setting assembly constraints for loose and interference fits

[kcleung]

I have just gone through the intro assembly basic tutorial:

http://www.freecadweb.org/wiki/index.ph ... c_Tutorial

It is very informative and gives a very good introduction to the concept of parts and assembly.

However when we assemble a machine, we use either loose fit or interference fit. In which the latter case, the diameter of the hole would be slightly smaller than the diameter of the axle, and the constraint solver will not allow the axle to be fitted into the hole.

So how can we specify the constraints to allow interference fit?

Also, if the use enters further parameters such as the Young's Modulus and the Possion's modulus of materials of both parts, and the press force exerted, will FreeCAD be able to work out whether such fit will be possible? If so, then does this require integration of the assembly module with other modules such as FEM?

[efyx]

That is a good question. I know the newest Assembly2 have an option of axial mates. What is missing for sure is symetrical and tangential (example. box +cylinder (round side)), and most important for me to create mates which have angle and lenght constrains, that when I move part I can see whole range of move, which will machine do in real life.

[emills2]

In-model limits and fits would be nice. What i've personally always done is model at the NOMINAL dimension of the specific fit. The allowance is usually baked into the final tolerance on the detail drawing. I know there are more 'complete' modelling systems out there though.

Limits and fits are physically specified by the parts themselves. Once you set a fit on both parts there is no freedom to change it when assembly time comes. The way ANSI and ISO work, there is a fit code for each hole, and a fit code for each shaft, which makes it easy to specify independently.

How would you see this working?
-model parts to nominal size
-set fit in assembly
-assembly fit changes part file and part drawing file?

[efyx]

@emills2 I think kcleung had on mind that for example in Solid Works you have hole creator which have function of close fit or interference fit.
For example, you have nominal bolt M12 and you create hole in "hole creator" M12 and you choose from dropdown menu loose fit/normal fit/interference fit and program adds exctra space to bolt hole or took some according to norms.

I am requesting for option in assembly module to check all constrains in the assembly. I mean not like in assembly2 that is checking all constrains in form of presentation, but the way I can take a mouse drag one part and see what is happening with all others. Is that possible? Also ranges (in distance and angle are very necessary), because I would have view that the move and constrains work on some for example length.

[ickby]

guys, we are working on and off on this since quite osme years and have not brought it to live yet, so requesting such specific things is way too eraly for us to consider

[Lotharyx]

Respectfully, specific requirements such as constraint styles should be considered as early in the development process as possible, and reconsidered frequently along the way, so as to avoid writing code that doesn't easily support something. Software development is my job and a LOT of my work goes to rewriting stuff because "well we didn't think of that when we started."

[dwizeno]

Respectfully, specific requirements such as constraint styles should be considered as early in the development process as possible, and reconsidered frequently along the way, so as to avoid writing code that doesn't easily support something. Software development is my job and a LOT of my work goes to rewriting stuff because "well we didn't think of that when we started."

+1 on the principle. This all being volunteer work, it's up all up to those doing the actual work.