These two plates go on either end of the boiler. They are referred to as "tube sheets", or "flue sheets". Here they are being drilled, then reamed to .626" so that the 5/8" copper tubes will just slide in, before being "rolled in". One of the hardest parts of this project was finding out how to roll in these tubes on this very small boiler. I made at least half a dozen calls to various steam experts, and they would give me their best advice, and then at the very end tell me to phone another "expert", just to make sure... It got confusing after a while.
The problem is that we are now three generations away from using steam. The last steam cars were built in the 1920's, and after that it was mostly industrial usage until the machines got updated with new technology, or wore out... Steam knowledge is out there, and it's slowly disappearing. Below is a genuine flue roller, made years and years ago. I bought it from 81-year-old Bob Davis, who had it in his tool box for a very long time. To roll a copper tube, it's inserted into the reamed flue sheet hole, then this roller is put into that tube. You turn the square end clockwise, and the slightly angled steel rollers turn and also pull the tapered mandrel into the roller housing, causing the rollers to expand out and into the copper. It's so simple and works so beautifully. You need to compress the copper 10%, so a wall thickness of .065" has to be rolled down, or expanded to .058 -.059". This means a lot of measuring with a snap gauge and micrometer.
Boiler under pressure. There's actually only 54 tubes, because the middle hole has the "fusable link". This is a brass plug with a 1/4" hole thru the middle, filled with solder. If the boiler ever runs out of water, the added heat will melt the solder, releasing pressure (downwards, very fast...), and prevent an explosion. Operating boiler pressure is 150 - 200 psi, so we figured that 310 psi showed a good safety margin. To get that pressure, I filled the boiler with water, put in a brass NPT fitting with a grease nipple, and hand-pumped in grease.
This is the sight glass that goes on the side of the boiler. That glass tube is high quality, and fairly thick. It shows how much water is in there.