Try a site called grabcad
have a look at thingiverse 
@Daniel_Porter in which program dud you design the ‘preciselymeasured object’? Did you try to export it, import in any other cad software and export it again? Maybe your program has a wrong setup for measurements…
I’ m going to combine mesh modeling with cad-modeling since there is no method to create the stuff I wand in cad
@Michael_Weber I set Blender to work in metric. So when I create an object that’s 10mm, the 'Blender Unit" is only .001. An STL file see’s the 10mm as .001mm not as 10mm, so by scalling the mesh up 1000 times, it fixes the size discrepancy I experience.
You can work in Blender on the basis of 1 Blender Unit = 1cm, but I prefer to work with actual figures.
FWIW, it’s straight from Blender to STL then to the slicing program.
@Christopher_Benjamin I work in Metric, the issue is when exporting to STL. I’ve had Normals issues when scalling & saving as STL, but no issues when exporting via the 3D Toolbox.
@Michael_Weber @Daniel_Porter i use Blender to design as I had a friend who does a lot of 3D renderings on it guide me as I started out. There is a really good tutorial that I can look up if you want but it cost money. It was made by the guy who did most the input for the 3dprinter extensions. Also, you can specify a Blender unit to equal a millimeter or meter or mile if you like and once you do this and use the keyboard to input dimensions while you create you can make accurate models very easily. (Scene->Units->Metric or Imperial)
@Michael_Weber Just following this up… Re: scaling. I was working in Blender yesterday and I noticed under the buttons which you use to set the units (ie Blender/Metric/Imperial), there is a scale option there. From memory I set it to 0.001 and that fixed the scaling issue when exporting.