Introduction: Cat-a-Comb
My daughter got a kitten, Jewel, about a year ago. She's now a teenage rambunctious maniac running around the house constantly knocking everything off the counter - the cat, that is, not my daughter. Well, I guess that too, but that's a different story.
Anyhow, what I noticed was Jewel was rubbing her cheeks on everything. She'd rub up against vases, glassware, picture frames, pencil cups, lamps. Get the hint here? Suffice it to say, we have a lot of repaired stuff in the house.
In the past with our other cats, we would just go out and buy one of those corner cat combs. They're cheap and very effective. But as I was trying to tell my daughter, who at the time was heads down distracted with musical.lys from her friends, that we needed to go out and buy one these, after which she just kept saying "what? what?", I blurted out "a cat comb!" And if you say that fast enough with enough fervor in your voice, it sounds just like "catacomb".
Of course, the first place I went to was Instructables to look for a cat-a-comb, not a cat comb, but a cat-a-comb. Nothing. I searched the web. Nothing. That's how this project came to be. If it doesn't exist, build it. One of the side benefits of this project was that I learned a bit more about catacombs and was able to share that with my kids, who thought this was just too weird and too creepy.
The Design
At first I had very high ambition. The Cat-a-Comb was going to be a tunnel-like cavern where Jewel would explore, hang out, etc., and she would rub her cheeks on the skulls and bones. After a few initial test prints of very large designs it became apparent that it would take months to print not to mention I was completing only about 10% of the print jobs. After many iterations, the final design just ended up being a simple archway with the comb teeth inside the arch for cheek rubbing and the skull and bones on the outside for decoration.
One important piece of advice upfront: buy a lot of filament. Buy 2x more than you think you need. I ran out twice and it looks too patchwork'y.
Step 1: Tools, Materials and Software
Tools
The Cat-a-Comb is primarily a 3D print project. So a 3D printer is needed, and a good one at that. I used an Ultimaker 2 (not 2+). Ultimaker no longer sells the 2 in favor of the 2+ which is supposed to be better. I wish I had the 2+ because I had tremendous amount of trouble with the 2. I'll explain below.
In addition to a 3D printer, I heavily used these tools:
Materials
The only material that's really needed for this project is the 3D filament. I used 3mm ABS because that's the size the printer uses and I wanted ABS so that the Cat-a-Comb could take a beating. In the course of this project, I had run out of black so I bought more from a different manufacturer. And then I had run out of that. The color and finish is noticeably different. I also tried a "coffee" just to see. Eh. If the entire Cat-a-Comb were to be just one color of one manufacturer, at least 2kg are needed, more if there are many print failures.
- Excelvan 3mm ABS black. It has a matt finish and is black grey.
- Excelvan 3mm ABS coffee. It has a matt finish and is like a Starbucks latte brownish cream.
- WYZWorks 3mm ABS black. It has a shiny finish and is black grey which when moved around in the light looks like black silver.
- E-6000 amazing hold glue
Software
For this project, Tinkercad was just not powerful enough. I had to use the next level up: 123D Design and MeshMixer. I'm very grateful for the existence of these FREE tools and the amount of tutorials out there for these tools. Thanks Autodesk.
For slicing, I used Cura because Utlimaker provides it and it is intimately aware of the Ultmaker 2 printer.
Modding the Ultimaker 2
Almost from the beginning it was apparent that the Ultimaker 2 was having problems with the intricate design of the skull and bones. After many, many experiments and filament changes, parameter tweaking, and design changes and many, many hours and meters of failed print jobs, I found that 98% of the problems seem to be directly related to the retraction feature. For those who don't know what this is, the printer can retract (or pull back) the filament just before moving the print head to a location that's not nearby thus preventing stringing from occurring. When the head gets to its new location, it then pushes the filament forward and resumes printing.
It turns out that this back and forth motion along with the knurled feeder which bites into the filament to move it and the Bowden tube which guides the filament but is not friction free causes the knurled feeder to chew into the filament. This is easily remedied by disabling all retractions both in the slicing settings and on the printer. Stringing will happen but at least the 12-hour print job will complete and I have something that I can clean up versus having nothing.
Disabling retractions had a side effect of creating too much back pressure in the nozzle area. The Ultimaker 2 has a spring that sits atop of a plastic coupler guide (PTFE) which goes into the brass nozzle. The build up of the filament in the nozzle pushed the PTFE upwards. The spring, though strong, was not strong enough from keeping the PTFE from moving and it resulted in clogging nearly every print after some number of hours. The solution was to replace the spring with a fixed cylindrical part.
