Thanks for the update.  Hope you can make mid-September.  Looking forward to getting mine I pre-ordered when ready.

I thought the new throttle was the UWT-50?

> I thought the new throttle was the UWT-50?

Did they change the model number?

Woops. I've updated the title to UWT-50. Thanks Jeff!

I feel your pain with printing parts yourself VS Shapeways.  What I have learned from printing on resin printers is that if you want an accurate surface you have to have that surface perpendicular to the build plate.  For example, to print the two halves of the throttle yourself they would need to be standing up, short end "on" the plate.  The downside of this orientation is that your part will take a very long time to print.  The upside is that no supports will be located on the mating surfaces and they would be on the outside and easy to sand smooth.  A second choice would be to have the parts horizontal with the mating surfaces parallel to the build plate and facing away, again the supports on the outside of the case and easy to sand off.

if the mating surfaces face the build plate you will have to put supports on those faces and that will cause lots of inaccuracies.  First, the parts always sag a little between supports, even if the supports are almost touching each other.  Second, the removal of supports will damage the mating surfaces slightly.  Third, you will have to sand the support surface smooth which will mean there is not way to actually check the accuracy of your fits.

I made a test part that had the same feature modeled on all three sides and printed to see which reproduced the most accurate, vertical was always the best.  To see some of the parts I am making look at my 3D printed shay blog.

As far as support removal, you need to take them off as soon as the part is off the printer and before post printing curing.  I remove my parts from the printer, do a quick "dirty IPA" bath, rip off the supports, then do a clean IPA bath, then cure.  The parts are most flexible as soon as the come off the printer and most supports will easily tear away with little to no damage to the part.  If you cure the part with supports then you have to cut them off or stand a chance for the part to break when flexing the supports.  With bigger parts you can try the hot water method for removing supports, which is where you wash in IPA and then run under really hot water, which cause the supports to just fall off.  I don't like the hot water method because I found that parts can warp at thin cross sections.

instead of making that S-curve extrusion did you try just using a chamfer?  I use Inventor and not Fusion 360 (however I am told they are similar) and there is an option to use a chamfer with two different distances.  Your bump out would have to be the total length at the base of your bump out (including the S-curve) and then you would set the chamfer to move the upper edge back to your original bump out size.  Then use the fillet tool to round the angled surfaces and smooth out the angles.

I find that Inventor can "do the math" easier working with features rather than trying to draw in the features, maybe fusion 360 has the same issues.