UMMD 3D Printer Master CAD File

I have posted the master CAD file to Youmagine.com,  or  you can access it here.  The second link is the google drive location that I may update occasionally as I make changes to the printer.

You will need a copy of DesignSpark Mechanical to open it.

About this site... Welcome!

I've been using Composer to set up and maintain my web site for many years, but most of my efforts have been devoted to working on more projects rather than learning how to set up and manage a web site, so the old site has been a little "undynamic" and lags many months behind my project activities.  I recently decided to try a different approach because I'd like the site to be more up-to-date and professional looking, and because I'd like to get some of that sweet Google Ad-sense money coming in to help offset the cost of the site.

Other factors that led to the change:

1. About 2 years ago I wrote an Instructable on a 3D printer design and after weeks of effort gathering, organizing, and presenting the information as a contest entry, I won a tee-shirt.  After that I decided that when I get my web site/blog set up the way I like, I was never going to go through that sort of effort to drive traffic to someone else's web site again.
2. I have numerous 3D print designs posted at Thingiverse and Youmagine.  I've decided to stop posting most of my designs to those sites, too.

In the future, I may still post relatively small projects at Instructables for contest entries, but big stuff is going to stay right here.  The same goes for Youmagine and Thingiverse.

Over the last few years I've been designing and building 3D printers, and trying to maintain and upgrade printers at the Milwaukee Makerspace.  My latest printer design will be posted here shortly, in bite-size pieces where I can describe specific aspects of the design in as much detail as I feel is necessary.  But now that that printer is just about complete, I want to move on to more creative work making use of the 3D printers I have designed, built, and maintained, so you can expect to see more print designs here.

Oh yeah, if you like my 3D printer designs and have a significant budget, I can design and build one for you.  A near duplicate of one of my existing designs will be faster turn-around, but a full custom design won't take that much longer, depending on what you want, of course.

UMMD 3D Printer Bed Design

Update 4/30/19

I have redesigned the PTFE leveling screw blocks.  Check the new stuff out here.

Also, don't mount the TCO on the bed plate.  Mount it on the heater so that if the heater comes off the plate the TCO will still do what it is supposed to do.

Back to the original post ....



After messing around with glass in my first printer and having the usual problems getting prints to stick, I did a lot of research and experimenting, and came to understand a few things about 3D printer beds.  Specifically, they should have the following characteristics:

• the surface should be flat
• the bed should be thermally conductive for even heating
• the bed should have a surface that molten plastic likes to stick to
• the bed should have adequate heater power so it heats up quickly
• the bed should be mounted on a system that lets it tilt so it can be leveled
• the support system should be physically stable so the bed doesn't require re-leveling

What I found works very well is cast aluminum tooling plate with a thin layer of PEI on the surface, on a 3 point leveling system, and a heater that delivers at least 0.4 W/cm², and lastly, solid printer frame construction.

When I designed UMMD, I stayed with what works and used 8 mm thick MIC6 tooling plate.  It sits on a unique 3 point leveling system described below, has a 0.7 mm layer of PEI on the top surface, and a 750 W line powered heater on the underside.  The printer's frame is made of 40 x 40 mm t-slot extrusion.

If you live in the Milwaukee or Minneapolis area and you want cheap cast aluminum tooling plate, you're in luck.  The MIC6 bed plate material was purchased from the random rack at Howard Precision Metals in Milwaukee for $2 per lb.  The plate started out about 15" x 13.5" and cost $15.  I used a lot of other cast tooling plate throughout the printer since it is available so cheaply.

Thermal Expansion of Aluminum

Like almost everything, aluminum expands when heated, by about 24 𝜇m/m-K.  That means the 300 mm square print bed expands by about 0.576 mm when heated from 25°C to 105°C.  The leveling system has to allow for the expansion without creating lateral forces that may cause the bed to lift, drop, or bow.

Kinematic Leveling System

In my last printer, Son of MegaMax (SoM), I did a lot of testing, measuring, and experimentation with the leveling system.  That bed moves in the Y axis, and to ensure mechanical stability, I mounted it on three flat head screws that went through countersunk holes in the plate.  It worked OK, but it always bothered me that the leveling screws were anchored in fixed positions on a much cooler piece of aluminum than the bed plate.  The bed plate expands when heated, putting a lot of lateral force on the the screws.  This could lead to problems with the plate lifting or dropping or bowing.  After all the experimenting with new undercarriage designs, I came to the conclusion that it works OK as originally designed- there's enough margin in the build to accommodate the expansion.

In UMMD, the bed moves in the Z axis, so there's no need to worry about it getting thrown back and forth at print speed, so no need for screws to go through the plate to keep it under control.  I stole an idea from an optical table lens mount and adapted it to UMMD's bed support structure.  It is called a kinematic mount, specifically, it is a Kelvin type kinematic mount.

