Setting Blender 4.3 to work in millimetres

I've started to use Blender again. It's been a couple of major versions and a couple of years since I last used Blender in anger. I'm a bit rusty to say the least.

That said, one of the first things I've needed to do still has the same, old school, non-intuitive setup that it has always had. That is setting the units to be suitable for 3D printing. That is millimetres.

Units

Setting the units is done in the Scene tab, usually on the right of the screen.

 
So that imported models, that are already at the correct size for 3D printing, to remain that size when exported again, it is necessary to not only set Blender to use Metric units and Millimetres for length but to also set the Unit Scale to 0.001.

I'll repeat. Unintuitively, it is necessary to set the Unit Scale to 0.001. That adjusts all the other setting, including importing.

[I have never understood why Blender's import routine does not simply leave the coordinates of imported models untouched unless I deliberately set an import scale. What Blender appears to do is assume that all imported models' units are in metres and so it multiplies everything by 1000 when the Length in Blender is set to millimetres. Very odd to me. Anyway, setting the Unit Scale to 0.001 gets round that problem.]

Object

I like to delete the default cube and add it back. Just to make sure it appears correctly as 2mm along each edge.

Create an object using [Shift][A]. Select Mesh and Cube.

I leave the default at 2mm but if I wanted another default size for created meshes, it can only be done before any other action is taken. The moment I click anywhere else, the option to change the size is no longer available. Once done, the next mesh created with [Shift][A] will create at my preferred size.

I use [N] to open up the Object Transform window to check.

Clipping

By setting the Unit Scale, the clipping is also automatically adjusted. To check, I zoom in on the newly created cube. It should be possible to zoom right up close and inside the cube, without the near corner being cut off.

To show the clipping settings. Pull out the side tab with the [N] key then select the [View] tab.

If the Unit Scale has been set to 0.001, then the original values have been divided by 1000, giving a near clip of 0.01mm and a far of 1000mm.

Focal Length

I usually leave this set at 50mm, however, I have noticed that some artists working on sculptures prefer an 80 to 90mm focal length.

Grid

The floor grid scale will also have been changed to of 0.001

That can be seen from the Viewport Overlays.

Camera and Light

When creating models for 3D printing, I do not use the cameras or the lights. I find they, more often than not, get in the way. So I delete them. If I was rendering models, I would move these to appropriate locations.

Saving as the Default

To keep these settings so that all new files already have these settings, arrange your default scene and:

File -> Defaults -> Save Startup File.

The factory default can be recovered from the same menu, if ever needed.

Changing an Existing File

I find that if I change an existing file to Millimetres it is very likely that I will need to change the size of any existing objects.

In Object Mode, select the object to scale, press [S] type 0.001 and hit [Return].

Then apply the scale, so it is baked in. Use [CTRL][A]+[S].

Having the Object Transform window open, [N], is useful to check the results.

Conclusion

If you don't mind the units showing as metres, you can avoid all that trouble and just leave Blender set to Metres. Models will import and export unchanged.

For 3D printing, I don't like that. I prefer to be able to quickly see the units I'm working in.

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34 hour print

I've had my Ultimaker 2 for nearly 10 years. A couple of days ago I did the longest running print that I have done. It lasted very nearly 34 hours. Followed shortly after by the second longest print I've done at 30 hours.

The first was a duct for our kitchen extractor fan.

The second is a cosmetic cover to fit in a cupboard to hide the extractor duct.

Both were successful prints.

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Heygears resin reminders

I've printed a few resin objects and in a couple of different resins.

I want to remind myself of the results. Bear in mind that I am new to resin printing and these are my experiences and opinions.

PARP10

Described by Heygears for "rapid prototyping".

My Experience:

Surface: Smooth and crisp.

Detail: Very good. Sharp corners.

Toughness: I can drop the models on the floor with no sign of damage.

Flex: Negligible. It'll break if bent.

Prep ease: Very easy. No additional thought needed just position and use auto-supports.

Minimum cure time: 5 minutes.

I would use this for: Miniatures, non-stressed components and decorative pieces.

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PAU10

Described by Heygears as "ABS-like".

My Experience:

Surface: Slightly soft.

Detail: Moderate. Slight curves on corners.

Toughness: I can drop the models on the floor with no sign of damage.

Flex: Some. Tricky to break. Bends a bit first.

Prep ease: Needs more supports on long thin objects otherwise they flex while printing.

Minimum cure time: 10 minutes.

I would use this for: Component cases and functional parts.

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Subjective

The above statements are a bit vague and very subjective. I will adjust them over time as I gain more experience, but they should be viewed only as a rough guide.

Drop Test

My very simple test is to drop the model from about a metre above ground onto a concrete or similar floor. Repeated a couple of times. For most of what I print, I want them to survive careless handling, but I don't need industrial strength.

Curing Times

I use the Heygears cure unit. I find that sending the model to the cure unit is an unnecessary step, especially as I rarely remember to turn on the cure unit in advance. I've sent a couple of test models, to gauge the times, then for most of my prints I manually set a cure time from the dial on the front of the machine.

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