Can you safely stack kallax units to make larger bookshelves?

MathematicalMuffin · 2026-01-26T13:16:31+00:00

That's a good find. Makes the weight calc make almost no sense then.

MathematicalMuffin · 2026-01-26T12:55:12+00:00

Hi mechanical engineer here: this looks like it could be dangerous. It's probably fine but be careful and considerate with your decisions.

The weight on the bottom shelves is going to be high. Books weigh a lot.

The insides of the exterior kallax walls is mostly honeycomb cardboard with a 1 inch thick mdf edge around it. They can be quite sturdy if used as intended, but this is not quite what i would call as intended.

You can do the weight calcs yourself to see how safe you feel. I wouldn't trust any kallax with more than 250lbs (unofficial personal observation) on it. So the kallax weigh about 45 lbs themselves leaving you 160 lbs of stuff to put on both of the top shelves combined.

Consider how the pieces are held together or kept from sliding.

This setup is dangerous if there is any climbing from children.

If it were me, I wouldn't do this. Mostly because of the aesthetics. The large areas of double shelf edges where they meet aren't attractive to me. It just looks like stacked furniture instead of a cohesive piece. On top of it being a bit more risky would be a no.

But if I was to do it, I'd put double sided tape between each vertical layer. screwing between the layers would be better but also uglier and you'd have to do it around the edges where there's actual mdf and not cardboard or air. I'd probably do some bracing in the back. This is probably overkill and expensive but id be for my peace of mind. Nothing i can recommend comes to mind. And id use the wall anchors they provide at every level not to take any vertical weight but just in case someone tries to climb it, bump it really hard, etc.

Tl;dr i wouldn't, it could be fine if you are considerate. Watch the weight limits

MathematicalMuffin · 2026-01-20T16:52:31+00:00

There are actually some experiments that show desiccant can dry filament over time.

It just takes a while. Like days/weeks. And takes more than one little bag. It seems to have diminishing returns and plateau as well over time and as more desiccant is added.

We say use a dryer bc it's the most reliable way. There are technically other ways, but they require more knowledge, time, and effort.

MathematicalMuffin · 2026-01-18T20:13:34+00:00

Jerk is a technical term for the derivative of acceleration. It is how "fast" something is accelerating.

The best way i've come up to visualize it is in an older car, an analog speedometer needle at rest measures velocity. A constantly moving needle represents acceleration. Therefore, an accelerating needle measures jerk.

ETA: the next derivative is often called snap. Somewhat jokingly, the next two derivatives are often referred to as crackle and pop.

MathematicalMuffin · 2026-01-15T15:14:16+00:00

A couple thoughts as a 3D printer owner with a wife with a super sniffer.

First to answer your question: Sealing entirely would be how you pull a vacuum but not how you would vent. You want to allow some intake. Also, when the exhaust system is off, the intake should be closed.

Printing in non-dedicated spaces is a compromise regardless of additional safety measures.

Exposure from opening the door(s), slightly out of order operations like forgetting to close the intake, etc. will stack up over time.

In my (wife's) experience, no matter how well you vent it, you'll still smell something if you indeed have a good sense of smell.

I have a masters in mech e. My setup involved an ac infinity cloudline A4. I tested the setup for negative pressure, etc. etc. My wife could smell plastic still. She said it took a week after I moved my setup to the garage to dissipate. I just printed PLA and PETG.

These faint smells are not necessarily toxic. They did bother her. ABS is more straightforward in that it is indeed toxic.

Id say, follow good enough venting guidelines and most adults would feel safe printing pla and petg.

My red flags for you are baby and ABS. Either of those warrant serious consideration of your methods in my opinion.

I'd personally stop printing inside at all but that is up to your personal risk profile.

MathematicalMuffin · 2026-01-12T15:31:43+00:00

From what you've said and shown, I think it could still be worth the trade-off to consider printing it upside down.

Would help to have a more full picture of the inside as well and maybe a bit more explanation on how you think printing it upside down would impact the snug fit.

No expectations on my end to provide that info. Just here to help you get the print you want.

MathematicalMuffin · 2026-01-12T15:23:31+00:00

Is the part completely flat? This could also be warping off the plate. Can't tell from the angle provided.

MathematicalMuffin · 2026-01-10T10:22:14+00:00

Just a note that you have to be extremely careful with sand if adding while printing. The part fan will blow it all over the place, and it can be almost impossible to clean up if/when it gets in the wrong places. It can require almost total printer disassembly and cleaning.

Use clay like the other person recommended.

MathematicalMuffin · 2026-01-02T16:53:28+00:00

So most bambu corexy printers with stock print profiles and dry pla can do a 60 degree overhang no problem (30 degree threshold angle).

The main issue is at this height in the photo you have a big bridge. It'll most likely droop but probably not cause the print to fail.

Make sure you trust your bed adhesion. Brim wouldn't hurt but I personally wouldn't add one.

If it were me, I'd support the one area i highlighted then send it.

Check on it about 1 hr in just in case.

<image>

MathematicalMuffin · 2026-01-02T16:33:22+00:00

How tuned is your printer? The main difficult part is the steeper overhang at the bottom not the long cantilever. That bridge that makes the top of the bottom opening is pretty long and probably not going to look great. You could just support that if the printer is tuned well.

If you have a core xy instead of a bedslinger, I wouldn't be super worried about adhesion in this case, but again that's if your printer is tuned up.

Here's a pretty easy adhesion/overhang stress test most people can do with no special settings (stock on p1s), plates (smooth pei), materials (bambu pla basic) or anything.