The whole bed plate is anchored to the support structure by springs that pull the plate down onto the leveling screw heads instead of pushing it up against the underside of the heads.  Two of the screws, the reference and pitch adjuster, are lined up along the X axis of the printer and the third, the roll adjuster, is located on the parallel edge of the bed.

The reference and pitch adjuster screws have spherical heads.  The reference adjuster sits in a chamfered (conical) hole in the plate.  The plate can't move in X or Y at the reference, but can rotate or swivel around the screw head and can only move in Z if the screw is turned.  The pitch adjuster sits in a chamfered X-parallel slot in the plate.  The plate can't move in the Y direction (which prevents rotation around the reference screw) but is free to expand in the X direction when heated.  Those two screws sitting in their hole and slot in the bed plate allow the bed to roll around the X axis and to expand without putting any lateral forces on the screws.  The roll adjuster is just a flat screw that touches the flat bottom side of the plate.  It controls the roll around the X axis while allowing the bed to expand in both X and Y.

The chamfers were made using countersink drill bits chucked in the milling machine.that I used to drill the hole and cut the slot in the bed plate.

Reference adjuster hole on underside of bed plate.  The chamfer was made using a counter-sink drill bit.

Pitch adjuster slot on underside of bed plate.  The chamfer was made using a counter sink drill bit on the milling machine.

The adjuster screws are anchored in Teflon blocks that grip the screws tightly and prevent wobble while ignoring the heat transferred to them from the bed plate through the screws.  The Teflon blocks are in turn screwed to a tee made from 40 x 40 mm t-slot extrusion.

The reference adjuster is just used to set the vertical height of the bed plate above the support structure and doesn't have to be adjusted when leveling the bed, so leveling the bed just requires two screw adjustments.  First, the pitch adjuster sets the bed's center line parallel to the X axis in the XZ plane, then the roll adjuster puts the plate parallel to the printer's XY plane (defined by the linear guides in the XY stage).  Changing the roll does not affect the pitch, so adjustment is quick and easy.  The reference and pitch adjustments are made using a hex key inserted through the holes in the bed plate from the top side of the bed.  Roll adjustment is done using the thumb-wheel located under the bed support structure.

The reference adjuster screw sitting in the chamfered hole in the bottom of the bed plate.

The pitch adjuster sitting in it's chamfered slot in the bottom of the bed plate.  The plate is free to expand in the X direction when heated.

The roll adjuster is just a flat screw contacting the flat underside of the bed plate.  The plate is free to expand in both X and Y without pushing against the screw.

The sturdy, well designed support structure, the solid construction of the Z axis, and the rigidity of the printer's frame ensure that the bed generally doesn't need to be re-leveled once set up.  Auto leveling is not needed.  I have driven this printer back and forth between home and the makerspace, laying on its back in my car, several times and have not had to readjust the bed leveling.

Bottom of the bed and support structure assembly.  The heater is a Keenovo 750 W line powered unit.

Thermal cut-off mounted on the edge of the print bed plate, protects against a failed SSR.  The TCO will open, cutting power to the bed plate heater, at 184C.  The body of the TCO is "hot" so it is wrapped in a layer of 5 mil kapton to electrically isolate it from the print bed plate.
NOTE:  don't do it this way!  Mount the TCO on the heater so that if the heater comes off the plate, the TCO will still do its job.

Top side view of the bed and support structure. This assembly weighs 3.2 kg.

The heater is line powered and gets hot, so safety is essential.  Power is switched to the heater via an SSR that is driven by the controller board.  Accidents can happen, parts can fail, and things can get weird, so I put an electrical fuse in series with the power to the heater and mounted a thermal cutoff on the bed plate.  The electrical fuse will protect against fires and other unsafe conditions if wires come loose (of course, they are secured mechanically, too).  The thermal cutoff will protect against the controller going crazy or the SSR failing in a shorted state (that's how they fail!).  When the bed temperature gets to 184°C, the TCO will open and shut off power to the heater.  The TCO will allow the bed to be operated as high as 160°C without causing problems.  They are one-shot devices, so I bought a couple spares to store on the printer, just in case.

This is the TCO I used.  It may not be what you need, so check the specs.  If you only need the bed to operate at 120°C maximum, get a lower temperature rated TCO.  Don't use a self resetting TCO, and don't go cheap and buy no-name, no-spec parts.  TCOs made by reputable manufacturers with various safety certifications cost only about $1 each.  Don't be penny-wise and pound-foolish.

NOTE:  don't mount the TCO on the bed plate!  Mount it on the heater using high temperature silicone.

Here's how to wire it.  The TCO protects against a controller that has lost its mind and SSR failure.  Mount the TCO on the heater using high temperature silicone, not the bed plate, unless you have mechanically (not glue) secured the heater to the plate.

