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MONTAC Enterprises
ATTN: MTB Madness
Pending New...
Azle, TX 76020


Front Panel Removal & Prevention
of "Lenticular Sag"


This part of the procedure begins with a newly modified screen stack, which includes the removal of the Front Panel and the installation of non-slip, low-compressibility front and back-side gaskets of the correct dimensions to insure a stable assembly. Once at this point, it should be relatively easy to "tune" the screen stack installation in the frame such that Lenticular Sag is virtually eliminated. 

You would think, right? Nope. Sorry. Not nearly as easy as one might suspect. A number of factors are seemingly conspiring to make "sag elimination" an elusive goal.

The number one "hang-up" is the barely adequate frame design/implementation. I'll explain it more completely below. 

Warning: Monkeying around inside an AC electrically powered device is DANGEROUS!! You could seriously injure or kill yourself if you make the wrong move. Do not attempt this procedure unless you have the requisite skills and knowledge to complete it successfully. This article is provided for information only, and I accept no responsibility for damage or injury resulting from the use of the information contained in this article.


Article Index:
(NOTE: You may click on any image to pop up a larger version of the image with arrows indicating action points.)
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Step 1
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Step 2
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Step 3
Here is where we left off... Long way to go to achieve single-planed nirvana! It is obvious from even cursory analysis of the light patterns, that the screen is "bottoming out" on the lower frame rail. This condition, in turn, is producing the observed buckling.   I decided to back up and try some diagnostic stuff. First I removed the bottom and both side clamps. Then I removed all of the gaskets from the bottom and sides.

Note: the blocks in the picture are an attempt to prevent the brackets on the bottom rail from causing deformation of the frame. One would think that supporting the frame at the corners would be conducive to a square frame....  nope.

Here are the piles of inner and outer gaskets removed from the frame. I'm going to hold on to these until I finish "fixing" whatever needs fixing. They might be needed later.
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Step 4
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Step 5
More to Come!!!
Step 6
While I had the frame shimmed up on the 2"x4" blocks, I came across these gaps in the upper corners of the frame... again. If you remember from Part I of this procedure, I paid specific attention to closing this gap before I tightened the upper clamp.

Gap closed when frame inverted; gap opens when frame is right side up on blocks. Conclusion: Frame materials (specifically the corner fittings and corner to side joinery) are flexing badly. In this situation it is virtually impossible to get the screen stack flat using frame tension (compression gaskets installed on all four sides).

Not bad...   Much improved!! If I was using a bright, indirect flash rather than the point flash in the camera, you'd see virtually no distortion at all no matter what light intensity was used. There is still a bit, but I'm confident that with a little time, I can eliminate the last 5% or so.

After removing all but the top rail gaskets. I re-installed the side and bottom clamps. I then inverted the frame and re-seated the screen stack in the upper clamp/gasket assembly (as in Part I), paying particular attention that the stack was centered side-to-side and that no gaps existed between the stack and the top frame rail.

Then I carefully (to avoid racking the assembly) turned the assembly right side up and re-installed the Front Mask Assembly onto the chassis.

Essentially, the screen stack is suspended from the top rail and is "floating" with respect to the side and bottom rails. I plan to leave it like this for a couple of weeks to observe any changes due to environmental conditions, frame/clamp flexing, etc.

I will continue to refine this procedure as I have time to ponder the problems, variables, etc. I considered attempting the "magazine maneuver" to get the stack flat with all clamps/gaskets installed, but changed my mind. 

Read on to see what my thoughts are currently for addressing the last 5% of the lenticular distortion. I say lenticular distortion because frankly it doesn't really meet the criteria for "sag" anymore. 

Problem: Frame is simply too flexible/unstable for tension mount of screen stack.

Discussion: I think the main cause of the unstable frame is simply that it is made out of a plastic in such dimensions that some flexing is inevitable. This inherent material instability is exacerbated by the fact that the rails and corner fittings are held together with only 2 screws each, rather than six screws as is evident from the design of the corner fittings. 

Additionally, the clamps also tend to flex excessively due to 1) construction in plastic, and 2) excessive spans between mounting screws. Clamp flexing results in the screen stack actually only being retained by smaller intermittent static contact areas, rather than a uniform static contact "strip" along the entire clamp/frame bearing surface.

Possible Courses of Action:

1) Employ necessary measures to increase the rigidity of the frame such that the screen stack can be securely clamped in on all sides under tension to maintain a uni-planar screen surface.

2) Do nothing. Accept the current results as "acceptable", and continue to use a gravity/free-floating screen assembly.

3) Refine the gravity/float method to achieve near zero lenticular distortion by utilizing the following approach:

a) Increase frame rigidity with the installation of 16 (4x4) additional screws in the corner fitting to frame rail joints. Frame will be secured in a truing fixture while additional hardware is installed to insure the frame is square.

b) Add at least two additional mounting points to the top clamp/frame rail to spread the suspension loading of the screen stack across the entire width of the stack.

c) Analyze the gasketting requirements for the sides and bottom of the frame to 1) maintain a free float, 2) limit the fore/aft travel of the screen stack to a minimum, and 3) encourage maximum contact between the fresnel and lenticular screen elements.

Chosen course of action: Number 3....  obviously. Number 1 would require a completely new build of the frame to achieve the necessary rigidity; the plastic frame as designed probably could not be reinforced enough (at least economically) to accomplish a tension mount. While I am happy with the improvement achieved thusfar, I am NOT satisfied. Not when it appears relatively certain that near perfect results can be achieved with a little more time and effort.

I will continue to refine this procedure, and will re-write it in final form once the entire procedure is complete and proven. The re-write will exclude the "misadventures" and simply present a step-by-step procedure to get from Point A to Point B. 



Copyright (C)2003 MONTAC Enterprises.  All Rights Reserved©
Revised: March 03, 2006 .