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ssembly-----

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This is what we will make for the base. There are three dual spool holders and one central support. All use the same 3 inch brackets with wood screws. Notice the brackets are offset so the screws from the opposite side do not touch each other. 

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Cut your oak base board that is .75 inches thick:

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First cut your three foot long 2.5 wide by .5 thick oak hobby board into:

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First we will mark and drill the holes where the buffer attaches to the 1x11 inch support beam. Just take this out and do one of the following steps. Do not attach it to the base yet. 

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SLOT BUFFER STEP

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Place the Buffer Bracket on the left side of the 11 inch long center support wood beam. The top of the bracket should be about a quarter inch lower than the end of the board. Mark the holes with a pen.   

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IMPORTANT - Now check the position of these holes relative to the top of the 11 inch vertical support beam. The holes must be about .75 inch from the top. redraw them if they are not. 

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PRUSA BUFFER STEP

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If you are planning to use a Prusa buffer box  do the following instead. Place the bracket against the left side of the beam and the box over the peg on the top. Make sure the box is resting on the ground for its weight and is not being supported by the peg in the bracket. Move the bracket up or down to fix this if needed.

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If using the prusa buffer also check that the bracket is positioned so the first plate holder (the thin prusa brackets that hold the plates together) is positioned inside the prusa bracket.

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Remove the bracket and then and drill the four holes all the way through with a quarter inch drill bit to make a larger diameter hole than needed. 

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Note the picture blow. This is what we will end up with soon.  Also note that the base board's corners can be rounded. and the left rear corner can be significantly cut out to reduce weight. You might consider staining or painting the wood prior to assembly. Also stainless steel brackets look much better than black if you can find them.

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This is for a setup where the printer is on the right side. (If you want the printer on the left then the back bracket needs to be on the back left corner and  and center bracket need to be six inches from the left side instead of the right side. Also, the central arch would then be on the left instead of the right. ) All of the remaining instructions are for a printer that will be on the right side of this.

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Ideally we use a base board that is 11x20 and .75 thick, although we can use one as small as 10x18.5. The vertical supports can also be .75 thick instead of .5 as .25 of an inch wont affect anything for spool clearance. For the three vertical supports you will drill these hole heights, but keep in mind if you use a board 10 inches wide the holes will not be able to be in center as the spools cant touch when mounted. 

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Here are the minimum dimensions for clearance. Note the two bolts in the front need to be at least 8.25 inches apart, which leaves about a half inch of clearance between two mounted spools. The longer center support needs to be at least 4.75 inches away from the fifth spool's rod in the back for spool clearance. Note the three spool vertical supports are always mounted as close to the edge and sides as possible. The length needs to be between 18.5 and 20 of the baseboard, and the width between 10 and 11 inches wide. Ideally it is 11x20.

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Drill holes for the five (six) spool rods in the 8 inch boards. If your baseboard is 11 inches wide these can all be centered, but if shorter then ensure your rods are at least 8.25 inches apart and you might have to drill them offset from center.

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For the three vertical supports:

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Get some 3 inch brackets that look similar to the ones here. They should come with .5 inch wood screws. You need 8 total. Here are the brackets and wood I used. Get two of these brackets packs of 4 and three feet of this oak wood.

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Position the three eight inch vertical spool boards on the front left, front right, and rear right corner, 3.25 inches from the ends and flush against the sides. Stagger the brackets so the screws dont collide.  Predrill the wood screw holes for the brackets.

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Each 5/16 rod is inserted into the washer, then goes through the board, and is secured with a 5/16 nut on the other side. Place all 6 rods in now. Note that the spool holder in the back holds a six spare spool on the backside of it. You dont need any nyloc nuts though, just bolts, washer, and normal nuts.

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Here is the rod hardware.

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The position of the 2.5 inch wide .5 inch thick eleven inch tall center support board is placed a a foot from the front end and six inches from the right side. Measure this position off the center right side of the board. Predrill these holes too for the wood screws that came with the brackets and attach it as well. 