The final issue I had was that the print bed is not completely equidistant from the print head guide rods everywhere in the x- and y-axis print plane. That is, the distance from the bed to the guide rods in the upper left quadrant (back left) is less than the distance in the lower right quadrant (front right). Ultimaker 2 has the ability to separately level the left and right sides of the bed but that only levels the front of the bed, not the back. The result of this misalignment is that the filament does not get laid down in the upper left quadrant because the bed is too close to the print head. Fortunately, the discrepancy between the distances seems to only be about 0.5mm. This can be fixed by squeezing together the top and bottom plates of the print bed (Ultimaker 2 has a 2-plate print bed with adjustment springs in between) in the upper left quadrant and holding it there with Kapton tape.
All of these many, many hours of discovery and wasted material. 3D printing is still very finicky.
Step 2: Source 3D Models
A bit about the source models. Human skeletal models are quite common and easy to find. There are tens if not hundreds of 3D models of skulls, leg bones, arms bones, spines, etc, and some of them quite good (and free to use for what I wanted it for). Cat skeletons, not so many. I needed two primary types of bones that were somewhat high fidelity: a cat skull with its mandible removed (in the catacombs, the mandible of human skulls are not present) and some leg bones. I could not find a high fidelity 3D model of a feline skull. The closest I could find was a bobcat skull. Using MeshMixer, I was able to remove its mandible.
Ohio Bobcat - skull - OUVC 9576 by WitmerLab at Ohio University on Sketchfab
As for cat leg bones, I could not find any of these as well. So I just used a human femur (by Mooselake) instead. If you squint, they look the same.
Interestingly, after about 2 weeks into the project I did find a full cat skeleton. If I could start over, I would use the bones from this project instead.
Feline Skeleton Dec by westerly on Sketchfab
The last 3D model I utilized was a stone floor (by onebitpixel) which I was able to use to assemble the floor for the Cat-a-Comb.
Step 3: Outer Wall Skull and Bones
The outer wall is a grid of femur bone ends with cat skulls. Because I had so many print failures in the beginning, I modularized the wall into small panels. This way if there is a failure with a 6-hour panel, i've only wasted at most 6 hours versus 36 or 72 hours.
A panel is comprised of 3 rows of one bone end sitting below 4 rows of another bone end which is then below a single cat skull. It would have been better to have a bigger panel so that a pattern wasn't apparent, but I was afraid of risking print failures and wasted time. Interestingly enough, as I was printing and tweaking the skull, I realized that I came up with 3 distinct panels where the skulls differed. I guess if I was so inclined, I could have tweaked the bones to have a bit more randomness. Anyhow, I don't really think Jewel will notice or get fussy about the pattern.
Each panel has something distinctive about it. Wall panel 10 has holes in the skull giving access to the cavity inside the skull. This makes it possible to remove the inside support material giving it a little bit of authentic look. Wall panel 12 is the standard plain appearance. Finally wall panel 15 has a larger cat skull like maybe for a Maine Coon.
Cura Settings
Default settings with the following exceptions:
- Quick print
- Fast print
- Print support structure
- Platform adhesion: Brim
- Full settings
- Shell thickness: 1.2
- Enable retractions: unchecked
- Fill density: 10%
- Support type: Everywhere
Ultimaker 2 Settings
Default settings for ABS plastic with the following exceptions:
- Change retraction settings to 0 so that there is no chance that it occurs
Print a total of 12 panels in any combination. The print time for each as computed by Cura is as follows:
- Wall panel 10: 6h 41m
- Wall panel 11: 6h 41m
- Wall panel 15: 8h 13m
Post Processing and Cleanup
There are three main things that need to be cleaned up:
- Strings: Use a pick and hook to scrape them off
- Dots: Use a pick and hook to scrape them off
- Print supports: Break them up with a pick and hook or tweezer and them pull them off with a tweezer
3D Models
Cat-a-Comb: Wall Panel 10 by gary fong on Sketchfab
Step 4: Inner Wall Comb
The inner wall comb is basically a grid of cones with tiny balls at the tip of each cone. At first I just had cones without the balls but it turned out to be too sharp. Adding the balls seem to help just a little bit. The panel size is much bigger than the outer wall panels. They are designed in such a way where 6 outer wall panels can mate back to back with 2 inner wall panels. When they are all glued together it will provide a nice rigid side wall.
As the pictures show, there is a lot of stringing. This means there is a lot of clean up.
Cura Settings
Default settings with the following exceptions:
- Quick print
- Fast print
- Platform adhesion: Brim
- Full settings
- Layer height: 0.1
- Shell thickness: 1.2
- Enable retraction: unchecked
- Fill density: 10
Ultimaker 2 Settings
Default settings for ABS plastic with the following exceptions:
- Change retraction settings to 0 so that there is no chance that it occurs
Print a total of 4 panels. The print time as computed by Cura is 8h 18m per panel.
