Want a hardcore 3D printer? Then you should probably consider the Makertoolworks MendelMax 3!
http://www.youtube.com/watch?v=EcGaBnDsdk4
I built one a month or so ago. The motion design is good. The attention to detail in some areas other than the motion parts is lacking. For example the implementation of the LED and the cable routing and management and material handling is less than optimal. The docs are improving but at the time I got mine there were some contridictions and assembly order issues. Those have been largely fixed but they still have some work to do on making the docs appropriate for a machine of this type and cost. It doesn’t include all the printed parts and requires about 20 hours of printing for the cable chain and fan ducts.
The X carriage and extruder implementation is a good bit better than on the MM2. On the MM2 the glides on the X wear out fairly quickly and the extruder design is poor for 1.75 mm material. They’ve fixed this on the MM3. The Y and bed on the MM2 can wobble a fair amount as the pillow blocks wear. They’ve fixed this as well.
They are holding the design pretty close to the vest as it’s not an open project. Even if it were you’d need laser cut and stamped or bend frame and mounting parts and machined extruder block parts. It’s really not a DIY raw build though the assembly isn’t too bad. It’s not a candidate for a first time build.
I’ve got parts inbound for retrofitting MM2s with the new X design using stock Openbuilds parts and printed parts, no machined parts required. I would have bought upgrades for my MM2s and a couple of clients MM2 to MM3 but the upgrade kits (now discontinued) were available only to those that bought the MM2 from MTW and not anyone that source or built their own.
I’ve certainly given up on MendleMax since self sourcing/building my MM1.5+. I don’t like the closed direction of the company, the pricing or the stuff with the upgrade kits. I also think the MM2 looked better than the MM3. In this price range my money would go to Lulzbot, Printrbot or a self-sourced metal Prusa i3 build - I think all can compete on print speed and quality.
I see the biggest advantage with an MM3 in the dual head. The Taz5 dual design isn’t as elegant or compact and is 3 mm material only. Brooke doesn’t have anything with near that print envelope nor does the i3 without significant mods or an extrusion frame. By the time the build is factored in the MM3 is more than buying a completed TAZ5 if you have to pay for labor. Including printing the extra parts I had about 40 hours or so into the build (about half of it printing parts) and tune though there were a few hours in backtracking and reassembly due to some of the instructions. About halfway through I went off on my own, using the docs as a rough guide. It appeared to me they did not use those docs in that order for the inhouse builds.
I had a client that was interested in an MM3 but went with a Replicator 2x mostly because of availability in that they needed to use it right away and that it came with a dual head. I don’t think I’ll get another MM3 kit though it is a robust machine that performs well. If you are savvy enough to build the MM3 kit you are likely savvy enough to merge some other designs to build an Open Builds V slot machine. This has really sold me on using the Open Builds rail and wheels. For an open source build a good direct drive dual extruder is a bit more difficult to source but there are a few out there.
@dstevens_lv that’s some good points, I guess I just don’t rate dual extruder setups as particularly useful. Have you printed anything over 200x200mm yet? If so how was the curling/warping?
@Liam_Jackson We’re implementing duals to be able to use PVA supports to minimize manual post processing to remove the supports. I did a few two color prints during the config but that’s not what we do generally.
I use most of the bed area on the MM2s and the i3s. I primarily make i3 and Smartrap parts with some one off prototyping. I don’t think I’ve ever printed over 120 mm on the Z. I nest the parts on the bed as I would with other CNC processes. I use adhension promoters to deal with curling, etc. The challenge on some plates is to not let the parts cool too much between passes while still finding an optimum temp not to string or blob.
@dstevens_lv as a recent mm3 owner I agree with your assessment for the most part. I don’t regret my purchase, though. It was the only printer that checked all my boxes. Taz and Ultimaker were the other two shortlisted bots, but lost due to 3mm filament.
I’m running single right now, but am considering dual upgrade. Are you finding the PVA supports work well? I’m interested in abs/rubber prints as well
The dual head kit is good. I had the same concern as Thomas about the nozzles being on a level plane but the the machined nozzle holder fitting is dead nuts accurate to fit side by side V6s and have the nozzles align. I suppose for a dual head the Chimera might make more sense but what I see on MTW IRC are mainly single head users.
The PVA is working well. It takes some tweaking. For the dual head prints I slice with S3D, it seems to have the best two head integration. The biggest issue so far is getting good adhesion on large builds that have quite a bit of support in the base and bottom layers. I see that as getting used to how PVA prints rather than an issue with the machine…
@Thomas_Sanladerer Thomas, great job on this review, I have been looking at the Mendelmax 3 and interested to see what you thought of it. I own three Mendelmax 2 printers, yes three, call me a fool! 
and I agree with your assessment that they are for more experienced DIY users. I have spent allot of time setting up and also improving my printers. I do like there ruggedness, but they also have issues that need attention. Someone who does not expect to be doing frequent maintenance or tuning should not consider these printers. I myself do like to do these extra things and feel that the benefit I get from it is a very good quality print as well as a very versatile printer. It has a nice large build platform and I have extruded many different types of filament with them. I have built and enclosure around one printer to deal with the wrapage issues and it works very well. I would be interested to hear more about your comment regarding not wanting to print with two extruders other than for support material. I would be interested to see you print a part with the Mendelmax 3 using support material as the 2nd filament. Keep up the good work.
Regards,
Mike A. from Minnesota
@dstevens_lv I have a chimera as well, but I’m not sure how to mount it, do the extruders. It’s in a Bowden setup on a Rostock currently. 
@Thomas_Sanladerer Great review, by the way. I definitely agree about the chimera. They make some odd decisions, but overall a solid printer. It’s my third, and so far most reliable, highest quality printer. That speaks to mtw’s, openbuilds, and E3D’s great designs. It was a smart move for mtw to not try and reinvent the wheel for components which are already working so well. … Like wheels.
Looking forward to what improvements you make to the beast. I think I’m going to try and wrap my head around mounting the chimera on there, rather than buying the second extruder upgrade.
I think an enclosure is also called for
@Mike_Auer after several weeks with the mm3, it has needed the least maintenance of any printer I have used. The bed leveling is a pita as Thomas mentions, but once it’s done it doesn’t seem to need much adjustment.
@Mark_Rehorst The MM2 used TR lead screws as well. The difference here is these are two start instead of single start. The quality of the nuts could be a bit better as you have to chase them to clean them out prior to install. It appears either they machine them or have them made. The MM2 also had three point bed leveling though on this version the rear doesn’t adjust.
The Open Builds wheels are hard Delrin. They won’t flat spot. There are scores examples of machines with greater stress and higher duty cycle using the same mechanisms.
The first paying part for the machine I built was a tooling prototype for a tank top with complex support and raft, no enclosure. ABS with HIPS support, convex and concave shell, 100 x 150 x 100 mm over 20 hours, no issues.
@dstevens_lv FYI the wheels that come in the MM3 kit are the Xtreme wheels - Polycarbonate, not delrin. So, even tougher than the delrin ones.
@Nathan_Ryan Indeed, thanks. They are hard. And quiet. Scary quiet. As I said in another post I hadn’t given them much of a look before but after using them I’m sold.
@Liam_Jackson if you want to build a Mendel Max, I desing the Mendel Max XL, you can find it in thingiverse, look for coricoco.
Just need 20x20 alumium profile