Prusa HT90 Comprehensive Review
There did not seem to be any big reviews out there for this printer that seems to have been available for most of this year. So here are my thoughts.
This is going to be a long post. So TL;DR version: the price is hard to accept coming from consumer-grade machines. But coming from industrial machines there does not seem to be anything close to this inexpensive. The entire experience seems very well-worth the cost and the printer competes well (to my knowledge) with many other exponentially higher priced machines. It is the best of the best with user experience - Prusa UI excellence all the way. If you have the need, or want to make the plunge into an industrial-grade machine, I can't think of a better printer in this size-range. It was mostly accurate for Prusa to say this is the only printer a design engineer would need (apart from the comparably-small build volume and the possible need for multi-material requirements).
Ordering / Total Cost
Surprisingly, this printer is as easy to order as any other Prusa machine. There was a very short advertised wait time of only 2 weeks (the least amount of time I have ever had to wait for a Prusa!) If you are in the US, it may be cheaper to buy direct from PrintedSolid if your state does not charge sales tax. The total cost of the printer delivered to me was $11,158 including import tax. Had I been able to go with PrintedSolid, it would have cost $11,370 with free shipping. I wish Prusa would put more effort into making PrintedSolid a true US-provider of Prusa products. As it stands, PrintedSolid only sells the HT90 to enterprise, govt or edu customers. And their prices are too high for Prusament.
Delivery
DHL was the only option on this. Shipping was $807 (!) for Express 2-3 day service. DHL sent me tracking info a few days before it was picked up. Then they sent me an import tax bill of $361 which I paid online within a couple hours of the notification. Tracking did not show it was out for delivery so it was a surprise when it arrived late in the evening, and a few days late. Possibly the reason is it does not fit in a normal DHL van - looked like they rented a box truck with a lift gate to deliver this. So if you are ordering, be prepared for a possibly complicated delivery.
Packaging
Well, if you are interested, you probably already know from their unpacking support page that it is packaged extremely well. It arrived strapped to a pallet with 2 damage indicators. Inside the box is the printer, pre-built and ready to go apart from having to remove the lifting straps, some internal foam and sliding on the filament holder. It's heavy, around 48kg. Accessory box I know, the first thing I looked for is the Haribos. the XL came with a huge tub of them. This one came with nothing. No treats of any kind. There is a full spool of Prusament Jet Black ASA, a wifi dongle, the printed filament holder, a huge 1.5kg bag of desiccant, a basic handbook, and a few small spare parts. Very boring stuff here. Would have been cool if they at least threw in a spool of PC-CF or at the very least Galaxy Black ASA instead of jet black. Oh well. Also, they provided a tiny tube of lube that says "Super-Lube PTFE". I thought they developed their own lube for the magnets and balls? SuperLube is nothing special.
Placement
This printer is 53cm in diameter x 103cm tall (150cm tall with door at normal half open position). They recommended a minimum area of 70cm in diameter for placement. So standard 61cm cabinet depth should be okay. 46cm depth ones would not work. Being able to support the 48kg printer along with anything else would be the main factor. I am using 19mm plywood wall mounted to hold both this printer and the XL5 with the enclosure. The shelf is 119cm wide x 69cm deep. But note that I removed the spool holders on the right of the XL so that gives me some extra space. I will be feeding filament for the XL and HT90 from a drybox dispenser under the shelf that I will make.
Filament holder
This gets a whole paragraph because I have a lot of thoughts. At first I was disappointed to see that it was just a standard holder attached to the side instead of a dedicated chamber inside to hold it. But I have changed my feeling on that because with it on the side and exposed it is extremely easy to load and you are not limited to any size spool. Regarding their $200+ optional filament dispenser: just get a normal dispenser from Amazon and save the money. I am using a PolyDryer/box combo and it works fine. Seems far easier to load than the Prusa one, it's clear so you can see the remaining filament, and you can add the heater to it to keep it dry while printing. The only downside is the color of the clips does not match the Prusa Pro Green on the door handle of the machine. I get that they wanted to produce their own dry box, but it's janky in my opinion especially compared to the printer and seems like an afterthought. Printed parts There are a lot of printed parts on this machine, surprisingly. The above mentioned spool holder is one, door handle, door slides, filter enclosure, display mount, and several parts on the print heads. The filter enclosure looks to be PC jet black, hot end components PC-CF, and the exterior parts are probably PC too.
