There is also the matter of consistency in printing.  For my dial indicator mount, I printed a bunch of plates with the hole pattern and kept tweaking the hole size until I got something that press fit the bolts.  Depending on how your printer is calibrated for flow rate, those same holes might come out too big or too small for you.  The difference between too loose and too tight might be only about .1mm.

Very true.

Let me try to explain my thinking.  What I tried to do here was make something that has enough play to fit a lot, if not most of the extruder faces.  The idea was NOT to make something that uses the tight fit of the bolt heads in the holes to keep it in place, rather let the magnet inserts to do the job. 

A lot of the tings we're likely to attach to this do not need to be and more likely shouldn't be rigidly attached anyway.  The dial indicator for example will be held in place very securely while measuring the surface alignment, but if you, like me, home in all the axis, then the pluger will snap below the bed surface.  If you forget that and bring it back over the bed in the Y axis, it will hit the edge of the bed and if attached too securely, it might break something.  With this setup it should just pop off.

The holes in my piece are 6.3mm (1/4") for the magnets, but on the back face that expands to 8mm.  The hex bolt heads are 5.5mm in diameter, which should allow for quite a bit of deviation in either direction.  When the pieces goes on, the magnets should be (almost) touching the face of the bolt head.  If not, you can push them in further, or conversely pull them out ever so slightly before glueing them in place.  That powerful magnetic attraction should be more than enough to secure the piece in place and prevent any shifting.

Most of the weird cutouts on the back face are to accommodate as many variations as possible.  I looked at a lot on line photos of SD print heads and I think this just might do it.  If not, heck, all it cost to try it is about 30 minutes and 20 cents worth of plastic.  Even less if you print only 2-3 layers, then kill the job and test the piece.

My point about universal btw, wasn't solely about stock vs non-stock mounts.. its that even 'stock' mounts all seem to have huge variances that means there isn't a 'one size fits all' solution.... the same issues will crop up for everyone be it bolt placement, or extruder depth setting (in your case) - as demonstrated by you having this particularly issue but 3 other SD3's that I know of not having it ...

Gotta love consistent inconsistencies in manufacture

Nice job! Looks great

But to be accurate, its not 'universal' as it wont work on a Mk4 extruder jigsaw-replacement or a Mk3 or a Minimalistic one.

And just further for your info - the problem isn't at all SD2/SD3 related - its that every extruder head seems to have slightly different tolerances on the screw placement. Hence when Jinja posted the original design that is sort of lifted above over at http://www.soliforum.com/post/1169/#p1169 , he included the OpenSCAD file and some details on how to adjust the screw hole positions.

So nice looking piece - but be aware its not really universal anymore than any of the previous designs since it doesn't solve the issue of what appears to be a large range of tolerances on bolt placement.

And you should try just using Jinja's openscad file and tweaking the bolt hole offsets as detailed in his post and the openscad file - worked for me on my SD3

Wish I'd seen Jinja's post first, it might have saved me some work, but I can tell it still wouldn't have worked, at least for me.  My extruder head need clearance for the hot end body, so I had to carve it out on the "back face".

Anyway, as for it being universal, well, as universal as you can get in this hobby.  I think it should fit most stock print heads, without the need to tweak the CAD models.  I haven't even seen the other print heads you mentioned, so I'm not going to claim it fits those.

But to be accurate, its not 'universal' as it wont work on a Mk4 extruder jigsaw-replacement or a Mk3 or a Minimalistic one.

And just further for your info - the problem isn't at all SD2/SD3 related - its that every extruder head seems to have slightly different tolerances on the screw placement. Hence when Jinja posted the original design that is sort of lifted above over at http://www.soliforum.com/post/1169/#p1169 , he included the OpenSCAD file and some details on how to adjust the screw hole positions.

So nice looking piece - but be aware its not really universal anymore than any of the previous designs since it doesn't solve the issue of what appears to be a large range of tolerances on bolt placement.

And you should try just using Jinja's openscad file and tweaking the bolt hole offsets as detailed in his post and the openscad file - worked for me on my SD3

Alas, the reality is quite different.  The problem is most likely related to variances introduced during assembly of each unit.  So I set out to make my own.

I did make a dial holder very similar in design to his, but dimensioned to fit my print head.  While I was working on that I started thinking about a better mount, that would also fit most print heads.

I liked the idea of holding the mount with magnets, but wanted a really good hold.  The black hex bolts that hold the extruder motor are all the same size, and they resent a fairly large magnetic surface while they are also on the same plane. 

So here is the result: "The Face Hugger" 

Take a look at the picture below, and feel free to try it.  I used 1/4"x3/32" neodymium magnets, 2 in each hole, and believe me, it really "hugs" the face of the print head.

You should be able to use this to attach just about anything you'd want to attach to the print head and not worry about it moving or falling off due to vibrations.  You could also consider making whatever you plan on attaching to it, modular.  By adding a mating surface that has a metal strip glued to it, you should be able to design various gadgets to work with this mount but don't have to be glued or otherwise permanently attached to it.

My next project will be my take on a cooling fan.  I didn't really like the current design becuase it's so large it blocks visibility as the model is being printed.  I like to monitor some areas of my prints at certain points during build, and the large size prevents me from doing this.

With that in mind, I'm working on a new design.  Once it's ready and tested to work, I'll post it in this forum.