SP 10250-51-52 (Part 3) - Track Cleaning Pad

In SP 10250-51-52 (Part 1) - Diner-Lounge 1949 Conversion blog post, I started to modify the diner unit to the 1949 San Joaquin Daylight configuration as a Diner-Lounge and also start to retrofit the Kitchen unit to the pre-1951 look.  This was followed shortly by a following post SP 10250-51-52 (Part 2) - Diner-Lounge 1949 Conversion where I go into depth on building a new lounge section for the diner.

Kitchen, SP 10260, refitted with a slider pad

In Part 3, we are returning to the Kitchen Unit, SP 10251.  I'm also including some photos of other MTH Kitchen units in-service at LMRC in this post.  The kitchen units have a very large water tank under the rear third of the car to supply the kitchen and pantries.  The tank hangs pretty low over the track and is a good candidate to modify and convert to hide a Masonite track cleaning pad without detracting from the look of the passenger train.

The water tank under the stock MTH Kitchen Unit.

Removing the Tank

This is actually a pretty easy conversion.  First start by removing the water tank from the bottom of the floor of the car.  I covered this briefly in Part 1 in terms of removing the tank.  This is most easily done by removing the kitchen shell, followed by the interior, which will expose the two mounting studs in the floor.

Here's the Kitchen unit with the tank removed and a section of Masonite pad cut for a 40ft freight car.

The pad that I'll be using is cut from 1/8" Masonite panel.  It already has the leading and trailing edges chamfered to ride over any uneven sections of track work.  This pad was a bit too long for the space allowed under the car between the truck and other underframe equipment boxes.

The underframe of SP 10251 with the tank removed.

The only other major modification to the underframe structure that I made was to remove the wire "pipe" running between the frame members.  I had to cut one end of the wire with my Dremal cutoff disc so that I could remove it without damaging the underframe sills.

Modifying the Masonite Pad

The pads that I stared with were cut to fit between the trucks of a 40ft freight car.  The kitchen installation will require the pad to be shorted to match the length of the prototype car's water tank, which is 1.900".  I did this with a razor saw.  A quick pass to put a chamfer on the cut end was easily done with a file and my bench sander.  The pad is 1.135" wide.

Building the Pad Structure

I did some quick measurements of the floors ride hight and bottom of the underframe ride hight also.  This would form the basis of the calculations of figuring out the heights for the pad and guiding structure.

The various parts laid out before I started working on building the pad.

The first step in building the pad suspending structure is cutting the "Centerboard" which will ride between the frame members of the underframe.  A "Centerboard" is a movable keel on sailboats which slides within a box or trunk.  This pretty well describes the relationship between the box formed by the sills of the underframe and the new guide structure for the pad, which I will refer to as the centerboard.

"Centerboard Trunk" of the Kitchen Unit, prepared for the pad to be test fit.

I also want to plan for the possible replacement of the Masonite pad without completely building a new pad structure, so I made a top-plate for the pad from 0.020" styrene sheet, cut about 0.06" narrower than the pad is.  The pad was mounted to the top-plate with RTV Silicone, which should provide some flex to the joint, which ACC-type (super) glues will not.

I marked the centerline of the top plate  and marked offsets 0.06" off the centerline so I could see the marks as I mounted the 0.125" wide Centerboard.  The Centerboard was then glued using liquid styrene cement (I prefer Tamiya brand) to the centerline of the top-plate.

RTV Silicon, the Masonite pad, and  styrene "Top-Plate" both of which are scribed to provide some tooth for the cement.

The bottom of the top-plate is scribed with my carbide scribe tool to give some tooth for the RTV Silicon cement to hang on to.  A very small amount of cement is applied to the top of the pad and clamped to the top-plate until it dries.

The Centerboard is a piece of 0.125"x 0.250" strip styrene cut to be 1.850" long or about 0.040" shorter than the span of the hole between the cross frames of the underframe.  This will allow slight forward and backward freedom of the pad while remaining trapped between the underframe members and the skirting of the car.

I was planning to suspend the pad and structure from the holes in the cross beams of the underframe using 6lb. test fishing line.  To do this I made some small brackets from 0.125"x 0.250" styrene strip.  I cut them square at one end and diagonally on the other between 0.300" and 0.170" with the tapered side towards the middle of the pad.  Later I will drill a hole for the fishing line rigging.

During test fitting at this point, I didn't like how exposed the pad was and being able to see the top of it.  I plan to paint the top and sides flat black, but I want to do better simulating the side of the water tank.

I add a couple of 0.188"x 0.020" styrene strips down the side of the top-plate which will ride inside the skirts of the car.

Finished track slider cleaning pad and structure.

The whole pad and structure assembly is painted with flat black spray paint.  I made sure to keep the cleaning surface down on the paint bench to keep it as clean as possible.

Pad fitted to the bottom of one of the Kitchen Units, ready for service.

At this point I elected not to rig the fishing line as I wanted to see how the pads preformed.  I also did not add any weights to the top of the pads, allowing them to ride with only the weight of the Masonite pad and the few bits of styrene on top.

Evaluating the Results

The pad not visible under SP 10260 in this lighting.

Two pads were completed for use at the La Mesa Model Railroad Club January 2017 TT/TO 1950s session.

SP 10260 with completed pad sticking out somewhat into the layout lighting in this view.

 I am still pondering about narrowing the width of these pads slightly, to make them less obvious.  In some staged photos the existing pads are pretty well camouflaged.  After the test runs it seems that the dirt marks from the traversing the curves shows within about 0.05" of the max width of the pads, so not much could be gained from narrowing them.  Making a pad too narrow will allow it to fall between the rails and derail the car as it exits the curve.

The pad from one of the kitchen units after only two laps!

The pads did their job as can be seen from this photo above.  I mounted a pad on each of the two MTH Triple Unit Diner sets worked out very well.  The pads caused no issues during testing or over the weekend event.  I took these photos after each car traveled two laps with fresh pads.

With the black carboning brushed off, it's ready for the next trip

A quick scrub with a wire brush and they're good to go again!

In Closing

The cleaning pad is barely visible in this photo in the shadows under the Kitchen Unit.

Being able to remove the pads from the car quickly and easily is one vote for not rigging the fishing lines to keep it captive under the car.  I will have to see how these preform in the next few months.  Perhaps rigging it with the fishing line will not be too much trouble.  Time will tell.

In the SP 10250-51-52 (Part 4) blog post, I will go into more depth with completing the Lounge-Diner interior module for the SP 10250.

Jason Hill

Related Links:
SP 10250-51-52 (Part 1) - Kitchen & Diner-Lounge 1949 Configuration

SP 10250-51-52 (Part 2) - Diner-Lounge 1949 Configuration

MTH Daylight Passenger Cars - Review & Mods

Index of SP Lightweight Passenger Cars Models