Cura, G Code and hole size issues!

[Martin King 2Participant @martinking2]

Hi All,

My 3D printing of small parts designed in Fusion has proved hugely successful in the main and is a useful small income generator, with one particular item now having sold 150+ units! To put that in context, several have sold precisely zero!

When designing my own parts that have holes or voids to take nuts or threaded fixings I find that either Fusion or Cura (5.5) consistently makes holes etc too small; not by much but enough to be irritating. I therefore do several trial runs before arriving at a proer fit; all done in Fusion and updating the versions.

I needed some small sanding blocks for leather edge finishing and found a good design as an .stl file on Thingiverse.

Opened this in Cura and it printed just fine but the recesses for the M5 nuts are too small and clearance holes for the M5 cap screws are also a bit small. I do not want the hassle of filing down the nuts to fit and wonder if it is possible to somehow edit the gcode in some way?

I know zero about gcode or programming! Happy to have a go if someone can point me in the right direction 🙂

I am not sure if I can attach the gcode file on here?

Cheers, Martin

 

[JourneymanParticipant @journeyman]

In the Cura slicer there is a setting ‘Hole Horizontal Expansion’ that is intended to sort that problem. Not sure where it is as I don’t use Cura anymore.

John

[Martin King 2]

On 25 November 2025 at 10:48 Martin King 2 Said:

.., I do not want the hassle of filing down the nuts to fit and wonder if it is possible to somehow edit the gcode in some way?

It is possible, but you will have to familiarise yourself with g-code commands to know what to change.   The code can be altered with a text editor, not a word processor, because they insert fancy-pants constructs like paragraphs.  Notepad or Nodepad++.

I know zero about gcode or programming! Happy to have a go if someone can point me in the right direction 🙂

That’s the main problem.  g-code isn’t human friendly – it’s generated by a machine for another machine. So the human has to familiarise himself with the commands (M and G) and how they are applied to situations like holes.  Fairly obvious in a CNC machine where the g-code tells the machine to tool-change and poke a hole with a drill.  3D-printing is less obvious – holes are made by not extruding, or by steering the nozzle around the gap. More complicated.

I handle the problem by over-sizing the holes in CAD.    Haven’t tried Journeyman’s Horizontal Expansion control (it’s in Cura Print Settings->Wall dialogue) but sounds right.   Easier to have CAD or the Slicer do the work than edit g-code.

If you want to have a go:

• 3D-CAD a square plate with one hole in it.  (The simplest possible example)
• Slice the model and output g-code.  Make sure it’s not set to output g-code in binary.
• Open the g-code file with an editor (Notepad) and inspect
• The code that prints the body would be fairly obvious if the body was told to print in solid plastic.  More likely, there will be lots of commands that move the nozzle X-Y so as to lay down a plastic-saving cell-structure. Straight lines but with the X and Y coordinates both changing to print diagonals,
• Somewhere in the middle will be the commands that steer the nozzle around the hole.  Usually a bit complicated because the slicer strengthens walls by blobbing extra plastic.  There probably isn’t a single command that can be tweaked to widen the hole.
• Try it and see.  If the g-code makes obvious sense, by all means edit it.   Beat a hasty retreat if holes are made by dozens of complicated X,Y, Z bed movements requiring an edit to make many coordinate changes.

I am not sure if I can attach the gcode file on here?

Sadly not, despite being requested .  I either post a screenshot, only good for short examples, or link to Dropbox.

Dave

[JasonBModerator @jasonb]

Just put Cura Hole compensation into google and you will get plenty on how it is done either text or video.

[DC31kParticipant @dc31k]

You are focussing here on holes. How are other dimensions of the parts coming out?

There are calibration models that can be downloaded from all the 3D model sites that would allow you to tune your printer (and/or slicer) so the output is correct.

Fiddling about with the 3D model is not a great way to solve the problem. You should be able to take a model with a 13mm A/F hole produced by anyone in the world and it print at 13mm A/F. Think how inefficient it would be for anyone producing models to have to make a bespoke one of 13.2mm A/F just in case Martin wants to print it on his printer.

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A quick and dirty way to proceed would be to print the model at 101% scale. Everything else, including the hole, will be bigger.

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Buy an M5 coupling nut, heat it up and push into the recess, same with the clearance hole.

[JasonBModerator @jasonb]

DC321K look at the video I posted, Overall size OK. it is just the holes that are small. Compensation enlarges the holes but not the O/A which would happen if you applied a blanket percentage.

[Roy VaughnParticipant @royvaughn26060]

My experience with 3D printing is that dimensional accuracy is not its strongest point, at least on our Men’s Shed printer with my level of expertise.  Holes always come out smaller than dimensioned.  I simply add 0.2 to any diameter in the Fusion design for a close fitting part and more for smaller than 3 mm or so.  It’s unusual for the first print of a new design to be usable as is so I treat it as a sighting shot.  The next one is often OK after adjustments.  Judging by what I see on YouTube this is common experience.

[Gerard O’TooleParticipant @gerardotoole60348]

Follow John Journeyman’s advice and change the setting for Hole Horizontal Expansion in Cura.

Here is a screenshot from Cura 5.3.0 with the relevant setting highlighted in red. I had adjusted holes and internal threads to fit using this setting without any problems. Although you might need to reset it for each material you use.

[Julie AnnParticipant @julieann]

I only 3D print things I have designed so cannot comment on tweaking the G-code to alter downloaded models.

Generally the 1% increase suggested by DC31k is too large, 0.3% to 0.4% is nearer the mark. Even with that increase holes are still on the small side. Generally I just make the holes a little bigger in CAD. I no longer use Cura, having retired my Ultimaker printer, so can’t comment on any commands. I now use the Prusa slicer. The holes are still a little undersize, but not by as much. That suits me as most of what I am currently printing are parts for my engines to check form and fit before cutting metal. I prefer to leave the holes as designed and open up with reamer so that parts are a tight running fit when installed on the engine. Like this trial for the valve gear:

Julie

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