I am about to begin my first O Scale building project, and I have a question for all of you rivet counters out there. Is it true that O scale and 1/4" scale are really the same, or are they just “close enough”? In researching scratchbuilding supplies I see a lot of dealer refrences that indiciate the two scales are interchangeable. I do not own an O scale rule, but I do have an architect’s rule that has graduations for 1/4"= 1ft. Is this rule going to work for me?
As long as I can remember O Scale 2 rail was 1/4" to the foot.HO can be 3.5mm to the foot.
That will work, because, yes, O scale is 1/4" to the foot.
Bear in mind that commercially-available track (in O scale two-rail), however, is NOT accurate to that standard; it is about 5 feet between the rails instead of 4’ 8 1/2"–but everything else in the 1/4" world is correct.
The quick answer is yes, 1/4" to the foot, or 1:48 is the O Scale standard. Though through history there have been many variations in different times and places.
Yes, American O scale is the same as 1/4 inch scale with the ratio of 1:48, however, in the UK the O scale standard is 7mm to the foot (1:43.5) which is exactly twice the size of HO. The architects 1/4 scale works for American O scale and frankly I find it much easier to read than a dedicated model railroad scale rule, however, you still need a scale ruler for measuring plans that are drawn in HO (you can use the 3/16 scale for S scale).
So-called “American O Scale” is 1:48, or 1/4" = 1’. A standard architect’s scale is perfect for making scale drawings. However, the track gauge of 1 1/4" is actually 5 scale feet (which is only accurate if you are modeling railroads in the South, pre Civil War.)
As Francisco stated, “English O Scale” is 1:43.5, or 7mm = 1’ (which is why Half-O, aka HO, is 3,5mm = 1’.) Why the mixing of two rather incompatible systems of measurement came about I’m not even going to try to guess. At least the track gauge, still 1 1/4", is closer to right.
Then there was (and still may be) “Q Scale,” 17/64" = 1’ or approximately 1:45.2. This was an attempt by some American modelers to reconcile the scale with the 1 1/4" track gauge common to all of the above.
Another school of thought kept the 1:48 scale which was easiest to use, but reduced the track gauge to 1 3/8"…
Fun, isn’t it.
The upshot of the whole thing is that the majority of Americans in O gauge use 1/4" = 1’ and run on 1 1/4" gauge track.
Chuck (modeling Central Japan in September, 1964 - in pure metric, 1:80 scale)
If your architect’s rule, like an engineer’s rule, has a 40th’s graduation then 10/40ths is going to be equal to one foot and 1/40th is going to be equal to 1.2 inches which is ABOUT 30.5mm.
A conventional 1/16ths or 1/32 inch rule gives you graduations equal to 3 inches (1/16) or 1.5 inches (1/32); if, perchance, you have a rule with 1/64th inch graduations that gives you a scale of .75inches.
However, since most scale drawings are drawn to 3.5mm/HO Scale why don’t you fork out ten to fifteen dollars and buy yourself a scale rule which has multiple scales on it and will give you the ability to translate one scale to the other.
Being as anal retentive as anybody out there I am finding this discussion with all its anomalies quite fascinating; however in the interest of providing a simple response to the initial question can we agree on the following:
“In American O Scale everything is 1:48, (i.e., 1/4” = 1 foot) except that when modeling standard gauge railroading, the scale of commercial track components is 1:45.2 (i.e., 1 1/4 actual inches = 56 1/2 scale inches)"
OK, just to throw in another curve, certain adjustments are necessary when building O gauge Standard gauge equipment to a scale of !/4" to the foot because of the non-scale track gauge which we inherited from the early tinplate equipment. Trucks will not be exactly to scale width because of the gauge of the track. This does make a practical difference with standard gauge steam engines. The distance between the cylinders will have to be fudged to get everything to work properly. In most cases the cylinders are made wider than scale. AHM/Rivarossi used a clever approach, making the crossheads and piston rods off center. The problems involved in building to scale lead to the adoption of Q scale.
This isn’t a problem in ON3 as those standards correctly reflect a true 1/4" scale
JBB
Thanks for the clarification everyone. It’s trite but you do learn something everyday, as I had no idea that O-scale track is not in correct guage with the rest of the scale. I guess I could have prevented the senseless death of thousands of innocent electrons if I had been clearer in the beginning in stating that my project is a structure, not a locomotive or rolling stock. And I am actually modelling in On30.
What’s the distance between the rails for Proto:48…???
29.9mm. Further to this matter there are nine ratios that I know of that the users call “0” scale. Most model steam locomotives have the cylinders further out than they should be, usually because the wheels used are more than scale width and model curves require more movement. 1:48 on 1.25" gauge requires even more cylinder spacing.
How is 1:80 “purely metric”, maybe 12.5mm to 1 metre?
Mark in Melbourne
Purely metric in that all of the dimensions, model and prototype, are metric - no confusion about how many scale millimeters in a full-scale inch. Just divide any dimension by 80, mark and cut.
Chuck (modeling Central Japan in September, 1964)