John Lewis kindly provided me with a copy of the Union Iron Works boiler for a 70 Ton Climax (1551).

The provided dimensions provide problems for me in the area of the firebox and firebox wrapper.

The mud ring is 3" and the drawing illustrates and dimensions specify that in the firebox and wrapper but I lack knowledge about the period drawings and/or fabrication assumptions of the period.

To allow for the space between the mud ring and wrapper I added a 9/16" filler/spacer to fill the space created by the backhead sheet and throat sheet which increases the space between the fire box from the specified 3" to 3 9/16".

If I follow the drawing for the firebox there are four (4) gaps at the corners. The firebox is 3/8" sheet, the flue sheet is 1/2" and the boiler wrapper is 9/16".

Any clarification would be much appreciated.

Note: Blue dimensions in 2D pdf per drawing. Red per my present drawing.

The drawing looks to show that the mud ring is 3" wide. There are dimentions shown for the firebox length inside the mud ring (7' 4 7/8") and inside the sheets (7' 4"). Also the width dimensions (45 3/4" & 46 1/2") Nowhere do I see a dimention for outside the rapper sheets. It looks like your gaps are in the grate hangers.

No spacer. The edges of the knuckled sheets would have been hammered down to a taper and the wrapper lapped over them, then everything riveted and the seams caulked with the caulking gun. Any miniscule leaks were hit again with the caulking gun or if necessary some iron filings would be dumped in the boiler before pressurizing (the rusting filings would find, fill and plug the leak passages). Later on the seams were sometimes seal welded.

Now I just have to visualize that, develop a concept to reproduce that in 3D CADD AND reproduce it 3D CADD so it is understood by me and those who examine the drawings. Any additional input with photos, etc., would be appreciated. I think I will spend some time thinking before attempt this real world early 20th Century method.

I will go with a welded firebox for now while a figure out how to assemble the the 9/16th wrapper, backhead and throat sheet.

Flush full penetration welded eliminates the need for kludging in the overlaps. No point not taking advantage of today's better way.

Would look something like one of these, depending on manufacturer, whatever the current practice was, MWAP, etc. Throat/tube sheets at top, wrapper on the left. Wherever you assume gaps would form, they would be filled by hammering the relatively malleable boiler plate in tight and then the caulking gun. The lower version represents more modern practice. I seem to recall seeing a picture or two over the years of mud rings that were stepped out on the sides to accommodate the 'spacer effect' you inferred, but that would have been extra expense and back then qualified boilermakers were plentiful and cheaper (and deaf from the hammers)...

Approximately what distance would you estimate the transition above the mud ring would typically be from the taper to the flat sheets?

I know that varied depending on the Shop and sheet material, but I find this type of detail very interesting and the next time I look at a boiler on a locomotive I will look for this detail.

Thanks much. The drawings are very helpful.

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Is this the U.S 152 from the Huckleberry?

Dont know if this drawing fits US practice fully, but it is an example of Danish boiler practice with a riveted copper firebox. The tapering of the sheets, both internal and external, is visible in the drawing

It happens right at the top of the mud ring. Just happens according to the hammering - the sheets flex to follow where they're driven. Been a while since I looked at older boiler assembly, but IIRC the inner tapered sheet (against the ring) was attached first, then edges tapered & reamed, then the wrapper applied with at least two or three lap rivets immediately above the ring finished off before the wrapper was hammered in to fit the taper, holes reamed and riveted. Keep in mind that hammering the taper tends to drive in the sheet a little right where it leaves the top ring edge, reducing the severity of the 'lap bulge'. Like Kelly said, the tapers were longer - so much so that you seldom notice the 'bulge' in the wrapper unless you really look close. I shortened them in the drawing for clarity and omitted rivets because they wouldn't accurately reflect practice with the shortened tapers.

Find a blacksmith who will let you pound some hot steel for a few minutes and you'll quickly get an idea of how sheet deforms over edges and other parts under impact load. It's as much art as science, so doing is the only way to fully understand it.