Start over at the edge of the panel and shrink more if you need more curvature. The higher the crown offered into the dies means the more they will shrink.

Now, as for the number of pieces: The upper die is two pieces, one inserted into a cup. The lower die is another piece. This makes the count of three pieces.

-Kent

A shrinking die on the Job!

These dies shrunk the edge of this .125" 3003 using the very heavy AU. Minor marks, if any.

T he shrinking dies for steel will do 16 gauge CRS. Not that softy AK, but the hard stuff, with the Very HAU. It can be done.

And the surface is nice!

These customers have done a great job of describing how shrinking dies work :

I'm no expert but here is how I think about it. The idea with many shrinking techniques is to somehow trap the excess metal in some form of ruffle, tuck or bubble and then drive it back into itself making the metal thicker.

With the air hammer you shrink the edge, which gathers the metal along the edge and this imparts a curve to the panel. Any edge shrinker does this. Anyway, if you were to now lay that panel on the floor and push the edges to the floor you would see a bulge just inboard of the edge you have just finished shrinking. This is in effect what you're doing on the air hammer when you start to drive the shrink inward ... you're flattening the edge of the panel on the lower die with gentle taps (so you don't stretch it back out) and this creates a the bubble of extra metal just ahead of the upper die which you then chase into the panel.

It's a bit like taking a rolling pin and rolling from the edge to the interior of the panel. If you're careful you catch up with the bubble and drive it down without expanding the surrounding material. On one of Kent's videos, he shows how to shrink with an E-wheel using this general idea.

I have found the system to be incredibly flexible ... and portable. Moreover since I have tendonitis in both arms (from playing the fiddle!!! ) .... and I have to keep the hand pounding work to a minimum, being able to stretch, shrink and planish all with the same power tool has been a real life saver. In some situations you can actually do all three operations with a single pair of dies just by varying the air pressure with the foot pedal.

The technique is not difficult, it's just hard to explain. The first time you see someone who's good at it work a piece at a quick pace, it really is almost like magic because the metal seems to flow like plastic as the ruffles appear and then are worked back in.

Cheers,
Howard

............................................

It is difficult to describe "HOW" to shrink on the Kent White style
dies. I'll try by describing what one does. It would be a hell of a
lot easier to just see one in action. The reaction is UH-OK.

You first use the power-hammer to bend a flange where you need a 'shrink'. Then, using the post, the hammering action and some "body-English", you bend the panel around the post of the tool, pull it out, rotate the panel and bend it again.

IF properly done a 'tuck' results. The tucks are flattened just as one would do with hand tools. These 'shrinks can be "Worked-in" or "chased" inside and as one becomes more proficient, the panel takes shape and gets partially planished at the same time- DOH.

A medium air unit seems about right for 20 Ga steel and 1.5 mm Aluminum. The pressure can be turned down and 1 mm Aluminum can be shaped/shrunk with the same unit - and same diameter tool shank (.498).

Smaller units can be used for planishing.

Ron