I've had a wonderful LG stove with induction cooktop and convection oven for a couple years. Everything about it is great, except the control knobs. The knobs are chrome plated plastic with black text stenciled on. The chrome plating reflects light in such a way that the thin black text is difficult to read in almost any light. The advantage of using a chrome finish is that it's easy to clean, but being able to read the text on the knobs is kind of important, too.
The front of my LG stove with the original, hard-to-read knobs.
I recently got a Bambu Lab H2C 3D printer so I decided to try to print some new knobs for the stove with easier to read text using the multicolor capability of the printer. I thought it would be nice to use contrasting colors for the bulk of the knob and the text, and even to raise the text above the knob surface. And of course, I will want to be able to put the knobs in the dishwasher once in a while, so printing with PLA is not an option.
As you can see, it is pretty hard to read the thin, black text on the chrome knobs. This is true under almost any lighting situation. Also note the positions of the burner maps on the stove panel. If you study it hard enough, you tell which knob goes with which burner!
Designing New Knobs
I started by making some measurements of the existing knobs, and the control shafts on the stove. The shafts are round with a single flat surface on one side, commonly called a "D" shaft. It will be critical to get the knobs to fit tightly on the shafts, but not so tightly that the knobs can't be installed and removed without breaking the controls. The original knobs have steel inserts lining the holes and providing spring pressure against the shaft.
There are multiple ways to approach the design, and naturally, I started with a bad way. I attempted to print the knobs to fit on the D shafts on the stove and just couldn't get the consistency I wanted. They were either too tight or too loose.
The underside of one of the knobs. You can see the large steel weight used to make the knobs feel less cheesy, and the thin steel insert that grabs the control shaft inside the hole. I was unable to extract that insert. Note the white plastic around the shaft hole and apparently under the steel disc.
Some failed test prints used when designing the new knobs. Don't try to print knobs that directly fit on the D shafts of the controls. It doesn't work.
I took another look at the original knobs and found that beneath the steel weight used to make the plastic knobs feel less cheesy, there is a white plastic insert glued into each knob. The glue they used was a sort of soft and rubbery, probably polyurethane. After a little prying with a screwdriver, the glue bond broke and the insert popped right out.
The insert is glued inside the knob shell with some sort of soft white glue.
The insert and steel weight extracted from the knob. I modeled this in just enough detail to design a knob to fit around it.
I put the insert assembly on the stove to check the clearance between it and the surface of the stove. In order to turn a burner on, you have to push in the knob 2 mm and then rotate it. I measured the clearance between the steel disc and the stove surface with the insert pushed in to figure out how far my knob design could extend toward the stove surface.
I went to work on modeling the insert in just enough detail to design a knob to fit around it. I printed a single color prototype and it fit perfectly on the first attempt.
The inside of the successful prototype knob with a cut-out designed to fit the insert and steel weight.
Single color prototype knob on the stove. I designed it so it sits 4mm closer to the stove control surface than the original knobs - it looks like it was specifically designed for this stove that way.
Multicolor Painting
I decided I wanted to use white text on a black background for maximum readability. Then I added some purple/blue color for the body of the knobs, and finally a little green, as you'll see below.
Coloring the print is done using a painting tool in the slicer. The knob is going to have white text against a black background. You can either start with a black knob and paint every surface of the text white (very tedious!), or you can start with a white knob and add the black color around the text- much easier!
Here's how you turn a CAD model into a multicolor print in Bambu Studio:
Bring the part into Bambu Studio as a white object...
Flip it over... That white tower is there because I have the smooth time-lapse feature enabled. It wouldn't be there otherwise.
Select the paint bucket and black color...
Mouse over the area to be painted black- note that the edge detection finds the outer edges of the text and the edges of the polygon.
Click to paint it black. Now you still have to fill in the holes in the text, such as the center of the letter "O", and the corners of the polygon, but that's a lot faster and easier than coloring the text itself.
When you start with a white knob and paint the black areas, the inside of the knob will be mostly white.
Start with a black part and paint the text white, and you'll get a mostly black interior.
