Jump to content

New Raft design Maybe


Recommended Posts

Posted · New Raft design Maybe




So over the time of printing for the better part of this Year, I have had a lot of troubleshooting Regarding warping in the material while doing larger prints (8*8*8 cm and above, more or less). I have looked at a lot of things…. temperature of the build plate, nozzle heat and wall thickness. While they all have a saying in the outcome, warping of the raft is still common when I print lager objects.

So the raft design that is currently in place is way better then what we had before, but I am a construction engineer and I make prefab concrete structures for a living and there might be a better way of avoiding the raft warp as it does now when making big prints.

Okay so to those of you that is printing with rafts we know that warping comes from shrinking materials when it goes from hot to cold…. When a material is heated up it expands and when it cools it contracts. So let’s have a look at our current method.

Pic. from 1-4 shows how the raft is made to day. The lines is almost making the raft solid, and all the lines is facing in one direction. This model of the raft has greater cohesion then the old version yes, but it still lacking in dealing with the problem of all the shrinking forces in the materiel itself. This is shown I pic 5 where all the layers is shown in a cross section.

The first layer is closest to the heat bed and doesn’t shrink that bad because it does not cool as much, but keep in mind that it still shrinks, one of the options to reduces the shrinking is to crank up the heat, but in my experience it doesn’t always do the trick.

So in picture 6 I have tried to illustrate what happens to a material that have a difference in temperature from the bottom to the top, and the longer the individual string is the more it will bend because the differences in tension is bigger the longer a single string is. So when we look at layer 2-3-4 we see long continues lines that builds up the tension between the layers and make them warp when you are doing big prints.

So the smaller a line, the smaller the tension is in the material and I may have a way of dealing with that problem…. Now I am no programmer so I don’t know if this is even possible or not, but my solution can be seen in pic. 7

So this is building a 4 layer raft as is done now but instead of doing it in strait lines you do in a zigzag order, Should you need the first lines like in pic 1 that is no problem because it is in the bottom layer were shrinking is a minor problem. In this way you reduce tension in one strait direction and this may reduce warping In bigger builds.

So the most important thing is that we don’t want all of the tension forces to be going in one direction, but spread them out so that warping becomes more difficult for the raft.

PS I have found that when doing big prints a tall raft has helped me many times, making it about 7 mm with the heat of the build plate at 75 C, the warping tops at about 5 mm. so that the rest of the build can be done without warping, but this is only possible when the rafts stays in place and doesn’t warp to bad. The heat signature will look at bit like pic 8.

Rafts solution 1




Rafts solution 2

Let me know what you think


  • Link to post
    Share on other sites

    Posted · New Raft design Maybe

    It would be helpful to say which machine and material you are using.

    I can print 200mm x 200mm ABS prints on the UM2 without a raft at all, just brim.

    I don't think a new raft design is really needed.


  • Link to post
    Share on other sites

    Posted · New Raft design Maybe

    For ABS I use 110 bed and 250 nozzle, for PLA I use 70 bed and 220 nozzle. I think 75 is too high for PLA, even my 70 is said to be too high. Readhttp://umforum.ultimaker.com/index.php?/topic/3404-printing-on-glass/ by gr5.


  • Link to post
    Share on other sites

    Posted · New Raft design Maybe

    You're spot on that the heat gradient is the killer. I've predominantly seen PVA glue used to combat warping.

    Other options are building a wall around your object that keeps in hot air, or modify your printer to be enclosed and heating it up to just under the glass temperature of the material.

    I'm not so sure whether your idea would fully work, since shrinkage is proportional to the size of the object, and changing the direction of your lines just changes the direction of shrinkage. Have you tried to write any gcode for it to do some experiments?


  • Link to post
    Share on other sites

    Posted · New Raft design Maybe

    @ woofy: I have tried that but talking to the community here in Denmark it seems to me that most people is in the need of keeping their printer in a heated room so they do not need to apply more heat to the build and I think that is way I need the bigger temps.…. I understand that now. And thank you 4 the feedback.

    I may have come to the conclusion that the room that I am printing in is too cold in the morning where I begin my prints, and when the printer has heated the room, the print stabilizes. And that I need to use glue to keep the print in place.

    @svanbennekom: thank you for confirming that :D … so no I haven’t ever written any gcode before, and that is kind of my hope that someone will find this idea inspiring enough to make a gcode and test it.

    So the theory of expansion and contraction in materials is the same in every material, according to elasticity theory. And in the pic below I have illustrated what will happen to an ordinary strait line contra a line that is zigzag shaped. Pic 1-2 and 4

    So when we look at the first strait line we see that the longer the line is the more it will expand when heated, the small line will only contract a bit and the long one will contract more, and the longer it becomes the force in the direction it faces will become greater. When applying Newtonian law every action has and equal reaction there by the 2 arrows.

