Supported overhang gets rounded
I'm trying to print a semicircular block with a (male) dovetail wrapped round the outside of the circular face. I've tried it in several orientations, and the best way seems to be to have one of the sides lay on the build plate, with the semicircular edge of the block on the build plate....gives me the best circular faces. Because of this, the dovetail attaches to the (now vertically oriented) curved face and needs supports.
However, the lower edge of the dovetail that is supported (on Slicer-generated supports from the build plate) gets rounded and distorted. The upper edge, without supports, is fine, nice sharp edge, but the lower one is just a mess, looks like where there should be an angle its just smeared the PLA. Has anyone seen this happen, and can advise of a fix....its weird, because a while ago, I did this same print, with slightly different dimensions, and it worked fine: good sharp edges on both sides of the dovetail wrapper
Thanks
Jim
Best Answer by bobstro:
That looks like a fairly typical result of printing atop supports. To be removable, supports require some distance (Print Settings->Support material->Options for support material and raft->Contact Z distance) between the support and supported layers. The greater this distance, the easier it is to remove supports. The problem is that the layers being supported are literally printed on air. There is no squish against the underlying layers, so extrusions come out round rather than flattened ovals. This reduces inter-layer adhesion and the initial layers above supports can sag. You'll see a similar stringy rough underside on the bigger supported areas.
- If this is your own design, include some sacrificial supports in the STL. Provide a ring that extends from the base and supports the lowest dovetail layers. Model it so the interface is thin and easily broken away after printing. This is the best fix. Angus has a good video on this topic on his Maker's Muse YouTube channel.
- Reduce temperature or increase cooling. Hot filament sags more readily.
- Print slower in those areas. With good cooling, this can help the extrusions firm up faster as they spend more time under the fan.
- Vary extrusion widths. This probably won't help much in this case, but wider extrusions provide more overlap between layers. When used with low layer heights like the 0.1mm you're already using, this can help with overhangs. Unfortunately, your supported dovetail is an overhang that begins in free air, so results may vary.
- Reduce Contact Z distance, but that may make the supports even harder to remove.
- Use dissolvable supports that don't require a contact Z distance, but you require a MMU or multi-extruder setup to use those successfully.
If you still have the gcode from earlier prints that yielded better results, you can import them into PrusaSlicer as a config file to recover the settings.
RE: Supported overhang gets rounded
Save your current 3MF project file, zip it up, and attach it to a reply here so we can see your part & settings and give better recommendations.
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He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Supported overhang gets rounded
Here is the part as requested
Jim
RE: Supported overhang gets rounded
And just to be complete, here are some photos of the part. Its only the external (male) dovetail that is affected, and only on the side that faces down, and should rest on supporting material. The female dovetail grooves (which I expected to be much harder to make) work fine.
The picture "successful Edge" shows not only the edge that worked (was facing uppermost) but also shows the orientation of the block when on the build plate. The photo "Failed Edge shows the mess thats left after the supporting PLA is removed
RE: Supported overhang gets rounded
That looks like a fairly typical result of printing atop supports. To be removable, supports require some distance (Print Settings->Support material->Options for support material and raft->Contact Z distance) between the support and supported layers. The greater this distance, the easier it is to remove supports. The problem is that the layers being supported are literally printed on air. There is no squish against the underlying layers, so extrusions come out round rather than flattened ovals. This reduces inter-layer adhesion and the initial layers above supports can sag. You'll see a similar stringy rough underside on the bigger supported areas.
- If this is your own design, include some sacrificial supports in the STL. Provide a ring that extends from the base and supports the lowest dovetail layers. Model it so the interface is thin and easily broken away after printing. This is the best fix. Angus has a good video on this topic on his Maker's Muse YouTube channel.
- Reduce temperature or increase cooling. Hot filament sags more readily.
- Print slower in those areas. With good cooling, this can help the extrusions firm up faster as they spend more time under the fan.
- Vary extrusion widths. This probably won't help much in this case, but wider extrusions provide more overlap between layers. When used with low layer heights like the 0.1mm you're already using, this can help with overhangs. Unfortunately, your supported dovetail is an overhang that begins in free air, so results may vary.
- Reduce Contact Z distance, but that may make the supports even harder to remove.
- Use dissolvable supports that don't require a contact Z distance, but you require a MMU or multi-extruder setup to use those successfully.
If you still have the gcode from earlier prints that yielded better results, you can import them into PrusaSlicer as a config file to recover the settings.
and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Supported overhang gets rounded
Thanks Bobstro, I'll follow your suggestions, all of which make sense. I appreciate your quick and very full response, I've only had the printer a month or so, and it's a vertical learning curve, but VERY interesting and I'm enjoying myself, which isn't bad when the printer was a means to an end (rapid prototyping an idea I have...)
Thanks
Jim
RE: Supported overhang gets rounded
Most of all, have fun with it and experiment. I've made a few accidental discoveries that are really opening up opportunities. Let us know what results you get. Lots of users search these posts weeks or months later looking for the same answers.
and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Supported overhang gets rounded
@bobstro
You gave me all I needed....one day later and three different experimental prints and I got a reproducably good-quality print. There is one additional point I discovered when "playing"...mine is a Mk3S+, and the cooling fan is at the front of the print head. I found that by orienting the dovetail towards the fan, I got much better results than when it was facing the other way (the way Slicer wanted to put it).
Thanks for your helpand encouragement!
Jim