Optional oven
Any forced air lab oven will work. You don't have to go with their only option. The model they offer is cheaper from them compared with any other source I could find, but there are other brands/models that work just as well at half the price. I got one on Amazon for about $1400 and it fits 4 1kg spools at once. I also use it for annealing parts. You can find smaller models for less too. The normal filament dryers / dehydrators do not get hot enough to dry nylon let alone any of the higher-temp filaments like PEI or PEEK. You need an actual oven and best to get a lab oven for the accuracy and stable temperature control. Also, avoid getting a gravity lab oven because the lack of fan will make drying times much, much greater (I tried that route to save some money - ended up costing me more). Is the oven necessary? It is if you are printing with PEI or Nylon. Even new PEI fresh from the package is likely too wet to print. It has to be dried at 150ºC for 6-8 hours then immediately transferred to a dry box that you can dispense from. And it needs to stay dry because it can get wet in a very short time. That's why I think the PolyDryer is a much better option.
Prusament PEI vs 3DXTech
Prusament PEI is frequently out of stock (like their CF-PC which seems is always out of stock). I scored two spools after I already went with 3DXTech directly and got their PEI as well as some others. 3DXTech is US-based and I have dealt with them before. I think their higher-end filaments are probably the best you can buy. Plus, there are profiles for their filaments ready to use on the HT90. Honestly, the 3DXTech website is a candy store of exotic filaments and my HT90 would love to shop there if it had legs and a credit card.
HT90 print profiles
You cannot download these profiles prior to receiving the printer. You cannot find them anywhere online. The only way to get them is to purchase the printer and when it arrives, your Prusa account will be associated with the printer so when you log into your account through PrusaSlicer, the profiles will show up in the configuration wizard. I have no clue why they do this. I wanted to experiment with some print settings prior to getting the printer but the best I could do was to have chat support provide me with a screenshot of their profile settings to see supported filaments. Maybe it has something to do with them wanting to keep it locked down since it's running Klipper? If you do not normally log into PrusaConnect via PrusaSlicer, you can instead transfer the profiles via a USB drive.
About Klipper
Yes, it is the first Prusa I have ever had that uses Klipper. And not only that, it's running Klipper on a Duet board which I thought normally runs RepRap firmware. I do not know why they went with Duet instead of making their own board in-house since I believe they make all the other boards for their other printers. But as you are probably aware, this Klipper version is locked and cannot be accessed through SSH. So no fiddling with config files remotely. And it is using MainSail as a web interface (with most options removed). Having a pre-built Klipper system is a big deal for me knowing how much effort it takes to get the firmware working perfectly.
Main board
As mentioned, it is a Duet-branded board running a locked version of Klipper. The board is Duet 6HC with a custom TriLab-branded shield. There is also a Raspberry Pi 4. There are some printed parts inside here too, mostly the big fan shroud. Looks like it made from PC-CF. The fact that I gained access to the board area at the top was a bit of a mistake. The top plastic panel had a protective liner along with what looked like three pieces of tape with pull tabs. After I removed them and saw the tabs left behind some adhesive text I understood that they were tamper-proof stickers. Well, it's my printer so I can do what I want but still, oops. While I am in there though, I may as well replace the small, loud electronics bay cooling fan with a larger, quieter one. In fact, I think it would work better if a larger, low speed but similar cfm fan was relocated to the plastic top panel sucking air out while bringing cool air in from the vents on the sides. This is going to be mod #1 because I really dislike the constantly-on high pitch whine of the small fan. There's no getting around the fan noise when it's printing, but at least it can be silent when idle.
Printer display
It's a big touchscreen with a good interface. It's plugged into the Raspberry Pi. It does not look like the XL/MK4 interface, more like the SL1. There are some things like the on screen keyboard and some buttons with setup that are not formatted very well. And there are not that many options on the settings. I don't know what more I could want, but it does seem like the screen could do more than it is doing or at least be a little customizable. I don't see anywhere to edit the header/footer like you can on the XL/MK4. There is no z height indication or number of layers to go. It only shows the temps on the main screen. I love the big emergency stop button that is integrated into the OS very well. Pressing it does not shut down the whole system, just the heaters and motion I think. When you press it, the screen changes to emergency stop condition, then when you release it, it switches back to normal operation immediately without rebooting or any delays. This is the first time I have seen stop button integration into the OS. Normally it is just hard-wired to the motion control power so it's really impressive, this level of programming.
