The longest-running grate replacement project in SACA-NE history is over! I have in hand a completed grate which looks wonderful, and a partially machined casting.

My old grate failed beyond any reasonable hope of repair about a year ago. Surely, I thought, modern technology would allow a simple and cheap replacement. First thought: get a disk of 316 or 310, and have slits cut with a CNC laser. No problem said the laser engineer, and "It'll only cost you $500". Three weeks later, the report was that they'd created a very large and expensive facsimile of a potato chip - they gave up.

On to the water-jet folk. Several people not directly connected with this technology assured me it would work fine. But when I talked to the folks who might actually do the work, I discovered that it wouldn't be possible to hold the necessary tolerance on slit width.

There's truth in the old Yankee slogan that "--- if you can't make it out of cast iron, sonny, it ain't worth making---". However, even here we hit a stumbling block: The foundry didn't think they could hold the thickness close enough on a disk that large.

So here's what we, (John Layport, actually), did: Made a pattern for a simple disk just under an inch thick, and about 22" in diameter. Using a lathe, machined the thickness down to .7" - only slightly more than the overall height of the finished grate. Also machined a bit off the diameter. Weight of the disk was then about 65 lbs..

Then the disk was mounted on a rotary table in a Bridgeport. Using a ball-end mill, the circumferential grooves in the bottom of the plate were machined. Then the plate was turned over, and using a corner-rounding mill, the upper surface was machined. Because the end of the cutter was larger than the available space between the rows, the head of the machine was tilted. Then, using ganged slitting saws, the 1300+ slits were cut. Weight is now down to 15 lbs (The old grate weighs about 13 lbs). Lots of chips!

The photos show the old and new grates, and the partially machined disk with the finished grate. John did a beautiful job, and I'm looking forward to lots of light-back-free miles.

Richard Wells, December, 2002

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