Controller: leaning towards Duet Wifi 2 + PanelDue 5 at the moment. I may go with a smoothieboard if v2 comes out soon.
Bed: A 400x400mm bed could fit, but it looks like I'll only have 350x350mm of printable area with a single extruder. I'll confirm this once the CAD's done (see below). My plan is to buy a big silicon heating pad and solid state relay (SSR) and hook up the SSR to mains and the bed heater pins from the control board. I'm aiming for 0.6 W/cm^2, or about 750W. The heating pad will be bonded to the bottom of an aluminum build plate, which will be a little oversized. I'm planning to use cast aluminum jig plate so that it's actually flat, probably 3-5 ish mm thick. I'll likely use glass, PEI, or some other removable build surface on top, and I'll probably insulate the bottom of the heating pad. The oversized aluminum plate will have holes in it for the leveling screws. The two screws at the back are about 360mm apart, so that works well. Unfortunately, the screw in the front is pretty close to the center of the build plate. Since I can't drill through a heating pad, I'll have to machine an extension bracket that replaces the current support piece there (the one that joins the two angled arms that hold the current bed). That will move the third leveling screw out to close to the front of the machine. If the bed being cantilevered ends up being a stiffness or vibration problem, my plan is to add linear bearings to the two front vertical posts, join them with a plate, and bolt that plate to the extension bracket I mentioned earlier. I may also replace the NEMA23 with a NEMA17 and add another 10mm Z rod at the front of the machine, though that'll make getting parts out tricky...could also rotate the base 90 degrees since it's square.Anyways, all of that will only be necessary if the cantilevered bed ends up being a problem.
X-axis carriage: I have a few options here. I could replace the bearing in the short X bearing block with two bearings (or one long one), then machine a new extruder mounting plate. The problem with that is that the super long x-axis bearing block will limit y travel a lot. I could replace both bearing blocks with SC12UU standard blocks, but those would interfere with the belt. I could replace just the longer bearing block with a SC12UU. I could also make my own bearing blocks.
Extruder/hot end: Compact hot ends like the titan aero don't extend down far enough in Z to clear the X axis linear bearing blocks. A titan + e3d-v6 hot end would, though. I can't use one of the stock extruders with an e3d-v6 unless I machine down the e3d-v6 mount OD to ~11-12mm and machine out the extruder clamp from 10mm to the same, both of which will be a huge pain to do. I don't want to use the stock hot ends since they don't have exchangeable nozzles and people complained about them clogging often.
X-axis replacement: Another option would be to completely replace the X axis. This option would replace the two Y-axis bearing blocks with standard SC12UU or similar bearing blocks and adapters to 20mm 8020 aluminum extrusion that would replace the X-axis linear shafts. An MGN12 rail/slide screwed to the aluminum extrusion would replace the X axis linear bearings. This solves a few problems: 1. Can now use compact extruder-hot ends setups, and mounts for MGN slides already exist on thingiverse, 2. the x-axis will be lighter and should be less finicky than two linear shafts, 3. x-axis travel will be maximized. The current X-axis motor mount is ~5mm thick laser cut acrylic. The y-axis belt holders are also 5mm laser cut acrylic, and they just sandwich the belt ends. Both poor designs that need to be fixed anyways, so they would be designed into the y-axis bearing block-extrusion adapters.
Given the above, there's kind of two major options for the X axis: 1. Keep the shorter X-axis linear block, replace its bearings, replace the longer x-axis linear block with a SC12UU, machine an extruder plate, use a titan (or similar) extruder + e3d-v6 hot end, redesign the X-axis motor mounts and y-axis belt tensioners. 2. Replace the whole X-axis with extrusion + MGN12 rail, use standard SC12UU bearing blocks on y-axis shafts, design and 3D print/machine adapters from the bearing blocks to the extrusion that include a new X-axis motor mount and y-axis belt tensioners, use a titan aero (or similar) extruder + hot end, and 3d print/machine a MGN extruder mount. Option 1 should be a little cheaper and uses more of the current hardware. Option 2 maximizes X, Y, and Z travel. I'll probably design both and weigh the options once I know rough costs and how much more travel option 2 gets me.
There are some other minor plans, but those are the major changes planned.
I started the CAD. Right now just modeling what it is currently. I'm not being super detailed...leaving out most of the screws, the belts, etc. Once all the relevant components are modeled, I'll start modeling modifications and adding details where necessary.
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