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General feedback on 3D printed Preonic case design

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golfiros:
Hello y'all!

I'm just getting into the world of custom keyboards, and have decided to jump right in and do a 3D printed hand wired build. I'm not sure about the etiquette of attachments here, so I'm just including the full design (in a blender file for now) as an attachment. It's basically a Preonic, but I have some questions about the design.

1) I really wanted a bezel around the keys, and the solution I came up with is the following: I'll print out a plate for the switches, and a wall. I'll later superglue the plate to the wall so they become one piece. Is this a bad idea?

2) Is a 1.5mm plate with 100% infill sturdy enough as a switch plate? Does it actually need reinforment? I wonder because the plate is going to be subject to way stricter tolerances than the rest of the board, and therefore printing it with reinforcements would be pricier

3) Are 3mm thick walls sturdy enough for the rest of the build? Too strong, and I can save with thinner ones?

4) I'm fixing the backplate by supergluing M2 nuts at the bottom of the walls, and then screwing in the plate from the other side. Should I be woried about this not being enough to hold the back plate in?

With respect to all of those questions, the idea is to have all prints done in PLA. I can't print them myself because they are too large for my tiny hobbyist printer, so I'd rather have something that's going to be almost fully functional on the first or second iteration.

Thanks everyone for taking a look,

GG

Leslieann:
1. I can't see the design, but, glueing depends on the plastic. PETG doesn't glue well, PLA does. Important in a moment.
2. 1.5mm is not strong enough even at 100%, but it only needs to be 1.5-1.6mm at the switch itself, this isn't a thin metal plate being laser cut, you can make ribs underneath the plate and if you do this, 40% infill and 3 walls is fine. BUT... and this is a big one, if your printer is not square this can create massive problems. You will need to print one part right side up another upside down and if your printer is off by 0.03mm it means a 0.6mm deviation/skew by the time you add them together. While it pays to get it as close as possible, printing one rotated 90 degrees will help offset some of it. Under plate ribs can be 5mm tall, at this point they should just touch the pcb. Beware the printer's tolerances.
3. 3mm is good for structural parts, but I tend to prefer 4 or 5mm. 3 just comes across as too thin looks-wise and often comes across as cheap. Again, I can't see your design, so it may be fine on your design. It wasn't on mine.
4. Get brass inserts but even they may not fit in your walls. Try what I do.. just use small wood screws. Pre-fit them in far enough to grab then heat with a lighter, screw them in to create threads, leave them to cool. It works surprisingly well. I tend to use #2 or #4 screws.

PLA for keyboards is HORRIBLE(!), it's rough, scratchy, sharp and "tinny" sounding. ABS is better but I DESPISE ABS. PET feels nice and sounds actually pretty decent believe it or not. The bad part is PETG needs to be printed in one piece or use screws. The other problem is PETG shrinks, not as bad as ABS, but more than PLA. Again, not seen your board, but doing even a 65% in PETG will take a LARGE printer and some real experience. Not trying to sound conceited but it really is beyond the capabilities of most people (skill/experience and printer-wise). Frankly, even in PLA a 65% is pushing the limits of FDM printing because at 3% shrink, it's way more than enough to cause lifting and of course it's too big for most printers anyhow. And ABS, PC and more, even an ergo design is a stretch.  There is ways to work around this issue, but again, this comes down to experience and most people simply never have. I keep meaning to write an article about it but just haven't had a chance, the link at the bottom of this post has much of it though.

Going back to #2...  If you aren't doing some right side up or down, try and keep them oriented the same. Again, skew is an issue and most people simply have never checked their printer and if they have, they've never done it at extremes. Being off 0.1mm at 100mm is perfectly fine for most things. Being off 0.1mm at 100 scaled out to 400mm now suddenly means 0.4mm skew and when flipped it becomes nearly a full mm. It may not impact your holes too bad but your outer walls will be off by that much and that is painfully obvious. This is another reason printing parts on one machine may not fit parts from another, which is surprisingly difficult.

I would highly take a look at my 65% build, tons more printed keyboard tips there.
https://geekhack.org/index.php?topic=109345.0

pca006132:
1. You can try to make some slots to reinforce the joint and increase the surface area for the glue, so it will stick better and potentially help you to hide the seam. But I personally prefer using screws rather than glue, glue will usually make a mess if you are not careful enough.
2. No. You can try to join the plate with the walls to give better support for the plate, but I think you will still need to add ribs in the middle to avoid flex.
3. Should be enough, the problem is the middle of the plate with no support from the walls. IMO wall height is more important in this case as you apply forces in the vertical direction rather than horizontal to the wall.
4. Use brass inserts or self-tapping screws with a slightly smaller hole. Note that brass inserts are cheap, lasts much longer, and are really strong.
 
Regarding small printer, I think you can print the keyboard in two parts, but have to be careful about the dimension error and adjust your design based on your test prints. For better mechanical strength, you can do a slightly more complicated cut and add brass inserts to both sides, use the screw to hold the two parts together, similar to this:


I think it would be much better to print it with your own keyboard instead of using printing service, because you can adjust the design based on the printed object, e.g. tolerance, and it is much cheaper.

Leslieann:

--- Quote from: pca006132 on Tue, 04 October 2022, 08:41:44 ---I think it would be much better to print it with your own keyboard instead of using printing service, because you can adjust the design based on the printed object, e.g. tolerance, and it is much cheaper.

--- End quote ---
Good point...

It's very often cheaper to buy a printer and do it yourself than to pay someone.
Especially your first time because odds of this fitting, much less working, and even far less likely to have the fit and finish you expect is pretty much zero. meaning you're going to need to redo it at least a few times before you're happy. You can quickly exceed the cost of a basic printer.

mk:
Plate thickness:
You can make the plate very thick if you just make it in two parts, one that's 1.6mm to support switch snap-in, and then the rest of the plate. An example can be found with the QEZ keyboard. You can make the edges even taller than the height of the keyboard to reinforce it even more. But with high infill rate PLA it should be ok. Tight tolerance on the cutouts can cause some plate bend.

Material
PLA is quite nice for keyboards, both for plates and exterior. It can look quite good (especially if the design is optimized to overcome the FDM shortcomings). Resin can look good, but has a tendency to be brittle, where PLA is better in that regard. There is also MJF nylon which is a bit expensive, but is very elegant, I can hardly tell that it is 3d printed. PLA also allows you to do it at home on your smaller printer. In general, I would really recommend prototyping the different parts on your own printer to make sure you got everything right. Making the keyboard in multiple parts and gluing them together is also fine - if using different colors it can even seem like a feature!

Mounting of the plate
There are so many ways to do this. Personally I prefer to be able to disassemble the keyboard, so I prefer using screws/bolts. A classical "tray mount" approach is easier to implement and quite elegant. There are also gasket mounting options, which gives a bit nicer typing feel (again you can look at QEZ that I linked above for an example). As mentioned, heat inserts work great. It is possible to make things stick together by screwing directly into a printed hole slightly smaller than the screw, but it is not super durable.

But in general? Just print the smaller components, experiment, see what works. Make a 2x3 keyboard on your printer to see if the design works out and scale it up. Re-iterate. Don't get caught up in perfection. Don't focus too much on doing things "the right way". A janky keyboard is better than no keyboard. Get inspired by other designs and what others have gone. Have fun.

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