As others have mentioned above, I've frequently read that ATX supplies are designed to have some load on each rail/voltage supply to work properly. Without that loading, any given voltage may not not perform anywhere near spec.
Personally, I was happy to leave computer supplies behind a few years ago and go with proper power supplies. At least in the States, MeanWell supplies work very well and are <$30 for the sizes used in printers, and are smaller as well.
Thanks for all the information, everyone. I'm of the opinion now that a small amount of preload is desirable, which rules out the Misumi Standard Grade. The HiWin sets are specified as "Z0 - very light preload" with (apparently) 0µm clearance. The Misumi High Grade are listed as "-3 - 0 µm" clearance.
Based on experience posted here, I would think either is fine for typical printers. I actually have been very pleased with the stainless RobotDigg rails & guides I used on my delta. However, my RailCore is worth the extra money 
I'm planning on upgrading the linear guides that are currently in my RailCore (core XY printer with 3 independent Z leadscrews & rails for bed leveling, 2 parallel X rails, single Y rail). Has anyone tried the Misumi standard grade guides? From my interpretation of specs, they seem identical to HiWin's normal grade for not much more money. One concern with the Misumi standard grade though is no preload. Opinions?
And if I were to only buy 3 guides initially, would they be of better use on the 3 Z motors, or on X & Y?
@danal It's not cheap, but Zoro has your size. I bought a 12x24" sheet, cut 1/2 of it down to fit my delta, and used the same piece on glass for 3+ years. I still use it occasionally, but have primarily switched to thinner adhesive PEI on a flex steel sheet from TH3D. Yeah, it isn't round, but works great for the price.
Bear in mind that if 1.8deg steppers are used for Z, I believe the leadscrew pitch will need to be changed as well, to achieve the correct stepping. I don't know the exact pitch to use, but a web search should get you the answer. Perhaps @kraegar or @jstevewhite (co-developers of the RailCore) will jump in with the correct value.
I do know the BOM uses a particular 0.9deg & leadscrew pairing, while the ProjectR3D kit uses 1.8deg steppers with a different leadscrew pitch to achieve the same 0.01 stepping.
That's a very nice write-up for your vacuum dryer. I may investigate it myself. I currently use a large food dehydrator for the filament, and a small convection oven for silica gel, but they each just dump the humidity back into the room. I already have a nice vacuum pump, so I'd save on that.
I haven't tried this yet myself, but I would think you'd want to see an even depression in the water, centered around the nozzle. You don't want air blowing on the nozzle, so the depression would look like a doughnut/torus, with the water level under the nozzle not depressed.
Getting a fan duct to do this, is another story. Obviously circular ducts, like Berd Air, can do it more easily than others. OTOH, it doesn't have to be perfect - just better than whatever you're using now 
I read it elsewhere. I'm not that ingenious.
Try placing a small dish of water on the bed, under the nozzle, to help visualize the air flow.
This one has become popular on the RailCore II coreXY printers: https://www.thingiverse.com/thing:3367622. One fellow did mod his further by adding a small hole in the center, between the two primary outlets. This design is actually similar to MHackney's tusk technique.
I dry it around 60-65C for 2-4 hours, in a dehydrator. I monitor the humidity in the dry box as well, and dry it again if it hits 25-30%. That seems to be below the hissing & popping point, which is good.
Be cautious about going too high in temperature - some spools can begin to deform, and you'll be plagued with feed problems from then on.
@puterpro said in "Backup" for 12V systems if powerloss?:
@PlasticMetal - Those are sweet units! Wish I has room for one.
Well, I certainly don't have them in a rack. One is on a metal shelf (restaurant-style wire shelves, plenty of air circulation), & the unused one is over in a corner.
While these ideas are certainly worthy, I think they're being over-thought. As @PuterPro mentioned, surplus UPS units are pretty inexpensive if you keep your eyes open. I purchased two 1000VA/800W rack-mount TrippLite units off eBay for less than $50 each, with shipping. Right now, I'm only using one, so I replaced its internal batteries and added 2 parallel 18Ah UPS-rated deep cycles externally for about $100 (commercial units such as these frequently are designed with external battery pack connections; batteries were on sale).
So, I have at least a few hours worth of power for the printer, PC and monitors, all with pure sine-wave, double-conversion smooth electrical goodness, and don't worry about power loss routines. The one concession I did make is the 120V bed heater is not on the UPS - that would just be wasteful for a home printer. It's a good chunk of aluminum, though, so it takes a while to cool down.
Add /reprap.htm to the end of your browser link. e.g. 'http://192.168.3.239/reprap.htm'.
Sorry to be grumpy on the Discord comment - I realize it takes a lot of personal time to organize and maintain all these sites. My main concern with Discord, and one of the concerns with FB, is that information gets lost. Discord in particular is just a rolling chat. Forums allow much better organization of issues, and the invaluable search function.
I'm pretty sure the DesktopMetal Studio is USD120K+. It uses rods as filament, maybe 300-400mm long (don't recall the diameter, but maybe 5mm?). The rods are factory-packaged in a dispenser, and the head periodically stops extruding, goes over the the dispensing box of rods and grabs another one, then resumes the job. It's exactly like a hot glue gun, but these rods are a blend of polymer binder mixed with metal powder. The part is then placed in the microwave furnace (which is why it can be used in an office) to drive the binder out. There has to be waste, but I don't know what forms it's all in.
They also have a larger system, and from what I recall, it's broadly similar to ExOne, HP and others that use a spray binder onto a bed of metal powder, producing a green part. You then bake it, driving the binder out, and shrinking the green part by 15-20% to get a pretty dense "solid" metal part.
GE is also coming out with a similar binder jet system. They made some news last year by producing their own system in-house, from concept to working prototype, in like 90 days. Impressive, but not quite so much when it was realized they had extensive experience with multiple other companies' systems, and had already done a lot of "mental homework" of picking & choosing the best features, learning from other's mistakes, and treading a path between patents.
The lowest cost laser powder-bed fusion machine I'm familiar with is from Xact Metal. A couple years ago their small unit was about USD80K.
@DocTrucker - speaking of EOS, I'm traveling next week to their Texas office to evaluate an M400-4 (4x400W lasers) machine for our needs.
Thanks for the update and alternatives. Not a fan of Discord, either, but it's better than FB.
Are you still using SuperLube brand oil with PTFE for your linear rail carriages?
What's up with the RailCore forum and wiki? The security certificates expired over 2 weeks ago on the forum, and 10 days ago on the wiki. Prior to that, the forum had been getting bombed by Russian spam, and it didn't seem any admins were paying attention.
I'm trying my best to not get sucked into the cesspool that is Facebook, but it seems that's the only place still alive.
While the acronym DMLS (direct metal laser sintering) is still used somewhat, I don't know of any system that sinters anymore. SLM (selective laser melting) is not a process for the basement hobbyist. As @DocTrucker described, the powders are very fine (10~45 micron diameter), making them combustible and the soot produced by the melting process is also combustible. Respirators are highly recommended, as are NFPA-rated (or European/Asian comparable) wet separation vacuum cleaners. And then, you have to start talking about proper disposal of the waste.
All in all, not for the faint of heart. But, oh, it's a cool process!
Somewhere last year, I saw a hobbyist-grade SLS system. That would be cool, too, but even nylon powder can get quite expensive.