Scrap-Together Belt Grinder

I've been looking around for a new project to dig my teeth into and got hooked on a belt grinder for the workshop. I was lacking a reliable all-rounder for sanding and shaping different tougher materials as I was running a 1/2 horsepower regular bench grinder for that purpose. The machine I already had had problems with overheating while grinding for longer periods of time and at most times were not powerful enough to meet my needs. So I decided to look into making my own from scratch, challenging myself to make it out of as much recycled materials as possible, both for the additional challenge as well as for trying to keep the costs down. The goals I had for the machine were that it would be powerful enough to chew through metal, that it would be simple enough that I could design and make the whole thing myself, without professional tools or machines, and that it could be modified in the future with new attachments. These goals played a central role in the designing process and combined with the choice of sourcing scrap made the planning phase a exercise in imagination and creativity.

I am pretty pleased with the final result and it works well! I am also very happy to have found most of the scrap that it is made of for free or at a very low cost, keeping working parts out of landfills. Total cost for the machine landed just under $150. The build taught me a bunch about designing parts digitally from a restricted amount of real world material, working with different tools to create parts that fit together neatly as well as planning, designing and executing a project of a larger scale!

As one of the main goals were to source mainly scrap supplies these items were the once I was able to get my hands on. As is the nature of scrap hunting you take what you can find, however this list gives a rough outline on what to look for. Some items, like electronics, are hard to find and might need to be bought. As for tools these are the once that I used however some are not necessary and only simplify the building process.

Materials:

1. An old treadmill (check that the motor is in decent condition)
2. An exercise bench or similar frame of square steel tubing
3. Heavy spring
4. Ball bearings
5. Nuts, washers and bolts (preferably locking nuts)
6. Larger square hinge
7. High power speed controller
8. Emergency stop button
9. Bridge rectifier
10. An old PSU case (for housing the electronics)
11. Various cables for connecting components

Tools:

1. Angle grinder
2. Belt sander (for cleaning up cut parts)
3. Drill press
4. Welder
5. Various screwdrivers, sockets, hex keys
6. Files
7. Drills
8. Wire brush (for cleaning old paint and rust)
9. Set square
10. Can of spray paint
11. Friction tape
12. 3D-Printer (optional but handy)

Programs:

1. Autodesk Fusion360
2. UltiMaker Cura

The first challenge was to look around for the main components that were needed for the machine. A motor and material to create the frame are the most crucial pieces to find. For this build I zeroed in on gym equipment such as a treadmill for the strong motor, and an exercise bench for the main frame. The treadmill I got for free as it had a broken power connector and the benches were about $20 from marketplace. The reason to go for these to items in particular is that the motors of treadmill are reasonably strong and durable and exercise benches often come with adjustable tubes ideal for making different attachments.

After disassembly and rough cleaning I was able to assess the pieces that I had collected and begin to draw up a simple design in Fusion360.

When I had sorted through and picked out pieces that looked good for this project I sat down and threw together a rough sketch of the design. The most important part in this process was to fit the wheels so that it could run a standard size sanding belt. I didn't want to have to make my own belts and therefore it was important to decide measurements for the individual parts so that it would all fit together nicely. The process also allowed me to design the wheels themselves as I was planning on 3D-printing them.

To be able to have an digital design behind you as you work on the parts is a nice backup for double checking measurements and fittings as well as to avoid making parts multiple times as the result of mess ups.

First let's focus on the frame of the belt grinder. This part was assembled with parts of square tubing from the exercise bench which was cut using the angle grinder, sanded and welded together to form the body. I spent a while cleaning the pieces from rust and old paint using the wire brush to make sure that it would hold up when the motor was turning. The adjustable pieces are used to make the slot for the platen attachment later on and use plastic rails inside the steel tube to ensure a snug fit between the parts.

From the treadmill I was also able to extract some square steel tubing that would serve as the base of the grinder. The most important part is the motor mount that was scavenged from the treadmill. Using the mount it would be easier to attach the motor in a way that minimized eventual vibrations compared to trying to make a mount from scratch. Using the drill press I was also able to drill the holes that would allow the parts to be bolted together.

