calibrating wall thickness (for fitting parts together)

I have a TAZ 6 printing with Gizmo ABS and slicing with Cura 2.1 “normal” settings. I am forgetting which setting to check / correct for the following situation:

Test object:

  • a capital “E” laying on its back
  • designed to fit onto the 20mm aluminum extrusions of the printer frame

Design dimensions:

  • overall size 30mm x 20mm x 10mm
  • 5mm back
  • 5mm wide extensions for the top, middle, and bottom “legs”
  • 7.5mm gaps in between “legs”

Result dimensions:

  • overall size 30.25mm x 20.28mm x 10.05mm
  • 5.02mm back
  • 5.20 wide extensions for the top, middle, and bottom “legs”
  • 7.34mm gaps in between “legs”

Given the overall horizontal dimensions and the horizontal dimensions of the “legs” are off by similar amounts, my working theory is the walls are “fat”.

I tested lowering the extrusion multiplier below 1.00 did not help significantly and it caused infill to become sparse.

I measured the filament and it was between 2.82 and 2.85 across a series of measurement locations.

What other calibration settings will help with horizontal dimension accuracy?

You can try calibrating the e-steps:

But reducing the multiplier from 1 to .95-.97 should have similar affect… speaking of which you mentioned the infill was affected by this, just increase the infill percentage?

Regardless, I’d try a better “known” object for calibration. A metal object of a standard width/diameter… I designed a thumbwheel that fits on a M5 socket cap. Not sure what type of socket caps are prevalent on the TAZ 6, but maybe that’s a better calibration.

Here’s my M5 thumbscrew cap if you want to try it…
M5 Thumbcap.SingleColor.v8.stl (285 KB)

Thanks for the suggestion and the test model.

I tried the standard 20mm cube and I could adjust E-steps to accommodate about 50% of the error (from 20.28 down to 20.15) but then I’d have to tweak the infill. I couldn’t get down close to 20mm.

The reason for my test object was …

  • its small and fast to print
  • is based off the typical cube test prints
  • it lets me test both inner and outer fit

I need to be able to print parts which fit together. Nearly all of my work is dimensionally critical and at least 80% are parts which must fit with other parts.

The only solution I’ve found that is working well is switching to Simplify3D and using its “XY dimension adjustment” feature to apply a small amount of “shrinkage”. In the horizontal plane.

Absolutely understand the need for accuracy. I use the multiplier to account for part accuracy (95-97% seems to be the sweet spot for my printer and eSUN ABS). There’s also a Horizontal size compensation setting in S3D… good for pre-designed STLs, but shouldn’t be necessary for original designs. I’ve never thought about infill as affecting the external dimensions… primarily for strength of part.

FWIW, if you’re printing ABS, the part will usually shrink… ~8% seems to be consensus. ABS is also malleable, and it should compress to fit.

Well… good luck on your quest for accuracy. :slight_smile: Its a challenge and at some point its going to be a compromise.

I was thinking about this the other night… specifically the infill getting sparse when you decreased the multiplier.

I use the “Infill Extrusion Width” setting to create solid infill walls… mine is cranked up to 200%. I think 175% is enough. This results in an almost solid 1 extrusion width walls for infill… helps increase model strength legacy from when there wasn’t any diversity in infill patterns.

Looking at your expected versus printed dimensions you might try to re-calibrate the X&Y steps instead of the extrusion steps. The Z steps look to be within .5 % which is pretty good, but the X/Y look closer to 1%.

What is interesting (?) about my initial results is that the ratio of design vs actual is not proportional. The error at 30mm is nearly the same as the error at 5mm.

I would think, calibrating the XY would result in a proportional change.

I would also think that changing the extrusion steps (or the multiplier) would also change layer adhesion similar to what happens to infill.

It does. But when you factor in under-speed of the outside perimeter (I like to have an underspeed percentage = ~2500), the affect is minimal.

OK. Looks like I have a couple options.

  • Cura
    • change the extrusion multiplier downward
    • increase the infill upward
    • adjust the underspeed
  • Simplify3D
    • use the XY adjustment

The Cura steps are more applicable to S3D… but it looks like some good next steps.

I’ve been printing complex assemblies for several days now with just a single change to the “XY adjustment”. It has been very consistent, independent on the parts, complexity, of type of fit required.

Hmm… ok. I’m not sure what “XY Adjustment” is in S3D… but you’ll be hard pressed to find a specifically “multiplier”, “underspeed” and possibly infill % in Cura… :slight_smile: I don’t use Cura enough to know all the settings…

Regardless… glad you’re making progress.

I may not have the correct label in the UI (I’ll double check). Simplify3D added a feature specifically for aiding in printing inter-fitting parts.

Update: there is a setting on the “Other” tab, categorized as “Dimensional Adjustments” and labeled “Horizontal size compensation”.

Here is a post on the feature:

Note: I realize that Simplify3D is not an open software project and many will not find its price worth the investment. I’ll attempt to find a configuration of Cura that has the same effect so others facing my problem will have options.

The “dimensional adjustmet” setting seems to be unique to S3D… or I haven’t seen it in Cura or Slic3r. Its helpful for downloaded or pre-made STLs. Good compensation for the varied range of machine calibrations of designers.

If you haven’t, try creating your own fitment objects. Maybe a 10mm diameter peg, along with a corresponding ring / hollow cylinder which is 10.2mm I.D. (or try 10.1 I.D.). That would be the ultimate test of fitment.

I have designed many inter-fitting parts where I allow a gap. That has not been an issue.

However, when printing, the wall thickness has been off - just the wall thickness. A 10mm cube has the same linear 0.25-0.28mm error as a 50mm cube. It’s not proportional to the size of the object.

Seems like Cura should have a similar setting; not sure how hard it would be to implement - I’m new to this slicer stuff and don’t even know the basic algorithms. Anybody know what it does? Actually thin the walls, or does it “inset” them a little?