Once the unit has reached the set temperature.... How does letting it sit at that same temp longer help the stem fit better? I can understand a minute or 2 but how would 10 minutes help more than 5? Max temp is still the max temp after either 3, 5, or 10 minutes right?
No, not really. It's not stable until
the entire oven area reaches normal temperature, the insulation that saves us battery power makes that slower. Yes, the cup (the important part to making vapor) is at temperature in a minute or two, but not the entire oven.
Think about a sheet of material (for ease of discussion here, consider the composite as a single uniform plate). As you heat it, the atoms all vibrate more and more (the definition of heat at that level) so each 'needs' more room. Every atom moves further away from every atom, it expands.
Now, think about a ring cut from the material. As it gets hot the outside obviously expands, but the atoms still need to move away from each other so the hole gets bigger as well. Still with me?
But, as it heats from the inside out the hole is trying to expand faster than the outside, but it can't because
the outside is strong and constrains it putting the inside in compression (forcing it to expand slower). It's not until it reaches full temperature everywhere that the final hole size becomes available. It's not going to take 8 minutes 25.5 seconds or anything that exact, the ideas is to wait 'plenty long' for the initial try. I agree, 10 minutes is probably a safe number?
This brings up a fun technique sometimes use for things like big gun barrels (like aboard ships). An 'interference fit' a slightly to big OD sleeve and slightly small ID jacket are made. This means the precision rifling is done on a thin tube, not the whole barrel as normal. Then you heat the barrel body (making the ID bigger), seriously freeze the inner tube (making it smaller OD) allowing you to quickly slip one inside the other. Once at the same temperature (which they will be forever after that) they're locked together like nobody's business. Precision bearings are often fitted this way. Some even have to be cut up to remove.
Fun stuff, at least to a few of us geeks.
OF