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  #31  
Old 03-21-2016, 03:10 AM
Bart Bart is offline
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You're right I haven't don this with plastic paint, I have used paper.
Just a thought I had and wanted opinions, I thought to keep shape maybe use fiberglass mesh??

Quote:
Originally Posted by KAD View Post
I think that when you pull it off of the original your trying to copy it might easily distort in a way that would alter the information your trying to capture.

Any change in the pattern that alters the "area information" will result in the problem being transferred to the new part your trying to make.

If you will note I started with "I think" which means that I'm guessing here as I haven't done it, but looking at the video of it being peeled off it looks like it distorts to much to capture information correctly

Having said that, if you have some give it a try and report back I'm always looking for better ways to do things.
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  #32  
Old 03-21-2016, 07:03 PM
sblack sblack is offline
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I was thinking of some kind of rubber dip, like the stuff they dip tool handles in. There must be some sort of rubber, or vinyl or urethane that would work. What a time saver that would be. They are great tools but tedious to make.
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  #33  
Old 03-21-2016, 07:07 PM
sblack sblack is offline
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Quote:
Originally Posted by ShawnMarsh View Post
I think I need to see what you guys are doing, because as someone who has very little shaping experience, I'm not really sure what you mean by keeping a panel in arrangement. I'll be at the Santa Cruz meet in a few weeks, so hopefully I can see this in action because I'm a much better visual learner.
Look up the youtube video of Fay Butler making a high crown part on a yoder. He wraps it up in a ball to do the shrinking and shaping. Then he unwraps it and bends it in to the proper configuration. All the shrinking/stretching is already done, but the part just needs bending to fit. The reason? Because it is easier to shrink when the edges are curved. Much less internal stress resisting the he shrink.

http://youtu.be/CgG1tA3vecs

Look how he curles it up before he starts hammering. Then look how he rolls it back out when he is done. That's changing the arrangement, or the form (same thing)
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Last edited by sblack; 03-21-2016 at 07:11 PM.
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  #34  
Old 03-21-2016, 09:25 PM
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Kerry Pinkerton Kerry Pinkerton is offline
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Two comments:

1- On slick surfaces, I prefer Glad Press-N-Seal for the release layer. Cuts the time in half and peels right up.

2- Plasti-dip comes in rattle cans. I agree it might stretch but if you used fiberglas mesh tape (drywall tape), the Press-N-Seal, MIGHT bind it together in a non-stretch but flexible pattern. It would only cost about 10 bucks to give it a try. Go for it.
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  #35  
Old 09-11-2020, 04:35 PM
crystallographic crystallographic is offline
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Default airplane tail skins, subtle shapes

Quote:
Originally Posted by Kerry Pinkerton View Post
Ahhh arrangement. That's almost a different subject. You FREQUENTLY can't work a panel in the proper arrangement. The problem comes when you can't 'see' how the panel can go into proper arrangement while you're shaping it.

I'll say this. When the panel fits the FSP, it WILL go into arrangement although sometimes you have to pop it to get it to reverse. It it doesn't fit the FSP it won't be the proper arrangement. Period full stop as our Brit friends say.

Inserting a bit of shop work here, supporting the concepts :
flexible 3D pattern,
shape analysis,
and matching the shape to the pattern.

I need to make two contoured airplane tail skins, one Left and one Right. (prop driven, so P factor yields tailfin canted 17deg off airframe axis, so skins are not shaped the same. )

https://en.wikipedia.org/wiki/P-factor

P1110812[19341].jpg
First skin done and fit.
.025 2024 T3
polished
Shapes are subtle. So it is a bit tricky working to small measurements of shape.

P1040410 copy.jpg
Using original panel for pattern. Thin springy metal can be weighted flat.("out of arrangement")
P1040412 copy.jpg
Straightedge helps define shaped areas and distances.(in the flat)
P1040413 copy.jpg
P1040415 copy.jpg
Reverse shape made by Punishing Hammer, carefully following pattern "map" for both area and lift (one inch).


I "snap" panel into shape-arrangement, and do a hand massage to help it conform to the framework.

One tiny bit of added tap-tap-tap ... = confirmed fit.

