Duender MGN9 Top Motor Mount w/ Double Shear

This project contains a re-design of the motor mounts from Andizzle, however adds 8mm to the deck height to make them compatible with the MGN9 Duender project. Redesign outer shape to provide better access to belts and pulleys. Bolt hole positions are not identical to original so top and bottom halves don't inter-mix.

I also removed the triangular mount from the bottom, as in the future I will have a 20x40 extrusion there to support a 3rd heated bed mount. It seems plenty strong enough without it.

Finally it uses the M5x45 bolts from the Ender 3 (you need to tap your threads into the extrusion at least 20mm) to mount into the 2040 Y-axis extrusions to make for a very strong connection.

You need to mount both of the motor mounts to 2020 extrusion first, as the M5x45 bolts prevent access to the bolts that go into the end of the 2020 extrusion. Then you use the M5x45 bolts to mount the assembly to the frame.

Note that this redesign moves the bolt positions somewhat, so that you cannot mix and match the top and bottom parts from Andizzles project. The belt path remains compatible so there should not be any effect on kinematics.

Printing

Print with the flat side down, it should import in the correct orientation. In order for the flange bearing recess to print correctly, enable manual supports, and paint the circular flange bearing recess in the slicer, and when sliced check that support is generated just in that area.

I hope to produce a file with support designed in, but for now you will have to use manual support and paint it on. Automatic support will work, however it will fill the holes intended for the heatset inserts, and they are a pain to remove.

Installation

You will need an M8 tap to cut a thread into the largest hole. This should be easy as it is just plastic. If possible I will try and figure out how to design a thread so that it gets 3D printed in a future revision.

Next you need 5 heatset inserts per mount, M3x5x4, which go into the 5 middle sized holes. The circular end on the insert should fit into the hole, then push it all the way in with a soldering iron.

Note: In order to get the insert properly aligned, I push it almost in, then flip the part over and press down hard on a flat heat resistance surface. The remaining heat allows the insert to go all the way in, and the flat surface ensures the insert is properly aligned.

Move your bearing stacks from the existing top cover to the new top cover.

Mount the top cover to the bottom part. The existing bolts should be OK, 6 x M3x30 and 1 x M8x35 (from Ender 3 Y-axis tensioner).

You will likely need to tap a longer M5 thread into the end of your Y extrusions. I have designed for the M5x45 bolts to have 18mm of thread protruding from the mount, so I suggest extending the thread length to 20mm with a tap.

Use some tape on the tap to make the 20mm position. Make sure to use the original thread to guide the tap in, as you don't want it cutting a new thread that is out of alignment.

You will also need to tap a thread into the 2020 extrusion, the length of the thread depends on the bolt length you use, but use a button head bolt as there is no clearance for anything else. I would suggest an M5x16 as a minimum to provide a strong connection.

You then mount both of the motor mounts to 2020 extrusion first. Start with a T-nut and M5x8 from the back of the mount, don't fully tighten. Next install the M5x16 into the end of the 2020 extrusion, tighten this first then go back and tighten the M5x8. Repeat for the other motor mount on the other side of the extrusion.

Finally use the M5x45 bolts to mount the rear-motor mount assembly onto the frame. You might find that you need to flex the frame to line up the bolts so that they go in, if your frame is not aligned.

The rear of the frame should now be very rigid, and you should look at adding a brace to the front of the frame to provide similar rigidity.

CAD

The part is designed using FreeCAD. I can't provide STEP files, sorry, as FreeCAD can only import STEP files, it cannot export them as far as I know.