Post Processing and Cleanup
After being grateful that the print completed, all of the strings and dots need to be removed.
3D Model
Step 5: Base and Supports
The base is just a collection of stone floor panels put together. It's wide enough to fit Jewel and a bit more. It has 4 support pillars at each of the corners. This is where the side walls will attach.
Cura Settings
- Quick Print
- Fast Print
- Print support structure (not really necessary)
- Platform adhesion: Brim
- Full settings
- Shell thickness: 1.2
- Enable retractions: unchecked
- Fill density: 10%
- Support type: Everywhere
Ultimaker 2 Settings
Default settings for ABS plastic with the following exceptions:
- Change retraction settings to 0 so that there is no chance that it occurs
Print one of each base and two of each base supports. The print time for each as computed by Cura is as follows:
- Base 5a: 11h 37m
- Base 5b: 11h 45m
- Base support 1a: 1h 29m
- Base support 1b: 1h 29m
Post Processing and Cleanup
Clean up the strings and dots as usual. Then clean the edges of the two bases such that they fit together snuggly.
3D Models
Cat-a-Comb: Base 5a by gary fong on Sketchfab
Step 6: Arch
The arch is just a longer version of the floor without the pillars and at each stone panel it is rotated 15 degrees downward. I tried to wrap it around a cylinder but I didn't have the tools nor the know how. I had to print the 2nd arch in a different color. I ran out of black and to order it and have it arrive in time wasn't going to happen. I picked the best color I had laying around.
Cura Settings
- Quick Print
- Fast Print
- Print support structure
- Platform adhesion: Brim
- Full settings
- Shell thickness: 1.2
- Enable retractions: unchecked
- Fill density: 10%
- Support type: Everywhere
Ultimaker 2 Settings
Default settings for ABS plastic with the following exceptions:
- Change retraction settings to 0 so that there is no chance that it occurs
Load each model into Cura, rotate it so that it is on its side, then print it. The print time for each as computed by Cura is as follows:
- Arch 5a: 10h 53m
- Arch 5b: 11h 40m
Post Processing and Cleanup
Clean up the strings and dots as usual. Then clean the edges of the two arches such that they fit together snuggly.
3D Models
Step 7: Assembly
Step 1: Base
- Make sure the two base pieces fit snugly together. Trim the edges if necessary.
- Glue them
- Let dry
Step 2: Walls
- Lay out two inner comb panels tip to tip with the teeth pointing downwards
- Glue six outer skull and bone panels onto the two inner comb panels
- Make particularly sure that there is sufficient glue between the center row skulls and bones and the comb
- Let dry
- Trim the edge all the way around so that it is flat and square
Step 3: Arch
- With a pair of extra helping hands, like a son, glue the arch onto the top of the walls and hold it there until it sets.
- Glue the arch parts together at the top
- Tip the Cat-a-Comb on its side
- Let dry
Step 4: Ancillary Supports
- Glue the side supports onto the supports that are on the base and glue them onto the skull and bones wall
Step 8: Miscellaneous and Lessons Learned
 | When I created my first 3D print, I tried to make it look like the Catacombs of Paris. Of course it took my daughter to tell me that I was using the wrong skulls. Back to the drawing board. |
This is what happens when there's a 0.5mm gap between the objects. They appear to be connected but in reality they're not. |  |
 | One manufacturer's black is not the same as another manufacturer's black. |
The bed is just a tad higher on the (back) left than on the right. |  |
 | Finally, all the failed prints and a few test prints. |
Lessons Learned
- 3D printing is complicated. But just like complex wood or metal tools, the complexity provides power and control if one understands and knows how to use it.
- Buy much more filament than planned. The final design doesn't look like I intended in one part because I ran out of filament twice.
- Modularize parts so that if there's a print failure just that part needs to be reprinted. Saves on frustration.
- Orientation of the print matters. Sometimes the print may warp causing imprecise fits between two parts. Sometimes the appearance changes like the layers (or grain if you think in terms of wood) may be visible and not what you intended. Sometimes the print faces are rough particularly where it attaches to the plate or has print supports causing an unfinished appearance.
- Orientation matters also in terms of time. To print an object that is in a particular orientation which may have a better final appearance may take two or three times longer. This was true with the Cat-a-Comb arches. I didn't want to wait that long so I ended up with a rougher, slightly warped arch.
- The penultimate thing I found was that Jewel was scared of it. It took her a few days to become accustomed to it.
- The last thing was the odor. I guess the filament and the glue wasn't to her liking. I added a bit of catnip to get her to overcome this. Now she doesn't mind the odor.