The Home Machinist!

Im looking for some help on how to attach the smokebox to the barrel of the boiler for my shay.
The barrel has a 0.5" wide lip turned on it and the smokebox has a matching lip on the inside. Im having a tough time deciding on a way to fasten the smokebox though. I though about rivets, but bucking inside 8"nom pipe is going to be tricky. So my two current ideas are either button head screws and nuts, or use type U drive screws. Any thoughts?

What about using some hex-head model bolts?

They might look more appropriate than screws.

Steve

SteveM wrote:What about using some hex-head model bolts?

They might look more appropriate than screws.

Steve

The prototype smokebox-boiler connection would've originally been done with hot riveting. So a round head screw would be the closest match if I went with some kind of screw.

My vote is a couple of real round head screws that actually hold the smokebox and the remainder are only aesthetic drive screws that have the same or similar sized head. I wouldn't rely on the drive screws to actually hold that joint.

Peter

PeterCraymer wrote:My vote is a couple of real round head screws that actually hold the smokebox and the remainder are only aesthetic drive screws that have the same or similar sized head. I wouldn't rely on the drive screws to actually hold that joint.

Peter

Peter, I'm with you on the drive screws, but I prefer to use rounded head Allen screws to actually hold the smokebox. From a distance it's hard to tell them apart from rivets.

I would put dummy rivets or drive screws on the outside for appearance, but for actually attaching the smokebox, weld 1/2 or 3/8" nuts to the inside of the boiler barrel at 4, 8 and 12 o''clock positions. Then weld short pieces of angle inside the smokebox corresponding to the nuts. Short bolts passing through holes in the angles will screw into the nuts and pull the joint up tightly. Use plenty of high-temp anti-sieze on the threads.

I use flat head socket head cap screws, countersink and cover them with the boiler cladding. Nobody will know they are there. Dope in never-seize

4 or 6 screws are more than enough.

I cannot tell you how much work it was to get out 72 screws on a boiler that I rebuilt for a friend. They had been in there for 50 years and each one had to be drilled out (to save the smokebox).

The visual 'rivets', which are offset TOWARD THE FRONT of the smokebox, are there for show only.

Suggest you not put the smokebox on with rivets because there may come a day when you want to take it off.

Recommend avoiding stainless - if you NEED TO drill them out you will have a heck of a time.

Who made the boiler?
Is the smoke box the same diameter? Perhaps make it from 9" structural tube and slip fit one over other, then use a bolt ring to hold the two together. Don't tap either one. Nuts and bolts. Sure rivets would be prototypical, but you might want to take it apart one day. I don't know why noone leave more lenght between the front flue sheet and the shell length. I have the same issue on my 4-4-0.

Another method I have heard of is to cut a aligning taper on the boiler shell, and the inverse taper on the smoke box shell (assumes they ar the same size) then you pull the two together via longitudinal fasteners on the inside of the smoke box. Say, 4 tab pairs welded to the inside of the boiler and smokebox.

JP

A trick I learned from Don Fite (Dan has the same idea) that I used on my mogul was to weld tabs with threaded holes inside the lip of the boiler and brackets with through-holes in the smokebox. I used stainless cap screws to tighten the two together. This pulls the smokebox and boiler nice and tight.

In this photo there's one more tab around the 1 o'clock position thats hidden behind the petticoat. (on a side note, I had my hands in there this morning repairing the blower line. Wish it was still as clean as it was in that photo!)

I think going with Peter and Marty's suggestion of 4 round head screws and a bunch of decorative drive screws will be my best bet for me. And I'll use nuts inside the smokebox instead of tapping the flange of the barrel, that should also prove helpful when the time comes to remove the boiler from the smokebox. Hopefully I wont be the one doing that though!
What about sealing? Theres 0.005" clearance all the way around between the mating flanges. Should I put any red RTV or muffler cement in that joint to help seal it?

dear mr. soot
i have used two boilers made by the late ray pennell for allen moguls. i asked him to turn down the smokebox end of the boilers to around half the thickness of the boiler shell for about five eighths of an inch. then, when i built the smoke box, i bored out said smokebox so that it would slip over the turned down portion. when we mounted the boiler onto the frame as per the print, we slid the boiler into the smokebox and left about an eighth inch gap before the boiler bottomed out. when everything was in place, we tack welded the boiler to the rear mounts. the idea being, when the boiler heated up and expanded, it would slide into the smoke box. that was our expansion joint. one engine is 18 yo, the other is 15 yo. no problems have cropped up with this arrangement.

my allen mogul, which was put on the road back 1982, used the same design. i had a heck of a time wrestling that chunk of pipe onto the lathe so that i could do the turn down process. it still works to this day. that engine was the product of the wilson locomotive works shop.

respectfully submitted
big c
bluff city locomotive works

The Central of Georgia tenwheeler that I rebuilt for Mike A was secured with three stainless screws around the periphery of the smokebox into tapped holes in the boiler shell. This is how it was originally built so I kept it the same. I gave those three screws a good coating of anti-seize before they went in. The original screws came out without issue.

Those screws, and the entire joint between the boiler and the smokebox, are covered by a decorative band.