What is tolerance? according to wikipedia the best definition of tolerance is “the permissible limit or limits of variation […] (of a measure)”.
So why is it important and what does it have to do with Fabtotum?
Anyone working with CNC machinery knows what tolerance is, so we do (apparently!).
Tolerance in the digital workflow is a pain in the butt,because it can make a perfect component on screen not even being able to fit where it was supposed to.
For example last week we had 4 Nema 17 motor mounts milled with good accuracy, accounting for small tolerance (even if it was unnecessary in that particular case).

We then moved from one strong aluminium alloy to a softer one for producing some screw supports.
Since the pieces where produced with our humble CNC router the expected tolerance was less than 0.1 mm,and the piece was okay.
When we used the same flat-end mill on the softer aluminium we had the great idea to speed up the process by 30-40% moving cutting feedrate from 400 to 650 mm/s or so.
The result was that the load on the machine was greater in magnitude than expected.
However the tolerance we had was not enough to account for the deformation of the structure wich, according to some testing we did was over 0.1mm!

Way too much for just 0.1mm,and the result was that one test component had holes smaller than the CAD project and the CAM simulation.
The lesson here is clear, we live in the digital age and we are comfortable making perfect fits with snaps and CAD help,but in the digital workflow, when we need to produce something physical we need to account the right tolerance for the tools we are using,and the experience we have.There is no standard tolerance,you can foresee it but if you change just one variable it can break your whole effort.
During the digital work flow you should always remember, unlike we did here, that production techniques can impact the tolerance you choose,and therefore you always have to know HOW to make stuff,not only how to design it on a pc screen.

The piece itself was corrected later with a digital probe and a custom g code to enlarge the holes just so they met the measure needed.
The funny thing about this is that i (Marco) wrote the same thing on a paper about Digital Architecture and CAM,and my conclusion was that the architects who succeed where the ones with a strong understanding of production techniques.Those architects (Toyo Ito, Foster and others) where able to use tolerances of 1-2mm in huge buildings,so they where able to fulfill their digital vision to the very limits of current CAD/CAM technologies.
The implications of tolerance in the future and usage of those technologies are immense,not only because it makes a machine more reliable than another,but because the knowledge means that i will be able to fulfill the digital work flow with proper production techniques.
I guess that making a mistake is the best way to learn then!

Lesson learned 🙂
Here’s a pic of the finished component (2 pcs) ready to be bolted.