Hi
For design reasons, I often need a radius that starts from the first layer.
And I don’t want any support.
The radius is usually between R0.5 and R3 mm.
This seems almost impossible, especially since the overhang is very large on the second layer,
I print from the inside out!
I have already unsuccessfully experimented with adaptive layer height,
starting with 0,08mm layer hight.
Reducing the elephant foot compensation also did not bring any real progress.
For me, it always looks as if the radius starts at 45°. Radii smaller than R1 are hardly depicted at all.
A 45° chamfer with small radii is, of course, easier—but that’s not what I want!
A true unsupported fillet can not print totally cleanly with FDM. It is not possible.
Small layer heights will help, but the first few layers will always sag. This is a problem caused by gravity. There are exactly two options for getting clean ‘fillets’ from the bed.
1-use breakaway support with a support filament as the interface, and use a zero z support interface distance. This will only work with a dissimilar filament (like petg with pla), or a dedicated breakaway/soluable support filament.
2-use modified fillets that begin as a chamfer. These can print with no support and usually still look good. Check this video:
Not all geometries are possible with FDM. You need to design-for-manufacturing, not design first and then hope your tech can make it. It takes a change in thinking in the design stage. I don’t mean that to be bossy or harsh - it’s a lesson that took me a long time and much frustration to learn. In the end, Learning to design within the constraints of the production technology yields better designs, and less frustration!
I got a resin printer to overcome of the things that are not or hardly possible in FDM - especially when it comes to very fine details and structures.
Even with this great machine those first few layers not always come out as perfect as the model itself.
I have several dedicated print and filament profiles to address certain print issues - you have to make compromises in FDM, starting but not ending on the design level already.
If you have to use a FDM printer for prototyping then there is no way around using a design software that allows you to apply modifiers reliable to the entire model.
One for those FDM models, one for injection moulding, one for machining in steel - all with matching tolerances for the manufacturing process.
Back to your particular issue…
The type of filament matters, some behave nicer than others.
For first layers as good as possible while they have rounded edges and overhangs you need a smooth plate.
The inconsistencies from the textured PEI plate are great for adhesion but bad for precision.
All filament and process setting have to combine to result in the first layer already printing smooth and clean for it’s top surface.
Anything less means those defects will affect the following layers.
Speaking of layers - they matter as much as the number of walls for those overhangs and curved walls…
Ideally you want and overlap to the previous layer and you don’t want to go over the outermost part of it by more than 10 to 15%.
Anything above means the extruded filament just sags away and precision goes down the drain as much as the surface quality.
How does that translate to you model now ???
R3.0 is certainly doable to a certain level, R0.5 is something near impossible in a print level but very easy to do in post processing.
Ever played with Lego ?
Same principle when it it comes to those growing layers that love to curl up or get messy…
Every layer is a brick - your layer height.
If you use a layer height of 0.1mm and the initial radius of your wall is 3mm:
Starting with 0.1 instead of the default 0.2 would give you 30 layers to deal with this curve.
Using 5 walls in that section should result in clean results - sadly Studio does not make this easy.
But for R0.5 and just 10 layers to form it you would need a layer height of 0.05 from the start - hence the impossibility.
Unless your models are rather complex ceramic de-burring tools might be easier than trying the impossible.
Available not just in the usual straight and angled edge but also in sets with curved and V-shaped edges.
Far from ideal in terms of getting accurate results but well worth investing in to as they make the clean up of slightly messy first layers quick and easy.
Whenever I need and accurate radius around the edge of a flat part I prefer to split it if I can’t change the orientation to make it a top or side wall.
Far easier to use some filament cuts as orientation pins and to to glue or solvent weld the two parts then trying to print the impossible.
Only way I know to overcome all this would be using disolvable filament for strong supports right from the build plate.
These however won’t work with all filaments, are quite costly and still need a lot of tuning to make it all work out as planned.
Might be easier to print the first layers a bit stronger and to use a router with matching bit for the matching radius…