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IMPORTANT - the 1x11 board needs to be perfectly aligned and not twisted to the left or right. We will later attach a metal bar to this and the end of the bar needs to be in the right position between the spools.

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Place your choice of small feet on the bottom. I am using these clear rubber .75 inch square adhesive back ones from Home Depot.  Place them about an inch from each corner. The board should now not slide around, and also small imperfections in leveling should be fixed.

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Congrats you now have the base assembled! Eat a gummy bear!

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----Part 2. Bracket Assembly-----

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SLOT BUFFER

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If using a slot buffer, attach the sides to the buffer bracket first with 20 mm m3 hex bolts and nuts.  

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SLOT BUFFER

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If using a slot buffer. Place the Central arch support on the other side and secure with 4x 30mm m3 bolts and 4x m3 hex nuts.  You can faster from either side.  If that doesn't work examine the holes and use a 1/8 inch drill bit to further widen or straighten them.  For the Prusa Buffer, use the Prusa Buffer Bracket Part instead.

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PRUSA BUFFER

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If using the Prusa Buffer and not the slot buffer, use the Prusabuffer bracket part instead.  The peg points upwards.  All four screws go through to the other side. Ignore the metal bar in the picture. we put that in later.

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BOTH BUFFERS

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This is the aluminum bar you will need from Home Depot for the next step. It is 36 inches long, .75 inches wide, and 1/8 inch thick. It can make two 16 inch bars, so if you are building two MCS units you only need one of these and can cut it in half.

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Cut the aluminum bar in half to a length of 16 inches and file/sand the ends so there are no sharp edges. I had to use Goo Gone spray to get the sticker residue off.  Insert the bar into the slot on the Central Arch and position it so the end is even with the front of the base. (Note that the bar in the pics has unneeded holes drilled in it - this is an older bar I had around)

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Insert two m3 hex nuts into the two pocket holes in the Central Arch (there is one in the back and one on the right side).  Do not force the nut in the back in. It should drop in the hole - widen the back hole opening if needed. Position the bar holder printed with the central arch, and secure with four 14mm m3 hex bolts and nuts for all four. The front two can take longer ones. 16mm will also work but not as well on the rear two.  Tighten all of these to secure the bar in position. 

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SLOT BUFFER

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If using a slot buffer, you should have an assembled slot buffer with PC4m10 inserts. This is a lot of printing and all of it should be in PETG. I used Layerneer bed wed on the bed plate so I could detach the thin screen dividers in particular. 

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Insert the slot buffer into the bracket and tighten the two sides. The slot buffer is very secure with this strong bracket and sits above the table so it doesn't take up any space! The angle gives the filament a natural loop shape as it goes through it to reduce friction.

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PRUSA BUFFER

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If using a Prusa MMU3 Buffer, you need to first remove the long attachment arm part and print more of the smaller bars to cover any exposed corner slots on the buffer. 

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Just hang the Prusa buffer on the single peg. It should slide down the peg and have its weight on the wood baseboard. (This pic shows an insert missing as I have not printed the last one yet.)

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The buffer sits on the baseboard against the vertical support. There is nothing to adjust. 

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Congrats you finished the bracket assembly. Have a gummy bear!

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----Part 3. Hanging PTFE Assembly----

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ENTIRE SECTION IS THE SAME FOR SLOT AND PRUSA BUFFER

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Print out three of the hanging PTFE Holders and screw in the PC4m10 adapters into them.

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Insert a 14 or 16mm m3 hex bolt into each with a hex nut to secure it. Slide two of these onto the bar in front and one onto the back.

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Cut out these lengths of 3mm inner diameter, 4mm outer diameter PTFE tube with a PTFE cutter. It is well worth it to get one as they are only a few bucks and make perfect cuts. I  just  cut these and these lengths provide a perfect and even arch pattern.  

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(For the Prusa buffer the distance can be a bit smaller, but I would cut these lengths anyway in case you want to switch to the slot buffer later.)