Coloring the bulk of the knob- positioning the mouse pointer highlights the boundaries.
One click of the mouse fills in the color.
Roll the mouse pointer over the target area and the boundaries get highlighted.
One click and the color is applied. Repeat 11 more times going around the knob.
More Details
There are three different kinds of knobs on this stove. There's one for the oven, that has a LOT of text, one for the warming burner, and four identical knobs for the induction burners. The oven knob was the most challenging- I had to fit a lot of text on it but the printer managed to produce easily readable text even with just 3 mm high characters.
The inserts weren't just glued into the original knob shells. They have concavities that mate with retention features inside the shells. There's also an index notch in the insert so that it can only go into the knob in the correct orientation (the flat side of the control shaft is down while the "off" text is up when the knob is on the stove).
Concavities used to retain the inserts in the outer shells.
Retention bumps that snap into the concavities in the inserts. I'm sure these have a name, but I don't know what it is. On the left side you can also see the indexing bump that prevents the insert from being installed in the wrong orientation.
I made a test print with added retention bumps and an indexing bump in the interior of the knob design. The inserts with attached steel weight snap in tightly and don't wiggle at all. They can be easily popped out with a screw driver so the printed covers can be cleaned in the dishwasher.
While I was at it, I also reduced the bulk of plastic on the interior of the knobs so they'd print a little faster and use a little less filament (instead of the bulk of the interior printing, it has to print larger tree supports).
CAD render of the interior of my knob design. You can see two of the four circular bumps that fit the concavities in the inserts. Toward the right you can see the index bump that ensures the knob fits on the insert in the correct orientation. The walls are about 3 mm thick - more than strong enough for the job that the knobs need to do.
Finally, I added burner maps to the front surfaces of the knobs so it's easy to tell which knob controls which burner. I marked the target burners with green filament which matches the green sparklies in the purple/blue filament.
Printing
This is a situation where printing all the knobs at once saves a lot of time and reduces wasted filament. There are 292 filament changes and only one prime tower (about 20g of filament) for the full set, which requires about 21 hours to print - a little over 3 hours per knob. If you print the knobs individually, the printer performs 292 filament changes and prints a 20g prime tower for each knob. So it takes about 5.5 hours to print a single knob.
The knobs are printed in 0.2 mm layers, with tree supports, 4 perimeters, 3 mm top and bottom thickness. The knobs print solid- there's no sparse infill. The filaments were Bambu Lab Black PETG-HF, some random white and transparent green PETG filaments I am still trying to use up, and the sparkly stuff is Stronghero 3D Mirror Chrome PETG in Wizard Voodoo Purple/Blue that I first opened in October of 2023. My hot girlfriend pointed out that it's a nice match for the blue porcelain interior of the oven.
Sliced set of LG stove knobs in Bambu Studio. The full set uses about 420g of PETG filament - about $10 worth. The 292 filament changes add about 2.5 hours to the total print time of 21 hours.
The Results
I printed one knob first as a test of the fit and finish, was satisfied with the result, so I printed the remaining five on one plate:
The remaining five knobs took about 18 hours to print. The four burner control knobs go into the slicer as identical parts. The green color that makes them unique gets added in the slicer.
The printer has cameras built in and it's easy to make a time-lapse video:
And here they are on the stove. The purple/blue filament looks different depending on the light source and viewing angles. It's also full of green sparkles!
It's so much easier to read the knobs and to identify the burners being controlled.
UMMD is still a great printer 9 years after I built it, but its 1mm nozzle makes it unsuitable for printing small, detailed objects, which I need to do more often than printing large objects. I could swap the nozzle for a smaller one, but then I'd have to go through the whole recalibration process, and the next time I want to print something big, I'd have to swap it again and recalibrate again. Ugh!
Bambu Lab H2C with AMS HT and AMS 2 Pro filament feeders/dryers. There's a nice touch screen color display for local control, or you can control the printer from the wifi connected slicer, Bambu Studio. One especially nice feature is that the display shows a render of the file to be printed or that is printing.
The H2C/AMS 2/AMS HT has some interesting features.
