Ultra MegaMax Dominator (UMMD) CoreXY 3D Printer

CoreXY printer with 300 x 300 x 695 mm build envelope

3D printer parts and enhancements

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This is my third and latest 3D printer design targeting high quality, reliability, and moderate print speeds. It stands about 1.5 m tall and weighs about 35 kg. It fits into my Prius laying on its back, with the hatch closed. I can transport it across town that way, take it out, stand it up, and start printing without any adjustments. Autoleveling is neither wanted nor needed.

The bed plate is a 300 x 300 x 8 mm piece of MIC6 cast aluminum tooling plate with a 0.7 mm layer of PEI on top and a 750 W line powered heater on the bottom. It stands on a unique, kinematic, 3-point leveling system that allows for thermal expansion of the plate without putting any lateral force on the leveling screws. There is a 184C thermal cutoff mounted on the bed plate to protect against thermal runaway in the event of a controller or SSR failure.

The bed is lifted on two linear guides in the 700 mm tall Z axis by belts using an OnDrives Rino 30:1 worm gear reducer on a 164 oz-in NEMA-23 motor. The worm gear mechanism prevents bed-crash when power is cut. Belts are 10 mm wide, steel core HTD-3M type. The belt stretch has been measured under load at 42 um/kg, which is utterly insignificant.

The CoreXY mechanism uses two level, 9 mm wide, glass core, Gates LL2MR09 GT2 belts. 24 x 8 mm linear guides are used in both the X and Y axes. A and B motors are 64 oz-in, 400 step/rev, NEMA-17 size. The X axis is a unique design that allows for thermal expansion of the printer's frame without creating huge side loading on the Y axis bearing blocks and rails. This printer has a single Titan extruder with a v6 hot-end.

The controller is a Smoothieboard that drives all the motors directly, including the NEMA-23 motor that powers the Z axis. Printing is done from SD cards plugged into the LCD interface for ultimate reliability.

The frame is made of 40x40 mm aluminum t-slot extrusions with corner braces added to the sides to increase fore-aft rigidity. There is about 18 W of white LED and about 20 W of UV LED illumination built in. The machine is fully enclosed for printing ABS with all electronics and A and B motors located outside the enclosure. The side back and bottom walls are made of 8 mm thick dual layer polycarbonate that fits into the slots in the frame and provides obstructed light transmission and thermal insulation (and makes modifications sort of difficult, too). Front panels are made of clear polycarbonate sheet. The upper front panel fits into the slots in the frame, the lower front panel is attached using magnetic strips.

I actively worked to minimize the number of 3D printed parts in this machine and will be replacing the few that remain with metal when I manage to get around to it.

Full details of the design concepts are being posted to my blog at

Materials and methods

Far too many to list. You can get most of the information you need from the CAD file. You'll need a copy of DesignSpark Mechanical to open the file.


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    Ummd Final
    RSDOC  –  96 mb
    Version 1 - Jul 23, 2017


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Mini nancydwilliamsNancyDWilliams added this to the Nice collection ago
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9ced43b50f80a218281af53f96ff473e?default=blank&size=40erickwill added this to the CoreXY collection ago
Mini sp logo grain 400x390Stamos added this to the 3D Printer collection ago
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472bc416da5d3775e60fbee86a9271f1?default=blank&size=40Patrick Szewczyk added this to the CORE XY collection ago
Mini gold hands croppedMark Rehorst commented ago

I made a test print with the new worm drive installed in UMMD and I have to declare it a failure. There is a lot of Z ribbing at 2mm intervals- so there is some quality problem, most likely with the worm gear because it spins one full rev for every 2mm of Z motion.

Photo here: https://4.bp.blogspot.com/-_WnQ6nhaZ60/WsmkTYmsJ4I/AAAAAAAAVT4/lJ-1Y7xupYAy1mQkcWOniAC0kroV-nFkwCLcBGAs/s1600/04080001.jpg

The problem was hinted at in the second video linked in my previous post. When I moved Z in 1 mm intervals, every other step was good and the steps inbetween were off a bit.

I'll be putting the Rino back into the machine today.

472bc416da5d3775e60fbee86a9271f1?default=blank&size=40Patrick Szewczyk commented ago

Thank you very much for your efforts and your advice. I will move to a 500x500x695 build envelope to make things easier and keep some dimensions the same. Can't wait for the new post

Mini gold hands croppedMark Rehorst commented ago

I don't know where you'll find a 700x300 heater unless you pay to have one custom made. That's 2100 cm^2 and at 0.4W/cm^2 you're looking at almost 1 kW for the heater. You can use lower power, but it will take a while to heat up.

The bed may sag a bit over a 700 mm span, so you might have to change the support and leveling structure or use a sensor and map the bed to compensate in the controller. It really depends on the print layer thickness you intend to use. If you want to print in 50 um layers over the entire bed surface you'll need to make changes. If you want to print in 0.5 mm layers you probably won't have to do anything.

Otherwise, I don't see any issues.

I've been working on a cheaper alternative to the Rino worm gear drive which cost about $140 via ebay, including shipping and the long, keyed 8mm shaft. The new design uses inexpensive worm gears from China and a NEMA-17 motor and costs about $40. I just installed it in UMMD and started testing two days ago. Video here: https://vimeo.com/263456441 and https://vimeo.com/263606489

I'll be publishing a blog post on the new design in a day or two.

I switched to GT2 belt and pulleys which required a redesign of the belt clamps and the spacers that stand the pillow blocks off the plates at the bottom of the Z axis. I also redesigned the upper pulley plates with ridges that fits into the slots in the frame to prevent them from rotating. They now use a single bolt to hold them in position.

The new worm drive uses 40:1 gears and 40 tooth drive pulleys which results in 1600 usteps/mm or 100 full steps/mm resolution, so full-step-multiple print layer thickness can be any multiple of 0.01 mm. The increased gear reduction will probably limit maximum speed to somewhere between 10 and 20 mm/sec, depending on the motor you use, but that's OK for the Z axis.

472bc416da5d3775e60fbee86a9271f1?default=blank&size=40Patrick Szewczyk commented ago

Do you foresee any issues if I did this in 700x300x300? All the design features should still work just lengthen here and shorten there...

Aa31f0f1e3b68101db6a7e4585d29db5?default=blank&size=40crazycraig added this to the 3d printer parts collection ago
Mini euLeonardo Aguiar commented ago

Hi Mark, thanks! Got it to work!

Mini gold hands croppedMark Rehorst commented ago

DesignSpark doesn't export to any other format, unless you want STL, OBJ, or a 2D DXF file, none of which seem very useful.

DesignSpark is free. All you have to do is install it.

Mini euLeonardo Aguiar commented ago

If anyone else has DesignSpark and could do the favor of exporting to a more common file format I think it would be greatly appreciated.

Mini euLeonardo Aguiar commented ago

Hi, this printer looks awesome. I've read your blog and your attention to detail is amazing. The Z-axis design is fantastic. I'm planning on building my own printer and I'm convinced your design is the best. I just have one problem. Could you upload a file format other than rsdoc?

381f6cb90d910f1dc9f874d81ea2b8d1?default=blank&size=40mifga commented ago

having seen machines in this series at the Milwaukee Makerspace, I must say I am incredibly impressed by these!! so great!

1c815758525430911356ad5ea88a3d6d?default=blank&size=40Orodorin added this to the 3D Printers collection ago
Mini gold hands croppedMark Rehorst published this design ago