inch vs mm

[red Dog]

Hello gents,

 

I need a bit of guidance if I may

 

Years ago I followed Timmy's converting a hawk to a T-45 with envy:

Timmy was gracious enough to provide all the stl and drawings to help others do the same conversion - Thank you Timmy

This was out of my reach at that time but now that I own a 3D printer and have a bit of experience with it, i am thinking of trying the same stunt.

 

So I downloaded his files and send them straight to the slicer (chitubox)

But these are very tiny and are certainly not scaled to 1/32 when they land in chitubox (the ventral pylon is barely 2.2mm long

 

Look how small the pylon is when imported straight in chitubox (2.2mm long) . The bigger one is scaled to 2540% and is thus 55mm long as per below reasonning

 

 

I tried to import the mesh in fusion 360 and then I realised that there I need to set a reference (mm or inches) which made me realise that the stl was probably designed in inches and therefore quite smaller in scale when fusion (or the slicer) imports it in mm.

I suppose it takes the value without unit. 

so if a stl was 1 inch long, and the software set to mm, that 1inch becomes 1 mm, reducing the part in scale by quite a bit.

 

With that in mind, 1 inch is 25.4mm so I should increase the stl by a factor of 25.4

That means that when I import Timmy's stl into chitubox I scale it 2540 % and I get the right 1/32 scale.

 

Or I can import each stl into fusion , set the import to inch and reproduce a STL -( because I didn't find the option to do that straight into chitubox  - Maybe I missed it?)
When I do that I get that centerline pylon to a length of 55mm which seems quite OK for 1/32 and if I import that modified stl file into chitubox alongside the one above scaled 2540% they are of the same scale, confirming the ratio.

 

BUT

When I look at my chitubox plate, the parts looks too big, so now I doubt my logic is correct.

 

 

 

What do you guys think, how do you overcome this unit aspect in the downloaded STLs depending on the unit the author used? 

Thanks for any input

 

 

 

Edited December 12, 2024 by red Dog
sp

[Timmy!]

So if I read this correctly, and forgive me I don’t remember what scale I exported the file, they’re probably inch dimensions.  Here’s what I know.  Set Fusion units to inches in the file, import the files.  They should be the correct size.  When you export to Chitu Box, you MUST convert to mm by changing the file units to mm, then save as mesh.  Or you could keep the file in mm scale up the parts by 24.5 and save as mesh.  Either way get the parts the correct size using an inch to mm conversion then save as mesh in mm.

 

Hope that helps,

Timmy!

[red Dog]

Yes it does Timmy. Many thanks You just confirmed the logic above.

And thank you very much for making these files available to us. 

I'll have a bit of fun and I hope to find a way to make the front gear as I'd like my model to be gear down

[LSP_Kevin]

I had to do the same with Pat's BOMARC STL files - upscale them in Chitubox by 2540%. In terms of overall dimensional accuracy, I can't be sure it's correctly 1/32 scale now, but all the parts fit together properly, so it became a moot point.

 

Good luck with this one!

 

Kev