Accurate Dimensions

Hello, would someone please advice me how to correct the following problem.

My printer is an Ormerod 2

When I print, the X Y dimensions are fairly accurate. For example, a ring with an outside diameter of 70mm only has a difference of 0.3mm between the X and Y axis. The problem is that the dimension of 70mm shrinks in diameter as it rises beyond the first few layers. I printed the ring 8mm high, At the top of the ring the diameter has shrunk by between 0.5 and 0.75mm. I realise this shrinking which is a bit like a curved taper must be related to bed temperature etc.. but not sure how to correct for it. This example given is printed with PLA at 185 degrees and a bed temperature of 65degrees.

Any advice greatly received.


Brian

Something that you need to remember is the lower half of the part is positionally constricted by the bed adhesion, whilst the upper layers are much free'er to contract, this will actually form an exponentially curved side, its unlikely that a round part that's getting smaller as it gets higher is down to any calibration issues.

you could possibly reduce this effect by printing on a low density raft this may give the lower layers of the part more contraction freedom so the final part is much more parallel

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RepRapPro Mendel 3 Tricolour
RepRapPro Fisher
-Carbon Arms
-Easy adjust Carriage+effector
-axis stiffness mods
HE3D -600 delta
-Duet 0.8.5
-PanelDue
-DC42 Height probe
-RobotDigg metal components
Simplyfy3D
RS Design Spark CAD

Thanks for your advice BGK.

I will try a raft to see if that helps. I suppose I could also reduce the bed temperature, dropping it right down after the first couple of layers. This should not cause adhesion problems as I need to prise the part off the bed when it is cold, the problem might be the cool down time.

Brian

Did you print the calibration piece and did you calibrate your printer?

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Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

The calibration piece is to correct orthogonal errors, this error as described is not orthogonal.

As I originally stated calibration would help a lot of issues, but not a tapering as the print gets higher.

---

RepRapPro Mendel 3 Tricolour
RepRapPro Fisher
-Carbon Arms
-Easy adjust Carriage+effector
-axis stiffness mods
HE3D -600 delta
-Duet 0.8.5
-PanelDue
-DC42 Height probe
-RobotDigg metal components
Simplyfy3D
RS Design Spark CAD

Maybe your extrusion is set a little low? At the bottom because of the pressure and temperate of the bed it will set out slightly and look to be the correct diameter, but as the head goes up the plastic gets spread out less and as the temperature decreases the plastic shrinks ever so slightly?

Hii Pandionx, the extrusion layers are set as per the RepRap configuration, i.e... first layer height 0.36mm, subsequent layers at 0.24mm. First layer width is set to 0.8mm.

Brian

Quote
Europa
Hii Pandionx, the extrusion layers are set as per the RepRap configuration, i.e... first layer height 0.36mm, subsequent layers at 0.24mm. First layer width is set to 0.8mm.

Brian

The extrusion amount refers to the extrusion factor setting in your slicing program - or if you use the web interface you can increase the extrusion factor using the slider on the web page.

Dave

Yes I understand that but I need an indication of what to change it to rather than trial and error!


Brian

Hi Europa,

The following section explains the extrusion parameter that I am referring to:

Getting extrusion just right

The E value refers to how many pulses the stepper motor needs to make per mm of filament. By making the E value lower, you will extrude slightly less, by making it higher, you will extrude slightly more.
The link will give you a good indication of what is 95% correct for you, however I have found this to be a "soft science" - after setting my printer's correct E value, some filaments sometimes still need slightly more or slightly less than this value to be perfect. I usually use the slider in the web interface to add or decrease 5% at a time until I figure out what is ideal for a particular filament/printer object combination. I usually leave the E value set after I've configured it correctly, and only use the slider to experiment after that.

Edited 2 time(s). Last edit at 08/26/2015 06:17PM by pandionx.

But your link has one problem: It is for filament with 1.75 mm.
Of course this is the first step you have to make. This setting has to be correct.
But it is fact that the filament never has exactly 1.75 mm.
Second step: You have no other chance to use a precise measuring tool to get the real diameter of the filament and then calculate the factor.
1 - (measured value in mm / 1.75 mm - 1) = extrusion factor simplified: 2 - (measured value in mm / 1.75 mm)
Mathematically not correct but it gives you a good nearby value: 1.75 mm / measured value in mm. The error by this incorrect calculation should stay <0.5% practically in this case. But you should use the long formula to be correct.

Edited 1 time(s). Last edit at 08/26/2015 08:44PM by Treito.

---

Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

Quote
Europa
Yes I understand that but I need an indication of what to change it to rather than trial and error!
Brian

I'm afraid a great many settings can only be established empirically. There are many variables and no two builds will be exactly the same. Furthermore, if you need extreme accuracy, you will find that the shape of the printed part makes a difference, so settings need to be tweaked for individual prints. Printed parts do not shrink in anything like the same way that moulded parts shrink - there is imperceptible shrinking in the Z axis, nor in the XY axis of a solid print. The walls of hollow objects can however become concave to a greater or lesser degree.

Dave

Gentlemen, thank you for your suggestions.

Pandionx, the first thing I did was to calibrate the extrusion steps. I recently fitted one of the aluminium X arms which I followed by a full calibration.

I will make an accurate measurement of the filament size as Treito suggest and use the formular he gives.

Brian