This is a project that has been on my to-do list for a while. My first thoughts were to make it completely from steel and up until a few months ago that was the plan. After finishing my 1″ belt / 5″ disk sander project and seeing how how well that worked and how easy it is to build, I decided I’d put a design together for a wooden version. In order to come close to the strength and rigidity of steel, I’d have to pay close attention to how it was structured to avoid flexing and excess vibration.
I worked up a design that has parts that are nearly twice as big as what I would normally do. If I figured that the boom arm would be strong enough at 3″ wide and 2″ thick, I increased this to 5″ wide and 3″ thick. Originally the entire build was going to be made from 1/2″ plywood, and I bumped that up to 3/4″ for nearly every component. For a machine like this, it’s better to be too strong than just strong enough.
After the plan was basically completed, I got started cutting out the parts. The majority of the grinder is made from 3/4″ cabinet grade plywood. Baltic birch would be the best choice, but any good quality plywood will do. MDO or (new) forming plywood would be a good choice, but I would strongly recommend not using a sheathing grade of plywood, since there is too much irregularity in the surface and too many voids in the laminations.
MDF and particle board are not suitable for this project.
This is the base, part “A” cut to size with the screw holes laid out and drilled. Four 1/2″ holes were drilled in the corners to bolt the grinder down to a bench or stand after it is finished:
All of the screw holes are drilled and countersunk for #8 flathead wood screws.
Parts “B1” and “B2” are next:
These parts need a 1″ hole drilled through that lines up, so I’ve clamped them together to drill both at the same time.
The plan was made so that all of the parts will be easy to cut accurately on a table saw with very few curves or odd shapes. These are an example of the most complex ones:
The plans were made with accurate thicknesses for the materials, like 1/2″ (12.7mm) and 3/4″ (19.05mm) for the plywood and MDF. Since there is variation from one manufacturer to the next, you will have to make some adjustments to allow for this difference.
There is really only one place where this may cause a problem, and that’s where the boom arm fits into the base unit. If the plywood is thinner, you may have to adjust the thickness of the boom arm to compensate.
Parts “D”, “C” and “E” are just simple, rectangular parts:
Take note of the grain direction on the plywood. The cut diagram for the 3/4″ plywood shows the grain direction and it’s best if that is followed for maximum strength and durability.
Part “F” and “G” also need matching holes, and I’ve clamped them tightly together to do this. The holes in these two parts house the drive shaft bearings and will need to be accurately placed. Take the extra time now to make sure the parts are exactly the right size and the holes are drilled in both parts so that they match. If there is an error, it will be best to remake one or both parts now before going forward.
If your drill press is not set up accurately (square to the table), it will be better to mark and drill each hole individually:
Part “F” needs two slots cut part of the way through to form a tab and I did these on the table saw, stopping the saw when it reached the mark.
The top of the tab was cut with the band saw (or jigsaw) and the parts are drilled and countersunk for screws, following the layout from the plan:
Part “H” is just a block of wood cut to shape with a 1/2″ counterbore for a single screw:
Parts “I1” and “I2″ make up the boom arm for the grinder. These can be made from solid wood (hardwood is best) or from plywood, or from a combination of both. I chose to make mine mainly from plywood, with some solid maple. First, I cut four pieces of 1/2” Baltic birch plywood to size:
Then two pieces of maple to make up the rest of the thickness.
The 1/2″ plywood parts are glued in pairs:
Then the maple is glued on flush with the end.
These are clamped together in two pieces and set aside to dry for a few hours.
When the glue has set, the parts are clamped together as shown in the picture above (right) and a 5/8″ hole is drilled through from both sides.
Another 5/8″ hole is drilled through the parts at the end:
The final step is to cut a shallow recess in each using the table saw with the blade sticking up around 1/16″. Make a series of cuts until all of the material is removed.
The recommended procedure for building the machine is to cut out and prepare all of the parts before starting assembly. The first part of this article goes though each part as listed alabetically starting on page one with part “A”.
Part “J” has a slot that is 3/4″ wide and I’m making stop cuts on the table saw to a 3/4″ hole that was drilled:
The rest of the cut was finished with a handsaw. Again, these parts are simple rectangles that are easy to cut with a table saw.
Parts “J” and “K” form the tool rest on the grinder:
Part “L” is the main part of the belt tensioner assembly.
Parts “O1” and “O2” are part of the tracking assembly and need holes that are accurately placed to receive the idler shaft bearings:
Part “R” needs a recess cut into it for a 5/8″ washer to fit. I did this on the table saw by making a series of shallow cuts.
Part “M” is a shim that I made by cutting 1/8″ off of a piece of 1/2″ plywood. Part “N” is a simple recangle with a slot cut. I cut the slot using the drill press, drilling a series of holes:
Parts “P1” and “P2” in the picture above (right) are glued to parts “O1” and “O2” later in the assembly, but are shown here already glued in place (since my machine was already assembled during the mockup). Part “R” holds a 5/8″ nut and keeps it from turning. Part “Q” is another plywood shim.
