Advice on my first 'real world' functional part - 92-120mm fan adapter

Hi, so having finally got the printer setup and a few small test prints out of the way, I’m looking forward to printing my first functional part - a fan adapter which takes my NAS from 92mm to 120mm fans so I’ll get more air flow and lower noise levels.

I’ve designed the following in Fusion 360 as a starting point but I haven’t really got any idea on PLA strength for such a design so things such as the thickness of the plates which will mount to the NAS and the 120mm fan, or the thickness of the tube connecting the two plates. I obviously don’t want to waste PLA and go overboard but I also need to make it strong for its intended purpose.

In the image, the rear most plate is 94mm and the front most 122mm, the distance between them is around 40mm with the upper top corner lining up.

When making decisions on wall thickness, does it come down to each design and experience or are there some good rules of thumb to get me started?

will be printing this on a stock Ender 3 S1 Pro

I think before asking about thickness, you’re going to have to go back and break the model up into two pieces or you’re going to have a big overhang that will require supports.

Now, the supports for the flange may be manageable but the narrowing looks like it has an angle of around 30 degrees that will require supports and they will be problematic as you will have to smooth the inside of the narrowing. I generally design angles of 45 degrees or greater to avoid the need for supports.

Just a word of caution; noise caused by air flow through ducts is a tricky thing to predict without doing some modeling (and knowing how to perform said modeling). You can very easily end up with more noise at the outlet, even though your larger fan is quieter without the duct.

I understand that you want to do a good first part but this is going to be trickier to get right than you may expect.

Hi, thank for the response.

I did wonder if multiple parts are the way to go. If cut into 2 parts and a maybe something like a ring to act as a mating surface at each flat mounting section to connect the centre tube, what would be the recommended glue for PLA? Would a typical 2 part epoxy tube do the trick?

From a supports view point, other than it using additional material in the process, is there a reason why that would be a negative?

I understand there is a lot more to duct design etc than my simple cobbled together design but I’m running low cfm fans at very reduced speeds so I’ve no doubts my design won’t be of the best flow design, for the intended us It should be ok.

Everyone has different preferences when it comes to supports. Personally, I would print it with the small end face down and support everywhere enabled. You would need to be careful removing the support between the two plates, but should be very doable, I have printed similar ducts in the past. This way, surface defects from support under the taper angle won’t be an airflow issue.

I assume that there is a reason you haven’t designed it with the duct centered, as opposed to the offset you have now?

As to thickness, are you talking about slicer settings, or the actual thickness of the part? If talking about the actual part thickness, I would start at 2mm for the tube, and 3mm for the plates.

Personally, I’d screw the two parts together as it’s generally more precise, you’re not racing against time to get things positioned before things harden together and it’s less toxic.

We had the discussion sometime ago about PLA solvents as glues and it seems like the best one is Methyl Acetate (Canadian Tire, if there’s one available to you has it). Epoxy doesn’t work well although a gel cyanoacrylate (ie Krazy Glue) will work quite well on a roughed up surface.

PLA may be the wrong material for this application - it’s usually recommended to use ABS for structural parts as it’s not as brittle. For gluing, acetone (100% - available at Dollarama) is usually used.

if you’re just starting out, supports can be a pain, especially if you don’t have your printer completely dialed in. They can be hard to remove, difficult to get a smooth surface and you will take out more material than you want. I really suggest avoiding them when you start out.

If you have two parts that get screwed/bolted together, you still potentially have to deal with supports anyway. If you orient the bolts so they are parallel with the fan’s center of rotation, you still will have flanges that need support, unless you make the non-mating faces have a angle of 45 degrees to obviate the need for supports. This of course ignores the difficulty of fitting a tool in to tighten said bolt.

One way to get around that would be to have the division between one plate and the start of the tube. Then the two parts could be screwed together with screws countersunk into said plate. That would likely necessitate a thickening of the plate though.

One other option is to have the screws/bolts oriented perpendicular to the fan’s center of rotation. That would be the simplest from a tool access standpoint, but then the tolerances need to be much tighter to prevent air leakage, unless you use sealant too.

It’s all a choice of which compromises to go with. A one piece design feels like the simplest to me, but it really does come down to preferences to a large degree. What your preferences are might take some time to figure out. The best way to do that is experiment with different designs until you discover what works best for you; at least, that is my preference. :stuck_out_tongue_winking_eye:

Why would you put connecting screws in perpendicularly to the direction of air flow (which is what I think you are saying)?

