Photo above of MRSR91 shows that the cab is fully enclosed and attached to the oil tank. The plan is to make the model the same way with the combined cab and outer oil tank removable as a unit. The roof will have a large U shaped opening at the back and there will be no rear cab wall above the oil tank.
Another view of the MRSR91 cab on a cool damp morning.
This is a cab from a late Heisler that is a bit smaller then MRSR91. This cab was more open and not attached to the coal bunker. It gives some insight as to how the late cabs were constructed.
This shows how the cab side and oil tank fit together. The forward row of vertical rivets behind the door are into a 3/8" wide stiffener bar. The rear vertical row of rivets are into the outer oil tank. The drawing shows the rivets in the oil tank as slightly larger than those in the cab side; that is an error. All the rivets have ~ 1/8" diameter heads.
This is a more detailed drawing of the upper part of the cab front. Two rivet spacing used on the cab is 0.7" like on the the oil and water tanks and 3/8". CFS 1/16" stiffening strips 3/8", 1/2" or 3/4" wide are behind each row of rivets. The plate is 16 gauge (~1/16") HRS. The stiffening strips are soft soldered to the plate after they are riveted in place. Cutouts are required on each side for the pipes over the walkways and the steam feed to the turret as well as the throttle rod on the top of the boiler. The opening around the boiler was cut as shown and then made larger as required to go over the welded joints of the boiler.
Architectural brass angles 1/16" X 3 /4" X 3/4" (McMaster) were used in the corners between the front and the sides. These were first riveted to the upper front and the sides were then attached to the front via rivets. This joint was also soft soldered after the riveting.
All the rivets on the cab are 1/16" diameter (1/8" head) X 1/4" long brass. The ends of the rivets were inserted into the holes, the ends cut close with diagonal cutters and then peened flat.
Photo above shows the front side of the finished cab front with the lower plates attached.
This is the rear side of the cab front. The stiffener strips around the windows and above the door are 1/16" X 3/4" CFS. The stiffeners on the boiler side of the doors are 1/16" X 1/2" CFS. The brass corner angles are 1/16" X 3/4" X 3/4" brass. Note that the leg of the brass angle must be cut back for the door opening. A 1/8" X 3/8" CFS strip was riveted and soldered to the lower part of the angle to provide material for the tapped 6-32 holes for the screws that attach the lower plates to the angles. These four screws will be taken out to remove the cab.
The drawing above is of the right cab side; the left side is the mirror image. The side is made as three pieces, the large forward piece, the 3/4" strip on the rear side of the door opening and the piece above the door. The sides are 20 gauge HRS with 1/16" CFS stiffener strips behind the rows of rivets. A small section of 16 gauge cab floor is fastened to the side to keep the door opening square.
The rivets are 1/16" diameter brass on 3/8" or 0.7" spacing. The parts for both sides were cut on the three-in-one sheet metal tool. The pieces for the two sides were soft soldered together in a couple places the then the hole for the window and the radius in the upper corner piece cut in both sides at once. The rivet holes were drilled in both sides at once using drilling fixtures as was done on the tanks.
This photo shows the finished cab side. The holes along the front edge are for rivets into the brass angel between the side and the front. The holes along the the rear side are for rivets into the oil tank.
This is the inside of the cab side. The middle stiffener is 1/16" X 1/2" CFS, the strip along the rear edge is 1/16" X 3/8" CFS and the remainder of the stiffeners are all 1/16" X 3/4" CFS.
The small section of cab floor is a 1" X 6" piece of 16 gauge HRS plate. It is attached with pieces of 1/16" X 3/4" X 3/4" brass angle with one leg cut down to 9/16". The 9/16" dimension is the size of the square frame bars. The rear sill is attached to the under side of the top frame bar. The bottom of outer oil tank sets on that rear sill. The bottom of the cab side is even with the bottom of the outer oil tank. The cab floor sets on the top side of the upper frame bar so the bottom of the cab floor is the width of the frame bar (9/16") above the lower edge of the cab side. The cab steps will attach to this little section of cab floor.
The stiffeners are soft soldered in place after they are riveted. The solder used was 3/32" diameter Kester Aquabond silver bearing solder ----- I think it is 95% tin and 5% silver. This solder seems to have poor filling properties but wicks into the joints really well. Ruby liquid flux was used . The process was to apply the flux, heat the joint with a small propane torch, touch the end of the solder to the joint; if the joint is hot enough the solder will melt and wick into the joint much like soldering copper plumbing fixtures. The final step was to reheat the joint and then bush on some of the liquid flux to smooth any bumps in the solder. After all the soldering is finished the piece is a mess of burnt brush fibers and residue. A bath and then a light bead blasting produces the finish shown in the photos.
The next step was to test fit everything together as shown in photo above. After a bit of bending, filing, etc everything fit just fine.
The next step was to join the front to the sides and the sides to the oil tank with rivets as shown above.
The cab was then test fit on the locomotive and the notches cut in the front or the throttle rod and the steam feed to the manifold.
After the sharp corners were made on the roller the excess material was cut off the edges. About 3/8" of the roof edge was then clamped in a large vise and the roof bent as necessary to achieve the exact shape required for the edges. The photo above shows test fitting the roof. It was possible to get the roof shape such that the gaps where the clamps are positioned was less than 1/4" before the clamps were tightened.
The next step was to use a saber saw to cut the hole in the rear part of the roof ---- 9 3/8" wide and 9" front-to-back. A 1" radius was used on the corners. The edges were smoothed with files.
The roof was then clamped in position and the joint between the roof and cab front tack welded in a half dozen places on the inside. Rivets were then used to join the roof to the sides. The roof side joint was then soft soldered.
The prototype has a piece of angle along the roof-side joint to serve as a gutter/drip edges. That was let off --- if it were made to scale it would be flimsy and would likely cut the engineer's arm when he adjusted some of the controls in the cab.
The prototype had half round bead on both the front and rear roof edges and on the lower and front edges of the large side windows. That didn't seem to add anything to the model. The half round bead on the oil tank top edge was continued up the curved edge of the side at the upper rear of the door and terminated at the roof joint.
All the edges were rounded with files and a sanding drum in the Dremel before the cab was painted.
The cab is secured by two screws on each side in the front. When the front is tightened down one side of the back raises slightly. Before the final paint short lengths of brass rod will be soldered in the rear corners of the tank. The rods will be tapped for screws that come up through the rear sill.
The view from the front.......
This is the engineer's view of the cab interior. The reversing lever can be accessed through the opening in the roof. The park brake can be accessed through the right side window. The fuel controls are below the lip of the oil tank but easily accessed by reaching down into the cab. The atomizer regulators are not so easy to get to--- the lower one is best adjusted by reaching through the left side door; fortunately these are typically adjusted when firing up and then not messed with. The blower regulator is to the left of the large gauge (boiler pressure). The throttle is the long lever just to the right of the pressure gauge --- it is the most used control and fairly easy to reach.
This pretty well wraps up the cab except for those added attachment screws, steps and the final painting.