Revised: 4/13/2013 Subject to Revisions
Sand Dome and Transition Boiler Section
The author elected to build the sand dome section and a tapered transition section between the sand dome and steam dome sections as one piece. This part would be a near maximum Z axis height capability of the 3D printer. The success with the smoke box section prompted this decision. The design looks as follows from the Alibre Solid Modeling CAD software.
Sand Dome and Taper Section Part
View of the Sand Dome and Taper Section Composite in 3D Printer
View of Composite Sand Dome and Taper Sections
After 25 hrs 49 min the 3D printer completed the composite section. The ruler in the photo above shows the model section is over 7" tall. Inspection of the model section shows fairly good definition. The sand dome section at the top has two mounting holes built in for sand dome alignment and installation. The sand dome itself is a separate model part to be built separately. This is the largest part made on the 3D printer so far. The part is very rigid and strong, barely flexing even under considerable pressure. The upper reduced diameter portion is a flange that nests inside the smoke box section.
Sand Dome and Taper Section CAD Model with Sand Dome in Place
The 3D CAD model above shows the sand dome in position on the front of the composite section. The sand dome will be built next.
View of Composite Sand Dome and Taper Section Fit Checked With Smoke Box Section
Sand Dome
The sand dome part is fairly large and curved to fit on the boiler section. An attempt to build the sand dome as a single part was made with the top up. The support material where the thin lower edges were to be located separated preventing the model bottom most edges from forming. The print was stopped. The author then did a notional design splitting the dome in halves along the radius of the boiler curve. The author contemplated putting the two halves in a structural box to permit grinding the joint flat on the mill. This did not work out either, once again the support edges lifted preventing the outer box frame from starting on the support material.
View of a Split Half of the Sand Dome
Author's Notional Design of a Structural Frame Around A Pair of Sand Dome Halves
The red structural frame shown around the pair of sand dome halves was to provide a way to support the dome halves during milling. The large frame required a large support structure which separated before the frame started printing. The author stopped the print cycle and went back to the drawing board.
Two Successful Sand Dome Halves
Sand Dome Halves With Support Material Along Joint Ends
Top and Bottom View of Sand Dome Halves Before Removing Support Material
The sand dome halves each took 6 hr 15 min to print. Both came out quite well with a small tendency of the support material to lift at the access side of the printer. The detail was as expected with the sand fill covers showing good detail. Each half has a pin extending down into the respective hole in the sand dome section.
The support material was removed and the center joint cleaned up with the Dremel sanding wheel. The joined boiler sections are shown fit checked on the locomotive chassis below.
Fit Checking of Joined Smoke Box, Sand Dome and Taper Sections on Chassis
Steam Dome Boiler Section
The steam dome section is very similar to the smoke box section except slighter larger in diameter and having the steam dome instead of smoke stack.
Steam Dome Section Design Illustration From 3D CAD Software
The print time of the steam dome boiler section was 10 hr 43 min. The wall thickness and forward flange were similar to the front portion of the sand dome and taper composite section. The print quality and part sizing were similar to that experienced in both the smoke box and sand dome composite sections. Not shown is separate view of the new section. The steam dome section was joined to the previous sections for a fit check on the locomotive chassis.
View of the Completed Boiler Sections Fit Checked on Locomotive Chassis
The fit checks clearly show that the boiler mount flanges on the locomotive chassis fit correctly with the boiler. They will not be secured to the boiler. The boiler will be secured to the chassis using a single screw accessed down through the smoke stack and one or two screws at the rear, location TBD.
Steam Dome
Steam Dome Just After Printing
The steam dome is a very curved shape which took a few hours of 3D CAD work to develop the model. The author decided to print the dome directly on the raft material rather than first build a layer of support material as had been done on most other printing efforts. After 3hr 37min the dome was printed. It was done solid as it is fairly thin compared to the sand dome for instance. The printed article came out well with some of the support material lapping over on the top. Two pins were printed on the bottom to mate with the two holes printed in the boiler.
Steam Dome Being Fit Checked on Boiler
The dome fit well on the boiler. An interesting result of using the 3D printer is that the complex curved shapes all fit very close and required little trimming to mate with the boiler. It's a bit of design work to achieve the compound curved shapes, but the 3D printer did a very good job with them.
Locomotive Boiler With Domes During Fit Checks
Four of the boiler sections are now completed along with the smoke stack, sand dome and steam dome. The next portion of the boiler the author will tackle will be the firebox section. This is a fairly complex shape that will have a ring on the front to mate inside the steam dome section and flat sides extending downward from roughly the center line of the boiler axis. The back end is tapered somewhat. The cab will surround the back end with the tapered portion inside. The flat sides below where the walkway will be located will have many detail bolts that connect the outside of the water jacket around the actual firebox inside.
The design of the firebox section will also eventually have the ash chutes attached that go down thru the opening in the rear frame. Those will be made separately and attached to the firebox during assembly.
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