This post is about the detailed design of a 3D printed simple kitchen sink strainer. I tried a few existing models but none fitted properly and none worked perfectly. This is an article about all the details needed for such a simple piece.
Initial Research
Looking at the strainer that came with the sink, I noted a few details that made it limited in functionality. Mainly, it was not great at catching smaller particles as the sink emptied in the pipe. We live in the country and our house has a sceptic system. It is recommended to send as little food particles in the system as possible. Yes, very small particles will eventually get “digested” in the tank, but it is a good idea to limit those quantities (this article has more info). The strainer is also very shallow and quickly gets clogged by particles.
Design parameters
1- Diameter of the sink hole: How tight should it fit? What is the printing tolerance (Answer: tight, no space and use a good printer)
2- Depth of the sink hole: Should it touch anything except the side? (Answer: As deep as possible, to catch as much sink debris as possible)
3- Shape of the sink hole: Goes with the previous point
4- Diameter of each hole in the strainer: Will fine food particle go through? (Answer: As many as possible without affecting solidity, and as small as 3 mm)
5- Number of holes in the strainer: There can be a lot of water in that sink… (Answer: As many as possible without affecting solidity)
6- Diameter of each hole in the strainer: Will fine food particle go through? (Answer: My tests show that 3 mm catches nearly all the debris)
7- Type of plastic used: PLA warps (see this post)
8- The strainer should be contained completely IN the hole instead of resting at the bottom of the sink. This design parameter allows all the water to evacuate faster without leaving a thin layer of water at the bottom of the sink, which lets gunk (bacteria) build up fast.
Process
First, let’s measure the existing sink hole! I used a precision caliper to measure de diameter of the hole. In this case, it is 84.5 millimetres. I also measured the metal sink hole plug that came with the sink. Its diameter is 83 mm. We will come back to this in a bit. The metal strainer is about 15 mm deep and has a rounded side, to fit the shape of the sink hole. It also has a pin under the bottom to let it engage in the hole at the bottom of the sink hole. The metal used (stainless steel) is quite thin (0.40 mm). Although I can print the part that thin, it will deform too easily and will definitely won’t be solid enough. It’s clearer in the photo…
I decided to use Autodesk Fusion 360 to design the part. I also made a version in shapr3D on my iPad. Both offer a fairly straightforward way to make curved surfaces and also offer a simple way to fill a surface with holes without having to insert them all one by one…
I made a total of 7 versions of the strainer to finally get it right! Here’s the story, in all the (boring?) details…
A simple version
This version works, but it is not deep enough so it does not collect enough detritus before it fills. Plus, because it only touches the sides, it has a tendency to shift position. Also, the diameter is 83.00 mm. This was my choice because it is the diameter of the original metal strainer and to make sure it would fit the hole (tolerance). The problem is that it is lose in the hole so it eventually tilts sideways. Another problem is the diameter. Small bits of sink garbage get lodged between the strainer and the side of the hole. Some will just go through, but the main problem is that when you pick up the strainer, whatever is resting between the strainer and the hole goes in the pipe, negating the whole purpose (or the hole purpose…).
A more complete version
This version is deeper, and the diameter is 84.5 mm, matching the sink hole diameter. I use a high precision printer and the fit is perfect. A few problems left: the holes in the strainer are 5 mm. This will let particules of food through. So I decided to try with 3 mm holes.
A nearly final version
This version uses 3 mm holes. Note the ring of holes in the transition face between the bottom and the side. When I tested this version, the water would take forever to drain from the sink. I figured that surface tension of the water and not enough air escaping the sink hole to balance the pressure differential were causing the problem. I also limited the total number of holes in the strainer. The quantity I use is enough to allow a rapid passage of water, and by leaving more than one millimetre between holes, the strainer is much more solid.
In the final version, I replaced these holes by air relief “holes” or dimples on the same face to let the side holes act as air intakes. In the original metal strainer, the rim was not touching the side of the sink hole. This allowed air to pass between the rim and the sink hole side, facilitating water and air passage. My design is air tight, but because I added the dimples, air can pass from the side holes to the space under the strainer to relieve pressure.
A few more details
The lip at the top of the strainer has a special design. The top is flat (I might try a slightly angled version) and the rounded edge under the lip allows the strainer to have a minimal contact surface with the side of the sink hole. The reason for this feature is because the side of the hole is rounded and a thicker lip would have compromised the tight fit. The Fusion 360 design does not include a center pin, used to pick up the strainer to empty it. I could have done this in Fusion, but decided to use Bambu Studio instead. I know how to add geometric features in Bambu Studio and I also did it just for the “challenge” (plus it would have taken me longer in Fusion…). This detailed 3D print design process is using more than one tool on purpose.
Ready to print
The final version in Bambu Studio. The center pin is just a cylinder, to which I added a sphere. I also made a hole in the middle of that pin to let more air through directly into the pipe. The top of the pin sticks out above the rim of the sink hole. This prevent water from going into the hole in the pin and makes the strainer easier to pick.
The hole in the pin is a “negative part” and appears when the part is sliced into STL code for the printer.
Here are the printing parameters.
Printing time is about an hour and the print uses about 16 grams of plastic. Plastic is about 20 $ per kilo, so the cost of the part is about 0.32 $. I used PETG plastic because it is heat resistant, slightly more flexible than ABS and cheap. So I can print a few of these strainers and change them when they get warped and/or disgusting.
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