Baldwin Unitah 2-6-6-2T Frame Mods

I’ll be referencing the takeoffs that were shown on the page you used to navigate to this page.

Unitah Takeoffs

Also, the frame image on that page is the starting point for the discussion on this page.

2-6-6-2T Frame3

The takeoff table shows the spacing between the rearmost driver in the front block and the front driver in the rear block (Driver Front/Rear Wheelbase).  Using the drawing it was estimated at 1.016″.  In the bashed drive train it was initially estimated at 1.37″. We want to reduce that discrepancy.  In the above photo a portion of the rear frame protrudes from the cylinders.  In addition, in remeasuring, I found the cylinders were too far forward.  So I moved the rear cylinders back to a position where their distance from the front axle in their motor block would be the same for both cylinders.  I then cut off the protruding section of the rear frame and rounded the end so when the front driver block rotates to the right and left there will be no interference.

Unitah Frame Mod1

I also notched the frame where the cylinders will ride, but not as much as I originally anticipated.  I realized the the slide plate mounted above the front cylinders would raise the total height of that unit.  In this photo you can see where I filed the front cylinders to receive a brass plate that will allow the boiler to slide as the front driver block rotates.  The brass plate is not shown in this photo.

Unitah Frame Mod2

The slide plate is effectively a place for the boiler to slide and a shim bringing the saddles of the two sets of cylinders level with each other.  I have additional work to do on the drive train before making final adjustments to the relative height of the two sets of cylinders.  But here is how the drive train would look with the front and rear frame aligned as they will be once the frame is complete.  This is a much more compact unit than the image near the top of this page.

Unitah Frame Mod 3

This shot shows the front/rear driver block wheelbase.  The length of 1.111 inches is just a bit longer than the converted takeoff from the drawing which was 1.016″.

2-6-6-2 Front:Rear Whlb

While I had the digital calipers out I also wanted to measure the boiler extension needed for the front of the smokebox to fall at the midpoint of the front cylinders.  The calipers are telling me I need to add a 0.8″ extension to the boiler that comes with the Roundhouse 2-8-0 kit to meet that objective.

2-6-6-2 Unitah Boiler Ext

My next step was to clean out the wheel bearings.  No, your wheels are not going to drop into the bearings and turn nicely for a number of reasons.

  1. Your axles may be rusted.  After all, this is a 40 year old kit that was stored in somebody’s damp musty basement.  A little work with some very fine sandpaper will get them shiny again.
  2. The bearings have flash or were cast undersized.  A small rat tail file will solve this problem.  But go easy here.  You want an axle that turns freely but is not sloppy.  Make sure you have addressed the third problem before finalizing work on the second problem.
  3. You violated the Roundhouse 2-8-2 blind/flanged driver rule.  You see, on a 2-8-2 the flanged drivers go in the two outside bearings and the blind drivers in the two inside bearings.  If you are building a 2-8-2, simple.  Move the flanged wheel set to an outside bearing.  Roundhouse designed the kit to make sure you didn’t screw up the driver order.  If you are building a six coupled wheel set, you have a problem.  You need to put a flanged wheel set in an opening designed for a blind wheel set.  This photo illustrates the problem.

Mallet 2-6-6-2 Wheels1

The driver won’t even go into the bearing — because the flange is hung up on the frame.  Set this assembly aside until you have accumulated a fair amount of patience.  Then get out your small set of files.  I used a rat tail, a triangle, and a moon shaped file with one flat side.  Then work on the inside of the frame element where the flange contacts the frame.  Figure 30 minutes to do two sets, one for the front wheel set and the other for the rear wheel set.  Resist the temptation to get out your Dremel, your table saw, your chain saw or some other weapon of force.  Keep saying to yourself, “This is an antique part.  If I screw this up, I’m going to have to buy another whole kit to get this part.”  When you are finished cutting the notch where the flange hangs up, you should have something that looks like this.  All three axels should spin freely.

Mallet 2-6-6-2 Wheels 2

Smile.  You just beat one of the more frustrating problems in building this loco.  Yes, I realize my shaft on the blind driver is rusty.  Fixing that problem is nothing relative to what I just fixed.  But notice how nicely polished my bearings are.  That is the result of addressing the second problem in the above list.

We are not ready to put the plate on that holds our drivers in place for two reasons.

  1. The plates have not been modified for the six coupled wheel sets.  We’ll do that next.
  2. This locomotive isn’t going anywhere without gears.  No, I’m not going to attempt to run live steam in HOn3.  We’ll deal with the gears in the drive train section.

Underframe Modifications

All I did here is screw the under frames to the frames and mark the cuts needed to shorten the under frames to match the frames.  While I was doing it I did the same for my 2-4-4-2 frames.  This shot shows the bashed under frames in their correct orientation.

Mallet Underframe1

And this shot shows them laid in place on the undersides of the frame.

Mallet Underframe2

There are two places on the 2-6-6-2 frame and two places on the 2-4-4-2 frame where the end of the underframe is not secured by a cross piece.  See the photo before this one for visual look at the problem.  These are white metal castings.  Those ears without cross pieces are weak.  A small brass strip will be superglued to these pieces across the bottom of the engine strengthen these parts and to keep them in alignment.  I also need to fabricate the piece that connects the front and rear driver blocks and provides a hinge on one end so my frame can articulate.  Finally, holes will need to be drilled and tapped for screws that will secure the underframe to the frame in at least two places.  The steps discussed in this paragraph will be the next steps in frame modifications.

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