[OpenSCAD] Engineering Fits and Tolerance

nop head nop.head at gmail.com
Tue Oct 29 18:07:40 EDT 2019

Not sure I understand. h7 specifies a tolerance, i.e. a range of possible
sizes that can be tested with a limit gauge or a micrometer. How can that
be expressed in a model, which always has a definite size?

On Tue, 29 Oct 2019 at 22:00, Hugo Jackson <hugo at apres.net> wrote:

> Has any thought been given to incorporating engineering fits and
> tolerances into OpenSCAD? As I understand it, OpenSCAD was originally
> conceived for the creation of STL files for a 3D printer and I’ve been
> thinking that the base functionality might be improved by a little more CAM
> in the CAD.
> For some time I’ve been using wrappers around most of the OpenSCAD modules
> in order to introduce engineering fits into the parts I create as 3d
> printers on the whole offer increasing precision and repeatability.
> Using a special variable $fit I can arbitrarily call up a module and it
> will adjust the the final size of the geometry according to the engineering
> fit I specify. e.g.
>         cylinder(d = 5, h = 2, $fit = “g6”);
> I think anyone who has created interconnecting parts is familiar with the
> requirement to adjust for tolerance, but the core language as it stands
> requires this to be accomplished on a piecemeal basis, but to my way of
> thinking fit and tolerance are integral to the original purpose of OpenSCAD.
> I think this is particularly relevant as more and more users are acquiring
> machines that use different processes and that I might well wish to print a
> part on an FDM printer one day and a DLP the next, which I think would
> naturally call for a different fit specification.
> I also created some constants: kLeft, kRight, kFront, kBack, kTop &
> kBottom and use 6 element arrays to selectively apply tolerance, and use a
> special variable $faces to pass on that information as required:
>         cube([7,3,8], $fit = “H11”, $faces = kLeft + kRight);
> And of course if I’m creating a project with lots of references to fit
> then I simply create an identifier for the fit, e.g.
> shaftFit = “h7”;
> So that if I move to a different type of machine where more or less
> tolerance is indicated, I only need to change the definition of shaftFit.
> I did some poking around in the mailing list archives and couldn’t see any
> reference to a discussion on this, but I’m sure it’s occurred to others
> before me, I just thought I’d ask where the community stands on
> incorporating this kind of functionality into the core language.
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