Why Do I Need a Raft or Brim In 3D Printing?
If you are this far along in your 3D printing education, you probably already know how a 3D printer works. But just in case you don’t, here are the basics:
- The printer heats a filament, typically plastic.
- The printer injects the filament through an extruder onto a printing bed.
- Layers are built up as the extruder moves, resulting in your final model.
Potential problems can arise when using certain filaments. If you use ABS, it can be prone to warping when it does not adhere to the surface of the printing bed. This can result in a mangled, unusable final printed object.
Another possible issue is that your extruder may not begin printing optimally as soon as you start. Since you are just starting the print, it could come out unevenly, or the material may not be fully engaged. In this case, you could wind up with gaps, lumps, or bubbles in your physical, printed model.
Both of these issues can be addressed using a raft or a brim. Each is a solution intended to improve adhesion and prevent warping on the finished model.
There are some options for improving adherence, of course. You can put glue onto your printing bed, but smearing a glue stick all over your printing bed (and then having to clean it up afterward) might not be a great solution. That’s where a raft or brim comes in. The extra filament used to print a raft or brim adds some expense in unusable material, but it can make sure your final print is picture perfect.
What Is A Raft In 3D Printing?
For the best chance of printing out a perfect model, a raft is the most failsafe option. A raft is added to your digital model and prints out underneath the piece. It supports the printed model and provides a sturdy base for it. If warping occurs on the bottom of the raft, it is fine because you will be discarding that material anyway.
A raft starts with a few flat layers built up directly on top of the printing bed. The bottom layers are generally printed thicker and slower than the top layers. This makes sure that the base is solid. It also helps to ensure adequate adhesion, which translates to a more pristine finished piece.
Once the base layers of a raft are printed, several layers of a mesh are printed on top of that. Think of these layers like the spines of a dense hairbrush. They extend up from the thick base but do not cover the bottom of the model. This mesh will support the model, but when you are finished with the print, they will separate from the model itself to be discarded.
Raft Design Details
A few factors will go into the design of your raft when you decide to add one to your model. You will have to find the settings in your 3D printing software to adjust them for these parameters, as they will affect the speed of your print, the amount of filament you use, the effectiveness of the raft and the ease with which your piece is separated from the raft.
- Raft Base Layers. You will generally want to print the base layers of the raft more slowly than the rest of the model. You are printing the raft to improve adhesion, and thicker layers at the base of the raft will do just that. It is worth the extra time to make sure that your raft base is solid and fully adhered to the printing bed.
- Raft Top Layers. The top layer is the mesh that supports the model itself. Your software may generate the mesh automatically, leaving you to decide how many layers of the mesh you want to use. You will want at least 2-3 layers to make a surface that will support the model printed on top of it and still allow it to be separated when the print is finished.
- Separation Between Model and Raft. You will need a very small gap between the raft and the model to make sure you can disconnect it easily after printing but still maintain contact during printing. The exact distance will depend on the printer, your material, and the software you’re using. If you find that your models don’t sit where they’re supposed to, reduce the separation. If they are hard to separate, increase that separation.
- Raft Offset. When you design your raft, you will need to decide how far out from the model the raft extends. It should stick out a little to make sure it supports the model adequately, but remember that more offset means a larger raft, and a larger raft means more material wasted.
Advantages and Disadvantages of a Raft
Should you use a raft when you are printing your model? There are a few advantages and disadvantages to consider when making that decision. The decision comes down to a trade-off between time and material versus end-product finished quality.
Some advantages of using a raft include:
- Superior adhesion to the printing bed. A raft is essentially the ultimate solution for adhesion problems. Superior adhesion is critical for a polished final product.
- Less warping. Because the base is printed so thick, it is less likely to warp. If it does warp, it doesn’t matter because you can throw it away.
- Better printing if your piece has small points of contact with the bed. A raft provides a more stable surface if your model touches the printing bed at multiple, smaller points, rather than having a broad base. Spindly legs are extremely prone to warping, so placing a raft under each leg is a good way to make sure they print correctly.
Some disadvantages of using a raft include:
- Waste. A raft uses considerably more material than a brim, and since you are going to throw the whole thing away, that’s a lot more waste in both time and material.
- More difficult separation. Because a raft makes contact with the entire base of your model, it can be tricky to separate it. You may have to use a small trowel or another tool to separate the model. A smaller model may come away easily, but the mesh is designed to hold the model in place, and separating it from a larger model could require some effort.
- Added finishing time. When you do get the model separated from the raft, the base of the model will be rough and likely require sanding. This adds to the time you will have to invest in getting a polished piece. If you are producing pieces for sale, either as custom pieces or as mass-produced items, this could wind up increasing what you need to charge for your finished pieces.
What Is A Brim In 3D Printing?
