YOU CAN BUILD THE 3,500 DOLLARS BELT GRINDER KNIFE MAKERS USE — THE KEY PART IS IN EVERY DEAD TREADMILL
The 3,500 dollars variable-speed grinder knife makers use — built from a motor people give away free.
by Making Stuff
Workshop
- difficulty
- ●●●●○
- time
- a long weekend
- license
- license not specified
- repo
- repo 0 stars
●●●●○ · a long weekend · license not specified · 0 stars · repo
WHAT YOU’LL NEED
- 3D printer + filament — printable parts — files are in the repo
Partner
COMPAREE VERDICT
This is a documented path to a real 2×72 variable-speed belt grinder for around 164 dollars in parts plus steel, assuming you can weld and already have access to basic metalworking tools. The hook is true: professional 2×72 grinders from Brodbeck or AmeriBrade start at 1,485 dollars, and the motor and controller from a dead treadmill (2.5 HP, 130 V DC, variable speed) are functionally identical to what ships in those machines. The build guide shows the finished grinder, the parts list, and progress photos, but it is not a paint-by-numbers tutorial. You need to be comfortable welding a steel frame, sourcing or cutting a flat platen, and wiring mains-voltage DC motor control — the MC-60 controller from eBay does not come with project-specific instructions. The single biggest thing that will go wrong: buying a treadmill with the wrong motor (some are AC, some are underpowered) or discovering your local metal supplier charges more for small-run flat steel than the guide assumes. The FreeCAD files give you exact dimensions for the frame but you still have to fabricate it. If you have the tools and the skills, this is a legitimately cost-effective route to a workshop-grade grinder. If you have never welded or worked with mains voltage, start with something smaller.
IN THE REPO
NOT IN THE REPO
- —FreeCAD frame files are published under CC BY-SA 4.0 at open-source-belt-grinder repo
- —Build guide at makingstuff.info/Projects/Belt_Grinder has photos, part numbers, and a BOM
- —No wiring diagrams for the MC-60 controller — you follow the generic eBay instructions and the treadmill's existing wiring
- —The platen design is documented but you either CNC-cut it yourself or pay a shop to do it
- —Licence permits commercial builds (CC BY-SA 4.0) but the guide itself is informal documentation, not a step-by-step manual
- —The treadmill motor is free only if you source a broken treadmill locally — prices vary if you buy used
Can I build this?
This build involves mains voltage — for adults comfortable with electrical work only.
Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.
Partner · KickstarterHeyGears G1: 10M+ colors and transparent parts in one print, plus UV printing on flat objects. Figures, parts and labels — no painting.
Videos
Making Stuff — treadmill motor belt grinder build
587,000 views, shows the finished grinder running and some of the fabrication process, but this is a progress/demo video not a step-by-step tutorial
Gallery
Start here
Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.
- 1.Read the build guide at makingstuff.info/Projects/Belt_Grinder and the open-source-belt-grinder FreeCAD files to understand the frame geometry and part list (The guide has photos and a BOM but assumes you know how to weld and wire a DC motor controller)
- 2.Source a dead treadmill with a 130 V DC motor rated 2.5 HP or higher — check local classifieds, gyms clearing old equipment, or appliance recyclers(Some treadmills use AC motors or lower-power DC motors that will not have enough torque; confirm the motor specs before you haul it home)
- 3.Order the MC-60 controller from eBay (~$30) and the belt grinder wheels ($34 from the supplier in the guide)(The MC-60 is a generic PWM controller for DC motors; it will ship with basic wiring notes but not a schematic for this specific project)
- 4.Cut or order the flat steel platen and frame pieces per the FreeCAD drawings — if you do not have CNC access, a local waterjet or plasma shop can cut the platen for you(The platen must be flat and rigid or the belt will not track properly and you will burn through sandpaper)
Resources
Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.
KNOWN ISSUES
- Buying a treadmill with the wrong motor — some are AC induction motors that will not give you variable speed, and some older or cheaper treadmills use underpowered DC motors that will stall under load
- Underestimating the cost of steel — the guide assumes ~$100 for flat bar and tubing, but prices vary wildly by region and small-quantity orders from a metal supplier often cost more than bulk pricing suggests
- Wiring the MC-60 controller incorrectly — it is a generic eBay part with minimal English documentation, and incorrect wiring can destroy the controller or create a mains-voltage short
- Building a frame that is not square or rigid enough — any flex in the frame will cause the belt to wander off the wheels, and you will spend hours trying to track it down
- Skipping a belt guard or face shield — 2×72 belts run fast enough to throw sparks, metal shavings, and broken abrasive across the room, and a snapped belt can whip back with enough force to injure you
- Expecting a step-by-step build manual — the guide documents what was built and shows photos, but it assumes you already know how to weld, read a technical drawing, and wire a motor controller
Can I use a different motor controller instead of the MC-60?
Yes, any PWM motor controller rated for 130 V DC and at least 15 A continuous will work, but the MC-60 is cheap and widely available on eBay so it is the documented choice.
Do I need a CNC to cut the platen, or can I do it by hand?
The platen is a flat piece of steel — you can have a local waterjet or plasma shop cut it for $20-50 if you send them the FreeCAD file, or you can cut it by hand with an angle grinder and files, but it will take longer and flatness matters for belt tracking.
How do I know if a treadmill motor is powerful enough?
Look for 2.5 HP or higher and 130 V DC — it will usually say on the motor nameplate. If the treadmill is very old or a budget model, the motor might be rated lower or run on AC, which will not give you variable speed with the MC-60 controller.
Is this as good as a $3,500 commercial grinder?
It uses the same belt size (2×72) and a comparable motor, so for grinding and shaping metal it performs similarly. Commercial grinders have better fit and finish, tool-less belt changes, and often include a work rest and dust extraction, but the core function — variable-speed abrasive grinding — is the same.
Community builds
No community builds yet — be the first, we feature the best ones.
Discussion1
FROM THE COMPAREE TEAM
The guide documents a $164 build using a free treadmill motor and an MC-60 controller from eBay — no custom PCB, no firmware, just wiring and welding. What is the first thing you would grind if you built one?
Making Stuff
The build guide and video come from Making Stuff, a maker who documents metalworking and shop builds. The FreeCAD frame files are published separately under CC BY-SA 4.0 at the open-source-belt-grinder repository, so the design can be modified and shared.
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DISCLAIMER
- Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
- Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
- Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
CompareeTEAM5d agoedited
Practical notes from our verification: the build video at youtube.com/watch?v=6GoEXR5NuHo has 587,000 views and shows the grinder running, but it is a progress/demo video not a step-by-step tutorial. The written guide at makingstuff.info/Projects/Belt_Grinder has the BOM and photos but assumes you already know how to weld and wire a DC motor controller. The FreeCAD files for the frame are published under CC BY-SA 4.0 at the open-source-belt-grinder repository (the guide links to it), so you can modify the design or send the drawings to a fabrication shop. The single biggest variable is steel cost — the guide assumes ~$100 for flat bar and tubing, but regional prices vary and small-quantity orders often cost more. The MC-60 controller ships from eBay with minimal English documentation, so if you have never wired a PWM motor controller before, budget time to learn or find someone who has. Photo note, 22 August 2026: this page had no images. We added 4 photographs of this specific build, each credited above; nothing here is a stock shot or another project.