I haven’t written in the blog for a while. It’s summer, and there is so much more to do around the house that sitting down and writing gets pushed way down on the to-do list.
After I maneuvered some free time, I wanted to write this post because, after reading for a few minutes on Facebook, there have been many asking the same questions, and I wanted to write about how I solved this problem and why I no longer deal with that problem anymore.
The question I have been hearing over and over again is: “In 3D printing, can I take an HO scale STL and print it in N scale? If I can, how do I do that?”
To start off, the answer is YES. You can take just about any 3D print and reduce it down to the scale you want. You need to do a little math first and then realize that when you start to reduce STL files, you might or most likely will lose some detailing in the model that you are reducing. Ridges on the sides of buildings may become smooth, roofs might lose the shingle look, walls may be thinner, and some smaller details may not print at all. So when you reduce models, even from HO to N scale, don’t be disappointed about losing some detailing because it will happen.
Okay, so what about math?
Here we go.
HO scale is 1:87, or 1 inch in HO is equal to 87 inches or 7.25 feet in real life.
N scale is 1:160, or 1 inch in N scale is 160 inches or 13.33 feet in real life.
So as you can see, N scale is just about half the size of HO. N scale 13.33 feet, HO 7.25 feet. Not an exact half, but pretty close.
So when it comes to taking HO STLs to print in N scale STL, you will need to reduce the print in your slicer program by 0.525%. Be careful though. Not all HO models will transfer over to the right size you want. Even if you do the math right, sometimes they will look too big or too small. I will talk about how to fix that in a minute.
So, most STLs are in millimeters; you will find some in inches. So how do you calculate inches into millimeters?
Here is a simple equation.
Multiply inches exactly by 25.4 to get your millimeters. SAMPLE:
5″ x 25.4 = 127mm. mm = inches x 25.4.
I hope that clears up math problems. Now back to scale printing.
Just because on your slicer you reduced your print by .545″ or 55% doesn’t mean, when it’s done printing, it’s going to look proportionally correct on your layout. Why? 1. You don’t know if the original model was correctly calculated at 1:87 scale. It could have been at 1:100 or 1:70 or anywhere in between. 2. Depending on what you’re printing, it may just look “out of place” with the rest of your scenery. 3. Other scenery or objects on your layout may be off scale a little bit.
All these factors, and I am sure there may be more, have an influence on how much % you reduce the STL to N scale.
How do you fix this problem?
You first measure the total area on your layout you want filled. Not just the buildings but the total space you are going to use. Then you want to get your three axes of your buildings or main features measured: length, width, height/depth.
Now that you have a good idea of the proper size you want, you can take the HO STL, put it in the slicer such as Cura, and reduce the three axes. (3D printer axes are X length, Y width, Z height.)
Now that you’re ready to print, at this point, I would only print, if I can, the shell of the building (just the walls) if you have a model that is in multiple parts, or just take the main part or focal area. After it’s done printing, take it over to your layout and put it in place. This will just help you visualize if it’s proportional or not. If you think it’s too big or too small, you can go back to your slicer and adjust your axes up or down. Once changes are made, do that step again and recheck.
The reason you want to do this is so you don’t waste filament printing everything and then find out it’s too small or too big. This method will save you frustration from what I just mentioned, and lastly, you will save time printing. If you printed your model and it took 6 hours to print, you get it to your layout, and you find it just looks too big or small; now you have to resize and reprint everything all over again. Now you have got 12+ hours in this model, wasted filament on a print you can’t use, and the frustration of having to do it all over again.
So as you can see, reducing an HO STL to N scale is not always as simple as reducing it by 55%.
I mentioned at the beginning that I would tell you how I have avoided all of this.
Yes, you can just print only N scale stuff. But even that does not always work. Again, somebody else’s design might not have been to scale, and again could end up bigger or smaller than what you wanted.
My answer to this problem was to design my own. It is amazing what you can do with a little instruction and practice. I downloaded a free 3D design CAD from Tinkercad, used their free tutorials, and started learning to design simple boxes, boxes with holes, etc. Within a matter of 3 nights, 3 hours each night, or a total of 9 hours, I was designing my first N scale house. From that basic start, I have now designed more complete designs, like a baby grand piano Christmas ornament for my niece.
If you would have asked me last year, I would not have believed that I could have designed almost every single building on my layout. I even have a small amusement park that was all my design, and best of all, the rides are working rides driven by small motors.
How you reduce HO 3D STLs to N scale is pretty easy on paper, but in my experience, the end results usually require some small adjustments to enlarge or further reduce the print to make it look right on the layout.
Always start your reducing at 55% and work from there. It’s a good starting point. The final results on how it looks are all in your eye. Just don’t be too rigid about being exactly to scale. The goal is to make it look proportionally pleasing to the eye. I have yet to have anyone look at my layout and measure anything to see if it was “to scale.”
Build and have fun doing it. That’s what a hobby is really all about anyway. Besides, the only one that has to be happy with it is YOU!