About the spring hold-downs...

Some people have pointed out that if a heavy print were offset from the center of the bed, near the back edge, it might cause the bed plate to tilt by stretching out the spring hold-down at the roll adjuster.  It's unlikely such a heavy print would end up near the back edge of the bed plate, but if one did it is theoretically possible to tilt the bed.  OTOH, if this sort of thing proves to be a problem, I can always put a stronger spring at the roll adjuster.  I haven't measured the mass required to tilt the bed that way with the current spring, but it is definitely more than a few kg, so I'm not worried about it.

Some people asked why I put the "ears" for the reference and pitch adjusters at the center of the bed instead of putting them off of the back edge.  I wanted the adjusters to be located as close as possible to the Z axis bearing blocks for maximum stability.

Ultra MegaMax Dominator (UMMD) 3D Printer

UMMD has lots of  white and UV lighting built in.  The UV really makes fluorescent filament prints look great!

UPDATE!

I have made many changes to the design of this machine since I built it a few years ago. Changes include switching to a Duet controller (see the photos above for the updated electronics enclosure and LCD control panel), switched to a Bondtech BMG extruder, shortened the extruder carriage, switched to glass core belts and changed pulleys in the Z axis, redesigned the kinematic bed support, switched to a 400 step/rev motor in the extruder, tried some cheap Chinese servomotors, put optical endstops in all three axes, etc. Search this blog for "UMMD" to find all the updates.

Now back to the original post...

Ultra MegaMax Dominator (aka UMMD) is my third 3D printer design/build.  I used much of what I learned from its predecessors, and tried a few experiments, resulting in a very high quality machine that produces very high quality prints.  Time will tell if it meets my reliability goals.

Basic specs:

• Print volume 300 x 300 x 695 mm
• Frame made of 40 x 40 mm aluminum t-slot extrusion
• Overall dimensions: 610 mm w x 530 mm d x ~1.5 m tall
• Weight: about 35 kg
• CoreXY mechanism
• Smoothieboard 32 bit controller
• Belt (!) lifted Z axis
• Fully enclosed, mostly using dual layer polycarbonate sheet
• Minimal use of 3D printed parts
• Cast aluminum tooling plate bed with PEI print surface and 750W line powered heater on kinematic mount
• Linear guides used in all axes

This project started about a year ago with the design of the XY mechanism.  That sat for about 6 months until I decided to finish it up, adding the Z axis design and finally the frame and enclosure.  I posted progress reports at the reprap forums as the design work and construction progressed.

A lot of the work was done in the machine shop at the Milwaukee Makerspace.  I could not have progressed as far or as fast without the people, equipment, materials, and tools available at the makerspace.  I strongly recommend that you find and join your local makerspace.

Upcoming posts will be using a lot of CAD drawings, photos, and hand drawn diagrams to explain the details of the design, hopefully without too much text.  This printer was designed using DesignSpark Mechanical, a very powerful, yet easy to learn and use, free-enough CAD package.  I will be posting the master file for download, but you'll need a copy of DSM to open and edit it.  A few people have asked, and the answer is no, DesignSpark can't export the design to a different CAD format.  You'll just have to load DSM and open the file with it.

Here is a link to the final design file: https://www.youmagine.com/designs/ultra-megamax-dominator-ummd-corexy-3d-printer

Someone was able to convert the rsdoc file to a STEP file so it could be brought into Fusion360:
https://a360.co/2IF77sa

In the future I'll be switching over to Autodesk Fusion360 because of its built in ability to produce files for CAM.  Fusion360 CAM files can drive CNC mills and routers at the makerspace.

UMMD printing a fluorescent green vase with PETG filament.   The blue dots in the background are reflections of the UV LEDs in the dual layer polycarbonate enclosure panels.

Parts sources

I bought the used, 40x40 mm t-slot from a local scrap yard for $1 per lb.  Cast aluminum tooling plate came from Howard Precision Metals in Milwaukee for $2 per lb.  Motors, belts, linear guides, power supplies, and miscellaneous hardware were purchased through Amazon.com, ebay, and Aliexpress.  A few other parts came from the Milwaukee Makerspace and from people at the makerspace.  All of the machining of parts was done at the makerspace.

I won't be providing a BOM for this printer, but you'll be able to gather a lot of it from the CAD file. Your chances of finding the exact same parts I used at reasonable prices are slim to none, so you're going to have to adapt the design to the parts you have or can get.  If you can't figure out the necessary mods to the design, you might be better off buying a kit.

Details, details...

Check some of the other posts for details about:

Latest Z axis updates

Print Bed and Support Structure
CoreXY Mechanism
Z Axis Design Rev 1
Z Axis Design Rev 2
Z Axis Design Rev 3 (final)
Electronics
Frame Construction and Enclosure