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.
Let me know what you think