K2 Plus Kinematic Style Bed Mount

*** June 27th, 2025 Update:

I finished my design and testing for the moment.  While this design did seem to help with the warping when heated, it did not fully resolve it.

This is what the build plate looked like at room temperature after running the Screw Tilt Macro.:

It worth noting that the Screw Tilt Macro had the most significant impact on the baseline flatness of the bed.

This is what it looked like after heat soaking at 100C for 20min:

Before the mod, my delta between room temp and 100C was over 0.80mm.  Reducing that to approximately 0.40mm is a partial win, but not as good as I wanted to see.  It's possible that further tinkering with the design could improve this, but I'm inclined to believe that some of this is due to the base material of the stock build plate.  Even with the constraints removed, I think the cold rolled aluminum plate will deflect when heat is applied due to residual stresses in the plate.  

I've uploaded the latest files so people can try it if they like.  Even though it is an improvement,  I can't recommend this as a fully baked solution. For people who need a flatter bed, I would look for a machined cast aluminum plate or graphite plate solution.

I still welcome feedback though and I may revisit this!

Thanks,

Josh  

***

I've been struggling with getting a good first layer on my K2 Plus when printing large objects.  The ABL doesn't seem to be able to compensate fully when the bed is heated for materials like ABS, ASA, PC, etc.  Even after heat soaking, the nozzle gets too close to the build plate and causes the extruder to jam every time.

It's obvious that the build plate is over-constrained and that it bows when heated due to thermal expansion of aluminum.  Many other large format printers have acknowledged this and developed kinematic mounting systems for the bed to allow them to expand and contract based on the thermal properties of the aluminum beds.  All of those systems use a 3-point mounting configuration.

I wanted to design a simple system with the following goals:

1. Be fully reversible if needed.
2. Keep as simple as possible. Fewest parts possible, no complex machining, easy to print parts, etc. 
3. Utilize the existing 4 mounting points if possible.
4. Be able to be printed on current machine prior to applying mod.  So keep the parts small.

Hopefully I've accomplished these objectives, and this can help the community.  I welcome any and all feedback on the design.

BOM:

Printed Parts:

I printed these using PC due to the heat exposure so close to the bed.  I would recommend ABS at least and using fiber filled filament if possible.  It may not be necessary, but we want these to be dimensionally accurate, thermally stable, and rigid.

• (Qty 3) - Magnetic Base (Offset)
• (Qty 2) - Planar Top
• (Qty 1) - Fixed Top
• (Qty 1) - Axial Top
• (Qty 1) - Base Rotation Lock (Front LH)
• (Qty 1) - Base Rotation Lock (Front RH)
• (Qty 1) - Base Rotation Lock (Rear LH)
• (Qty 1) - Base Rotation Lock (Rear RH)
• (Qty 4) - Bed Level Knob

Reused Parts:

I initially tried to reuse as much of the hardware as possible, but I found that the spacers weren't needed, and the thread pitch made it hard to reuse the adjustment knobs.  In the end, the only reused parts are the springs.

Purchased Parts:

I've included links to the exact parts I purchased.  Some of these I had on hand from previous projects, but others I needed to buy for this.

• (Qty 4) - M4x20 Hex Head Bolts (this may need to be longer)
• (Qty 4) - M4 Washer
• (Qty 4) - M4x20 Countersunk Screws
• (Qty 4) - M4 Threaded 10mm Steel Ball Studs (if looking for others, make sure they're not Stainless Steel or the magnets won't work)
• (Qty 4) - 25mmx4m Round Magnets
• (Qty 16) - M3x12 Cap Head Screws
• (Qty 5) - 3mmx12mm Dowel Pins
• (Qty 16) - M3x8 Heat Set Inserts (could probably go shorter, but I wanted as much engagement as possible)

Installation:

I've added some pictures of the basic assembly.  And I'll put together a more thorough guide if this works and people find it useful.

Heat set the inserts into the four holes on each of the Magnetic Bases.

Press the dowel pins into their slots on the Fixed Top and the Axial Top.

Press the hex head bolt into the Magnetic Base, Place a washer on the end of the bolt and slide the stock spring over the bolt.  Press the bases down into their mounting holes on the frame and secure using the stock adjustment knobs.  Place the magnets in their recesses on each base.

On the foward left-hand corner, install the Fixed Top with dowels installed to the magnetic base using (Qty 4) M3 Cap Head Screws.

On the forward right-hand corner, install the Axial Top with dowels installed to the magnetic base using (Qty 4) M3 Cap Head Screws.

On the back 2 corners install the Planar Tops using (Qty 4) M3 Cap Head Screws each.

Install the bases above the appropriate rotation lock part.  Note the orientation of the bases in the pictures.  All of the bases are offset except the forward LH base.  

At each of the 4 mounting holes on the bed, insert the countersunk M4 screw through the plate, through the reused spacer (still evaluating this), and into the threaded ball stud.  I recommend using blue Loctite.  Set the build plate on the bases, and the installation should be complete.

Level the bed corners using the knobs.  There are several ways to accomplish this.  I'll add links to some references latter if needed.

Run the bed mesh, with the plate at room temp.  Then heat to 100 (or whatever would typically be your max) and rerun the bed mesh.  If everything has worked, the meshes should be very similar.  If your bed was already bowed at room temperature, you can shim it to improve your results.

If there are improvements that can be made, please let me know.  Thanks!