The vision encoder plate works with the toolhead camera to check and adjust squareness of XY motion.
3 cameras- one to monitor the print process and make timelapse videos, and two mounted on the toolhead to spot errors like layer shifts, spaghetti, etc., and to align the nozzles of the extruders, and XY motion.
Vibration compensation- at the start of each print, the machine vibrates the toolhead and print bed and automatically compensates for resonances, maintaining high print quality. The vibration is a little noisy.
Vortek hotend swapping system- a motorized rack that holds 6 induction heated nozzles. To be honest, I'm not so sure about the reliability of this system. Time will tell. Reviews I have seen that include prints having thousands of nozzle swaps indicate that it is reliable. The idea behind it is that you assign specific filaments in the AMS 2 Pro to specific nozzles, so during a multicolor print, there's no purge waste. Swapping the hotends reduces filament waste compared to swapping filament using a single or dual extruder alone, but it wastes a little bit more filament than a printer with multiple toolheads, such as the Prusa XL or the Snap Maker U1.
Induction heater for the right side extruder- the extruder that swaps hotends uses induction heating to bring the hotend up to print temperature in about 8 seconds. You'd think that would make swapping nozzles really fast, but cutting, retracting, and loading filament with the AMS take a lot longer. Using induction heating allows wireless operation of the hotends, which simplifies wiring going to the toolhead, and that bodes well for reliability.
Automatic venting/filtering of enclosure air- There's a HEPA filter, fan, and automatic vents that work to reduce VOCs and particles from some filaments. I have noticed that I still smell ABS when it is printing.
Automatic bed leveling (I know, they all do that these days). This is a particularly interesting topic to me as I spent a lot of time developing kinematic mounts for my printer's beds so that they wouldn't have to be leveled (trammed) before every print. In fact, I haven't trammed UMMD's bed in at least 2 years. In the H2C the bed is lifted using 3 screws all driven by one motor and a belt, however, the bed is leveled (trammed) using 4 corner screws (whaaaat? That's so 2012!) and is then secured by tightening some screws in slots on the side of the bed assembly. When a print starts the toolhead probes the bed in several places and makes a map of the variations in bed height. It can't physically adjust the bed tram- that would take three Z axis motors- so it just tweaks the Z axis position/extrusion during printing, based on the height map, probably just for the first few layers. It seems to work OK, as it was able to map the factory trammed bed right out of the box, without retramming.
The AMS HT and AMS 2 Pro are both capable of drying filaments and storing them in (almost) air tight enclosures and feeding the filament to the printer. The AMS HT can get up to 85C, while the AMS 2 Pro is limited to 65C, so the HT is good for drying filaments like ABS, nylon, and PC. Both units report temperature and humidity to Bambu Studio, and the HT displays them on the front of the unit. You have to periodically replace desiccant packs in the AMS units to keep them drying filament properly.
Bambu Lab filament spools come with an attached RFID tag. The AMS 2 Pro and HT both have RFID chip readers that will automatically configure the printer for the filaments in the AMS units, if they are Bambu Lab filaments. The RFID tag also allows the printer to monitor the quantity of filament left on each spool and communicates it to the slicer (Bambu Studio) so you won't run out mid print. The spools are perforated to expose more of the filament to the warm air when drying. You don't have to use Bambu Lab filament with the RFID tags, but then you'll have manually assign filaments to hotends, and watch the quantity of filament on the spools yourself.
When a print is started, the printer goes through a list of about 10 calibrations and adjustments before it actually starts printing. If you print a material that requires chamber heating, it can take 20 minutes before the printing actually starts after you hit the print button.
The filament swapping process, and several of the preparation steps before a print starts, move the toolhead back and forth which flips out the filament cutter levers located on the right and left sides of the printer, making a clunking sound each time it does. The vibration compensation, which causes the toolhead and the bed to vibrate for a few seconds at the start of each print, is also a little noisy.