    The same thing is happening in the steal in concrete elements, and in steel structures when heated and cooled.

    Now bear in mind that cohesion to the build plate is to stop the object from moving upwards, so if we look at the bending line the forces will move the object ass shown pic 3. The upward motion is a side effect of the material cooling down.

    So to minimize the forces in a single direction the zigzags will have to be small so the upward motion is less than the cohesion to the plate.

    I have illustrated that as well, as you can see the small zigzag pattern could cut the force in one direction in half, and counter the upward motion that the long strait lines have, and making them zigzag will help counter line length reduction in one strait direction.

    So when you make zigzag layers instead of strait lines you will help spared the contraction forces in the raft.

    In the last illustration I have tried to illustrate how I think the forces will go in a zigzag line, and that making it zigzag maybe will help reduce contraction in the material a bit.

    raft solution 3


  • Link to post
    Share on other sites

    Posted · New Raft design Maybe

    pic 4... the arrows that have an angel is pointet in the wrong direktion,,, you will have to imagene them pointing in the opposit direktion... sorry


  • Link to post
    Share on other sites

    Create an account or sign in to comment

    You need to be a member in order to leave a comment

    Create an account

    Sign up for a new account in our community. It's easy!

    Register a new account

    Sign in

    Already have an account? Sign in here.

    Sign In Now
    • Our picks

      • 🎄✨ Thingiverse Tree Ornament Challenge! ✨🎄
        We've been running a Tree Ornament Challenge with a chance to win an UltiMaker S3 or colorFabb filament.
        Design a 3D printable tree ornament and join our festive challenge on Thingiverse. 🎁✨

        📆 Submission Deadline: December 22
        🏷️Tag your designs with Holidays2023

        Click here to join and check out the over 300 other amazing designs

        How to Enter
        Design an Ornament
        Create a 3D printable tree ornament that captures the magic of the winter season. Think snowflakes, sleighs, reindeer, cozy mittens, or anything that embodies the joy of the holidays. Upload to Thingiverse
        Share your masterpiece on Thingiverse and add the tag Holidays2023. Don't forget to include a captivating description and images that showcase your design from different angles. Submit by December 22
        All entries must be submitted by December 22nd to be eligible for consideration.
          Entering a new design
        Entering an existing design
        Winning designs should:
        Be original Creations
        Your designs should be original works, avoiding the use of others' intellectual property without permission. Include STL Files
        Each submission must include at least one STL file for 3D printing. Showcase a Completed Print
        Provide at least one photograph featuring a completed print of your design. Include Documentation
        Share the creative journey! Include documentation of your design process, giving us a peek behind the scenes. For example, show a screenshot of the model in your design program. Use the Tag Holidays2023.
        Use this tag to ensure your entry is counted in the Tree Ornament Challenge. Be submitted after October 1st, 2023
        Ensure your design was uploaded to Thingiverse after October 1st, 2023. Adhere to Submission Guidelines and Terms of Service
        Make sure your submission aligns with our guidelines and Thingiverse's Terms of Service.  
        Good luck 🎉
        • 1 reply
      • S-Line Firmware 8.3.0 was released Nov. 20th on the "Latest" firmware branch.
        (Sorry, was out of office when this released)

        This update is for...
        All UltiMaker S series  
        New features
        Temperature status. During print preparation, the temperatures of the print cores and build plate will be shown on the display. This gives a better indication of the progress and remaining wait time. Save log files in paused state. It is now possible to save the printer's log files to USB if the currently active print job is paused. Previously, the Dump logs to USB option was only enabled if the printer was in idle state. Confirm print removal via Digital Factory. If the printer is connected to the Digital Factory, it is now possible to confirm the removal of a previous print job via the Digital Factory interface. This is useful in situations where the build plate is clear, but the operator forgot to select Confirm removal on the printer’s display. Visit this page for more information about this feature.
          • Like
        • 0 replies
      • Ultimaker Cura 5.6 stable released
        Cura now supports Method series printers!
        A year after the merger of Ultimaker and MakerBotQQ, we have unlocked the ability for users of our Method series printers to slice files using UltiMaker Cura. As of this release, users can find profiles for our Method and Method XL printers, as well as material profiles for ABS-R, ABS-CF, and RapidRinse. Meaning it’s now possible to use either Cura or the existing cloud-slicing software CloudPrint when printing with these printers or materials
        • 13 replies
    • Create New...