I would think it’s a lot simpler to connect the pieces with bolts running parallel to the direction of air flow and, ideally, use the fan mounting screws rather than anything extra. It would also make sealing the fan much easier and avoid anything poking into the airflow (which can cause noise).

I personally wouldn’t design that part with screws perpendicular to the airflow, because I think it isn’t the best way to do it, although yes, that is what I was meaning. If I would do such a design, it wouldn’t have anything sticking into the airflow though.

I put it out there as a way that it could be done, because it does have some small advantages, although none big enough to really justify its other disadvantages.

How would you attach it using the fan screws? If the joint is between the small plate and the tube, you will have, shall we say, suboptimal tool access to the bottom two screws(as oriented in above picture), as the additional flange needed will limit the already tight space still further. Support for said flanges will still be needed, unless you design in 45° supports for the flange that do not get in the way of the screw. If you are using bolts, then the limited space would be less of an issue.

If the joint is between the large plate and the tube, tool access will be a non issue, but the lower two flanges, if not the top ones, will definitely need support

I still think a one piece print is the optimal solution, at least for my preferences/printer configuration. It might even be possible to get away with support only touching build surface. That would simplify support removal considerably.

Just a quick thought about glues. There is one called E6000 and it’s copies e7000,8000, t9000,b7000, etc., and they work quite well with PLA and PETG, they have a 3-5 minute working time vs seconds with CA glue (which most people use), and E6000 remains just slighlty less rigid than CA glue so it isn’t brittle. The downside is that E6000 takes 24-72 hours to fully cure.
The only expoxy that I have found to work really well, even with TPU, is JB weld plastic bond - the black stuff.

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Use long screws to pass through the frame the 40mm fan connects to and the 40mm fan flange into the rest of the assembly. It would probably be best to use heat insert nuts in the rest of the assembly, but if there were no plans to take things apart, you could make the holes in the rest of the assembly 0.3mm or so smaller in diameter than the screws and let the screws cut the threads.

Thinking about it - it probably is the right way to go about it. You would have the frame attachment screws (where the 40mm fan connects to the frame) go into the top of the assembly with, again, heat insert nuts or let the screws cut the threads.

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Late to this discussion. There are clear advantages to screws. For something like this I would take a completely different approach.

I would just take the original file, where the tunnel attached to the flat add a very large fillet on the top and might as well be the bottom too. They will then be printable, you can use relatively low infil and few extra parameters to maintain strength it will be relatively low filament usage but less alignment and tinkering to cut the part and use screws. I don’t believe the added strength is needed that screws bring.

Thanks to everyone who’s commented and apologies for the late response, afraid I don’t get as much time on this stuff as I’d like at the moment.

The casing to to which the 92mm side is to be mounted is removeable from the case easily and refits with a single screw so I’ll be using something like M4 nut/bolt to mount that side and the 120mm side will be screwed though the plate into a 120mm fan using fan screws. Once setup Its very unlikely I’ll need to work on it again unless I have fan failure so I’m not too worried about accessing mounting holes etc.

I had another play with Fusion 360 as I always intended a smooth transition between the two sides but initially couldn’t figure it out but a bit of time over the weekend and I’ve managed to come up with something which is much closer to what I intended. I’m not sure if this changes the approach too much?

Looks good - can you post something like an .stl so we can take a look at it all over?

Sure, wasn’t really sure where best to upload to these day so I’ve uploaded to thingiverse - 92mm to 120mm offset fan adapter by dynamis_dk - Thingiverse

I’ve been able to click to download it from the site myself so I believe its uploaded ok

Downloaded without any issues. I don’t see what you mean about mounting with a single M4 nut/bolt?

Quesion, why do you have an eccentric mounting and not a co-axial one? I’m not sure if it affects the airflow, but it would have been easier to design.

For sharing, I’d probably recommend GitHub rather than Thingiverse as you can keep things like this more private.

Good job!

Sorry likely slightly unclear description on my part. The rear of the drive cage is a slide in design which is only secure by a single screen which luckily for my use case points out towards the side of the case so I’m able to easily remove the rear part, mount the fan to the rear without any access issues using some M4 nuts/bolts.

As for the design choices, couldn’t agree more :slight_smile: Unfortunately the layout on the rear of the drive cage means if design co-axially it would foul on the case side and limit access to some PC power connectors so I’ve had to offset it so make sure it fits. I’ve got 2 drive cages stacked on top of each other too so needed make sure each fan didn’t bump into each other.