I believe Albert Einstein once said "The more I learn, the more I realize I don't know." That largely sums up the history of the drawings. While I wanted to believe that my early efforts were accurate, I did not know (or even look up) most locomotive dimensions—nor did I know how inaccurate my renditions were as a result. I was only 14 years old when I started the 1:55 series in 2000, but with the relative simplicity of the drawings, the series quickly evolved to encompass almost every major locomotive model within about five years. Back in the day, I was working in a world of few reference books and a much smaller Internet, and the result was my broadest (and probably most well-known) drawing series... of not-so-accurate drawings.
Over the years, I've learned a lot and upped my standards, now striving for absolute accuracy in the latest 1:18 drawings. I have several books devoted solely to locomotive dimensions, along with tens of thousands of reference files obtained from the Internet. But the more dimensions I measure and the more resources I look up, the more sources of error I find—and so I still end up correcting my more recent drawings after their initial completion (albeit usually obsessively minor corrections). I doubt I'll ever redraw in 1:18 all the locomotive types I drew in 1:55—because I know there are some that I probably could never draw accurately.
Moral of the story: My old drawings are definitely not accurate, but my newer (1:18) drawings are as accurate as the dimensions I get from diagrams, photos and real-world measurements. And if ever you come across any inaccuracies in my 1:18 drawings, please let me know—so I can correct them!
As for the scale (1:55, 1:36 and so on)—well, it has little meaning on the screen beyond establishing the relative size of the drawings. The scale is based on a print resolution of 72 PPI, although the drawings are 96 PPI by default. This to maintain consistency with other drawings on the web, which are often scaled based on a 72 PPI resolution. In terms of the actual size of the drawings, the 1:36 and 1:18 series are drawn at 2 and 4 pixels per scale inch respectively, so at a given printing resolution, they are exactly 1:(PPI/2) and 1:(PPI/4) respectively.
Here's how the accuracy of the drawings has evolved over the years, along with comparisons of an EMD SD40-2 in each scale (in black) with my latest version in 1:18 (in red):
Up to now, the 1:55 series has the longest lifespan and therefore the widest variation in accuracy, which can be divided in three phases.
Drawings from 2000 to 2004 are not accurate, and in fact their inaccuracies (up to 14 scale inches in some major dimensions) spurred me to redraw many of them only a few years later. In particular, length dimensions are hit-or-miss, pilot-to-coupler distances tend to be too short, and walkways tend to be low, making the hoods too tall and the trucks "squashed". The worst offenders were late-model EMD SD units, which initially had underframes not much higher than a GP9. Some of these drawings may actually be somewhat accurate, but more by chance than by precise measurement. These drawings have white backgrounds.
Above: A 1:55 drawing from 2001 vs. a 1:18 drawing from 2014. Assuming the 1:18 version is more accurate (a safe assumption, I believe) I had a lot of work yet to do!
In 2005-2006, I redrew many 1:55 drawings to be more accurate. They follow major dimensions more closely and are generally accurate to within a few scale inches in other measurements. Although not perfect, they corrected many flaws found in the older drawings. These drawings have cyan backgrounds.
Above: A comparison with a 1:55 drawing from 2005 (with a few railroad variations between the scales since I don't have a CNW-style SD40-2 from 2005). Many dimensions were corrected when I started redrawing older 1:55 drawings in 2005.
In 2007, I started the third and last phase of the 1:55 series, which represents the shortest of the three 1:55 eras. These drawings observe dimensions more closely and also received substantial upgrades to smaller details. Their accuracy is generally to within one to three scale inches. These drawings have sky blue backgrounds, which were adopted for all later scales as well.
Above: A comparison with a 1:55 drawing from 2007. Only a few dimensions were changed from 2005, but more detail was added.
Why haven't I corrected all the old (and not-so-old) 1:55 drawings to be perfectly accurate? Well, given the variety of locomotives and rolling stock (some quite rare or obscure) I don't think I could ever actually make all of them 100% accurate—and even if I could, I figure my time is better spent making new, larger and more accurate drawings from scratch.
The primary goal of the 1:36 series was to include more detail than what the 1:55 series allowed, while carrying over the goal of increased accuracy started with the last 1:55 drawings. These drawings follow almost all major dimensions exactly and are generally accurate to within one scale inch in minor dimensions. I made no more 1:55 drawings after the start of the 1:36 series. Since they are drawn at 2 pixels per scale inch, the finest increment is 1/2 inch.
Above: A comparison between the 1:36 and 1:18 drawings. In the case of the SD40-2 (as with many EMD hood units) solid dimensional information was easy to come by when I drew the 1:36 version in 2008, so there were almost no dimensional corrections needed between the 1:36 and 1:18 series—aside from the hood height.
There are two noteworthy discrepancies that affect a large number of drawings. The first affects the majority EMD hood units. I used photos to measure the hood height on the first unit I drew in 2008 (an EMD RM-1, or GP38 rebuild) and my measurements were off. As a result, all EMD hood units derived from that first drawing have a hood that is 1 to 1.5 scale inches too short above the walkway (depending on dimension rounding). However, I only discovered this after completing many drawings, so I decided to live with it.
The second discrepancy affects all 1:36 ALCO and MLW hood units. The hood and cab are both 2.0 scale inches too tall above the walkway. This was the result of errors or inconsistencies between ALCO specifications for the frame height vs. railroad specifications for the cab roof height for the Century series. I only discovered this error when measuring a preserved M-636 in 2013, long after I had stopped work on the 1:36 series.
In November 2012 I started the 1:18 series, which is double the size of the 1:36 series (4 pixels per scale inch), making the finest increment 1/4 inch. While I aim for perfect accuracy in every dimension and detail, I can't make such a strong claim; nonetheless, the 1:18 drawings follow all major dimensions exactly and are accurate to within a fraction of a scale inch in minor dimensions. Any inaccuracies are the result of uncertainties or variations in the measurements I've made—not the result of "eyeballing" the dimensions.
As before, I now draw in the new scale exclusively and have made no more 1:36 or 1:55 drawings since the start of the 1:18 series. More information about the making of the 1:18 series can be found in the Development of 1:18 series and Creating the Drawings pages.
Above: The final 1:18 version of the SD40-2 used in the comparisons above with the other scales.
To a greater extent than with previous drawings, I measure everything. I've drawn many common components—trucks, couplers, horns, air dryers and even air brake control valves—based directly on patent or manufacturer engineering diagrams. When measuring from photos, I take repeated measurements until I get results within 1/2", or preferably less. Occasionally I've reached a stumbling block where one component (such as an ATS shoe or a unique antenna set-up) slows me down—or even prevents me from finishing a series of drawings. If I can't find sufficient reference material to make an accurate drawing (at a minimum, the major dimensions and a few good high-resolution photos) it doesn't get drawn in 1:18.
Diagrams and real-world measurements have benefited many models in the 1:18 series. The 1:18 GP30 drawings—among my earliest 1:18 drawings—were the first locomotive drawings on the site that I derived almost entirely from EMD mechanical drawings, including cutaway diagrams of the trucks, underframe, cab and most of the hood (supplemented with photos). In 2013, I also started taking detailed real-world measurements of preserved locomotives; the 1:18 MLW M-636 drawings were the first drawings to benefit from such measurements. When I don't have specifications or measurements to use, I derive measurements photos—or from related models, such as extrapolating a few hood dimensions from SD45 diagrams for drawing the GP40.
Below is an image illustrating some of the measurements I took of a preserved M-636 for use in the 1:18 MLW M-liner drawings. For more measurements, see the Locomotive Dimensions page.