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Insert the short 27 inch one into the back buffer slot. Thread it through the end of the long PTFE spacer.  It doesn't matter how you orient the spacer. Follow the natural curve of the PTFE tube.   Put it through the appropriate hole in the long PTFE Spacer (not pictured). Then insert the other end into the far hanger slot that is nearest the arch. 

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PRUSA BUFFER - Insert PTFE into buffers holes closest to the aluminum bar.

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SLOT BUFFER - Insert PTFE into buffers holes furthest from the aluminum bar.

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Repeat for the pair of 28 inch PTFE tubes, put it through the appropriate hole in the long PTFE Spacer (not pictured), and place these in the center hanger.

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Repeat for the pair of 29.5 inch PTFE tubes,.put it through the appropriate hole in the long PTFE Spacer (not pictured),  and place these in the closest hanger to the front.

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Note - the long PTFE spacer in the pic below is incorrectly installed - the bumps are on top because the tube holes have a slight curve to them. 

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Slide the long PTFE spacer so it evenly spaces them out and is level above the assembly. 

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When you look at it from the side the tubes should line up.

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Print out two of the bar end parts and slide them onto the ends of the aluminum bar. This is advised because the ends corners are sharp. These bar ends slide on and stay on under pressure as one side of the insert had a small nub on it.  You must use PETG for these so they can perform this slight flex. The side with the interior nub will deform slightly so place that underneath the bar for a better appearance. If it is too hard to get on, then sand the inside of the slot a little to widen it, but it should fit firmly and will get looser over time if you keep sliding it on and off due to wearing down the nub.

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Great you completed the hanging PTFE assembly have a gummy bear!

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----Part 4. Bridge PTFE Assembly----

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Examine the short PTFE tube first to make sure a piece of spare PTFE can go through all five holes. The PTFE tube should easily go through the holes. If not, take a drill bit and with your hand (not the drill) move it back and forth to widen the hole slightly. When you know the holes are wide enough, lightly sand the bottom to rough it up for gluing.

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Superglue the short PTFE holder onto the front plate. Carefully place it centered and straight on the plate. Hold it for 2 minutes to ensure it is dry.  (update 9/10 - I am also considering perhaps you connect this via magnets and not glue, so it it is easier to install the tubes into the rear of the MMU with less bending. You might use four or five as it might be nice to be able to remove this when installing the PTFE tubes. But I am have not tried this yet.)

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Sand the top bracket plate and the top bracket. Superglue these together as well.

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Sand and do the same to the coupler support bracket. Sand and glue that onto the top of the arch. Both should be centered on their plates and overlap the sides equally.

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If you haven't already, superglue 1x10 magnets to the sides of the PTFE Couplers so they are oriented the same way.   Make sure you can line them all next to each other and that the magnets work. There is a small mark on the couplers where the magnets are to be glued. Each one has two magnets on one side and two on the other.  

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One way to do this is attach the magnets to the first one and then stick the next magnets onto it using just the magnet force. Put some glue on the second coupler, and then place the first coupler against it, pressing the magnets into the glue. This way you ensure the magnets are exactly next to each other and oriented correctly from one coupler to the next.

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Place the assembled coupler set of five on the arch coupler bracket.

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SLOT BUFFER 

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For a slot buffer, cut five 8 inch PTFE lengths. Insert  these into one end of the couplers. 

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Make sure the couplers are magnetically together as one unit so you test that magnets are going the right way.

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Place the other end into the slot buffer PC4m10 adapters. It should insert about an inch past into the buffer to ensure the filament gets directed into a loop on retraction.

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PRUSA BUFFER

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For a Prusa buffer, cut five 10.5 inch PTFE lengths. Insert  these into one end of the adjustment couplers.  10.5 inches fits snugly, but you might prefer 10.75 inches. Try that first just in case and you can always take off more.

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Make sure the couplers are magnetically together as one unit so you test that magnets are going the right way.

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Place the other end into far slot of the Prusa buffer collet hole. It insert  as far it it can and hits a stop. The angle of the PTFE this way exactly follows the path of the entry hole angle around the new pulley design on the MMU3 buffer. 

