I have held on to the short (2x pitch-8x pitch) shafts (both plastic and metal). I don’t see much use for these parts with the introduction of capped and motor shafts. Should I throw these out, or continue to hold onto them?
imho plastic shafts are good for “in between” gears of a gear train. i.e. in a 5 gear train, for the middle 3 gears where the stresses are “simple”.
We use steel shafts at the ends of gear trains, at wheels or wherever the forces are complex. (engineering-speak for not easily guessed at)
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You use the plastic straight shafts, or capped shafts? the regular shafts are annoying because you have to anchor them on both sides.
We use the plastic capped shafts, similarly to using capped steel shafts.
You are also correct that the plastic shafts, like the steel shafts “need” to be retained on both ends using shaft collars. However, when we trial fit a shaft to a gear, a plastic shaft appears to have more friction than a steel shaft, i.e. the plastic shaft to plastic gear is less likely to slide out; and the risk of having a system failure is less.
The correct engineering practice is to ensure all shafts are properly retained, i.e. will not fall out. However, when the system is space constrained and there is no other solution, some technical risk may required to be taken by a team.
Bottom line, use you can use plastic shafts in appropriate locations and steel shafts in appropriate locations. And you can use plastic shafts in inappropriate locations as long as the students recognize the technical risk they need to take - and document the risk in the Engineering Notebook to get the credit for that recognition.
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