Scaling 3-D Designs

[Cransford]

I'd like to throw myself on the mercies of the assemvled throng please!



I'm (very) slowly learning my round Fusion 360 as a 3-D design programme, and have been drawing up some "small" items in 4mm (P4) that I'd like to print in resin. Historically, I used Turbocad and always drew at full size and then scaled to suit. I've kept this method of working with Fusion 360, but it throws a tantrum if one tries to scale at 1.76.2 - the decimal place gives an error and the closest I can get is 1.76, which gives an 18" long object a length of 5.941mm instead of 6mm.



1. How do other Fusion 360 users draw and scale? Is there a factor to give 4mm/ft that I'm missing?

2. Am I being pedantic about the error? However, this would translate into an error of 6mm in a 60 foot length.

3. I'm taking it for granted that you wouldn't rely on slicer programme for scaling?



Many thanks in advance for any assistance.



Cheers,



Paul

 

[JimG]

I gave up trying to scale in F360 when I was using it - I could never get anything to work properly. So I drew everything to size in the scale I was modelling, using a calculator with a conversion constant to do conversions from scale dimensions on drawings. I labelled all files generated with the scale used and then used a slicer to do rescaling to other scales where possible.

When I draw in 2D, I draw in full size units then scale down to whichever scale I require. Like you I thought I would do the same in 3D but could never work out if that was ever possible. I now use Solid Edge and I'm still drawing in the scale required since I've never fired up my enthusiasm to see if SE is any better than F360.

Jim.

 

[michael080]

I don't know F360, but can't you increase the size by factor 5 and then divide it by 381?
Michael

 

[Cransford]

Jim,

Thanks for the reply.

I get the feeling I'll be doing the same! Next on the agenda will be a spreadsheet to do the conversions for me. I think I'll be sticking with Fusion 360 as I don't want to have to learn yet another CAD package!

Cheers,

Paul

 

[Cransford]

Michael,

That sounds complicated, but I'll give it a try!

Cheers,

Paul

 

[Marc Dobson]

I scale stuff from 7mm to 4mm all the time with 360 never had a problem. I have had one or two problems with bringing stuff AutoCAD into 360 as it just makes up random scales factors but otherwise no problems. I always work out the maths before opening the scale command. I haven't tried to scale a 2d drawing.
Marc

 

[Brian McKenzie]

See if Fusion 360 can rescale your fullsize work to 7mm scale by multiplying it by:

0.02296587926

(this equals 1 divided by 43.5428571428)

 

[Big Train James]

Can you enter a fraction for the scale factor in Fusion? If so it's relatively simple to do odd scale conversions.

Multiply both the numerator and denominator by a factor of 10 (or 100, or 1000, depending on how many decimal places are involved) so that only whole numbers remain.

Instead of 1/76.2 as the scale factor, use 1(10)/76.2(10), or 10/762.

Edit: By the way, this is very much what Michael suggested above, but perhaps a bit easier as the numbers stay the same while the decimal point moves over a spot or two to the right.

It sounds like you are drawing in inches so you also need to convert to mm. You can combine the units conversion with the scale conversion, as in scale your full size drawing (in inches) up by 25.4 and then down by 1/76.2.

That equates to 25.4/76.2 --> 25.4(10)/76.2(10) --> 254/762 --> 18(254) / 762 = 6

Similarly, converting from 4mm to 7mm or back works the same way. 762/435 to get bigger, or 435/762 to go the other way.

It works the same no matter what figures you are using to scale, for whatever reason. I draw in inches in full scale, so I use 254/480 to scale full size objects to O scale, and convert to mm at the same time as mm are the units that Chitubox uses for slicing. Similarly, I typically use Autocad when possible for modeling, but also use Solidworks and Rhino at times. I almost always work in inches in Autocad, but both Solidworks and Rhino default to mm, so I have to scale by 25.4 when importing or exporting files between Autocad and the other programs.

Regarding your other questions above, the answers are of course personal to the way you use various software. But here are my thoughts.