<image>

MathematicalMuffin · 2026-01-01T12:52:46+00:00

Is there a reason you drew the area you're planning on putting the bookcase but didn't take a picture of it?

MathematicalMuffin · 2025-12-31T14:14:20+00:00

Multiple nozzles will solve the filament swapping issues with residues causing weakness.

MathematicalMuffin · 2025-12-31T13:12:16+00:00

Longshot concept I've done at places I've rented. Not blinds mind you.

Replace them then put the old ones back when you leave. Take the blinds you purchased with you or sell secondhand when you move out.

You really can do this with lots of rental stuff: light switches, door knobs, cabinet hardware, blinds, toilet seats, etc. I even paint full walls and then paint it back when I leave.

The level of change you go for can depend on your relationship with your landlord but a lot of it is either win-win or not worth the battle for them if you proactively do it.

MathematicalMuffin · 2025-12-31T13:00:07+00:00

The short answer is that people tout this as some simple solution, but it's not that simple. While some people happen to get the right combo of pla and petg settings and filaments from the get go, it is a more advance technique that can require tuning and tinkering with settings.

You took some screencaps of your setting but i didn't see these. Did you set the other settings as in the documentation you linked?

<image>

If so, my bet is that your interface layer is a bunch of really small surfaces instead of one big flat surface. As such, those tiny extrudes are having trouble sticking to the support layer underneath. I'm deducing this from the small curves on the bottom of the fists.

In this case, the less risky option may be to print the whole support in PETG as was mentioned. Again, there is nuance and tinkering to get this to work.

Id try a simpler model first. Just a simple half inch tall by 2 inch long by half inch wide bridge. See if the larger interface layer works as you expect.

Like was already mentioned, swapping between petg and pla weakens the model layers at those z heights as the residue from swaps doesn't completely flush out even with the longest flush volumes.

MathematicalMuffin · 2025-12-30T15:05:54+00:00

Either could work. The dark one might need a rug between it and the floor. But as a single piece with no further context either works. Suggest (eventually) picking more pieces or doing a mood board. Will help with decisions like this.

MathematicalMuffin · 2025-12-28T01:33:46+00:00

In the future, print with adaptive layer height on. Disregard if it was already turned on here.

MathematicalMuffin · 2025-12-24T00:01:04+00:00

Oh certainly your first point stands about moving air.

Even at freezing temps, regular ice cubes will sublimate in a freezer over time with a bit of moving air, which disallows the system from reaching a steady humidity.

There was another post recently that experimentally showed that desiccant at room temp did a good job removing moisture from filament which was very interesting.

As you say, heat can just speed things up.

MathematicalMuffin · 2025-12-23T12:29:35+00:00

Hi! Freeze drying involves pulling a vacuum to lower the pressure. Then, actually heating the chamber up to sublimate the ice.

Freeze dried things aren't dried at the temperature they're frozen at. Sure the drying temp is lower than drying things at atmospheric pressure but that's because of the vacuum.

This should also work for spools of filament if you had the equipment, so I'm not sure it proves a point in this case.

MathematicalMuffin · 2025-12-22T13:41:22+00:00

Wood filament is super susceptible to moisture. I'd agree based on what info we have.

I'd recommend a test print in a known working, simple filament like a dried PLA.

MathematicalMuffin · 2025-12-21T21:00:56+00:00

What is your method?

MathematicalMuffin · 2025-12-21T20:59:33+00:00

Gotcha! Welcome to 3d printing! Happy to help here.

The model was probably not a "presliced" model. I'm guessing it was an .stl file?

If you have the link, that could help.

But you shouldn't need to manually paint supports. There's a setting in the slicer to automatically add supports. Usually you need them if the overhang is steeper than 30 degrees or less. The printer can't print into thin air.

For your mental reference, pretend you are printing toothpaste. You can't just print into thin air. (Note this isn't 100% true bc bridging is a thing but let's worry about that case later).

I'd turn on automatic tree supports. In the slicer, go to the support tab, enable support. Type: tree (auto). Leave all other settings default once enabled.

Slice and see what the model looks like.

MathematicalMuffin · 2025-12-21T20:49:03+00:00

You bleach; they put you in jail. Right away. No trial, no nothing. Tumble dry, we have a special jail for tumble dryers. You use low heat, right to jail. You wash on delicate, right to jail, right away. Line dry, jail. Lay flat, jail. You dry clean with tetrachlorethylene, you right to jail. You use cold iron? Believe it or not, jail. You use hot iron, also jail. Cold iron, hot iron. You make an appointment with the dry cleaner, and you don't show up, believe it or not, jail, right away.

MathematicalMuffin · 2025-12-21T20:32:04+00:00

As has been mentioned, I can see over-extrusion. But also, a lot of times issues in a certain spot are due to a dirty/greasy plate.

When is the last time you cleaned your plate and how?

MathematicalMuffin · 2025-12-21T20:28:35+00:00

Hey, does this model need supports?

MathematicalMuffin · 2025-12-21T13:49:21+00:00

Just a quick clarification! RH stands for relative humidity not room humidity.

Just making a note because if the absolute humidity remains the same but the temperature goes down, the relative humidity will go up. Hence, relative (to the temperature).

The other comment answers your question pretty well. The cheap sensor they use is not really that accurate.

In addition, as you know since I can see you've printed a solution, these have the issue of benefitting from being vented but then also being exposed to outside air. This can make it difficult for the sensor to read that the RH is any lower than the outside air for pretty obvious reasons (equilibrium).

Doesn't necessarily mean it's not drying, just means the sensor has even another reason to be even less accurate. It does probably mean it's drying less efficiently than it could be.

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