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  #21  
Old 10-29-2019, 04:40 AM
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Gojeep Gojeep is offline
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Thank you for sharing such great insights.
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  #22  
Old 10-29-2019, 06:24 AM
cliffrod cliffrod is offline
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Quote:
Originally Posted by skintkarter View Post
Excellent stuff Kent - thanks.
Quote:
Originally Posted by crystallographic View Post
Hi Cliff,
There are favorable ways to use sheet metal stock so that its inherent geometry goes with the job, and less against it.
Some panels can be helped with orientation, but others not. When you get to shaping enough panels for a big job you will get a feel for these things, but until then it is a best guess and hoping.
Wheeling with the grain can open up the shape faster. Same for hammering.
Shrinking with grab-and-shove jaws can reveal grain separation working across the grain (jaws closing with the grain). But then, shrinking methods also yield differences in rates of work-hardening, depending on the type/method.


The following bits of info may be helpful:


Inherent geometries to observe in fresh sheet stock include: Grain, wane, and crown/bulge.

Grain is left by the rolling mill during its many passes longitudinally down the length of the huge roll of sheet stock. Grain is more or less visible, depending on alloy, temper, and specified finish. Titanium has less visible grain than say, 2024T3, but more than 304 stainless with a 2B finish. Like wood grain, bending with the grain, such as with a now-rare mahogany door skin, allows a tighter and less-strong radius. However bending across the grain shows an increase in strength, less bend radius is possible, but the resultant strength is higher. Translating to 2024 T3, the most-used structural aluminum in aviation, bending wing leading edge skins across the grain requires more force yet gives a stronger part. Otherwise going with the grain is an easier bend, and so, less strong. Sheets are limited in width but not length, so part size dictates, ultimately.
Getting bend radii down in size for tight bends, care must be taken more with bending along the grain than across it because of grain-induced separation (fatigue-failure). Take some plain old 3003 .050 and crank up two tight bends, one across and one parallel to the grain and then inspect the outside of your radii for grain openings.

Some care and scrutineering may alternately lay the blanks out so that bend edges are on the bias (diagonally angled)??
I've tested for gain-induced failure on some parts, with some emphasized operations, and know that grain goes omnidirectional with sufficient torture, and the sheet then becomes very compliant to my wishes. This is subject to alloy and temper, over a range of thicknesses.

Wane. The rolls in the mills are slightly crowned to control "steering" of the great lengths of material. By compressing the roll ends differentially, the sheet "steers" one way or the other as it comes down the line. The sheet can thus suffer "wane" at its edges, as thickness decreases due to these differential pressures. I pay more attention to aviation stock than else, so I can see 11 or 12 inches of wane to one long edge, going .003" to .005" thin at the very edge - on only one edge. When using thickness-based shaping machines (Wheels, for instance) pressures or numbers of passes have to compensate for this wane during shaping, or simply avoid shaping in the wane until the rest of the sheet decreases to match and then include the whole for the balance of the job.

Bow/bulge. When selecting a sheet of stock out of supply look for the side that has a slight bow or bulge to it. They all have this. This can save many long minutes of shaping on crowned panels such as hoods, roof skins, deck lids and door skins - IF the bulge is oriented favorably to the job. For panels less that 40in per side the bulge is not as noticeable and therefore not as helpful.

Other anomalies also exist - inclusions (less now than years ago), hard spots and soft spots - lots of cheap sheet for trailer mfg, aviation 2024 T3, mostly discovered when using a Wheel (thickness-based device), delamination of "clad" when hammering.

Hope this helps,
That does help and is the kind of information I hoped to learn- thank you very much, Kent.

It raises another question re wane, maybe nominal issues. I understand some will both test new sheets of metal for both hardness and thickness so they can be more closely matched with other like metal in inventory. If done, sounds like measuring & matching needs to consider multiple sides based upon wane. Would wane also induce some work hardening?
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  #23  
Old 10-29-2019, 12:35 PM
crystallographic crystallographic is offline
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Quote:
Originally Posted by cliffrod View Post
That does help and is the kind of information I hoped to learn- thank you very much, Kent.

It raises another question re wane, maybe nominal issues. I understand some will both test new sheets of metal for both hardness and thickness so they can be more closely matched with other like metal in inventory. If done, sounds like measuring & matching needs to consider multiple sides based upon wane. Would wane also induce some work hardening?

Cliff, The older senior aviation metal men have told me that when they receive a load of sheet and put the first into shape they are very watchful/critical of all of the possible anomalies - and when they get a really good batch of material they call the supplier right away and find out if they can double the load IF the available material is from the same run.


