The material looks like Siraya Tech Fast Navy Grey and if you're printing flat on it's back then your print should be reasonably concentric, however as you get to the edges of the build plate the light beams are not perfectly perpendicular as I found out on the HO bridge beams. They tend to bend outward so your vertical edges have a widening taper as it moves away from the build plate, that may also be down to the FEP which is very close to the securing rim plate so it's flexibility is vastly different to that in the middle.
The upshot of that is that the peel forces vary quite a lot from the edge to the centre, that can have an affect on warping and part squareness over large areas. The other factor is that most resin tanks are oblong so the peel forces are not uniform as you move out from the centre point, only a circular tank would achieve that. Peel forces pull the layers and can distort parts, especially if they cover reasonably large surface areas, one way around that is to increase your exposure time to harden the printed resin more and bond it to the previous layer a bit better.
Most people are in a rush so dial down their print settings, the given figure for FNG on my machine is about 2 - 2.2 seconds, I run vastly higher figures, now that may be down to a weaker UV lamp I have or any other unknown factor, but I found a massive increase in part tolerances by increasing the layer print time as well as reduced warping, but that may all just be local to my machine.
Inserting the crank pin and hub whilst the part is still green is a good idea, the resin will give a little and should grip/bond well to the metal parts but if you want to be really sure (top secret Area 51 tip here
) then just use a very fine brush and paint some raw resin from the tank onto the outside of the metal parts before inserting, then cure the whole assembly and the uncured resin will/should bond to the metal. It's best to paint the resin at night, there being no sunlight so no UV to upset or partially cure the resin on the brush or before it's all cured at once.
Once cured I would be tempted to turn the outer edge to accept the rim to be honest, that way it'll be concentric on the shaft and perfectly circular, you'd need to add a bit of sacrificial material to the rim to aid turning back so you get a nice fit. I'd be tempted to turn a small groove around the outside of the resin rim, something for the adhesive to soak into and bond with, perhaps the same on the inside of the steel rim, doesn't need to be much, just a shallow groove in either, there by making a sort of adhesive 'O' ring.
You could also trying witches brewing your own resin, lots of people mix tenacious with FNG, it makes it less brittle and a little more elastic, this is mainly for mini figures with swords, spears, horns and spikey bits etc; I think you loose some detail (but I've not seen that confirmed) but on a wheel there's little detail to loose so it might be a way forward. Ball park figure is 25% tenacious, 75% FNG, I've not tried it so not had any experience, but others who print minis by the thousand swear by it.
Finally, as you've found and just noted, resin printing is not consistent, what printed well yesterday does not mean it'll print well today, especially if you're working to tight tolerances in engineering type shapes, doesn't matter for Dwarfs, Elves and Dragons as they're organic shapes and no one will notice.
to a blanket but when you shine the UV curing pen on it the beam only penetrates so far so you run the risk of uncured resin inside your joint. Clear resin cures right though and I've seen many figure or fantasy modelers buy a tub of clear just as an adhesive to bond the two resin parts together.