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BOTH BUFFERS

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If you look at where you are now it should look like this from above. I places some spool holders here for fun. The Prusa buffer looks a little different of course but same idea. 

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Now place the unit exactly nine inches behind the MMU's rear frame.  Use a spare piece of wood and cut it nine inches long. This can be a 1x1 dowel or anything small - it just need to be nine inches long. You wont attach it to anything but always leave it there to remind you of the correct spaceing between the spool base and the printer.  The printer should be facing ninety degrees to the right as shown in the picture.  You might consider using this MK3S+ LCD side mount LCD bracket.

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Now we will cut the tubes that go into the back of the MMU.  This is the most important tube length to get correct because this curve is functional.  The filament in this curve needs to want to stay in position and not move forward or backward. The curve traps it, but the bend is not so tight that it wants to straighten out and move in a direction.  The curve need to be the same shape on both sides of the bottom of the bend so it doesn't prefer moving to the left or to the right, but equally, which lessens the overall movement.  

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A side note - you also probably should be using my rear PC4m10 jack for your MMU3 https://www.printables.com/model/542409-mmu3-pc4m10-rear-connector 

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The perfect length is one make an even curve downward and the up into the back of the MMU that is evenly curved. For the MMU2S this is 14.75 inches exactly.  You can see the nine inch bar behind the MMU to lock the distance in.  

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(Update 9/10) For the MMU3, 14.75  works fine but is a little short. Keep in mind on my new MMU3 I am using this https://www.printables.com/model/542409-mmu3-pc4m10-rear-connector so the measurements ireflect that I am connecting to that in the back.  If you already cut them to 14.75 just use that but the printer will be a little closer to the spools so the 9 inch bar will need to be shorter. On the MMU3 You should use 16 inches for the MMU3 which is what I am using on my second upgraded MMU2S- to MMU3 setup. I have two and one MMU3 is using 14.75 and the other is using 16. 16 inches also works fine with the 9 inch bar.

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This is a 14.75 inch length used with the MMU2S here in this picture with a nine inch wood spacer.

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This is a 16 inch one used with the MMU3 with a nine inch piece of wood spacer. If using 14.75  inch with the MMU3 you need a 8.5 inch spacer instead.

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Once you get one that is the right length a trick is to remove it and use it to measure the others. Use a permanent marker to mark the length on the rest of the tubes to get an exact match.   It is really important that the length is correct and that it is the same across all five or they wont line up nicely.

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This is optional, but this improves the appearance. Now clip on both of the 2 hole PTFE clips to better position the tubes between the hangers and the larger 5 hole PTFE spacer.

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Now put the other four in. 

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You are done the bridge PTFE assembly. Have a gummy bear!

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----Part 5. Spool Assembly----

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It is very important that you get a spool center size that works exactly with your spools!!!

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Why? Well if the spool isnt an exact fit the center will be off center and the lopsided weight of the extra filament on one side will cause the spool to roll backwards and a few loops of filament could loop off the edge, potentatially causing a snag.  What is an exact size? Well, if you are having to slightly force the hub into the roll then that is perfect. However, if you can jiggle the spool after it is loaded then it is not tight enough and might cause a snag. 

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For the spool hubs see the spool design here where you can download various size spool centers ranging from 50-60mm in diameter individually.  I mostly use 52 and 54mm sizes. 

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Recently I made a newer version of this spool holder that is a bit better design and is made specifically for 54.3 cardboard spools, as it fits them exactly. It fits the Polymaker brand cardboard spools and most Inland and Hatchbox ones, and one variation even has a Polymaker logo on it.  You don't have to print the logo of course and can use the plain variation too. I find that it fits Inland cardboard spools (many of which I think are black label polymaker) and Hatchbox3D plastic spools perfectly. I end up using this hub for about 75% of my spools in fact. This design has a few small tweaks that improve strength, insertion into the spool, print time, and easy of install on the rods.

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The pics at the begYou use the same bearings that came with your MMU spool trays. The bearings can come out and be placed in a different spool center if you need a different size. I have a bucket of several of these next to the printer in various sizes.  Print out some [spool sp

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