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Steam Stationary Engines, Traction Engines

Case Bunker Bends

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Old 06-23-2019, 08:12:58 PM
JLee JLee is offline
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Default Case Bunker Bends

When you make the Case steam engine contractors bunkers, what is the best way to make the bends for the corners? How do you bend them accurately so you get a nice tight fit?
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Old 06-24-2019, 01:27:30 AM
sawiley sawiley is offline
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Default Re: Case Bunker Bends

I assume you're asking about how to go about flanging the corners for the top and bottom heads. I made a set of bunkers for a friend's 40 hp Case some years back. As I recall, the plans called for a 1.25" flange, with corners nominally 2.625" radius.

I had a local metal shop waterjet cut six outside and two inside corners from 6" squares of 1" plate (should have used at least 1.25" plate), with radii adjusted for metal thickness offsets. I then built a frame to hold the corners, along with square tubes on the straight sides, making a full size die to bend on. The head blank was cut to shape with a plasma arc cutter, with the 1.25" for the flange added on to the basic shape. Blank was centered and securely clamped to the die frame, and I started bending. The straight sides bent fairly well cold, working back and forth along the side with a large hammer, using a piece or heavy stock to clamp along the edge just back of the bend. The corners i bent hot, clamping a piece of heavy angle diagonally across the corner both as a clamp and a heat barrier, then heating with a torch and hammering. Care must be taken to not allow the metal to form bottlecap wrinkles, they're hard to correct later.

The inside corners have to stretch, it may help to flatten the curve of the blank and leave some extra metal width to work with. If the die corners are not taller than the flange, the corners will wrap around the die and make it hard to remove the die. Die corners could also be made on a mill with a rotary table.

Drawings for many of the bunkers do still exist, Case kept much of the archive. I think most of the drawings are now in a museum in Racine, other threads will have the contact info. The drawings can be hard to read, and the one I was working with alternated between fractions and decimal measurements, even on a single side of a part.
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Old 06-24-2019, 04:53:47 PM
b7100 b7100 is offline
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Default Re: Case Bunker Bends

I bent the radius on my 3d scale case bunkers in an H press. I experimented with diffrent radius dies (pieces of pipe/rod) on the upper part to get the radius I wanted. The lower die was a good stiff piece of angle iron. I also made a gauge to get accurate dimensions. Of course this was on a 3d scate with 16 gauge steel. You would have to scale up. Another thing I highly recommend is a coating for the inside called coal tar epoxie. Bunkers are 3 years old and not a spec of rust inside. I have posts with pictures in the scale model engineering forum.
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