Saturday, January 18, 2014

Dishwasher Clean_Dirty Plaque

The full album for this post can be seen here. The original design can be downloaded or purchased here. The updated design can be downloaded or purchased here.

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My wife is home on maternity leave right not, which has caused a modicum of chaos to permeate our daily chore schedule. One of the victims of this chaos last week was our dishwasher schedule. On one particular night I loaded the dishwasher to near capacity and decided to wait to run it until I had a few more dirty dishes. The next day while I was at work my wife decided to do the dishes. She opened the dishwasher and proceeded to unload it. Apparently I did a bit too good a job of pre-washing. Fortunately we quickly realized the mistake once I got home and reloaded the dishwasher, which we then immediately ran.

Though this was the first time that this happened in our 5 years together, I decided that it needed to be the last. My initial thought was that I should just buy one of those clean/dirty magnets (of which Amazon stocks a myriad). But then I changed my mind and decided that I should 3D print a solution. Even though the magnets would cost about $5.00 shipped to my door and the design/printing time would be far more expensive in time, I wanted to do a quick fun project.

I started to think about the design and what challenges I might face. The base design would be a plaque with letters. My initial thought was to print a clean/dirty ambigram (there was even one on thingverse) and use a sticky magnet to affix it to the dishwasher. Then we would just have to rotate the plaque to match the state of the dishwasher. Unfortunately after looking at the ambigram a bit more closely, I decided that it was a bit to ambiguous. I searched for additional designs but couldn't find one that I liked.


I then decided that I would be better off have a two sided design with simple, clean, easy to read lettering. Since I have an unhealthy attachment to command strips, they would serve as the substrate for affixing a hook to the dishwasher. I decided to use a command hook to attach the placard and went with the wire style hook since it pivots and would help keep the placard from falling off when the dishwasher was opened.

The next step was to fire up Solidworks and get to designing. Designing the initial placard and the "Dirty" extrude was simple enough. My only initial concern was letter size. I am not sure what the minimum legible letter size is for a reprap running at 0.2 mm layer height is, but it ended up not being an issue here since I wanted a high visibility part (ie. big letters)


The reverse side proved to be a bit more tricky. One of the keys to a good print is to maximize surface area that contacts the bed. Creating a boss extrude for the "Clean" side of the placard would have minimized surface area. The obvious solution was to have the "Clean" side be a cut extrude instead.


Of course this schema created another issue in that printers that don't have support material capabilities generally have problems with overhangs. I personally prefer to keep bridges to less than 5 mm. In testing I know that my machine can bridge longer distances, but I feel that strength and visual appeal suffer. My solution to this was to create my own permanent "supports" in the part.


With all of the nitty gritty design stuff out of the way, it was off to the printer.


The mounting components


Installed






Update: The model describe in this post is bulky and truly designed for 3D printing on a single material reprap machine. I decided to create a similar model that is optimized for the professional grade machines at Shapeways. The link to the new model is at the top of this post.


Preventing Extruder and Hot End Jams

One of the most frustrating aspects of 3D printing from my perspective is dealing with clogged hot ends. I hate starting a print, walking away, and coming back to a stringy soupy mess with a hot end that won't spit out any resin. I hate disassembling my hot end (seriously, we need a quick disconnect design) while keeping it plugged in so that I can keep the heater on to scrape out plastic.

Fortunately I have found a small trick that works great for me in PLA. At the end of every print I retract my filament by 50 mm then I home the axes and kill the heat sources. Since I have implemented this custom code I have not had a single PLA jam in my hot end (results with ABS or Nylon may vary). The custom code to be added to the end of every G-code file is listed below:


End G-code


G28 X0  ; home X axis
G92 E0; reset extrude coordinates
G1 F250; set feed rate 250 mm/min
G1 E-50; reverse extruder 50mm
M104 S0; turn off temperature
M140 S0; Turn off bed
M84     ; disable motors


Please note that this g-code was created for and is running on the following printer configuration:

* Prusa i2 (makerfarm)
* slic3r for slicing
* Marlin for firmware
* Pronterface for comms
* Typically printing in PLA


As is often the case in the world of RepRap, you may need to adjust the code for your specific system. On my system, this end code retracts the filament from the hot portion of the hot and parks it in the cold portion of the hot end while keeping the filament engaged with the hobbed bolt. I do not know why this helps prevent filament jams. My guess would be that latent heat from the hot end is causing the plastic to cool at a very slow rate. Depending on the resin and additives (colorants, etc.) cooling rate can cause significant changes in the bonding structure of the polymer.

One thing to keep in mind when using this method is that you have to "prime" the hot end before every print by extruding 50 mm after the hot end is up to temp.

Helpful Tips

The purpose of this post is to serve as a bookmark of sorts for tips that I post to help keep your printer running smoothly.


Monday, January 13, 2014

Printing Service Bureaus

I will be the first to admit that sometimes my Prusa i2 just doesn't cut it.Certain part geometries are horrendously prone to warp. Thin wall and knife edge features have no strength or rigidity and at times do not fuse together properly.



In addition to the issues above there are also significant problems with overhangs (and let's face it, no one likes cleaning support during post processing).


Sure we have ways of overcoming these issues by varying speed and process settings or in the extreme we go full crazy and "pre-slice" prints to eliminate overhangs completely.




When all else fails or we don't want to risk weak joints due to assembling  individual parts into a final product, there is an additional (albeit much more expensive) option. The use of third party service bureaus can allow a designer to get strong parts (near injection molded strength with SLS), with great surface finish, and improved features.


Though there are many "pros" to using a service bureau there are also drawbacks. The model printed above was purchased through Shapeways so let's compare there service to a reprap:



This matrix shows Shapeways as the clear winner but upon closer inspection there are certainly some drawbacks to the Shapeways process. At $22.00/cu. in the resin cost will quickly overshadow the reprap initial investment, especially when doing iterative design. Also when designing a system, waiting two weeks for parts can be an eternity. With those reasons in mind I use reprap for primary development and Shapeways for special cases.





Wednesday, January 8, 2014

Custom Spinbrush Kids Toothbrush Holder

My son received a super awesome Spinbrush Kids Captain America toothbrush for Christmas this year. He loves it and gladly brushes his teeth morning and night (which as a parent, rocks). Unfortunately he was having quite a bit of trouble reaching his toothbrush on the sink as you can see in this Imgur album.


I'm quite happy with the way that the print came out. There was some slight warp on the bottom corners (hazard of printing in a freezing room with no enclosure) but the overhangs for the screw holes came out great.

The .stl for this file is available for free download here if you have a 3D printer and want to take a stab at this design.

If you don't have a 3D print but may have some use for this holder, you can purchase the holder here.

I recommend using Command Strips to mount the holder, though screws can be used to affix the holder as well.