Today we ran into a very annoying but avoidable problem. When assembling the elevator subframe roller wheels to their respective shafts, we realised that none of them would fit. This taught us a very important lesson on tolerances. A tolerance gives a maximum and minimum limit to a dimension, and can be shown as an allowable amount above and below a nominal dimension. In hindsight, we realise that we designed the shafts to have a diameter of 10mm without any tolerance when the inside diameter of the wheel bearings is also 10mm. We did fix the fitment issues by individually filing down all of the shafts, however, this got us thinking about what the proper way of designing a shaft to freely go through a hole is. The answer to our question lay in ISO 286-1:2010, which is an international standard for tolerances on linear sizes. In our case, we should have used the tolerance grade of h6 for our shafts. The tolerance standards work in such a way that for a shaft of 10mm, h6 would mean 10+0−0.009, which means the shaft may be as small as 0.009 mm smaller than the base dimension and 0 mm larger. This would have resulted in the correct fitment of the shafts but whether we were capable of producing such an accurate dimension is for another blog post.
- uniovi