Part “U” is the most complex, but starts as a simple rectangle:
None of the cuts on this part are critical, but the hole placement should be accurate.
Parts “S” and “T” form a nut holder that fits into the slot in part “J”:
With the nut pressed into part “T”, thread a 5/8″ bolt with a nut into it to clamp the parts together until the glue dries. This ensures the parts are lined up correctly:
With all of the part cut out and ready, we can begin assembly. I’ve made a video going through each step:
Since the video and the plan set fully cover the assembly of the base machine, the rest of the article covers specific details in the build.
I used 5/8″ cold rolled round bar for the shaft material and cut it with an angle grinder with a thin cut off wheel. A hacksaw would work as well:
The problem with using the round bar is that it’s just a bit too big for the bearings to slip onto easily. I fixed this by rubbing it with a coarse sanding sponge until the bearings slid on smoothly. It didn’t take long to do, since there was very little to remove:
On mine, I used two bearings on the drive pulley side, just to give it some more support. This is optional, but if you do it with yours an extra piece will have to be made to build out the side of part “F”:
Just a square of 1/4″ plywood with a 1-3/8″ hole in the centre.
Another option is to treat the bearing recesses with CA glue to harden the wood. I used spray urethane and applied a few coats, letting each one sink in and dry before applying the next:
After the base unit is assembled, it’s a good idea to put the drive shaft in and check to see if it’s square to the unit. If it’s slightly off, it’s not a major concern. When assembling the base unit, it’s a good idea to do a dry fit first, without glue, and check this. You can then make adjustments to correct the problem.
The drive wheel and idler wheel are made from layers of MDF cut to shape and glued together. I started with squares that are slightly oversize:
Then cut out roughly on the band saw or jigsaw. A 5/8″ hole is drilled in the centre of each piece and they are glued and clamped together using a piece of shaft to keep them in line.
After the glue dried, I sanded them fairly smooth with my disk sander.
There are more accurate ways to make the wheels, like setting up a circle cutting jig on a router table or disk sander, but since these wheels need to be trued on the machine, I decided to do it the fast and easy way.
Another option is to use ready made wheels made for this type of grinder. You’ll need to check that the shaft size is the same, or you will have to make changes early in the build to work with those wheels (shaft size and bearing size).
The large contact wheel is made in the same way as the drive and idler wheel, from layers of MDF. I made my wheel 10″, but the machine will accommodate smaller ones.
I started with squares of MDF with the centre marked and the diameter drawn using my beam compass:
Cut these out on the band saw close to the line.
Then sand to the line on the disk sander:
The two outside layers are drilled with 1-3/8″ holes for the bearings:
While the two inner layer get a 1″ hole drilled.
Spread glue on the layers:
And use a piece of shaft and a square to check that the stack is lined up correctly:
When the glue is dry, you can spin the wheel on the shaft to check to make sure it doesn’t wobble. A small amount is fine, but if it’s excessive you should remove the bearings and start over:
Like the other bearing recesses, treating the MDF with CA glue or polyurethane will greatly increase the durability.
The 2″ rollers are made the same way as the bigger ones. Here I’ve laid out the 2″ circles using my compact compass on a strip of MDF:
The 1-3/8″ holes and 1″ holes can then be drilled before cutting out the parts.
Glue them together and smooth them on the disk sander:
Then install the bearings. Another option for these rollers are wide skate board wheels, but the shaft size will be different.
The plans call for a common bearing size and it is recommended that you use that size. The outside diameter of the bearings in 1-3/8″ and to drill those holes I recommend buying a forstner bit. The bit will make holes that are exactly right for the bearings to fit in.
To key the wheels and my wooden step pulleys to the shafts, a groove is cut with the angle grinder:
It’s not a precision machining process, the grooves only need to be 1/16″ deep. I used a round file to clean up and widen the groove.
Just big enough for a #10 screw it fit into part of the way:
With the pulley on the shaft, I drill a pilot hole following the groove cut into the shaft:
And drive the screw in.
The same for the drive and idler wheels:
Where the shaft collars go on the shafts, it’s a good idea to file a flat spot for the set screw to go into. Just tighten the collar where it’s supposed to go, and file where the set screw made a mark on the shaft.
On the drive wheel side, there’s a plywood spacer that goes between the shaft collar and the bearing. This is made from 3/8″ thick plywood:
This spacer moves the shaft collar out so that the set screw can be tightened.
With the machine assembled, you’ll need to true the wheels. I made a video that goes through that process:
Truing the wheels may seem intimidating, but is easy and safe if you take your time and pay attention to what you are doing. Only take a small amount off at a time and only use the chisel as a scraper. Take the time to set up a study tool rest close to the wheel:
These wheels can be trued part of the way on a lathe, but really need to be finished on the shaft that drives them. If you are looking for high belt speeds (3000 sfpm and up), the wheels must be smooth and run true on the shafts to avoid excess vibration.
