Model Locomotive with 3D Print Technology: Cylinder Block Covers

Monday, November 12, 2012

Cylinder Block Covers

Revised: 11/12/2012 Subject to Revisions

Front Covers

Covers on front and back of the cylinder and valve bores complete the cylinder block assembly. The first covers built were the front covers. These do not have an opening for a rod. Photographs of front covers on various Mikado locomotives indicate that they are plain. More than likely the photographs depict insulated or isolated covers as no bolts are observed.

Cylinder and Valve Front Cover Sets

Front covers are plain with the exception of a protrusion in the center. In photographs protrusions on the larger cylinder covers appears to like a hockey puck in shape. The covers also have rounded outer edges. The valve covers have a short rod like protrusion. These features were estimated based on photographs as the author did not have those features shown on USRA plan views.

Inside and Outside of Front Covers

The outside of the covers do not have any remaining support material. The inside was down on the raft and had support material that needed removal before installation.

Inside View of Front Covers and Outside of Covers Placed on Cylinder Block

The Dremel sanding wheel was used to remove the bulk of the residual support material. Very little touch-up was needed otherwise. Some sanding of the interior of the cylinder block was done to provide a suitable fit for the front covers.

Front Covers Installed on Cylinder Block

The front covers were then glued in place on the cylinder block. Super glue was used as was done for all prior gluing operations.

View of Front of Cylinder Block with Covers

The front covers look very close to those seen in photographs of prototype locomotives.

Rear Covers

Isometric CAD View of Rear Valve Cover Design

Drawings and photographs of the rear valve covers were converted to CAD design as shown above. The rear valve cover has a modified bell-like housing to support the valve slide mechanism a short distance from the valve cover. The author elected to simplify the housing a bit and eliminate the use of the slide which would be too small for an effective working model. Instead a guide hole is provided to support the valve rod at the linkage end with dummy supports to surround the linkages.

Rear Valve Covers After Removal From 3D Printer

Printing went well with the rear valve covers. Even the relatively small dummy bolts turned out fairly well. The support material was used mainly to support the upper portion of the bell housing.

Rear Valve Covers After Removal of Support Material

Support material was removed fairly easily with a needle nose pliers and model knife. The valve rod holes were drilled out to make them clean for the eventual free movement of the valve rod.

Rear Covers Installed on Cylinder Block

The photos above and below show the rear valve covers installed on the cylinder block. The valve rod will be operable (but not the valve) to illustrate the motion of the valve and linkage mechanisms on the model.

Close-up View of Rear Valve Cover

The rear valve cover is fairly small and is readily built on the 3D printer. A small complex part such as this illustrates well the advantage of a 3D printer to make complex models.

CAD Isometric of Rear Cylinder Cover

The rear cylinder cover illustrated above will have two threaded blocks to attach the front of the cross slides to the cover. The cross slides support the front slider of the main drive rod to prevent bending or distortion of the cylinder rod. The rear of the slides are held on a support attached to the frame.

Rear Cylinder Covers As Removed From Printer

The rear cylinder covers have more details than those on the front. The rear has a ring of dummy bolts plus the attachment blocks for the slides and of course the cylinder rod hole. The printing came out very well with good detail.

Outside and Inside View of Rear Cylinder Covers

As for the rear valve covers support material inside the cover was removed to enable installation on the end of the cylinders. This was done with the sanding wheel.

Rear Cylinder Covers During Fit Check on Cylinder Block

Some grinding of the inside of the cylinders was done to facilitate a fit of the covers. The region around the cylinder rod hole was cleaned out using a model knife. After installation the rod hole will be drilled to final diameter.