DIY 2" x 72" Belt Grinder Project
Like almost every newbie knifemaker owning a decent belt grinder is dream. When I realized the price of a machine, my jaw hit the floor. Most of us getting started cannot afford a $2000 grinder. So I set out to design my own and I shamelessly borrowed as many ideas as I could. One special shout out to Alaskabearhawk for his great design and detailed videos on YouTube.
Wish ListMy wish list for my new grinder would be:
- 2 x 72" belts
- 1.5 to 3 horsepower
- Variable speed
- Removable attachments, platen and contact wheel
Before building I considered some variations:
Stepped sheaves for varying speed. This would be a lower cost build, but still allow some speed changing. I would need two pillow blocks, an axle and a stepped sheaves (or pulleys as some folks call them). The drive wheel could be 4" diameter still. This arrangement would let me use any motor, whether it can be reversed or not.
Fixed speed would be lowest cost and simplest build as there are less components and less alignment issues. The motor can be 2 pole or 4 pole and must be rotating in the CCW direction. That's fairly easy. Drive wheel size becomes a focus. For a 1800 RPM (4 pole) motor I'd use a 5" or 6" wheel. 2335 or 2826 surface feet per minute. For a 3600 RPM (2 pole) motor I'd use a 3" or 4" wheel. 2826 or 3768 surface feet per minute.
To get the surface feet per minute, use the formula:
(Motor Speed in RPM x 3.14 x Wheel Diameter) / 12.
Take a look at some of the other builds on the BG-272 Gallery of Builds page. Some very clever ideas going on there. Thanks to all that sent in photos and made such great suggestions.
ProcurementThe search for suitable wheels proved fruitless as the most common maker in the US did not ship to Canada at the time. I found these wheels from Europe on eBay. You may want to check out Oregon Blade Maker's belt grinder wheel set.
Note: If you want to machine your own wheels, here is a PDF and a CAD drawing graciously provided by K. Langeveld.
For the drive wheel, I am using a 4" nylon caster that is 2" wide. I had to push the roller bearing race out and insert a shim with a 7/8" inside diameter. I then had to cut a key way for the 3/16" key stock. A fair bit of work, but I have made what is effectively a sub $20 crowned drive wheel.
The motor came from an ad on Kijiji . I scored this 2 horsepower T145C face motor, 3 phase 230/460V for a whopping $35. I wasn't too sure about this but after a quick ohm meter test and a spin of the shaft I think we're going to be fine.
For the variable speed part, I chose a Yaskawa J1000 VFD. My work associations with Yaskawa have been top notch over the years and basic shaft spinner came into my hands at a very reasonable price.
I am going to install the VFD in a sealed enclosure (NEMA 4) and wire a control panel for the operator to start, stop and vary the speed of the motor from the front of the grinder.
For the basic electrical I sourced from eBay, Digi-Key and my locals like Home Depot, Canadian Tire and Peavey Mart.
Not everyone can chance upon a nearly free motor. I can recommend Dealers Industrial Equipment's TEFC Motor and VFD combo. Just remember to check the shaft size on the motor and make sure the drive wheel's bore is a match.
The basic construction is of HSS (Hollow Structural Steel) pieces and some plate and scrap pieces from my shop and from Metal Supermarket. The pieces I cut on a band saw so they are nice and square.
I bought 48" of 2" HSS, 0.188 wall and cut them like this.
As suggested by Ken DeRosier, make sure the welded seams are positioned on the left (where the lock down nuts will be installed.) This reduces the seams from being an issue, and provides a perfectly flat face for the tool arm to rest against.
Pieces A, B, C and D are squared, clamped and welded to make a frame like this.
I then welded the frame to a 12" x 20" plate of 1/4" steel, again checking for squareness and clamping everything in place before tacking.
I added four 1/4" x 1-1/2" studs for mounting the motor. These are flat head capscrews and I countersunk the underside so that they didn't stick out. I used hex nuts and placed fender washers on to support the motor. These being a bit smaller than the motor foot mount holes, allows for some rotating of the motor to get the belt to track properly. Also a 6" piece of strut to mount the operator control panel. The motor is positioned so that the center of the shaft is about 4" to the back of the vertical receiver.
30 pound spring. Thanks Dave! I measured this on a scale. Pressing down on the spring about 30 pounds caused it to deflect 1". More recently, we have found that springs from screen door chains will work okay.
Update March 2017. I have made some better drawings of the frame.
Tracking and Tensioning Pillar
The tracking and tensioning pillar slips into the upright receiver part C of our frame and sits on top of the spring. It has a tracking hinge that can be adjusted to tilt the tracking wheel.
The axle hole is 2" from the top, centered.
The pillar itself is 13" long. This may have to change depending on the spring that you have available. My spring is about 4" long, so add or subtract a little if your spring is shorter or longer.
The axle hole is 3/4" from the top and drilled right through. See photos below for construction.
The cutout hole for the tracking wheel axle is 2" from the top of the pillar so that the head of the axle bolt goes inside of this cutout. If you use a carriage head bolt for the axle, you need only make a round hole.
I clamped the hinge with shims around it before drilling a pilot hole right through both pieces on the drill press. Add 1/16" shims on the sides and 1/8" on the face.
I tacked a flat washer on either side then hit them with the belt to thin them down to a good friction fit inside the hinge piece. The pillar will need an area removed for the bolt head of the tracking wheel axle to come through. If you were to use a carriage head bolt, this could be a circle. I had no luck finding a 12 mm carriage head, so I made a square to fit the hex head of the bolt.
