Broken Angle Grinder to High Torque Drill Press Sander.

About: Just a fellow who want's to learn new tricks and skills.


This instructable supposed to be about fixing broken angle grinder..

Just happened that the one i suppose to fix, was burnt so badly, that best result that i got after rewiring was somewhat similar than four stroke engine working in two strokes.

So, i decided to find another way to re-use that broken grinder, and ended to this solution..

Maybe its fixed enough, even if its not on its original formation?

Wich actually seemed to be better for me.

Ratio of the angle grinder gear is 1/4.

It can be used to lower the rpm and increase torque, or to increase rpm with lower torque.

In my case, i wanted to have more torque, to be able to make precise grinding and sandings, also i like that using wire brushes with lower speed is much safer.

I have several angle grinders, but i did not had sander / grinder / polisher that would have enough torque when running in lower speeds. Now i have.

Because there are many different kind of grinders and drill presses, there's not much use to add measures to this instructable. But, i try to explain the idea as well as i can.

Video shows the making.

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Step 1: Tearing Down the Grinder..

Grinder that i used is Bosch model Gws-850 c.

I removed the guards and the angle head opening the screws, there was one screw on the back side next to the power cord too.

Gear and the shaft was connected with " cone fitting ". After opening the screw in the end of the shaft,

i needed to wobble it little to get it out.

Then i pulled armature out from the casing. Its little tight, but it comes out when you pull hard enough.

Then i brutally, cut the armature and shaft with angle grinder.

Pushed the shaft out with my diy press.

Removing shaft can be done with hammer too, then its better to sand shaft end smooth after cutting.

Coarse edges may get shaft to get stuck inside the armature.

Step 2: Supporting Bearing, and Adding Another One.

I tought that its somewhat important that shaft travels straight,

thats why i added another bearing to support it.

I used file and drill to "machine" slot to the shaft. Diameter of the shaft was 12mm, i filed it to 10mm to be able to mount 10mm x 30mm (outer) x 10mm ( thickness ) bearing to it.

Then i drilled 12.5mm hole to the 2mm thick mild steel sheet, blaced the shaft, bearings and casing.

Clamped casing on top of the plate and traced out lines of the casing to it.

Then drilled 5mm holes trought the plate using holes on the casing as a guide.

This plate is to support original bearing of the angle grinder. Originally its held with the plastic casing, that takes support from the grinder motor housing. Now when its removed, this plate does the supporting.

I cut the shape out and shaped edges with angle grinder following traced lines.

Step 3: Frame, Body, Casing..

I made frame for the drill press attachment from 3mm mild steel.

Again i traced holes to the plate from the angle head. And four new holes that holds new bearings casing.

Then i drilled 30mm hole to the center. ( extra bearings outer diameter is 30mm )

Cut the shape out, and made 90 degree bends with my diy press.

I made too plates with 90 degree bends. First with the mounting holes for the angle head.

Another, to be used for mounting new casing to the drill press. I measured places for the mounting holes from the drill press, and drilled 10mm holes to these locations

Step 4: Casing for the Extra Bearing.

To make casing for the extra bearing i used old cutting board thats made from nylon.

Its strong and elastic, also easy to shape.

I drilled hole for the bearing using 30mm forstner bit.

Then i cut the outer shape with scroll saw.

I threaded the housing trough the holes on the new frame.

And cut 10mm ( same thickness as a bearing ) thick piece from the original angle grinder body, to be used as a outer part of the bearing casing section. ( also it leaves little empty room around the casing, this will be filled with lubrication oil.

Step 5: Building the Frame..

Main frame could have been done from one piece too, but i tought that its much easier to get everything to the right line when i make it from two pieces.

I clamped pieces on their desired place on the drill press. Then i clamped pieces togehter with locking pliers and clamps. Then i weld parts together.

Made a part that connects to the handle mounting screw on the grinder head.

This also holds workpiece rest. To mount workpiece rest i used M12 bolt.

I later counted the threads and cut it to the lenght that when i twist the workpiece rest on its place, it ends in horizontal position. This is a simple solution, but works great.

When i need to change the grinding, sanding, polishing, burnishig.. wheel?

I just twist the rest to counter-clockwise, and close turning it back.

To get strong frame i weld "sidepanels" to both sides of the frame.

I liked that it looks better if i make little curved edges to the front end.

Step 6: Welding..

Bolt for mounting the workpiece rest is weld to the stand, also nuts that mount the frame to the drill.

I weld the side panels with full welds, all other are connected with tack welds.

For welding i used inverter and 1.6mm stick.

After welding i rounded the edges and removed splatters.

Finished the frame with black paint.

Step 7: Assembling..

1. Angle head is bolted to the frame with 5mm bolts.

2. New bearing casing is connected to the frame with M5 screws.

3. Workpiece rest connection is weld to the frame, and also bolted to the grindrer head with M10 screw.

4. Workpiece rest is simple screwed on its location.

Step 8: Finished..

1. To protect bearing from the dust, i made a rubber flap on top of it.

Its connected to the frame by pressing it between the small plate and the frame. It keeps dust out, but is easy to flip over when adding oil to the bearing.

2. I have diy cutting fluid system on my drills. I can use that same system when doing wet sanding with my new attachment.

This new gear gives four times more torque to my drill press than before.

Before using drum sanders etc was somewhat annoying, because i had to use too high speed to be able to sand, that made working accurate little difficult, because it removed material too fast.

Now i can use all those same sanding, grinding, polishing, burnishing.. wheels and discs that i was able to use with my angle grinder. But, i can use much lower speed, and be able to get more accurate results.

Easier to polish the plate edges, without need to worry that i have suddenly removed too much material.

Round the edges, without all around flying sparks and dust.

And, the most usefull option for me. Possibility to wet sand with 1000-2000 grit sanding pads, without water flying all around.

With my drill press, i can use rpm settings between 50-600rpm, and with very high torque, even when using lowest speed.

Video shows the making and examples of use.

Thanks for watching!

Stay tuned.


Tuomas Soikkeli

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