Yes, using "same" material as factory when doing repairs can have significant time savings - so finding spares/scraps that match can help a lot.
Otherwise, do your best with known measurements of alloy, temper and thickness. ( I'm thinking of Jaroslav here, with his "hard" and soft material being used for his trim pieces ...)
Note: Listening to the ring of the metal can give a trained ear a clear indication of hardness, or lack of hardness. BIG difference between the "clack" or "thud" of soft and the "broinngg" of hard - and variations between.
-end-
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  #24  
Old 11-02-2019, 01:20 PM
crystallographic crystallographic is offline
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Default ERCO power shrinker (HDAS4 by TM Tech)

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In addition to using the Air Power Hammer for shrinking, the ERCO power shrinker was also used.
Here we are "tuning up" an edge to fit more closely on a final fit.

We are going in about 3 inches at the most, but are working the edge more than anything.

Because it has a very fine adjustment on the hand wheel, shrinks are made accurately and repeatably, whether one at a time or in long sequences automatically.
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TM Tech also makes a variety of the ERCO jaws, so the degree of stipple can vary from barely visible to like driveway gravel. Shown here is the #2 stipple, for doing .050" and .063" aluminum.
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  #25  
Old 11-08-2019, 06:05 PM
crystallographic crystallographic is offline
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Default FLOW FORMING skins

The doors on the GT40 are complicated assemblies. (more on that later)
There are inner reinforcing doublers above the driver/passenger heads that are formed with enough detail to require forethought and planning.
We decided to flow form our parts, and the test parts would be done over the f'glas door frames (some f'glas deterioration risk involved.)
Using 4X rivet guns and a variety of shaping schnoobles, the annealed sheet went down into place with some application of the 7 P's (Proper Prior Planning Prevents Pxxx Poor Product).


Hence:

Blank is annealed in specific areas that will be shaped.
Blank is clamped to form.
4X gun is employed with correctly-shaped urethane schnooble.
Repeated passes lower the surrounding areas incrementally.
Part is re-annealed when resistant to another forming pass.
Schnoobles are changed periodically, as needed.
(It's not difficult to mount up a blank insert in a flow-form tool, spin w/drill press, and sand the shape needed. For chisel shapes, mount tool in vise, mark areas and shave off w/sander - OR use bandsaw very carefully and then sand. (Note: our tools are hardened steel and our inserts are a variety of heat-resistant hardnesses from our various polymer suppliers....)

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Cooling the guns and tools in water. Long stretches of forming builds up heat, so we take a moment and cool the tools, periodically. (Oily compressed air dries the guns out rapidly.)
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I've been doing this since ... um ... 1981, and I've collected a fair bit of schnooble-ishus stuff.
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Oh - might as well add this. George and I have worked together for over 13 years now, so we have a lot of shared history and methodology - and other students too, as well ...
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A few years ago I laid out a few guns on the table, to give students some creative ideas ...


- end -
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Last edited by crystallographic; 11-08-2019 at 06:09 PM.
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  #26  
Old 11-09-2019, 07:56 AM
Rex_A_Lott Rex_A_Lott is offline
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^^Thanks for sharing that Kent!. A friend of mine is fond of saying, " I know what I know, and I dont know what I dont know".
I learn something from all your posts.
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  #27  
Old 11-09-2019, 09:13 AM
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Steve Hamilton Steve Hamilton is offline
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George and Kent
What a neat project. I am sure that many including myself have dreamed about having a GT 40. George is one of few that have made that dream come true. The dedication required to stay with the project and not lose interest is honorable. Knowing your personal skill set and getting expert advise and or help is also commendable. The workmanship is top shelf! George you can be very proud of your accomplishments.

Thanks Kent for the wonderful tutorial. Posts like these are invaluable to our members.
Look forward to seeing more posts about this build.

Steve
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  #28  
Old 11-10-2019, 08:03 AM
RockHillWill RockHillWill is offline
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Geez, what a great project, I am impressed with the work of you both. I miss our chats, my friend, I will be in touch.
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  #29  
Old 11-10-2019, 03:34 PM
crystallographic crystallographic is offline
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Hi Barry,
Thanks, and very glad you are enjoying the saga.


Hi Steve, Yes it was a long slog, broken by doing other big projects, but still .... serious grit required. Glad to toss in the tutorial as it is one that I know pretty well, by now.


Hi Will,
It's been too long and too many projects. Missing those W.H. visits a LOT.
Looking forward to a good chat.
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