Horizontal Hole Expansion Issue

[catsco 0]

I'm trying to create some fairly precise holes.

I've done a number of trials with hole sizes around a quarter inch as follows:

6.35 mm

6.36 mm

6.37 mm

6.38 mm

 

Made three iterations using 0.1, 0.2, and 0.3 mm hole horizontal expansion on a 12 mm thick trial piece.

As expected, each horizontal hole expansion increased the hold size, but not as expected.

 

The smaller diameter holes are larger than the larger diameter holes in all three trials.

 

I have checked the model sizes numerous times.

 

This can be worked around, but I hate to kludge the diameter and the horizontal hole expansion to get the initial intended  precise size.

 

Thanks!

 

Attached STL file shows the test block w/holes that increase in size from the pointed end.

 

Hole Trial.stl

[GregValiant 1,112]

The "Snot Factor".   The molten plastic wants to pull towards the center of the hole.  The faster it cools, the less the effect.  What I found was that a 2mm hole needs HHE of .25 while a 30mm diameter hole requires no hole horizontal expansion at all.  The variance in my test wasn't linear.  A little thing like a chamfer on the holes made a difference.

I know that all of yours are nearly the same size, but a lot goes on in that little space below the nozzle.

 

I run a drill bit through them.  With any pressure on the sides all the holes deform anyway. Horizontal holes have to be drilled out for any sort of precision because they have flat tops and bottoms.

[catsco 0]

Thank!

 

Appears this is a great example of making things that is "high precision, low accuracy"! 😁

[GregValiant 1,112]

When I print a cube it will be +/- .01mm in the X, Y, and Z.  That's amazing.  When I print a hole...not so amazing.

I live in Florida where it is hot and humid.  If I measure a print while I'm inside the house I get one set of numbers.  If I leave the print outside for 15 minutes everything changes.