Two-Tau Multi-Pi Rack

by kevfquinn Jul 23, 2017
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I tried printing it on standard with my flashforge finder (15% infill) and it was too tight to fit the raspberry pi 3 in all the way, had to bend the plastic a bit to even get it half way. Do I just need to adjust the infill settings or should I be doing something else? The design looks great, cant wait to get it working

It is a reasonably tight fit, deliberately, but not so tight when I print it that the part has to be bent. It may be difference in calibration between our printers. On my prints, the sides touch the protruding components when I push the Raspberry Pis in, and it takes a bit of a wiggle to get the network and USB ports through their openings (although sounds like you've not reached that point yet!). So it is a tight fit.

Can you describe in more detail in what way it doesn't fit? Is the width of the piece overall too small, or is it just the slots for the cards that are tight? Also, just for sanity, check that all the support has been removed - the side where the HDMI, USB, and audio sockets are should be really thin around the sockets (see the render above in the viewer to compare). If you can measure a bunch of things where it seems tight with a vernier caliper that would be ideal, but if not just describe where it doesn't fit (or if everything is too small).

On the print you have, I suggest measuring all the dimensions, and comparing with what they should be (i.e. compare the sizes and locations of all the holes with what the Pi is). Assuming the supports are removed fine, there are two ways I can think it might be going differently to mine. One is difference in printer calibration - in which case everything you've printed is probably a touch smaller than mine - the other is the tolerance the printer is capable of, which might cause for example the slot for the card to be too narrow while leaving the overall dimensions ok, but if we can get accurate measurements on the difference in print size then we can modify the model to fit.

Are the other pieces fine? i.e. do the switch, power brick, and fan fit well?

Hey Kevquinn, thank you so much for such a fast reply, really appreciate all the help here!

Firstly, yeah, I can understand why it would be, it certainly makes sense. I do think theres a good chance that the printers would print differently. Also, as I am new, I just printed it at standard settings, which might be why it didnt work. The standard settings for my printer (Flashforge finder) is the following.

Layer height 0.18mm (first 0.27mm) infill 15%, so this might be where it went wrong, as I can see this is different from what you suggested!

The pi takes a lot of force to move it inside the alignment slots. I had to bend the plastic and push it at the same time to get it in.

I didnt print with any supports (unless they are in the design?) as I didnt seem to need any. If they are in the design you have here, then I havent removed them! The plastic around the hdmi and usb does seem thin (but only around those ports, the rest is relatively thick.

Sure, the measurements are as such.

Width at back (where you start to slot the pi in) 56.64mm.
Network hole 15,46mm
Entire length (network port to back of caddy) 106.63mm

In fairness, most things look right. It seems that it is exactly the right size for the pi, so I can push it along as its essentially stuck.
I can do more if needed, but thought that might be enough to tell you if my sizes are off.

I havent printed any other parts yet, but happy to do so if that would help. I was planning to print the fan part next.

I am really new to printers, and am using the Flashforge finder, which is perhaps a little cheaper than the printers most people use, so perhaps has a higher (?) tolerance than most printers.

Again, huge thank you for helping me look into it, I am really looking forward to making this.

You're more than welcome - this is a hobby for me, so it's all fun :)

On supports - if you didn't need any then great! Supports are something your slicer will add if you ask it to. I'm surprised you got away with it on the PI block which has the large bridging beams at the top of the print (back of the unit when fitted), and the lugs to the side of the print which need to be neat to fit into the other pieces.

Yes, it's only around the side mounted sockets that the strip is thin (to allow the sockets to fit as they protrude from the card). There's a 2mm recess taken out of the 2.8mm wall thickness.

My printer (Wanhao i3 Plus) is about the same price as the FlashForge finder - and the technical specifications that Flashforge quote on their web site sound plenty good enough.

Infill percentage won't make any difference; that's the density of the pattern the printer makes inside blocks of plastic - and there isn't much of that to speak of in this design as it's all walls.

The overall length is designed to be 106.6, so 106.63 is perfect. This means the layer height isn't a problem (assuming you printed the part the same way up as presented here - with the network and USB holes flat onto the build plate).