Next part of the project was to work out a system to be able to track the sanding belt. The tracking part is made on a horizontal arm connected through a slot in the top of the frame tower. The tracking requires two components, vertical adjustment and horizontal adjustment.

The vertical adjustment regards tracking the belt side to side to make sure it doesn't wander of the wheels. This is achieved using a hinge with a bolt through it as the attachment point for the wheel, and then running another bolt through the tube from behind to push against the back of the hinge. By welding a nut onto the tube we can screw the bolt in to lift the hinge, moving the belt inward. Screwing the bolt the other direction results in the belt moving out from the arm.

The horizontal adjustment regards keeping the belt under tension while it is running. We achieve this through a system of two bolts and a firm spring. One of the bolt is screwed through the tracking arm and the other is anchored in the frame. The spring pulls down the one side of the arm, pulling the other side up. The side that is pushed upwards is where the wheel is attached therefore putting tension on the belt. As a nice side effect of this system it is easy to change belts just by pushing down on the tracking arm to release the belt.

One of the more difficult parts of the project was to design the platen attachment. When I disassembled the scraps I noticed a pair of flat "ear-like" pieces of steel with a conveniently placed hole that I thought might be a good starting point. I cleaned them up and cut them straight at the bottom to be able to weld them together to form the plate for the platen to attach to. Next up was to attach the plate to a piece of smaller square tubing that would fit nicely in the slot in the frame. I then needed to address the attachment of the two wheels that would run the belt. I used the 3D-printer to design and print two bushings that would fit neatly in the large holes in the plate allowing me to then fasten the bolts using nuts and washers.

With the wheels in place I could move on to the platen itself. Using a bit of scrap tube I cut out a 90 degree bracket that would serve as the flat platen. This is probably the first part that would need an upgrade in the future as I would like an actual flat platen of hardened steel to make sure it stays true, but for now it will have to do. Using two bolts and bushings I was able to attach the platen and using a set square dial it in nicely vertical to the wheels.

To be able to control the speed of the motor I used a high power motor speed controller. This and the other electronics are some of the few things that are actually bought brand new. Using an old computer PSU case I mounted the emergency switch and the rest of the electronics. The motor controller came with a variable resistor that was used as the knob for changing the speed of the motor.

For the wheels I used Autodesk Fusion360 and a 3D-printer to design and manufacture the drive, tracking and platen wheels. The drive and tracking wheels are a bit crowned on the outside to better track the belt. By making a slightly cone shaped hole for the ball bearing I was able to press fit them into the wheels. Throughout multiple of the steps I've used the 3D-printer to create bushings for a tighter and more snug fit between the parts. Primarily in the platen attachment and to make sure the tracking arm doesn't tilt to the side where it is fastened on the frame tower. The printer has been very useful in this regard, allowing multiple iterations of the same part to be tested. The feet for the machine were also 3D-printed and fitted to the frame with bolts.

Next up was a test assembly of all the parts to look for issues that needed to be addressed. There were some problems that needed to be corrected:

Low drive wheel grip: When the grinder was started for the first time during test assembly the drive wheel was slipping quite a lot against the back of the belt and not grabbing on and pushing the belt forward. This problem was attributed to two things, poor grip on the drive wheel and insufficient tension on the belt. Using some friction tape on the drive wheel and moving one of the bolts used to mount the spring to a higher position fixed this issue and the belt ran and tracked much better.

Poor rotation of the wheels: When the machine was test run the wheels would either begin to wobble or tighten as the belt ran over them. This was caused by the ball bearings rotating the nuts at the end of the wheel axles, either loosening or tightening them respectively. This issue was fixed by swapping the ordinary nuts for locking nuts and using some thread locking compound to ensure that the nuts would stay in position.

With the issues addressed and the machine running smoothly it was back to disassembly to be ready for a coat of paint, and then final assembly.

And that would be it! With the belt grinder fully assembled and ready to go that concludes this Instructable, but not the project! There are still some upgrades I would like to implement before I am fully content with the machine. A work rest and a proper platen are on the list for upgrades that will come in time. But for now I am very pleased with how this turned out and quite impressed what is able to be done with a bunch of scraps and some old workout equipment. I hope you enjoyed the Instructable and thank you for reading all the way!