Scaling from a file drawn full size?

[bubbles2]

I’m trying to scale, or rather my son is for me (he’s the one with the 3d printer) from a file drawn full size down to 4mm, or 1/76 scale so it’s probably a silly question but do I reduce the scale to 1. 76? 

[ikcdab]

You divide all dimensions by 76.

Or if you are scaling it, scale it 1/76 or 1.31%

[billbedford]

... for the more mathematically challenged, draw your model at 12 mm to the foot, that is 1 mm to 1 inch. Then reduce your model to one-third or 33.333%.

[njee20]

Just now, billbedford said:

... for the more mathematically challenged, draw your model at 12 mm to the foot, that is 1 mm to 1 inch. Then reduce your model to one-third or 33.333%.

But then you have to calculate every dimension as you go. Surely that’s far harder?!

[billbedford]

Harder than what exactly?

 

The "calculation" is simple mental arithmetic, Multiply the feet by 12 and add the inches. 

 

Though I realise this may come easier to those of us schooled before decimalisation. 

[Jeremy Cumberland]

 

54 minutes ago, bubbles2 said:

I’m trying to scale, or rather my son is for me (he’s the one with the 3d printer) from a file drawn full size down to 4mm, or 1/76 scale so it’s probably a silly question but do I reduce the scale to 1. 76? 

Drawing files are usually in arbitrary "drawing units", which then need to be converted into a real-life measurement such as millimetres or inches for printing (either on paper or 3D).

 

16 minutes ago, njee20 said:

But then you have to calculate every dimension as you go. Surely that’s far harder?!

I generally create and save drawings/models using 1 drawing unit per inch for imperial-dimensioned originals and 1 drawing unit per millimeter for metric-dimensioned originals. Since my railway modelling activities are mostly of pre-1960s British prototypes, I usually work with imperial dimensions.

 

I always print in 1 mm per drawing unit, and therefore need to scale the orignal drawing to create a printing file, view or layout. To convert from 1 drawing unit per prototype inch to print at a scale of 4 mm/ft, this means scaling the drawing by 1:3 or 0.3333 to create the printing file or view. It is only if the drawing file was created in 1 drawing unit per prototype millimetre that I would scale the dtawing file by 1:76 or 0.0132.

[njee20]

1 hour ago, billbedford said:

Harder than what exactly?

 

The "calculation" is simple mental arithmetic, Multiply the feet by 12 and add the inches. 

 

Though I realise this may come easier to those of us schooled before decimalisation. 

I have no issues whatsoever with maths (gold star for the patronising tone 🙄), but I don't understand how taking the real dimensions of an object, and converting everything individually is easier than designing 'full size' and then converting once. It'll depend what you're using as a source though of course and what measurements are provided, and whether you 'think' in inches.

[Mike Harvey]

I am another one who draws in 1:1 and then scales afterwards when converting to an .stl file.

[Jeremy Cumberland]

If your reference drawing or description is in feet, inches and fractions of an inch, you will have to convert something. It doesn't matter whether you convert to full size inches, so that 3' 3¾" is 39.75, or whether you convert to full size millimetres, so 3' 3¾" is 1009.65, or whether you convert to scale millimeters, so 3' 3¾" is 13.25 in 4 mm scale. At different times I might use any of these, depending on what it is I am doing (except that I don't work in 4 mm scale, so I might convert 3' 3¾" to 49.6875 or 73.62 (and if you're bored, you might work out what scales I typically work in). What is important is that you are consistent throughout the drawing or model, and that you don't forget what your drawing units are when you come back to the same file a year or two later.

Edited November 19, 2023 by Jeremy Cumberland

[ikcdab]

none of that relates to the original question.

The OP has a file at full size.

every graphics package I have ever seen allows drawings to be rescaled.

all he has to do is to rescale by 1.31%

Job done.

[stevel]

3 hours ago, bubbles2 said:

I’m trying to scale, or rather my son is for me (he’s the one with the 3d printer) from a file drawn full size down to 4mm, or 1/76 scale so it’s probably a silly question but do I reduce the scale to 1. 76? 

what software are yo using to draw your model in.

[Jeremy Cumberland]

One of the points I was trying to make is that "full size" makes no sense in respect of an electronic CAD model. I dare say that our American friends routinely use 1 drawing unit = 1 inch, and I too generally do this when converting from imperial dimensions for pre-1960s railway prototypes. For everything in my professional work, I use 1 drawing unit = 1 mm, and this extends up to lengths of up to several hundred metres, but perhaps land surveyors and map makers routinely use 1 drawing unit = 1 metre.

 

What does 1 drawing unit represent in the OP's file? With railway prototypes often being dimensioned in feet and inches, I don't think it can be automatically assumed that 1 drawing unit = 1 mm.

[ikcdab]

19 minutes ago, Jeremy Cumberland said:

One of the points I was trying to make is that "full size" makes no sense in respect of an electronic CAD model. I dare say that our American friends routinely use 1 drawing unit = 1 inch, and I too generally do this when converting from imperial dimensions for pre-1960s railway prototypes. For everything in my professional work, I use 1 drawing unit = 1 mm, and this extends up to lengths of up to several hundred metres, but perhaps land surveyors and map makers routinely use 1 drawing unit = 1 metre.