Unlike a raft, a brim is extra material printed along the outside of the piece. It does not extend underneath your model. Where a raft supports the model, the brim merely extends from it. Since warping is more common along the edges of a print, the brim provides a safe area that can be discarded. If you print a brim onto your model, it can be peeled away with little effort once the piece is printed.
A brim is a great deal simpler than a raft, though not as reliable. You add a few extra layers to your model that extend outward from the base. It looks like a hat brim extending from the bottom of the model, which is where the name comes from.
Brim Design Details
A brim has fewer design considerations than a raft, but there are still some factors to consider as you are designing the brim to add to your model. As with the raft, your 3D software should have fields to adjust these settings.
- Brim Layers. You will need to tell your software how many layers tall you want to make the brim. Each layer adds additional protection against warping and improves adhesion. More layers, however, means more material used, more time spent, and potentially greater difficulty removing the brim from the finished model.
- Brim Outlines. Each ring you print around the base of the model improves adhesion and minimizes warping but also costs more material and time. Also, if you have concerns about priming the extruder and giving it time to extrude a consistent stream of material, you may want to extend the ring a little further. You can also use a skirt for extruding. (Keep reading for our discussion of using a skirt in 3D printing.)
- Brim Offset. Most 3D printing software should include the option to add a slight offset between the model and the brim. The default separation is probably zero, but if you are having trouble peeling the brim off the base of your model, you can add a very small separation (0.1mm or so), and this will make the brim easier to peel away.
Advantages and Disadvantages of a Brim
A brim is a simpler solution than a raft if you are trying to minimize warping, improve adhesion, and prime the extruder. Of course, it is not perfect for every situation, so here are a few things to consider when you are deciding if a brim is the best solution.
Some of the advantages of using a brim include:
- Prevents warping on your model. Because the edges of your brim are located away from the model itself, if any parts of the print do warp, you will be throwing them away anyway. Theoretically, the warping will not extend to the model itself, so you will not have to worry about compromising the final print.
- Uses less material. Since the brim is not built up underneath the model and is just a few rings around the outside of it, you will spend less time and material building a brim on your printed piece than if you used a raft.
- Easier to remove. Where a raft may require a special tool to separate it from the printed model, a properly printed brim should peel away. This means you spend less time cleaning up after you print. It also means you do not need any special tools to remove the brim.
- Smooth bottom layer. Since the bottom layer of your model is printed directly onto the printing bed, it is nice and smooth and will not require sanding. This can drastically impact post-production clean up time, and if you are printing for sale, time is money.
Some of the disadvantages of using a brim include:
- Less reliable than a raft. A brim is a great solution for an easy piece with a wide base, but it does not provide as stable a surface like a raft. Warping is more likely with a brim. If your model has spindly legs, a brim may not work at all and break off the feet and ruin the entire piece.
- Still requires some cleanup. After you peel off the brim, you may be left with an uneven ridge around the base of your model. This will require some sanding to finish the piece.
- May break the model. If you do not carefully peel the brim from the model, you may end up damaging the model itself. This is especially a concern if your model has tiny components around the base.
What is a Skirt in 3D Printing?
You now know the difference between a raft and a brim and how each of them addresses the issues of printing bed adhesion and material warping. Another feature can help protect your 3D printing projects, too – it is called a skirt.
A skirt in 3D printing is essentially just a ring that is displaced far enough away from the model that it will not touch the model at all. It is completely separate from the model. When you remove the model from the printing bed, the skirt will be left behind, and you will have to peel it up on its own.
The purpose of a skirt is simply to prime the extruder. When you initially begin your print, the extruder may be moving as if it were printing but not extruding any material. The material may also be coming out in fits and start leaving gaps that would compromise the finished model if printed directly onto the piece.
Printing a skirt allows you to make sure the printer is performing as expected. At the expense of a small amount of material, you give the printer time to warm up and perform consistently. You will also be able to monitor the beginning of the print and make sure it is printing properly.
Skirt Design Settings
Printing a skirt is a very simple process – much simpler than a raft or a brim. There are still factors that go into adding a skirt to your digital model to make sure you get the best results.
- Offset from model. Since a skirt is never supposed to touch the model itself, there is a lot of flexibility as to how far away you want it to print. A wider skirt means more material used, but the amount is relatively negligible, so give it ample space – somewhere around 5mm should be fine.
- Outlines. You can set the skirt to print multiple outlines. If your printer finishes the skirt and goes right on to the final model before the extruder is fully primed and ready to go, you may want to run another layer to make sure you are giving the printer enough time to warm up.
- Layers. You can add layers to your skirt, but there is rarely any good reason to do so. The only reason would be to allow the printer more time to prime the extruder, and you can accomplish that goal by increasing the outlines.
