Rock Sphere Lapidary (V1.0)

This is a modular, 3D-printable lapidary machine designed to grind and polish rough rock into perfect spheres. Because the stone-cutting process creates constant water exposure, wet abrasive slurry, and heavy motor torque, all structural components of this build are designed to be printed in PETG to ensure maximum durability, rigidity, and water resistance. Standard PLA will warp under the heat of the motors and degrade from moisture over time.

The machine features adjustable sliding motor mounts on a sturdy base chassis, allowing it to accommodate stones ranging from the size of a marble up to a baseball. While the core structural housings and splash guards are completely 3D printed, the assembly utilizes standard off-the-shelf hardware—including 24V DC gear motors(100RPM Geared), diamond grinding cups, and stainless steel fasteners—to handle the intense mechanical friction required to shape the stone.

Part 1: 3D Printing Parameters (Estimate 3 1KG Rolls)

• Filament Material: PETG. Do not use standard PLA.

• Wall Loops (Perimeters): 4 to 8 walls. Structural strength comes from the thickness of the outer shell, not the infill.

• Infill Density & Pattern: 30% to 50% Gyroid or Cubic. Both of these patterns provide uniform, three-dimensional strength to resist the twisting torque of the motors.

• Top/Bottom Layers: 4 to 8 layers to ensure a solid, watertight seal around the structural mounts.

• Layer Height: 0.2mm. Thicker layers actually provide better layer adhesion and mechanical strength than fine, highly detailed layers.

• Supports: All 3 should be printed with supports, track needs it for the underside groove, arm needs a little for the bolt holes. slide needs it for the bolt holes as well. I used tree supports and on build plate only.

Part 2: Hardware & Parts List

Motors & Motion

• (3)DC Gear Motors: 60GA775 24V 100rpm Motors. (AliExpress or Alibaba are probably cheapest, Amazon has some but expensive, Expect 30-40$ Each) https://a.aliexpress.com/_m0TqTPz

• (3)8MM to M10 Motor Arbor: https://a.co/d/03E1YCst

• (3)M10 to 5/8-11 Adapters)(Cheaper alternatives below V3 Cups): https://a.co/d/0gOJndYE

Electronics

• (3)PWM Speed Controllers: 24V Speed Controllers (I think either, I used the second one)

  • https://a.co/d/0ciJrM7f

  • https://a.co/d/0ePOnjI1

• (1)Power Supply: 24 Volt Meanwell LRS-350-24(Probably overkill)

  • https://a.co/d/096WDkaF

Miscellaneous

• (3) 8MMx100MM Bolt with lock nut (For the Motor Arm Swivel)

• (9) 6MMx40MM Carriage Bolts with nuts (6 for the Slide track, 3 for the top bungees)

• (12) M4x35MM Bolts (Motor Mounting and Motor Shroud, Can use 40MM, Just what I had)

• Diamond Core Bits(I use 35MM-50MM) Like this, have not tried these. Can find M10 or 5/8-11 with the adapter to M10 https://www.aliexpress.us/item/3256807100150576.html

• Polishing Pads

  • https://a.co/d/0cHc47o0

  • https://a.co/d/05l6kFwH

I have included all the SCAD files so that tolerances or motor mounts or polishing cups can be tweaked, resized, bigger cups printed if needed. Use OpenSCAD to open the files and export 3mf Files of adjusted parts.

Edit: Small addition of the type of water drip tower I used in other files. 3 sections. Needs PETG and thick walls and floors and top layers to be able to hold water for the reservoir. I lost the original files I made from a different project and this is a recreation and I have not fully tested yet. Uses a 3/8" MIP to 1/4" FIP Brass fitting and https://a.co/d/0cAZw4na 

Additional Links:

1. Core Bits(Untested): https://www.aliexpress.us/item/3256807100150576.html

2. 8MM Bolt: https://a.co/d/02BsrH7A

3. 6MM Carriage Bolt: https://a.co/d/004nejuI

4. 6MM Nut: https://a.co/d/0ehGBMsh

5. 8MM Lock Nut: https://a.co/d/02bgnlhE

6. M4 Bolt: https://a.co/d/0gB9SSRN

7. (V3 Cup)Alternative to M10 -> 5/8-11 (Update Cup SCAD to take M16) Needs testing but a lot cheaper than the 5/8-11 adapter) https://a.co/d/0dDcT9sA

8. (V2 or V3 Cup)Alternative to M10 -> 5/8-11 (Update Cup SCAD to take M16) Needs testing but a lot cheaper than the 5/8-11 adapter) https://a.co/d/0esFqNHY