This is a broken piece from my Frigidaire dishwasher. It connects the rotating upper spray arm to the dishwasher. You can see the wear on it by looking at the large ring at the bottom of the image. It should go all the way around, but a portion has broken off. You can also see additional wear on the upper right of the part. You can click on this image or any of them in this post if you want to see larger images.
The piece no longer fits properly, and the spray arm fails to spin and rinse the dishes in the upper shelf.
Disassembling the arm was very easy. The problem was getting the replacement part from Frigidaire. We tried several times, got the wrong part once, and ended up with an utter failure. I’m sure a repairman would have been more successful, but given how simple this repair is, why should I have to pay for that? This is where the MakerBot at CrashSpace comes in to the story.
CrashSpace has a MakerBot. This was a good excuse for me to learn how to use it to create a replacement part. The MarkerBot is a 3D extrusion printer. Above the red platform you see in the picture on the left is the extruder. It heats a thin strand of ABS plastic and extrudes it on to the red platform. The platform moves left to right and back to front until the plastic creates the first layer of the piece you’re trying to make. The extruder then moves up a small amount and the process is repeated until the entire piece is created.
ABS plastic is extremely strong and comes in a variety of colors. We have black, white, and red material at CrashSpace. LEGOs are made out of ABS plastic so you know how strong they are. The MakerBot had no problem making a replacement part for my DishWasher.
These are the $7 digital calipers that I bought from Harbor Freight. They allowed me to measure the part so that I could model it. They can be set to millimeters or inches. Millimeters worked very well for several reasons. First, the calipers show one decimal point, so that means I could get down to 1/10th of a millimeter. Second, the rest of the tool chain used for the MakerBot is referenced in millimeters, so there’s no additional scaling required. Finally, 1mm seems to be minimal feature size that is reasonably handled by the MakerBot. It can move in smaller increments, but it’s very tricky to do anything smaller.
The dishwasher piece is pretty simple. It is really three cylinders with a cylindrical core cut out of the middle. There’s also two little “antennae” at the top. I looked at how the piece fit in the dishwasher and it seemed that I could leave the antennae off. I made my drawing solid all the way up, and thought that I could always cut away the extra material to make the antennae if they were necessary. I also noticed that on the original part the largest cylinder was really thin. That’s why it wore out so easily, but given the way it fit in the other pieces it could be as large as I wanted. I made it 2mm thick, which should make it hold up much better.
This is my final model in Blender. Blender has a rather steep learning curve, so I won’t go in to much detail here. I’m putting together a Blender for MakerBot class that I’ll give at CrashSpace in the near future. The short description is that I created 3 mesh cylinders with the required sizes. I used the transform tool to enter the precise location of each piece. Next I joined them together in to a single object. Then I created a fourth cylinder that match the hole in the middle of the cylinder and used a technique called constructive solid geometry to subtract the cylinder from the piece. That leaves the picture to the left. That file is saved for Blender and as an STL file which we’ll feed in to the MakerBot software.
This is an image from the ReplicatorG software. On the left hand side you see the model. It has generated the g-code, which are the instructions that control the motions of the MakerBot. On the right hand side you see the path that the print head will take as it creates the part.
Once I created the part and made sure it looked like what I expected, it was time to head over to CrashSpace and connect my laptop up to the MakerBot. It takes a few minutes to connect everything up, let the extruder warm up, and position the head to the starting point. Once I pressed the build button the printing itself took about 5 minutes. I printed a couple just in case.
This is the final part. I forgot to include something for scale in the picture, but it’s about the size of a quarter. You can see the ridges from the bead of plastic. The plastic can easily be sanded if needed.
Another thing to note is that the original part has quite thin walls, but my piece is solid. That should make it stiffer and hold up much better with use.
These are the three pieces that make up the entire assembly. The new piece is placed inside the cog shaped piece at the top. The thinest cylinder fits through the hole and the widest cylinder fills the inside area, preventing the piece from dropping through the hole. Finally the arm is press fit on to the thing protruding thin cylinder.
When the dishwasher is turned on water will flow in to the center region of the cog, through the center of the piece, and finally out the arm. The arm has holes in the ends that push the water out the side as well, which causes the arm to turn.
The thin cylinder needed to be the right size so that the arm would press fit on to it, and still rotate smoothly. I measure carefully, but I also suspect the ridges on the side of the part helped make it fit nicely.
This image shows the pieces fully assembled. The black piece is hidden away in the middle where you can’t see it. The arm swings smoothly. The cog piece screws in to a fitting in the top of the dishwasher.
We made a few test runs and it seems to be working great. I think my version will hold up much longer than the original one.
I’d like to leave you with a few final comments on the process as a whole. It would have been cheaper (if you include my time) and easier to call a repairman. The hardest part was dealing with Blender to make the model. Blender has a rather steep learning curve, and it took me quite a while to get a hang of it.
With all that, I learned a lot in the process. I learned how my dishwasher works, how to use Blender, how to use the MakerBot, and even something about how modern equipment is created. So while this piece cost me more in time and effort, I think I can do my next project substantially faster. If you just want to print objects that already exist in Thingiverse, then you’d skip most of the hard parts.