Test fitting the hinge.
The top and bottom of the pillar get capped with some 1/8" flat bar. Before tacking the top plate in, I drilled and inserted 5/16" x 1" bolt, then tacked that around the head. This will be for my shifter ball. (The ball will make it easier to push the pillar down.)
Also note the 1/4" nut mounted for the tracking adjustment knob. The bolt going through here will press against the tracking wheel axle bolt and allow the tilt of the hinge to be adjusted.
The Platen AttachmentThe platen attachment slide into a receiver and is locked in place. The tool arm is of 1-1/2" HSS with 0.250" wall that is 17" long. The plate that the wheels attach to is 3" x 12" made of 3/16" steel. I set the holes 10-3/8" apart so as to leave a good amount of space between them for a 9" platen. The platen is made from a piece of 2" angle iron. The angle is 0.188" thick.
I put a backing piece of 1/4" plate behind the angle to step it away from the plate. This could be accomplished with a small stack of flat washers as well. This space is to bring the platen directly in line with the belt and wheels. If you need to tweak the platen to the left or right, add or remove a washer from three bolts securing the platen to the plate.
The wheels are mounted typically with 1/2" bolts. In my case I have metric wheel bearings, so 12 mm bolts. The wheels cannot run against the plate, so I made some spacers from schedule 40 3/8" pipe cut into short sections about 1/4" and with a hacksaw and shaped with a file to uniform thickness of close to 3/16". Slip the spacer over the bolt, slide the wheel on and the inner race should be kissing the spacer.
Below are some updated drawings for the flat platen.
Note that this work rest has been replaced with the Adjustable Work Rest.
Test fitting and tracking evaluation. Before painting, I added a 1/4" x 1/2" bolt on the vertical piece so I could mount a brush to remove static charge from the belt.
One thing to note here. The pillar is a little bit loose inside the vertical receiver. I added two strips of plastic (from an old oil jug) to act as shims. These are dusted with a little graphite to make them slippery.
Added the tool rest made of 1/4" plate on a 1/2" x 3/4" flat bar mounted to the underside of the platen tubing with 2 tapped 1/4" holes and hex socket capscrews to match.
Powered up the motor for live tracking test and VFD programming.
section on VFDs if you want to source 240V.
VFD Power WiringThe VFD requires a 240V / 20A supply. I have opted for a NEMA L6-20 receptacle and plug. The L means 'Locking' and this will assist in preventing any accidental un-plugging of said plug. I am using some supple SOOW 3 conductor #12 AWG for the input connection. I'd like some length so I piked up about 15 feet of this. Inside my VFD enclosure I have two midget type fuses that protect the VFD proper. A low current takeoff of 240V for the DC power supply is done immediately after the fusing. For convenience I've added some surplus terminal blocks mounted on DIN rail. The output of the VFD is rated for 10A (three phase) so I used some 4 conductor #14 AWG SOOW (cab tire) cable.
Operator's Control PanelTo control the VFD I am going to bring out the sequence inputs SC, S1, S3 and S5. This will allow me to START and STOP the motor as well as change the direction FWD and REV. I will also wire in the VFDs status contacts to drive two LEDs indicating motor on and off. Finally, I have a digital tachometer that will count pulses from a small magnet placed in the side of the drive wheel. The net result is that the operator's control panel will look something like this.
When the magnet passes close to the sensor the sensor switches to make a 24 VDC pulse going to the tachometer. This will count the revolutions per minute of the drive wheel.
Once the VFD enclosure was mounted to the frame, I could terminate one end of the control cable accurately estimate the cable length for the motor. The control wiring is fairly straight forward. One thing to pay attention to is the wire colours. The particular printer cable I had has insulation that is colored solid and some with white stripes. These can be easy to mix up. A quick check put with the ohmmeter will save the day and prevent a mistake here.
VFD EnclosureThe VFD enclosure is a surplus Hoffman NEMA 4 14" x 18" x 8". As it did not come with a mounting pan, I had to make one from something. Conveniently, I found some 1/8" utility grade aluminum that was pretty scratched up, but the price (free) was right.
I mounted the VFD and 24V power supply as well as some DIN rail to mount the terminal blocks.
For strain reliefs I used some nylon domed strain reliefs and one Heyco straight-thru for the tachometer sensor cable.
Tying it all TogetherWith the incoming power cord attached and the 4 wire motor lead connected it was a matter of programming the VFD to accept the 0-10V input (potentiometer) as the speed command and setting the top frequency to 80 Hz. I also set the acceleration time to 5 seconds and deceleration to 2 seconds.
Running The GrinderThe first run with the unit complete involved a little tweak in the tracking hinge. The belt ran fairly true and didn't walk off the wheels at 4500 RPM.
I took a chew through some 154CM and the blaze belt eats it like butter. I am so impressed I will toss my hacksaw out!
Grinder StandThe stand will hold the VFD enclosure and the grinder will be mounted on the top. For this I chose some scrap channel I had and welded it up. Adding two casters on the rear will allow easier moving, but only when tilting.
Before painting this space-ship silver, I welded some 5/16" x 1" flat head bolts to act as mounting studs for the grinder base.
Knowing where the motor and VFD enclosure line up, I can drill some holes for some chase nipples to pass the motor cable and control cable through the grinder base plate.
Small Wheel Attachmenthere.
10" Contact Wheel Attachment
October 2014 - 10" Contact Wheel Attachment is now here.
Always updating. I will keep you posted.
Mechanical Bill of Materials is here.
Updated April 2017