Camera
Yes! Finally, my Prusa has a camera pre-installed! But...it's all the way at the top so you can't really see things that are being printed but it's good enough to see if the print has failed or if it's complete (though the Prusa Connect app send a notification when complete so not sure what's the point of the camera in this capacity). Also, since it does the purge line as a curve on the bottom, every time I look at the camera view it looks like the purge line is a smile 🙂 Not so nice is the fact it is not video, just stills. So you are not going to be able to watch the print as it prints. There's a swivel cover in case you want privacy. And they include a blank in case you need to remove it completely. I know several companies in my area that have no imaging device rules so that was a nice thought. Also, I think you can plug in a USB camera and stick it to the outside looking in so that would work well for actual print monitoring. A dedicated print monitoring and recording camera mount will be my #2 mod for this printer.
Nozzles / Print Heads
Revo nozzles are readily available most places. The only thing I can't easily find are the high temp versions. Prusa seems to overcharge for the nozzles. The HT head comes with a 0.6mm nozzle which I switched out with a 0.4mm one that I will use with non-filled filaments. Happy that they went with the Revo. It comes with both the high flow head (0.4mm brass HF nozzle) and high temp head (0.6mm high temp hardened nozzle). Switching heads is fairly easy and takes a couple minutes. The power needs to be off. The door can raise up all the way by rotating the locking pins. But be aware the printer needs 200cm (!) between the bottom and ceiling to clear the door. If you have it on a normal-height table with normal-height ceilings, you will not be able to open the door fully. It's not really a problem to access the upper part of the printer with the door in the normal halfway open position though. It takes a few minutes to switch the heads. You have to reach way up with your fingers to undo the connector. And you also have to open the elastic harness support and reattach it to the new head assembly. Installing is harder because it is difficult to see where the connector goes. There is a ridge that helps alignment of the connector. The thumb screw tends to fall out during installation. You can't run normal filament like ABS, ASA, PETG, PLA on the high temp head (slicer profile limitation) so you have to switch between the heads. This makes the user experience less than ideal if you need to switch often (and of course, if you have this printer, you probably need to switch often). Another thing about the print head is it is so large so you really cannot see where it is printing other than through the little window at the bottom of the front door. Gone are the days of the ease of watching the nozzle print on the MK4. If you enjoy watching the printer print, you will be slightly disappointed once the novelty of the delta movements wears off. Something troubling about the print heads is the high cost of replacements. The HF head assembly is $760 and the HT head is $839. This gives me some apprehension when not monitoring the print directly because I am worried if I get a print detachment, will a blob of death be as easy to remove compared with the MK4 or will it completely kill the head? The entire bottom of the head is a printed part. On the HT head there is a manual control knob for the cooling but on the HF head there is a whole servo assembly. I just feel like they should be offering more parts instead of a whole assembly. I'm worried that will never change because it's not a very popular printer at this price compared with their other printers. Maybe they have some sort of un-advertised supply that can be purchased on request? Regarding Prusa's claim that the head cooling is innovative: well, yes. Some are arguing that the use of a CPAP fan is nothing new but I think the way the implemented it with an auto-servo in the high flow print head that directs the air to different locations was the innovative part. On the high temp head, that adjustment is manual only and the printer shows you the setting you need to select on the screen. But the selector dial index is very difficult to see and there are no detents. I think this part needs to be better. Regarding the extruders, they seem to be custom made. They have BondTech gears in a metal housing with a large plastic gear being driven by an LDO pancake motor. There is a tension adjustment thumb screw which I assume will be needed for running flexibles. Let's talk about nozzles. The Revo selection is huge! Currently, you can buy normal brass, high flow brass, DiamondBack, Obxidian, Obxidian high flow, high temp, high temp hardened, high temp/high flow, and belt/non-planar. Unfortunately there are only a few print profiles for the HT90: for the high flow head you can choose from 0.25 / 0.4 / 0.6 / 0.8 nozzles and for the high temp head 0.4 / 0.6. There is no indication on the profile to specify whether the nozzle is normal or high flow. So hopefully they will add profiles because I hate spending time tuning profiles myself. I am also really interested to see if they implement non-planar printing (will probably need a different head so that idea is probably not going to happen). But maybe a third-party would make one if they opened up the printer firmware to allow for that (also doubtful). Sigh...one could hope. Anyway, if you are in the US, I have found PartsBuilt3D to be a good source for parts like nozzles.
