Minolta used to be one of the more popular brands of 135 film SLRs and lenses. In fact, they were one of the very few lensmakers making their own glass, and their lenses are well known for exceptionally consistent color -- they famously even made some lenses for Leica. Minolta introduced their SR bayonet lens mount in 1958 and, with minor variants labeled MC and MD, continued producing lenses in that manual-focus mount until 2001. (Do not confuse these with the incompatible Minolta autofocus lens mount, A, which began with the Maxxum line in 1985 and has been continued by Sony since 2006.) Because SR has a relatively short flange distance, there were not many adapters to mount SR lenses on other bodies, but adapters to various mirrorless mounts, including Leica M, are commercially available.
Ok, so why 3D print this one? Because we can seems like a decent answer -- this is an easy print in 2 pieces: the adapter and a removable lens locking pin. However, an SR to M adapter allows the latest Sony E mount bodies to autofocus these manual lenses via the Techart Pro LM-EA7 adapter... which has a 700g weight drive limit, so we don't want to waste weight on a heavy adapter (this one weighs about 11g). There is also a potential issue in that some SR adapters -- but not this one -- are too thick on the M side to fit on the LM-EA7.
The last two photos were taken using the LM-EA7 on a Sony A7II with a Minolta Rokkor 58mm f/1.2 lens wide open. They are vertical shots that look much better if you click to see them in vertical orientation, rather than just seeing the horizontal crop Thingiverse makes.
A very straightforward print. I used "dishwasher safe" high-temp black PLA. It should be a little tight, so work a lens in the mount a bit before attaching to a camera -- that way, you can clean any little shards that the flange might cut the first time you fit a lens to it. The bayonet wings are designed to print in the given orientation without supports or post processing.
There are three files. Just printing sr_20160814.stl will give you the adapter body and two copies of the rather small lens locking pin (one and a spare). Alternatively, the adapter body by itself is sr_20160814adapter.stl and sr_20160814lockpin.stl is the lens locking pin.
The M side of the adapter has a dot in the bar-patterned grip portion of the adapter that you align with the M locking pin for mounting and then turn clockwise to lock. To unmount, you simply depress the M mount release lever/tab on the body (or LM-EA7) and turn counter-clockwise, lifting the adapter out when the dot aligns.
The SR side of the mount is marked "Minolta" on the bottom and "SR" on the top. To mount a lens, simply align the red dot with the top of the adapter (between the "S" and "R"), push the lens in, and turn clockwise until the lens focus mark is at the top. The lens should turn very freely... so now it is time to insert the locking pin. The locking pin fits into the slot on the right side after the "SR" marking. Although the pin is straight, the slot is actually curved to help seal against light leaks and to hold the pin better, so it might feel tight the first time you put the pin in, and you might have to file your pin a touch if your printer was at all sloppy in making it. You might have to wiggle the lens a bit to perfect the alignment with the pin, but the pin should push in to have the tab nearly flush with the outside of the adapter -- and, more importantly, to rotationally lock the lens so it cannot move. To later remove the lens, you shouldn't need to pull the locking pin all the way out, but merely a couple of mm to rotationally release the lens.
Minolta SR/MC/MD lenses default to stop-down operation, so you control the aperture by simply turning the aperture ring on the lens.