Easily Resizing models for 3D printing

[rue_d_etropal]

One of the best features of 3d print design is being able to produce models in virtually any scale, dependent on size and cost. So when someone comes up with a feeble excuse as to why they can't do a model in a bigger scale, I am dumbfounded. I won't name them, but I have seen their models on this forum.

 

It is not only unprofessional, but it can put off some from looking at 3D printed models. All it takes is a message and I will see if it is technically possible. In most cases I can do it. One person saying they can't do it, just opens the door for someone else to do it. When I get a negative reply to a request to resize, I will just go and see if I can do it myself.

 

Now there has been some discussion about resizing, and it is easy using the software I use. I have models in over 12 scales, and when someone asks I try to see if I can do a different scale for a particular model. Going smaller can be difficult, and you will lose detail. Going bigger is always possible, but in some cases I may make adjustments to wall thickness, or even use it as an excuse to add even more detail. Obviously there are size limits, and WSF can be done bigger than FUD, or that was the case, as some of my WW1 models hit that barrier.

 

[rue_d_etropal]

I think I now understand why the models in this case can not be resized upwards easily without a lot of work. The original reason given, was a bit vague. I wasn't after a perfect model, but something to the scale I wanted, and I was happy to then finish it to my standard.

 One thing I try to do now is start a design in a bigger scale. Then when resizing to smaller scales, some detail might be lost, but it still looks ok, and I am also covering  the bigger scales. It is something I would recommend to anyone starting out. I was lucky as first scale I did was1/35, but I now tend to start in different scales for different types of models. It is important to use software that can do the job easily. Everyone who gets involved in 3d printing knows that someone will always ask for a different scale, so build that into the business plan.

[Knuckles]

I figured out super simple rescale equasions that make life easy.

 

Say you model mainly in 4mm to 1 foot as I do and you want to go up to 7mm. Simply take any dimension on your model, the longest would probably be the best. Say it is 105mms for the sake of arguing.

 

Simply divide that by 4 and times the answer by 7, easy. Think it is called refraction.

 

Say you want to drop the 105 to British N gauge. 105 x the 4mm scale (which is 76.2) and divide that answer by your smaller scale (British N = 148).

 

It really is that easy. I tried it on a calculator and got consistent answers so then tried it on the 3D models and it worked. You may have to thicken walls or pull details or whatever but either way, this is how my first rescaled 4mm loco shell became N.

 

Should help a few of you.

[rue_d_etropal]

As I said, I start all my standard gauge designs in O scale(although I don't think it practical to actually offer them in that scale).

As many of the published drawings are in 4mm scale it is simple to resize drawings by 1.75.My scanner can only resize in exact amounts, no decimals, often resulting in a combination of resizing. It works out in the end. As some drawings are not to traditional scale, I have to juggle them around a bit.

My first designs are actually HO, so simple resize the 3D design by half. I then take it back to 4mm scale, by 1.143 which is as close as you are going to get, then 0.75 to take it down to 3mm/ft. All these are down without altering anything in original design, but if anything shows up, I will modify it.  I have a resize value for N scale, but always have to go through design, line by line to up wall thickness .

[Knuckles]

Would be good to get a rescale table but only saw one once. For physical paper scale drawings my method has been to find the wheel diameters, wheelbases and rail top to buffer centre figures and use those measurements as datums for scaling on paper. I usually waste 5-20 sheets getting it right as often the tweaks are really small but eventually it works.

Edited June 11, 2017 by Knuckles

[raymw]

I think it is best, if you have cad, to draw full size, then scale down if necessary for your working drawings in various scales, provided it is true scale that you want. You will have to tweak the detail, and allow for practicalities involving the strength of the modelling materials. I produced various scale tables, but eventually wrote a scale conversion program, which runs fine on a tablet pc under most versions of windows, on in a window with your cad/image software, whatever.  http://yertiz.com/cnc/scaler5.htm I found it quicker to use than looking down a list of values, and easy to make fine adjustments.

Ignore the windows frightener when you install. (and my typo wrt  'dimenensions')

 

hth

[rue_d_etropal]

I have a few problems getting a full sized carriage into my workroom to measure it! 

I find that using the bigger scale drawing, plus a few known dimensions results in something close enough. To get that last few points of correctness, you have to work far too hard, and more often than not, it gets undone by the 3D printing. I found this when I was first doing my inset track system. It was one step forward two steps back on occasions, until I realised I needed to compromise. I use different starting scales for other items. Knowing the best start point is best way to start anything, and also finish it. 

I aim to get things done, even if that means making small, and mostly un-noticable compromises. That way I finish something, and don't keep going round in circles, as some do. I learnt that working in IT. I know where my line is, and I am also aware of where there might be problems, so keep an eye out for them. As long as everything fits together and looks OK, then I am happy. That is easier to do with a complete design, as opposed to a kit, and I have encountered a few badly designed kits over the years. Only when you realise there is no such thing as perfection, that you actually succeed in what you are doing, or trying to do.

[raymw]

Working from full size/large scale and going down, errors reduce. going t'other way, errors increase. Still, whatever works for you. Hope you're not measuring models to prepare your drawings.

[rue_d_etropal]

Unless I have full sized drawings , or every single measurement, then I will always have to resize drawings upwards(and that will introduce some small errors). apart from some of my narrow gauge desgns, I only then resize downwards in the CAD design, thus reducing any errors. I also keep designs relatively simple, not putting every single detail on, as I know they won't print tat well, and any average modeller should be able to add those details if the want to.

I have found that those who don't seek absolute perfection tend to be happier, and those who accept some compromises(as most OO modellers do), tend to get where they want, and tend not to grumble as much.

3D printing was once described to me as an aid to scratchbuilding. That is how I tend to see it now, not a quick way to a r2r model,and not a kit, but something inbetween. As time goes on, 3D printing is getting better, so all designs can be improved to match that, if necessary.