First of all, let’s check out how easy and sweet it is to remove the supportive raft from your 3D print. All you need to do is just to follow my instructions in the rest of this blog!
The reason to print a supportive raft or base underneath your 3D model is obvious: the base absorbs any imperfections of your build plate; and if curling has to happen, it only affects the base, will not infect your model, so that your model bottom could retain flat. The raft, however, is not easy to come off if they are print in the same way as the real part. It is really a dilemma in which you hope your raft to be sticky enough to hold your model from corner-lifting, while at the same time, you don’t want your raft to stick too much to come off. Is it possible to achieve this if we use the same material printing with the same mechanism? The answer is yes, or at least, there is one product available on the market doing this just well — the UP! 3D Printer, famous for printing peel-able supportive raft/base.
Unfortunately, the UP!3D is not part of the open source RepRap community, which means the algorithm behind their famous peel-able base remains mysterious. Taking a closer look at the UP! 3D printer, I didn’t find anything special about the hardware — Nozzle, 3 DOF axis, HBP — pretty much every basic element you would expect on a 3D printer. So the key stays in the software, the slicer. Since the latest version 0.9.9 of open-source slic3r included a new feature of “Raft“, I decided to give it a try to see if it reproduces the same peel-able raft on my Type A Machine Series 1. I believe if my algorithm works, you should also be able to do the same thing on any other printers.
Figure 1. Visualization on Repetier-Host of print raft (left), without raft (middle), and real print from UP!3D with raft.
This photo makes me really excited! For the first time, the Slic3r is producing a similar raft to the UP!3D. My question is whether the raft could be peeled or removed easily. I went ahead printing this part and here is the result.
Figure 2. A big piece of the raft remains on my print. It sticks very tightly to the bottom of my part and couldn’t be removed. So my conclusion for the new feature of 0.9.9 is NO, the raft is not peel-able.
Let’s first take a look at the g-code generated by the new Slic3r to find out what exactly the “raft” is. I recommend using Repetier-Host to visualize the g-code as you can view your model layer by layer, which provides a very straightforward way of examining the output from Slic3r. I am slicing my test model, which is a 1.75″ x 1.75″ x 0.2″ plate, at 0.2mm layer height resolution with 49 extra raft layers. Here is what I saw from Repetier-Host (Used photoshop for better analysis).
Figure 3. As you can see, there are 1 layer of brim and 49 layers of supportive raft print below the real part. The top 3 layers of raft are set to print solid, also called “Interface layers” by Slic3r. The very top interface layer is only 0.129mm away from the the layer underneath, rather than 0.2mm. The interesting thing is the extra middle layer between the whole raft and the real part，marked as “separator layer” in the image. It is automatically generated by Slic3r, about 0.321mm away from the very top interface layer. It seems that Slic3r wants to make a very solid raft top by printing top 2 interface layers close together, and an easy peel-able upper part by printing the extra middle layer and everything on top of it a little bit far away.
This is a good idea! As we know, 3D print is basically stuck together one on top of another layer. Printing two layers closer together makes the binding stronger, and vice versa. But unfortunately, it doesn’t seem to work out completely, as Figure 2 shows that only part of the raft is removed, others stay very tightly on the bottom of the model. So, I tried to increased the upper model (including the separator layer) a little far away from the base by another 0.1mm. And also, since the nozzle temperature also affects the filament binding effect, printing the separator layer under 200°C rather than 235°C help reduce the material stickiness. Slic3r, however, doesn’t seem to support my idea at this point, I ended up writing my own codes to post-modify (increase gap, lower temperature) the g-code generated by Slic3r. For temperature change, I use:
M109 S200 ; Sets target temperature and waits until temperature is reached. M109 S235
It takes the nozzle about 1 minute to cool down to 200°C and pretty much the same amount of time to rise back to 235°C. I observed a small amount of filament flows out of the nozzle during the waiting, and inserted some codes to raised the nozzle 2-3 inches above the print for the purpose of easy cleaning.
Figure 4. The seam (left) between the model and raft has been increased to 0.4mm, wide enough to be visible in Repetier-Host. The line in cyan on the right is the nozzle travel. Here is the video of how the customized code is in action on my Type A Machine.
And here are some results!
Figure 5. Now the 3D print raft is peel-able with improved Slic3r. Hope Slic3r will soon include this feature into their upcoming version!