Build plate
Comes with the PEI textured plate and I also got the nylon texture plate. There is no smooth PEI option. They do recommend the use of a release agent like Magigoo if using the textured plate (but not the nylon plate). I ordered the Magigoo HT with the printer just so I would be ready for the hot stuff. I don't know why the plates are more expensive compared with the XL plates. They're smaller than the XL. Seems like a money-grab. Also, would have been nice to have a PEI smooth plate just to get that extra adhesion bonus. Also, there is no PP plate for their new PP filament.
Bed leveling
This is courtesy of the pressure sensors under the bed. The print heads have nothing in them other than the extruder, extruder motor, hot end, and a small servo for the fan (HF only). That's it as far as electronics so they are very lightweight. The bed sensors seem to work as good as anything else, with first layer accuracy perfect just like on the MK4s and XL. The heat bed seems to be anodized aluminum but I don't know how thick it is. It does not seem to be segmented like on the XL.
Lighting
Thanks to interior being glossy white, lighting is excellent and you can see all parts very easily through the massive front door. There are two long LED strips along each front side pointing back, so not blinding in the face like other Prusas. It is not RGB, so just white (I think, maybe they are RGB but hard to tell - they are small). It would have been cool to see them implement different colors to indicate things like problems or completion. There is a colored light indicator under the display though.
Slicing
As stated above, you have to wait until the printer arrives for you to be able to actually install the print profiles in PrusaSlicer. For some time comparisons, a standard benchy on a MK4S with HF nozzle takes 36m - the XL takes 47m, and the HT90 takes 37m with balanced print settings and 16m with super speed print setting. Larger models like the Robo Alpaka take 3h52m on the MK4S, 4h24m on the XL, and on the HT90, 4h27m balanced / 1h55m super speed. And if you are wondering, a benchy printed in PEEK-CF costs $10.65 compared with PLA which costs $0.32! If I printed the Robo-Alpaka in PEEK-CF, it would cost $115.85!
Printing and Special Considerations
Using this printer to print a PLA benchy seemed like an insult! But oh how fun it is to watch the delta work (no, not my first delta but still cool). Everything is somewhat quiet and smooth except for the fans. It's not as quiet as the XL. You could not have this printer in an office setting without issues due to the noise. Deltas sound different than Cartesions or CoreXY because all three belts are moving all the time. Even when printing PEI and PEEK, the fan noise was manageable. The two rear panels stay cool to slightly warm when chamber temps are high/heater is on. But the door gets really hot so something to consider if you are running this in a small room - it's like a 1500W space heater that also prints! I hardly ever print anything in PLA, but doing big PLA decorative prints on this is a joy especially since you can keep the door closed and it keeps the chamber nice and cool. It's a very fast printer with the high flow head installed. Compared with a Bambu Lab X1C, the difference is negligible. With the high temp head installed things slow down a lot. For example, the same print on the HT90 with the high temp head takes 5 hours using 3DXTech PEEK-CF and only 3 hours with the high flow head using Prusament PC-CF, both with the balanced setting print quality setting. Print quality is comparable to the MK4s/XL. There is no vertical banding visible. All of the Klipper features seem to be active and working such as pressure advance and input shaping. Because it's a delta, this is really great for prints that are cylindrical that take up the entire build volume. It is big enough for some helmets or life-size human heads. The build volume is substantially smaller than the XL. If I am doing volume production runs, I can obviously pack more on the XL build plate than the HT90 plate. But if I am doing large ABS / ASA objects that can fit on the HT90, that is always my choice since I can crank the chamber temp up to keep things from warping. I think that Prusa's advertisement that the HT90 can be the only printer one ever needs, the reality, I think, is that you also need the tool-changing XL if you want to be able to create anything, especially if you ever want to do any kind of multi-material like mixing TPU and other types, which I often do. Other considerations are simply knowing that although it is a really wonderful machine, it is still just a 3D printer and it comes with all of the limitations any 3D printer has. I have had no issues (apart from making sure filament is dry) with printing about 30-ish jobs on it with ABS, ASA, PEI, PA6-GF, PEEK-CF with jobs averaging 3-6 hours each. I have not done any overnight printing yet because I still don't trust the power solution I have (see below) when printing with these very expensive filaments. And I really haven't had the need yet. But I would feel fine with printing an overnight ABS job. The parts I am printing with the higher temp filaments are benefiting greatly with the switch from lower-temp filaments. Parts I used to print with Prusament PC-CF I now print with PEEK-CF for the incredibly-increased strength, especially along the Z-axis. These small parts are subject to a lot of stress and it is really great to be able to make parts without the need for metal fabrication. PEI is almost as strong and less than half the price of PEEK-CF. But I haven't been able to find anything but natural orange/amber colored PEI so it limits some applications to parts that don't need to be visually appealing. Also, PEI printing tends to string no matter how dry the filament is so I have not been able to get super-clean parts in PEI, even after drying it in a 150º blast oven for 12 hours and immediately printing from a drybox.