Swapping hotends/filaments can take 30 to 45 seconds, depending on the length of the PTFE tube between the AMS and the printer, which can add significantly to the print time if there are a lot of color swaps in the print. If you're printing 4 colors on each print layer, that's 4 filament swaps, adding a few minutes to each layer, even if the actual printing takes only 30 seconds or so for that layer. Multiply that by the total number of layers and you'll see that multicolor printing can be a time consuming process on this printer. It's best to keep the PTFE tube between the AMS and the printer as short as possible.
I have only made a few prints so far, using both PETG and ABS filament spools that I had in stock (not using the Bambu Lab spools yet), after drying the spools in the AMS units. The prints have been as close to perfect as any I have ever seen. There are no VFAs, nearly zero stringing in PETG prints, no warping, delamination, or lifting from the bed with ABS prints. The only defect I had was two different colors of PETG not bonding to each other completely in one print.
The only real print defect I had among the prints I have done so far. This was easily repaired with a couple drops of ethyl acetate to solvent weld the unbonded joint. this was my second multicolor print, so go easy on me. There is a calibration to run that should prevent this sort of thing, but I didn't have the recommended filament colors for it, so I have not run it yet.
The printer has a USB A port on the top front left corner of the box that you can use to load/store print files, and store timelapse videos, which the printer will make either as a fixed time interval per image or a series of images made each time the print layer changes, with the extruder moved away from the print. The latter wastes some filament as the extruder has to be "repressurized" after each layer change. Time lapse video is turned on/off in Bambu Studio or at the local control screen on the printer. FAT-32 is the preferred thumb drive format. For drives >2 TB, it wants exFAT. Bambu Lab sells an inexpensive add-on kit to trigger an external camera to make timelapse videos.
There is a setting in BS that allows a spool of filament in the AMS 2 Pro to serve as a back-up, so if you have a little filament left on a spool and a fresh spool of the same filament, you can start the print with the almost-empty spool and the new spool will take over when the first one runs out. You can merge 2, 3, or 4 filaments in one AMS 2, so theoretically, could make a 4 kg print using a single AMS 2 Pro.
Filaments can be merged manually in BS using these selections. If two filaments are the same material and color there is another setting that allows the printer to merge them automatically. This looks like a good way to use up the remnants of multiple spools of filament.
I haven't tried TPU on this printer yet, but I did on a P1S at the makerspace and it came out horribly under extruded. I have read that the PTFE extruder feed tubes create too much friction with the filament and the result can be uneven filament feed resulting in poor print quality. However, you can bypass the PTFE tube and feed the filament straight into the extruder (as UMMD does) by making a bracket to support the filament spool over the open top of the printer. I have also read it's a good idea to reduce the maximum volumetric extrusion rate and print speed. I will be making such a bracket because I like to print TPU parts. TPU's toughness and flexibility are very useful properties.
One of the first PETG prints I made on the H2C. All surfaces are as close to perfect as I have ever seen, and there were only a few hairs.
The top of the tubes. Excellent print quality.
My first multicolor print, all PETG. This is a comb to smooth out the sand in the Arrakis 3.0 sand table. This print came out perfect. I later printed a similar comb for Arrakis 2.0 and had a problem with two of the colors not bonding.
I printed this 100 mm threaded (M100 x 6 mm from F360) cylindrical box and cover to check the roundness of circular prints. I had to print the cover twice in order to get it to fit right. I reduced the top and bottom surfaces of the threads in the cover by 0.1 mm each to make it fit. It seems as circular as can be. The printer had no trouble with printing the overhanging threads without any support material.
This is what the threads looked like in F360. The tips of the threads have plenty of clearance, but the upper and lower faces are too close together. I moved the upper and lower faces on the cover threads by 0.1 mm to loosen things up enough to screw the two pieces together.
A large, transparent ABS print in the H2C. No warping, no delamination, and the whole thing stayed stuck to the bed throughout the 8 hour printing process. The walls are 3 lines thick (1.26 mm) everywhere. This is a spool of filament I opened about 2 years ago, and dried in the AMS HT for 8 hours prior to printing. The surface shows some irregularities, but they are primarily optical effects from using transparent filament. The surface feels very smooth.
Ms. Kitty has no complaints about the print quality, either.
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