highlight and shadow regions of the paper (toe and shoulder of the papers characteristic curve) and another contrast filter selection for the midtones where tonal separation is normally greater. He has shared that even a very costly Condit system that was incorporated was prone to registration problems.

    The potential for masking extends far beyond what Lynn Radeka has addressed. Lynn has taken from the earlier work of several photographers that were exploring masking. While beneficial and available to the masses it does not fully cover the potential of this process.
    Art is a step from what is obvious and well-known toward what is arcane and concealed.

    Visit my website at http://www.donaldmillerphotography.com

  2. #22
    Ed Sukach's Avatar
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    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...
    Carpe erratum!!

    Ed Sukach, FFP.

  3. #23

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    Ed,
    Obviously, once again, you are the person to address when it comes to matters of an extreme technical nature. All that I know, not being a machinist myself, is that the machinists that I have had contact with (including my son who works for Boeing here in Wichita) is that they commonly use the term "press fit" and that is identified by the clearance dimensions that I provided.

    Now I will give you that it may be a local machining term. However we have somewhat of a aircraft manufacturing hub here and normally employ a number of machinists and engineers. Therefore we are are not located in some remote technically impoverished hinterland.

    I indicated my reasons for doing what I did in regards to a registration system for my photographic applications. Beyond that I have "no dog in this fight". However, if in the future I want the real "skinny" on something of a technical nature I will contact you.

    Thanks for sharing your input.
    Art is a step from what is obvious and well-known toward what is arcane and concealed.

    Visit my website at http://www.donaldmillerphotography.com

  4. #24
    Ed Sukach's Avatar
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    Quote Originally Posted by dnmilikan
    ... Obviously, once again, you are the person to address when it comes to matters of an extreme technical nature. All that I know, not being a machinist myself,
    Aha!! Do I detect a smidgen of ....

    I'll apologize. In a different life, I wuz a "Quality Assurance Specialist" - one of my major duties was checking manufacturing prints *before* release for design anomalies .. and I HAD to be cognizant of fits, tolerances, strange configurations that would defy measurement ... stuff like "ANJ threads" that were NOT specified as "Class 2"....

    What triggered an old knee-jerk response was the idea of an .005" interference fit. Not hardly ... simply too much interference. Something would bulge/break/squash out of shape.
    Carpe erratum!!

    Ed Sukach, FFP.

  5. #25
    Alex Hawley's Avatar
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    Quote Originally Posted by dnmilikan
    [i][b]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.
    Don, Ed, you're both right.
    Don, I think you left off a decimal place. A .0005 interference would be appropriate for a pin in the 1/4" range or smaller, which is about the size I imagine your registration pins to be.

    Ed, you're right, a .005 interference would certainly bust things apart up to a certain size.

    Old machinist thumbrule for press fits: .0005" for less than 1/2", .001" up about 1-1/2", then add .001 for every 1" larger. A .005 interference would be appropriate for a 5" diameter.

    Caution: Thumbrules are known to vary from source to source.

    Alex (Once trained in Wichita area shops)

  6. #26
    Ed Sukach's Avatar
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    Quote Originally Posted by Alex Hawley
    add .001 for every 1" larger. A .005 interference would be appropriate for a 5" diameter.
    Caution: Thumbrules are known to vary from source to source.
    Oh, if only ths was the Materials and Mechanical Engineering conference --- it isn't ... so I will not argue in disqagreement all over the place. What is invloved here is elastic limits, materials, hardness, and geometry...
    And, and ....

    No. I'll place my patented Flavored Inner Tube Section - (latest flavor is "Daiquiri") - between my teeth and move on.
    Carpe erratum!!

    Ed Sukach, FFP.

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