Wait, I know the answer to that question, but what I really want to know if this idea is crazy.  Marlinguy and I have been discussing custom scope blocks and I had an idea of trying to 3D print some short odd length blocks using a  hard 3D printing filament.  I don't actually have one at this point 'cause I have never found anything useful enough to justify the cost and table space.
On a related issue, has anybody seen an end-mill that can cut the cupped mounting points.

One wild and crazy guy!

Jack

My “hobbyist “ neighbor has a 3D printer and seems game for new projects.  If I had the “code” to make it work, I could have him give it a try.
Mike.

Plastic is a very broad term.  But yes.  I did think that the cutouts would not be needed.  There are many different printer filaments including nylon and carbon fiber.

There was a nice post a few years ago on how to cut the divots for the scope mounts on these bases.  Maybe Frankeore?  The gist of it was using a single flute end mill, and it naturally cuts that shape, at least with a small amount of center relief grinding.  If I can find time, I'll go out and find one and post a picture.

Small fly cutter, Jack. You have the tools to do it. Or make a single point cutter the correct diameter on the end of a piece of drill rod.

Jack, among my HS metal shop projects was making a fly cutter. That was in the 1960s. We also made button dies if one chose to do the project. The shop class had a list of projects a student could do for a grade. Awe but that was way back in the old days so you probly never heard of it. 
Not long ago, a few weeks, I was using a fly cutter to make clear Polyethylene sight inserts for Anschutz globe sights. You shouldn't laugh and make fun of the old fly cutter. You can do an awful lot with one when you don't have a fancy schmansy multi flute store bought cutter. From big to tiny, fly cutters can be very handy.

Below is a slug gun blank machined to octagon with a fly cutter.

One of the fellows I shoot with has made several front sights on his 3d printer and they work fine except for the plastic look. But would a scope base be able to take the torque from recoil?
It's going to be holding alot more weight.

I've never really understood why target scope bases needed to be so darn hard? I think even mild steel would hold up and not be a problem to work with various scope clamping styles. Not sure about softer materials like plastic though as I can see someone not getting a posi-loc into the cut right and end up with numerous cuts over time. Not sure how it would handle recoil either?

Recent attempts to find scope base material in short lengths to cut up and make custom bases I need proved futile. I have a Bremer High Wall and a Zettler Bros. Ballard that both have oddball spacing and it looks like I'll have to dig through my baggie of scope bases and anneal some bases to drill new mounting holes to fit these two oddball spaced holes.