Craft & Technique: Creating Complex Shapes

works a flat sheet into a completely finished ... mensions to the flat sheet. To allow for slippage cut .... man or woman, to contact him in re- gard to preserving the ...
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As A QUICK

REVIEW

FROM

the second article in the series on the wheel (EAA

Sport

Aviation, May

2001), remember to take

these steps before start-

half-hard, or T4 (at the maximum) conditions.

Remember

that

strength varies inversely as to workability. For pure f o r m i n g shapes of

ing the job:

medium crown, the tem-

Clean both the rolls and the part to be formed

per can be T3, but very

and run a clean piece of

identical-but-smaller stock through the machine at the correct starting pressure. Next, shim the lower axle to establish trueness of flats between surfaces for that pressure and then mark the adjuster wheel at the pointer for this first pressure.

little shrinking can be accomplished, and stretching must proceed gradually to avoid stress concentrations. For fairing or fillet work, the material must be very soft because fairing or fillet

shapes can be complex (read "unusual") and often require a considerable

Make accurate tracks,

amount of stretching. The

overlapping each other by

leading edge fairings for

50 percent, and stagger the

the Hughes H - l replica

stops and starts to make the transition areas smooth.If

must match the ones in the

the tracks wander, the re-

photo of the o r i g i n a l a i r plane.

We scaled full-size dimensions off the photos

sult will be an erratic shape. Remember the Seven Dwarfs? There is an eighth,

and then marked them off

Lumpy, and he lives in the

on the replica's wings and

tin guy's shop.

fuselage. The fairings' con-

The wheel has two basic applications: pure forming or shaping, where the wheel

tours are non-developable surfaces and so cannot be

works a flat sheet i n t o a

set of plans. As an easy re-

completely finished shape, and planishing, the process

minder of the final shape and contour I tape the photos nearby. The finger patterns mock up the full solid dimension of the part, and pattern's fingers transfer these dimensions to the flat sheet. To allow for slippage cut the sheet 3/8-inch oversize and then fully anneal the blank. Now, for the sweaty part. We must heavily stretch

of smoothing by light applications of h a m m e r i n g or rolling. In the first two installments of this series, we addressed pure forming, but little planishing. For severe compound shapes, we must employ the s h r i n k i n g and stretching processes, and the metal must be workable, as in the soft, as-quenched, 112

adequately illustrated on a

pressure, I smoothed the whole part and then came back and worked more tor a fit. Then more smoothing, and then back over it again for a better fit. After contouring the front and rear sections to a satisfactory fit, I trimmed and gas welded them together. After shaving down the edges of the blank. This is called

roughing, or t a k i n g t h e metal through a controlled wreck. Ultimately, we'll see a 40-percent reduction in metal thickness at the edges, attended by a substantial increase in hardness and therefore strength. To rough the blank entirely on the wheel would be a glacial task. Therefore, t h i n k about using some related forming tools. A heavy mallet and a shot- or sand-filled leather or canvas bag offers the necessary heavy stretching capabilities. Driving the pointy end of the mallet into the sheet along the edge while supporting the sheet with the bag allows for maximum stretch, with minimum work hardening. Using a steel hammer over a steel die/dolly/bar stretches the metal quickly, but it also work hardens and thins the metal very quickly, r e q u i r i n g repeated a n n e a l i n g (which consumes more time). Using an air hammer saves time, but most air h a m m e r s are designed only to planish, meaning they cannot generate the power necessary to stretch heavily. I used an an power hammer, reasoning that if it's equipped with the proper tooling that I could save time, arm fatigue, and not work harden or thin the metal very quickly. It worked, and in a couple of hours I had the part roughed to a generally good fit and ready for the wheel. Besides fully annealing the part at the start, I spot annealed two edges once each during the process. Not bad for 1100 0.040-inch material. Setting the wheel for a moderate 113

the weld bead slightly, I wheeled it to a polish. One more pass blended in the contour, and a little more wheel work made the final fit. The wheel left a surface that will polish easily without any sanding. Tracking patterns must be as varied as the parts needing shaping. A little creativity helps here, but once you've assessed the contour and made some preliminary tests (which prove successful), you must stick to the plan. I'm very serious about this. If you must finish the part, you must overcome the "icky middle." Too many craftspeople give up just before the b r i g h t rays of dawn cast their cheery glow across the panel. Seeing the wheeling machine for the first time, many craftspeople note that it could be adapted for use as a bead roller or a l o n g i t u d i n a l forming machine. It can be, and your creativity is the only l i m i t i n g

114

factor in the variety of a particular machine's applications. For instance, in the late 1940s a car builder, Frank Kurtis, was using a cast i r o n wheel from England to roll very long narrow

panels. He made the upper wheelchain drive motor driven to overcome operator fatigue. A tootoperated startstop-reverse switch made the direction controllable, and various sprocket sizes were chosen for speed reduction. Using rubber to form parts in a large press is called the "Guerin forming process," and you can duplicate it by adapting uret h a n e or rubber rolls or wheels to the wheeling machine. Those mar115

velously creative men building the H1 replica adapted their wheel in this fashion to form curved leading edges for the horizontal stabilizer. Careful repeated passes enable the 5052-0 to form the flat condition all the way to fully fit, without any marks. Creating curved windshield fairings or fillets is another use for the wheel that is a bit off the main track. Selecting the number 1 lower position (fully flat) and canting it at a 5degree angle, opens into the bend

and enables both legs to be formed, making a compound angled section without marks. Shrinking this part is not necessary, unless the craftsperson makes an overly exuberant effort at stretching. Repeated light-to-medium passes enable the shape to be attained gradually—and safely. Now go practice! u&

EAA Technical Counselor Kent White achieved master technician's status in 1976 at Harrah's Auto Collection, where he restored metal components for aircraft and autos. He started his own metal restoration company in 1977 and now teaches, writes, and develops tools for metalworking while he still pounds out parts. He encourages any welder or metalworker, man or woman, to contact him in regard to preserving the traditions of aircraft metalworking. To contact him, call 530/292-3506, e-mail kent(e>tinmantech.com, or snail mail 17167 Salmon Mine Road, Nevada City, CA 95959. 116