Undersized IDs

Filament
1

I cannot print any tube-like object (washer or tube) where the inside diameter is not too small. I’ve calibrated my TAZ for X, Y and E steps. I’ve tried to run this calibration routine (http://blog.mcmelectronics.com/post/3D-printer-calibration#.Ue7-AdKRCrA )and get almost perfect ODs, but the IDs are small. I’ve tried multiple Slic3r 0.9.10b iterations with no success. I’m using Repetier-Host V0.90C. I’m using natural 3mm ABS. Can anyone shed some light on this? It doesn’t seem to be related to shrinkage, since the very fist layer measures small as soon as it is printed.

; generated by Slic3r 0.9.10b on 2013-07-23 at 16:58:40

; layer_height = .21
; perimeters = 2
; top_solid_layers = 3
; bottom_solid_layers = 3
; fill_density = .4
; perimeter_speed = 30
; infill_speed = 60
; travel_speed = 150
; nozzle_diameter = .35
; filament_diameter = 2.78
; extrusion_multiplier = .95
; perimeters extrusion width = 0.24mm
; infill extrusion width = 0.42mm
; solid infill extrusion width = 0.24mm
; top infill extrusion width = 0.24mm

G21 ; set units to millimeters
M203 X192 Y208 Z4
M104 S230 ; set extruder temperature
M190 S85 ; wait for bed temperature to be reached
G28 ; home all axes
G90 ; use absolute coordinates
G92 E0 ; reset extrusion distance
M82 ; use absolute distances for extrusion
G1 F2400.000 E-1.60000 ; retract
G92 E0 ; reset extrusion distance
G1 Z0.350 F9000.000 ; move to next layer (0)
G1 X86.780 Y119.430 ; move to first skirt point
G1 F2400.000 E1.60000 ; compensate retraction

2

There’s a couple of guides that can better explain the common trait of holes with undersized IDs:
RepRap Wiki and Nophead’s Blog.

Nophead’s blog is great for some in depth FFF thoughts and explanations. I highly recommend giving it a read. Undersized IDs can be caused by: faceting errors, segment pausing, arc shrinkage and corner cutting. It’s broken down at the link.

3

The “secondary effect” in Nophead’s blog might be that the pressure is slightly higher on the inside of the arc than on the outside, because equal amounts of plastic are trying to be extruded into different areas. This would cause some flow from the higher-pressure area (inside) to the lower pressure area (outside) and thus tend to reduce the undersizing slightly.

4

Is there any slicer that allows calibration for inner diameters? 3DHubs clients tend to expect ID sizes to be similar to their CAD design. It is unsatisfying to tell everyone to adjust their hole diameters or else drill them out.