Power Panic (none!)
Unfortunately, this printer has no black or brown out recovery like every other printer I have (except for Vorons). Maybe the Duet board or Klipper firmware have some limitation with this. That means using a UPS to keep it powered during occasional flickers. At a max 1600w for the 110v version, it also means any UPS will not power it for more than a few minutes if it's running at high temps. We get very random power cuts that last a few seconds especially during stormy weather so having something is really necessary. For the time being, I am using a CyberPower 1500VA UPS that I picked up at Home Depot for about $550. This model has a max output of 1500W only, so the HT90 is right at the limit. Thankfully, CyberPower UPS units allow for higher than 100% output for short periods without doing an auto-shutdown. I was unable to find a UPS with higher output that was not designed for a rack server mount and cost of over $1000. In any event, even the most expensive UPS is only going to power the HT90 for a few minutes. This being the case, I simply won't be running the HT90 during storms. Regarding powering off, there is no menu selection to turn off the system, only the power switch. On all of my other Klipper systems, I use the power down function to avoid corruption of the Raspberry Pi files. There is a system shutdown option in the MainSail interface only, but there should be one on the printer display as well since I do not have the printer networked.
Networking
PrusaConnect works on this printer just like any other Prusa. You can choose from the PrusaConnect control within PrusaSlicer or via the web. You can also log into the IP of the printer to see the MainSail interface. Unfortunately, the version of MainSail has very little options, no macros like chamber preheat, and no way to see config files or anything like that. It's really locked up tight - guess Prusa is worried about clones. There is an ethernet port on the back and two USB ports you can use for the included wifi dongle. Wifi setup is easy via the on-screen keyboard.
Comparisons
Compared with the closest printer I have in terms of capabilities, the Bambu Lab X1E, the HT90 is in a different category completely. Two things set it apart: the chamber heat and the high temp head. I really don't know of any other printer close to this price that can get this hot with reliability (I understand there are some self-builds that can but boy are you having to do a lot of work to get there). Compared with the FLSUN S1: this is the most similar-looking printer I have. But the S1 is a piece of junk, really. It cannot maintain temps like the X1E, and was a very regretful purchase. I got rid of it after less than a month (it would have cost me more to return due to their poor return policy so I just sold it to a friend for half the price I paid). Compared with printing on any other Prusa, it's basically the same. All the same things in PrusaSlicer apart from some added profiles. Compared with printing on my next best printer interfaces, let's say one of my Vorons, huge difference. The HT90 has so many features and capabilities that my Vorons do not have. And the HT90 is tuned and ready to roll. If you factor your time as an expense, the HT90 makes sense and is a bargain (ha ha). I think the only limitation is that of the closed-off firmware - it is not great to be at the mercy of Prusa to produce firmware updates for the only source of upgrades or new features. Since the printer was released 5 months ago there has only been one firmware update with just a few changes.
What I would like to see changed
1. Switch the electronics bay fan out with a larger, low-speed, high volume model to reduce the whine noise when idle, or have it turn on only when necessary.
2. Make changes to the front door to make it removable so that access when changing heads is easier. I get that it was a nice design choice to make it slide up but having it open on hinges seems like a better idea to me.
3. About the door, would be really great to have it insulated - it transmits a lot of heat into the work space.
4. Camera needs an upgrade with both the location and quality.
5. Would be useful to have handles built into the base for easier moving. The straps that it comes with only work well for the initial removal from the foam packing.
6. Make replacement parts available in the Prusa store, especially hot end components.
7. More material profiles would be awesome.
8. More options to control via PrusaConnect such as preheat.
9. Change with the firmware and/or profiles with clarification on nozzles. The profiles do not indicate whether they are for the normal or high flow nozzles. And when I switch to the 0.25 nozzle, the firmware complains that the profile is asking for the 0.25mm high flow nozzle (as far as I know, the 0.25mm nozzle in the high flow version does not exist.)
10. Add a shutdown system option on the printer screen.
That's it! If you have any questions about the machine, I am happy to answer them.