THIS PART IS OBSOLETED BY THE NEW DESIGN. THIS ONLY FITS IF YOU HAVE THE OLD PARTS.
The original user, Camar0, deleted their account and removed all of their designs, but I found an archive of these files and am simply providing them to the community here again.
This Make from user markdoll01 has excellent photos showing the correct assembly and bolt orientation:
This add on makes the middle assembly stiffer. It allows the MPCNC to cut more aggressively before the tool begins to chatter. It also simplifies squaring your machine since it holds the middle assembly square from the moment it is installed. In comparing to the stock machine higher travel speed and cutting speed have been confirmed in real world testing with the add on parts. Internal testing was performed on a full 5' x 5' 3/4" EMT frame with a 4' x 4' cutting area. The 25sf frame used for testing these parts has 9 times more cutting area than the build size recommended in the MPCNC Bill of Materials. Pushing the footprint to this scale and ramping up the speed is a true torture test of the machine and middle assembly. Testing confirmed the ability of the machine to achieve rapids 1.67x higher than the stock MPCNC settings. The rapids demo video posted shows rapids faster than the $2,595 CNC Router Parts Standard 4x4 kit with NEMA 23 motors. Cutting has also been tested and compared to stock MPCNC cutting speeds and even with the stock machine having a huge advantage due to having the 9x smaller cutting area the 5x5 frame was able to cut faster.
These brackets add 6 more 608 bearings to the crossbar assembly to give it a wider footprint to transfer the torque into the tubes without sacrificing cut area. This is add on middle bracket stiffens the 'better middle Z.' The stock design holds the x to y tubes 90 with the 2x small better middle z plastic cross sections in the center assembly and is helped by the motors at the ends of your tubes.
When assembling the stock middle assembly I noticed that with 16" long pieces of 3/4" EMT installed as my cross bars I could flex the middle Z part with fairly small forces. Assemble your middle assembly and put in a couple tubes and see how much play you have. Run the machine without this add on and see how it performs. You will be surprised by how it feels and performs after the add on.
You need 1/2" longer bolts where the bracket attaches to the 'middle joiners.' The print has an overhang at the top bolt flange. I didn't have any issues printing it but if you have trouble with the supports you might apply some Elmer's glue to the supports. See the pictures for bolt orientation for clearance. The IE version has been posted, built and tested.
2pc Rigid Middle Bracket
2pc Outer Coupler
6pc 608RS bearings
6pc 5/16" x 1 1/2" bolts (2pc for add on bracket + 4pc for outer coupler) (M8x40 for IE)
4pc 5/16" x 3 1/2" bolts (M8x90 for IE)
6pc 5/16" nylon lock nuts (10pc total, 4pc reuse)
The stock MPCNC is a good machine. So is the Shapoko that was introduced at $300, Shapoko 2, Shapoko 3, X-Carve, Shopbot, CNC Router Parts Kits, Joe's CNC kits... the list goes on and on. Don't be afraid to customize your machine or do something different. In the end that is how this machine and everything before it came about. We are makers. Being a maker involves more than hitting buy or print. Have fun with it!
Note: The 'Middle Ends' still get used with this setup but were not drawn in to this CAD file shown in the rendering.
12/30 update: The IE edition has been checked and an STL has been updloaded (IE Middle Assembly CHECK.stl) allowing you to look down the bearings to see that everything should line up. To check it i reassembled the middle using a fresh download of the rigid Z and middle ends and kept the previously aligned middle couplers. If your print has the bolt holes under 8mm you need to open up the holes. The stock MPCNC bolt holes were 8.1mm and my parts match Allted's bolt holes. Please let me know if you still have concerns with the IE parts. There have been two reported builds where the IE fit perfectly. Another had to open up the holes to 8mm to get things to fit okay. I dont have an IE machine but have done my best to ensure the fit and function by creating a full IE assembly in cad using Allted's shared STL parts aligned down to 0.01mm.
12/4 update: There have been a total of 5 known rigid middle add ons built and everyone has been very happy with the very noticeable added rigidity. There have been US and international builds tested on both cncs and 3d printers. At this point I highly encourage all MP CNC users to give it a shot. When I first installed my add on parts I couldn't believe how much stronger the middle felt. For a roughly $20 add on with hardware and bearings you will not find a better bang for your buck. Over 40 hours of engineering went into the design which in and of itself is an amazing value that you can just download the end parts free. Cheers!
11/28 update: Cut out a rudolph head at 20mm/s 5mm doc in plywood with no chatter. The end result can be seen in my builds. I tried to take a video but my battery died during the cut. I will be bumping up my driver current from 1.54a to 2.2a per motor and bringing the voltage up from 12.5v to around 40v dc next and see if i gain anything in rapids or cutting speed.
11/27 update: Just had a chance to make my first test cut. Everything went great. I took 1mm off the side of a 2x4 at 9mm depth with no problems. I will do more testing this weekend and post up the results.
11/25 update: machine is assembled with all mods and moves at up to 19,000 mm/min currently with a very agressive acceleration on 12.5v. The machine did not need any additional squaring after adding these parts as the middle z no longer flexes. I will be cutting this weekend and will post the results.
Updated Assembly STL is also posted so you can see how everything fits together in Thingiview or on your device. Do not print the assembly!
*11/3 Update - IE Parts posted and needs tested. Please post your Make once you have a chance to build it.
*11/1 Update - The Outer Bracket has been uploaded. The spacer for the bearing was added vs. what I had in the rendered images. I've printed / installed the 2 middle brackets and outer couplers and the difference is night and day. With 17" rods in the X Y spots previously i could bend the middle z all over the place. As far as I can tell with this setup it is completely rigid. I have separate mods that I'm working on that will be posted but this one is good to go. Enjoy!
Added a second outer bracket to connect the add on brackets together as shown in the updated renderings. I'm going to print tomorrow and will post up the finished pictures. It should be 100% rigid at this point. To use the the outer coupler brackets swap out for 1 1/2" bolts on the bearings (1/4" longer).