 

What does 1 drawing unit represent in the OP's file? With railway prototypes often being dimensioned in feet and inches, I don't think it can be automatically assumed that 1 drawing unit = 1 mm.

That isnt as i understand it. The OP says he has a "file", not a drawing. I use Fusion360 and when i create objects at their full size - ie when i draw something in Fusion360, i specify its size to be its real, full size. 

My understanding is that the OP has now imported this into something like Chitubox so that he can print it at 4mm scale. To do that, in chitubox (or any other software) it needs to be scaled at 1.31%.

Ian

[bubbles2]

I’m using a file from  Jonathan Duffett on Thingiverse https://www.thingiverse.com/ironmink/designs

I’m sure I read somewhere he draws to full size so they need to be scaled down as required.

[billbedford]

1 hour ago, njee20 said:

but I don't understand how taking the real dimensions of an object, and converting everything individually is easier than designing 'full size' and then converting once.

 

It's because I'm designing models. I want them to work as models and know how they will be made and assembled before I start on the cosmetic bits. I find it much easier to work on drawings with a simple relationship to the dimensions specific to the manufacturing method. 

[Pete the Elaner]

35 minutes ago, billbedford said:

 

It's because I'm designing models. I want them to work as models and know how they will be made and assembled before I start on the cosmetic bits. I find it much easier to work on drawings with a simple relationship to the dimensions specific to the manufacturing method. 

 

Re-sizing is quite a simple function with Sketchup but I cannot import a .stl file with the free version. 

[meld]

1 hour ago, bubbles2 said:

I’m using a file from  Jonathan Duffett on Thingiverse https://www.thingiverse.com/ironmink/designs

I’m sure I read somewhere he draws to full size so they need to be scaled down as required.

He does.

You do.

1.31% for 4mm or 00 or 1/76 or 1/76.2.

 

HTH.

 

Meld

[Crosland]

How thin will the thinnest parts be when scaled? Will it even print?

[amandalee]

Ive found some parts at 1:76 are too thin for my printer's (filament) I have done my own chassis on a few to be a little more robust. Cutting the model just below the body base allow's the chassis to then attach to that. Very well designed models but until my resin printer arrives later this week i'm unable to try a full print to see how that goes.

 

Amanda

bygone-wagons.com

[figworthy]

7 hours ago, Crosland said:

How thin will the thinnest parts be when scaled? Will it even print?

 

Very thin.

 

I've tried printing a couple of his models (scaled to 4mm).  The bodies seem to come out OK, but the W irons and tie rods don't work well for me.

 

0.25mm nozzle. 0.15mm layer which is as fine as I can go.

 

A decent etched chassis kit with a printed body would work well I think.

 

Adrian

[Carlislecitadel2]

Hi,

I have printed quite a few of Jonnys files on my Ender 3 S1 in 4mm using PLA+ or more usually Esun ePLA. I usually slice with Cura at 0.08mm height, more recently at 0.04mm, and a print speed of 30mms on a 0.4mm nozzle. The Cura slicer does not always pick up the thin edges, though it does most of the time. However I have sliced the awkward ones, like the pig irons, with Prusa and it works everyt time. I have just dropped won to a 0.2mm nozzle and the results look stunning. The problem is not in Jonny's designs, its in the slicer. Set up your slicer right and they will print. If you are used to Creality or Cura, the switch to Prusa is a little daunting at first as the user interface is quite different, but you can soon gett the hang of it. That said I'm still struggling to set my rafts up as nicely in Prusa as I had them in Cura.

[DCB]

1 to 1 ? There is  a 1 to 1 drawing of a building in Cirencester, It's huge and is mounted in front of the building being  renovated.  Its usually easier to do a scaled drawing say 1/76 or 1 /12th scale.     (sensible people model in 1 :100 scale to avoid awkward calculations)

[Mike Harvey]

Those of us drawing  in 1:1 scale will have in mind the practicality of turning the model into a 3D printed version. So the size (or even the presence) of some details will be determined by what will be printable, as will the wall thickness of structures, etc.  And, certainly in the smaller scales, what the eye can see and recognise needs to be taken into account. I have recently been drawing some fire stations for printing in 1/150 scale. The principal dimensions are drawn in 1:1 scale in SketchUp but the detail of the brickwork has needed to overemphasise the mortar courses for them to be visible in the final printed version. So in the SketchUp file a brick is surrounded by a 12mm deep and wide trench for it to be recognised as part of a brick wall when printed. That 12 mm mortar trench is printed as a 0.08mm channel inset by 0.08mm into the wall and looks convincing enough for me before detailed painting. From normal viewing distance it is a brick wall enhanced by the slight printing variations and clumsy priming.

 

Edited November 21, 2023 by Mike Harvey
spelling

[IronMink]

Mike, I agree 100%. I draw at full size but ensure all details will scale to at least 4mm/ft. This means some dimensions are exaggerated to print on a resin printer at optimal orientation to produce resilient models. Every design has several iterations before publication to ensure they work. Drawing at 1:1 scale in millimetres is waay more convenient than working in fractions of millimetres, the 3D slicing software allows the scaling to suit models.

 

Jonny