If you're measuring into the recess for the sockets (i.e. the very thin bit - I think you probably are) then 56.64 is too small; it should be 58mm at that point.

The network hole sounds small. It should be 16mm x 14mm; the USB holes 16mm x 17mm.

Those two measurements suggest your X/Y sizes are not calibrated accurately; small by somewhere around 2.5% to 3%.

However, before we make that conclusion based on just my models, can you print "3DBenchy" (http://www.3dbenchy.com/) and test all the measurements they describe (http://www.3dbenchy.com/dimensions/)?

Assuming the 3DBenchy print comes out slightly small in the same way, one easy way forward is to tell your slicer software to scale the model before slicing and sending to the printer (e.g. scale to 103% in X and Y, but leave 100% for Z as the height seems fine).

Solved! (I think).

So, I got a bit sidetracked with family stuff, but I did manage to print benchy. I wasnt sure what to make of it, in some ways the measurements seemed right, but they were almost always a little bit too big. It seemed odd, but I saw other people note the same thing and ignored it.

I then remembered that I tried to print some parts that were meant to fit together (lukes lightsaber) and they wouldnt fit together, as they were too big. So I figured it was something improperly configured on my printer.

Finally I found this, and tried it out and it of course didnt work.


Turns out, flashforge fingers own software sets the flow rate to 109% (In this case its called Extrusion Ratio, in the Advanced tab, with Expert mode switched on).

Switching this down even to 100% makes a huge difference. I have found 97%(ish) seems to give the best results.

Thanks again kevfquinn, your help was really appreciated. I finally have my first pi in the case. Although its not in there 100%, I think its looking much better than before!

Expansion / Flow Calibrator

Glad it's working out better! Yes, 109% does seem unusually high, and would cause the print to be bulged out, slightly. Wanhao ship with the software for my printer set to 107% which is similarly high, and I've long since dialled that back (varies by filament).

I am thinking of revising the design so that instead of the very tight fit to hold the PIs in place, loosen the fit slightly and add a retaining brace bar at the back similar to the fan module brace (with a looser fit, pushing in the cables in the front could easily the PI back in the rack).

Love this design, it inspired me to buy all the parts. I am having trouble getting my RavPower 60 to slide in and pretty sure it is the same one you used. Is there any trick?

Great to hear you're giving it a try!

There's no trick, it should just slide in, with the obvious orientation. Perhaps the RavPower 60 isn't manufactured to the same dimensions, or the tolerance on the print is tighter than mine. Are the other parts all fitting ok?

Does the print look like the model above? Use Thingiview to see all around the model above - I'm wondering if there's some support on your print that needs to be removed.

Can you measure the dimensions of your RavPower 60 and the dimensions of the aperture on the power brick part? Mine is nominally 69mm by 102mm by 30mm.

OK thanks for the reply! Mine measures the same (actually 101mm in the dimension that is tight). It seems to be due to the reinforcements in the corners, so I am just filing those out and it will fit. I thought those might be supports but did verify they are in the design. The netgear seems to fit perfect. Just printed the pi rack but haven't finished removing the supports yet. Just need to do the fan parts and put it together! Will post pics of my make soon. I'm going to use it do to this: https://blog.alexellis.io/your-serverless-raspberry-pi-cluster/. What do you do with yours?

It sounds like your USB power block is slightly different to mine, which has round edges to its side panels and the guide beams in the corners fit in the gap they make with the box.

As it's an OpenSCAD design which is a free tool and I've published the source code it's easy to modify yourself, and generate the STL how you like. There's a line towards the top of the source file setting variable "uprv_g" to 2 (line 160). This is the height (in mm) of the guide beams; if you change that 2 to a 0, the guide beams top and bottom inside the box will disappear when the model is generated again.

Look forward to seeing pics of your print!

Thanks for the tip, but think I will just finish filing them out for now rather than reprint. But will probably reprint it like that later. Mine has rounded edges too but maybe not as rounded as yours. This is the one I got: https://www.amazon.com/gp/product/B00OQ19QYA/

love the addition of the fan! Really nice design, thanks for sharing!!!

Thanks - it was a lot of fun to put together :) Particularly proud of using red for the power brick, blue for the network switch!