Friday, June 25, 2021

Running Board Milling

When describing the build of a freight car with a wood running board I may state I milled the running board thinner or to prototype thickness.  I have been asked why and how I do that.  Why?  A plastic or resin kit running board that is too thick, normally 4 scale inches, does not look right as it is a couple of inches thicker than the prototype.  A plastic running board may already be painted in the same color as the car body and a replacement if used may not match in color.  How I accomplish the milling task I will describe after a review of running board design standards.

The prototype freight car has one longitudinal running board that safety appliances from the 1943 Car Builders Cyclopedia tell us shall not be less than eighteen (18), preferably 20 inches in width, shall extend the full length of car at the center of roof and securely fastened to the car by saddle blocks  (roof saddles) which hold the running board at a level position.  The ends of the running board shall extend beyond the roof to not less than six (6) and not more than ten (10) inches from a vertical plane measured from the inside face of the car’s coupler.

On outside-metal roof cars there shall be two latitudinal extensions not less than twenty-four (24) inches in width from longitudinal running board to ladder locations except on refrigerator cars.

The common wood construction is of three parallel pieces separated sufficiently to allow snow and water to drain through.  The length and width of running boards may be made up of a number of pieces securely fastened to saddle blocks.  The safety standards do not give the thickness dimension for the wood pieces, however, the common size was one-one half (1 1/2) inches to two (2) inches thick.

Various wood running boards
Photo found on internet
(click or tap to enlarge)

Based on the common thickness dimension, I would like a wood running board to be between the two dimensions of 1 1/2 and 2 inches so I chose 1 3/4 inches or .020” in HO scale.  And, I chose .020” as that is an available Evergreen strip styrene size to make a jig to hold a running board during the milling process. 

The jig was made with .040” styrene for the base, mine is 1 1/4” x 7”, on which a running board could be placed and a pencil used to trace around it.  I used Evergreen .020” strip styrene to form a frame around the tracing to hold the running board when inserted.  I found the .040” styrene base to be an insufficient thickness when milling the running board so I glued the existing jig onto .105” styrene to create a thick sturdy base.

Styrene jig

Since I felt I could not justify the price of a mill, I use a Dremel tool mounted in a old style Dremel drill press stand.  The Dremel tool has a Dremel No. 199 cutter bit mounted in the chuck.  I originally found a mill setup described in the April 1982 Railroad Model Craftsman article “5 boxcar improvements” by Dennis Storzek.  I have attached a drill press stand vise into which I added a wood piece cut from a 2 x 4 to serve as my drill press stand table onto which the jig can ride during milling.  The cutter bit is set to just clear the .020” frame on the jig holding the inserted running board.

Milling setup

To start the running board milling process, I cut off the mounting pins on the back side of the running board and insert the running board into the jig with the back side up.

Running board inserted into jig of milling.

I hold the running board in the jig with two hands (not with one in photo as other holding camera), one on each side of the cutter, and push the jig under the cutter removing about a 1/3 to 1/2 of the cutter width from the running board.

Holding running board during milling.

The milling begins at one end of the running board and is repeated until the entire running board is finished.  You want to pace yourself removing the material as if done too fast you can heat up deforming or melting the running board.  I know from experience.

Running board milling started.

Running board milling complete

Once the running board milling is finished it does not have a real smooth surface so I use a single edge razor blade (SERB) as a scraper to scrape the back side of the running board to get a smooth back side.  You must hold down the running board while doing the scraping and do it carefully.  If not the SERB can catch the running board and break it due to its thinned thickness.  You could sand the back side to get the same result.

Single edged razor blade used as scraper

Running board scraped smooth.

My milling method does not always yield the exact target result.  Even after milling and scraping the running board may end up at around .025” thickness which is acceptable to me as that is a HO scale thickness of 2 1/8 inches.  

Once thinned, the running board is ready for mounting on the freight car.  The running board can be installed with various glue types: CA, Barge Cement (a contact cement) and Formula 560 Canopy glue. 

Running board milled as casting was too thick.

Running board milled for color match.

Running board milled for prototype look
and color match.

As myself I believe you too will fine a prototype thick running board makes for a better looking freight car.  And, the thin running board will provide you the satisfaction of having built a better model.

Thank You for taking time to read my blog.  You can share a comment in the section below if you choose to do so.  Please sign your comment with your name if you choose to leave one.  Please share the blog link with other model railroaders.

Lester Breuer



  1. This is a very interesting technique to add a lot of realism. Running boards are a very visible part of models and it pays to spend some time and effort to make them more realistic looking. I've noticed some of the very thick running boards on the tops of model grain cars and they really spoil the effect, more than most other details.

    1. Steve Thank You for your comment. Appreciated.