1) I firmly believe that everything should be drawn in CAD in full scale (I think of it as input), and scaling should occur at the output stage, like creating 2d drawings or 3d prints. If I'm drawing a 1:1 prototype item from field measurements or drawings, say a 63" diameter driver, then I model it at 63" diameter. I can then scale it as required.

2) This is truly personal, depending on what your goals and preferences are. I'm way over on the end of the spectrum where detail and accuracy mean a lot to me, so the discrepancy you describe would trouble me if I knew I could avoid it. It sounds like you are also concerned about it, which is all that really matters.

3) I am currently using Chitubox for my slicer, so it's the only software that I can comment on. But I never rely on the tools in Chitubox for any sort of meaningful editing of models. Model in a modeling software, slice in a slicing software. I will use it to copy iterations, and to do imprecise cutting apart of models (for example to test only a part of a larger model). I won't use it for anything critical like scaling, as it only allows factors as percentages, and to only two decimal places. The other thing to keep in mind is that modifications are only applicable to the stl file, not to the original source 3d model, so changes are essentially a one time thing. I'm not the least bit interested in trying to take an stl back into the modeling software to create a new model, as it's only a representation of the original source 3d model.

Hope all that helps. Feel free to ask questions if my descriptions of the math don't make sense.

Jim

 

[AndyH]

Hello,
You can change units to swap between imperial and metric.
I agree with always drawing at 1:1.
If I know a model is going to be output in different scales I tend to use expressions when drawing. All I need to do is change the values in the expressions table, particularly valuable for wall thicknesses.
Hope that helps,
Andy

 

[Lancastrian]

I draw the full size dimensions, but in mms. Therefore, an actual dimension of 12 inches is drawn as 12mm. Scaling is then 1 ÷12 × 7 = 0.583333 for 7mm. For 4mm scale you would have 1 ÷12 × 4 = 0.33333.

Ian

 

[Cransford]

People of the Forum, may I thank one andd all for he comments and sage advice.

To summarise where I'm at; is to have recognised a couple of self inflicted mistakes such as selecting a wrong value to (by good fortune) use as reciprocal, that's where the scaling and linear errors crept in. Having used a correct value, the error effectively disappears. It certainly sorts the issue of drawing full size - as mentioned, it's the best way, even when the original is imperial and needs converting to metric to draw!

I'll continue to learn how Fusion 360 works, it seems quite intuitive - as long as you can recognise what to do, which is where Youtube wins out! I'll use slicer for final tinmering and generating mass quantities of items.

Cheers,

Paul

 

[simond]

Just to add a contrary note, I typically draw at scale when 3D Printing. I’ve tried doing everything at 12”=1’ and post-scaling and still do it occasionally, but generally prefer the other approach.

So an inch is 0.5833mm and fractions and multiples thereof are simply typed into Solidworks as I go.

This does allow a bit of forward planning regarding material thicknesses.

 

[Arun Sharma]

Just to add a contrary note, I typically draw at scale when 3D Printing. I’ve tried doing everything at 12”=1’ and post-scaling and still do it occasionally, but generally prefer the other approach.

So an inch is 0.5833mm and fractions and multiples thereof are simply typed into Solidworks as I go.

This does allow a bit of forward planning regarding material thicknesses.

I normally draw to the scale size - the reason being that if the part is to be printed and used as a master for WM or LW casting, an adjustment to the print size will be required to counter metal shrinkage on cooling. In Autodesk Inventor, this is normally done via the 'Derive' function.

 

[Andy Ross]

I draw everything in full size both in Auto cad LT and Fusion 360.

Would have to work it out for 4mm but to go from full size to 7mm scale. I use the scale function and when it asks for the scale factor I use 0.0229885 and have not had any problems. For example the drawing below was all done full size.

And then reduced by the value above, then processed through printer and th results are below.



I use the same method in 2d when drawing parts for etching.

Andy

 

[simond]

and just to be contrary once more, I have drawn my match trck full size, and will scale it, as it is much easier when working from the real thing when you're taking the measurements yourself. Th bit that will not be easy is the fiddling around with material thicknesses after scaling but I hope I have pre-empted that in the few areas it is likely to be a problem.

Simon