The idler wheel is slightly crowned. This will help to keep the belt centred on that wheel:
The contact wheel, drive wheel and rollers should all be flat, not crowned.
The knob that locks the tensioner is just a 1/2″ plywood disk, about 2-1/2″ in diameter. In the plans, a 3/8″ t-nut is shown, but a regular nut can work as well, just drill the right size hole and drive it in:
The tension adjust knob is 1/2″ plywood in any convenient size and shape:
The tracking adjust locking knob is 1/2″ plywood with a 1/4″ t-nut driven in:
This needs to be fairly small to fit into the space and still leave room for your fingers. I made mine 1-1/2″ diameter.
I made a belt guard to fit around the pulleys and belt:
Nothing fancy, just some scrap plywood. You need to leave an opening in the guard to access the boom locking nut.
My motor is a 1 hp induction motor that runs at 1725 rpm. That is the recommended power and speed for the grinder.
After putting my machine back together, I needed to re-true the wheels. Wood is a material that will change slightly with humidity and temperature and stress, so expect that you will have to do this occasionally to keep the machine running smoothly:
Although the plan calls for a 3/4″ plywood platen, as you can see (from the scorch marks) it may not be the best choice. Some people use aluminum or steel, while others use glass or ceramic tile. I think the plywood will work well if it is soaked in oil and I will try this. Another option is a graphite backer used on hand-held belt sanders. I think that even a thin layer of smooth sheet metal wrapped around the plywood would work well.
Since I’m using an open frame motor, I made a shroud to partially cover it:
The idea is to stop larger things from falling into the motor, but not block airflow.
It’s also a handy place to put the switch:
I’m using a 20 amp 2 pole light switch for this in a regular steel electrical box. I’ve attached a long, heavy duty cord and a heavy duty plug.
I made three videos while building the grinder. The second one is at the top of this page and it covers truing the wheels.
The first is on the basic design and some of the problems I needed to work out, and you can watch that here.
The third concerns the platen attachment and trueing the rollers on that, and you can watch that by clinking here.
And with the contact wheel:
I’ll need to build a stand to put it on and figure out where it will go in my shop. I also want to get it painted to keep it clean and make it look even more awesome.
I’ll be using this grinder in a lot of upcoming projects to shape all types of material, not just metal. I think it will become a very key member of my workshop tool collection, and even more appreciated since I made it myself.
Next, I change the platen to 1/4″ steel and show how to make a new 5″ drive wheel.
To be honest, I didn’t give the plywood platen a fair chance. The idea was to soak it in oil to make it more slick, but instead I decided that it would be better to just replace it altogether with a piece of 1/4″ steel. The steel is more suitable and also considerably thinner, so that the grinder can reach into a recess in a work piece.
The steel flat bar is 2″ wide and cut to the same length as the plywood platen:
I clamped the old one on to use it as a drilling template, then made 1/8″ holes at each screw location.
To enlarge the holes and countersink for the screw heads, I used a step drill:
To build out the platen brackets to make up for the thinner part, I cut pieces of 1/2″ plywood and glued those on with the screws driven to clamp them on until the glue dried.
The new platen installed:
1/8″ steel would also be great for this. I used the 1/4″ because that’s what I had on hand. To make it super slick and super flat, glass or ceramic tile can be double sided taped to the platen, although I don’t think I need to go to that extreme.
New Drive Wheel
In this video I show how easy it is to make a drive wheel (or idler wheel) for the grinder from MDF using a simple jig:
I started with a piece of MDF that wasn’t quite wide enough to get five disks straight across, so I used 5″ sanding disks to do a rough layout:
Then used my compact compass to draw the circles accurately.
The centre holes were drilled and then the disks were cut out close to the line on the band saw:
As shown in the video above, I used a jig on my disk sander to shape the disks to perfectly round. They are then glued together using a piece of 5/8″ shaft for alignment. I used a square to check to make sure the shaft is perpendicular to the wheel before the glue set.
Details on the jig I used are here: perfect circle jig.
To keep the disks from sliding when clamped, I waited about 10 minutes before applying light clamping pressure:
Using a small amount of glue avoids squeeze out and the parts won’t have to be tightly clamped.
To fix the wheel to the shaft, I mixed a small amount of epoxy and spread that on the shaft and into the hole in the wheel. The epoxy will make the wheel installation somewhat permanent, but the wheel will be better balanced on the shaft to begin with. After the epoxy sets, the locking screw is driven into the keyway cut in the shaft:
The new wheel is 5″ diameter and will give the grinder a top belt speed of 3760 fpm, which is a substantial increase. There is room for a wheel as big as 5-3/4″, but the gain in speed will be marginal.