P1040420 copy.jpg
Checking shape by overlaying and pressing skins together is confirmation, as well as clamping to the tail framework.
I finish the part by using the MB aviation-style 3.5in dia. "punch-flare" dies.
It's a miracle - no change in shape and access hole is correct!
P1110814[19343].jpg


Next skin has lots more shape over 4 separate areas ....
Time for a flexible pattern that accurately indicates topography so I can mark and transfer all info to the blank, accurately. (4X the number of shapes = 4X chance/degree of error.
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Last edited by crystallographic; 09-11-2020 at 04:53 PM.
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  #36  
Old 09-12-2020, 04:05 PM
crystallographic crystallographic is offline
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Here is the back side layout of the first part done as a test sample and checked for fit. (Cleco holes visible... and finger prints. )
P1040967 c.jpg

Test parts are a good thing to do for panels having subtle shapes, and being done without benefit of a hard buck.
Some buck varieties used in aviation follow:

Bucks, C195, C3, misc EMT c.jpg
Fiberglass buck and wooden eggcrate buck.

The odd black/white thing is a standard aircraft factory aviation "buck" used in manufacturing production airplanes.
AKA: "EMT" - "Engineering/Manufacturing Template."
These are available when making replacement parts, which I was doing for an Aero Commander at the time I had this in my shop.
These are marine-grade plywood, glued and screwed and covered with fiberglass for weather protection and shop wear. Very strong, heavy and durable.

CMCT _ Orford Aviation c.jpg
The standard old-school aviation 3D flexible pattern is called a "CMCT," or "Chem-Milled Contour Template." This printed designation on this part is partly hidden by the man's hand, left side of image. (photo taken circa 1992 of a pattern probably made late 1950's - early 1960's.)

This flexible 3D pattern is also kept in inventory during production, and is later used for making replacement parts. Once the first skins are made in production and "proofed" both on the master air frame and against the EMT's, the first proofed skins are taken out and chem-milled to create the openings and thinned areas that make them so light and flexible. Inventory numbers are painted on (or machined in) and the press dies, stretch dies, EMT's and CMCT's are all inventoried in large warehouses during and after production runs. They may be drawn from inventory at any time there is a need to confirm the way any part fits. (Dies do wear down, get nicked and banged, dropped or mishandled in the presses.) The webs remaining are where the bulkheads, stringers, and spars rivet to the skins - being the most important of all the fit-points.

A newer technology for the EMT manufacture is cast foam which is then milled on all surfaces. This was for a prototype job done in my shop a few years ago:
P1120373 c.jpg
P1110374 c.jpg
Since proto work mostly involves "scratch" builds there were no CMCT's ready - I was making them for one prototype.
....
Anyway, on to the other side of the tail ...
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Last edited by crystallographic; 09-12-2020 at 10:13 PM.
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  #37  
Old 09-15-2020, 02:51 PM
crystallographic crystallographic is offline
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Default flexible 3D shape pattern

Aircraft building and construction for the small shop involves wood work, aluminum working of sheet and extrusions, twisted multi-strand cable cutting and crimping, fabric work, steel tube construction, loads of fasteners of many varieties, brackets, frame construction and etc etc. And it is all done to correct levels of inspection. Having experienced help is pretty important.



Creativity is also very important.


P1110802 copy.jpg

This is a fiberglas covering fabric used for covering wings and fuselages.
("crowfoot" weave has great warp and weft/woof - both about equal so the fabric can cover reverse shapes nicely.) Comes in 2 or 3 fabric "weights." Your choice.
P1110806 copy.jpg
The goop that smears over it is a polycrylic water-soluble wood coating, either a foo can or quart can and brush. I used the foo can and a brush, 3 soggy coats, minimum. Warm days help dry in half hour/coat.
Brush-on thicker coats and warm days dry in 45 min to one hour.


P1110809 copy.jpg
I patterned both sides, comparing results.


---- Fire Bombers now going over one after the other. North Complex Fire is 10 miles off and looking this way. Can run 1000 acres in 20 minutes ... Internet now unhappy.
Back when I can be.
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  #38  
Old 09-15-2020, 05:28 PM
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Kerry Pinkerton Kerry Pinkerton is offline
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Stay safe Ken. Don't wait to get out when they tell you.
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  #39  
Old 09-15-2020, 09:24 PM
crystallographic crystallographic is offline
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Quote:
Originally Posted by Kerry Pinkerton View Post
Stay safe Ken. Don't wait to get out when they tell you.

Thanks Kerry.
We have a registered "Firewise" neighborhood, cleared distances, defensible spaces, metal roofs, and are prepared by firefighters with the basics in gear, attire, and bug-out stuff. Been on the local fireline once, 2004. Phoned in a burn once, 1992. Drove through the 49er fire to get back here and defend, 1988.

4wd ready, with fuel.

Next 24 hrs are key.
(thumbs up)
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  #40  
Old 09-15-2020, 10:26 PM
Chris_Hamilton Chris_Hamilton is offline
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Thinking good thoughts for you Kent and keeping you and your family in my prayers. Shame that it's happening.
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