Mini Circular Bench Saw From Scrap [UPDATED]





Introduction: Mini Circular Bench Saw From Scrap [UPDATED]

About: I'm an Italian freelance structural engineer, graphic designer and photographer, and I'm teaching physics in Waldorf schools. I always investigate electronics, robotics and science in general, I'm a passiona...

Try to salvage little electric motors from scrap, because you can usually find a way to reuse them. I don't remember where this motor comes from, I've got it many years ago when I used to dismount everything I bumped into, anyway when I found it the other day I immediately pictured a small bench saw to cut metal. Not wood, because motor has a belt and a ratio so that the gear turns at a speed of about 600-1000 RPM which is good for metal, bricks, stones but wood needs very fast speed. To cut these materials you can use a disc grinder, so I bought a pair of discs to apply to my motor.
[UPDATE] I also can apply a disk of sand-paper if needed. To check speed of the disk see last step.

Step 1: Motor and Pulley

I already put together motor, pivot, belt and gear with a wood block when I was a boy, so I left that mounted. The pivot is a very sturdy steel beam and at that time I drilled an hole in the wood and I wedged the pivot into it. The gear has not bearings but uses a metal bushing to rotate around the pivot. The mechanism you see around the little gear on the motor pivot is meant to release the rotation when motor stops, anyway I don't need this feature.
The motor has 30W power, and with this gear the final disc has a very strong cutting force.

Step 2: Finding a Fastening

To attach and change easily the discs on the gear I needed a simple and effective way. After some research I retrieved a piece of hydraulic pipe and a cylindrical nut. Since the pipe's external diameter is almost equal to the disc hole measure, and the pipe fits very good on the gear's steel pivot, that solution works perfectly. I only had to glue with two-components adhesive the pipe on the pivot, adding a plastic ring where discs will be pushed by the cylindrical nut. This nut is very easy to tight by hand, and changing the disc will be fast.

Step 3: The Base and the Top Surface

Also to build the body of the saw I used what I already had, so you can see some wood boards and a little metal L beam, which I thought it was good to keep the disk adjacent to the plane edge.

Step 4: Gluing Together

With vinyl glue I attached the three wood parts together, I clamped them with a pair of vises, and I left everything to dry meanwhile I carried on with the making.

Step 5: The Disc Runner

Using a pair of existent holes in the metal L profile, on the thinner side, I screwed to the wood side edge. With three washers for each screw you can keep the space for the disk. Just add or remove washers if you change disk thickness. The disc obviously has to rotate freely.

Step 6: The Electrical Section

Since the motor had a big capacitor and an ON-OFF switch, I left everything in its box. To lock this box on the left side of the saw, with the switch on the front, I drilled a three holes in the wood and added a pair of holes in the plastic container.
After closing everything the switch is easily accessible and the electric box remains under the wood top board, so it's not very ugly to see.

Step 7: Last Details

I ended up to change the cable and the wall plug, since the original one was too much rigid. Then I added four silicon feet on the bottom four corners. You can see the other disc I bought, that one is to cur bricks and stones, who knows if I will ever use it ;-)
I know that I will have some problem when the discs will wear out, and the diameter will reduce, but anyway I don't imagine I will use it very much for long operations.

Step 8: Ready!

Woah! The new mini circular bench saw to cut steel bots, copper circuit boards, metal plates, or to refine screwdrivers heads or to make many other operations, is ready to use! Admire it in all its ugliness! ;-)

Step 9: [UPDATE] Sand-paper and Disk Speed

I found very useful applying a sand paper disk. And with the occasion I also checked the speed of the disk. Looking the angle covered by the white paper in the slow photography we can easily determine the exact speed. Indeed, since the photo exposure is 1/20 sec, and the disk makes in that time less than half turn (let's say 3/8) we can calculate that 1/20 * 8/3 =  0.13 secs to make an entire turn, and 1 / 0.13 = 7.5 revolutions per second, which is the same as 7.5 * 60 =  450 rpm (revolutions per minute). A good speed to not burn wood or melt plastic.

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    118 Discussions

    This very useful! Thanks for sharing!

    Oh that's brilliant. So going to have to make one of these, thank you. No room in my tiny flat for a real workshop, so micro-tools like this are ideal

    From these pictures it doesn't seem like you have anything to stop that grinder disc from rotating off the pipe that ypu are using as its axis. You should really be careful with that as it can be VERY VERY dangerous.

    I found a small Mini grinder in clean up (Spring ) and I got it working but it has no guide on it so I thought maybe I can use it for cutting metal using the bigger blade. It worked but it slipped and cut a nice gouge out of my finger. It would work safer if it were mounted on a plank or angle iron frame. I may try that one day. Your idea is good but it just needs a guide to protect fingers.

    nice and useful project

    nice and useful project. i was surprised how easy you determined the speed of disk. that white paper hack is really clever. good job ;)

    This is a great project and I'm very keen to make one of these. Yes I can see improvements and will try to post when done, but while I don't want to name anyone and some of the comments are valid,but anyone wearing a ring take it off when using dangerous power tools and lathes either wood or steel and spinning blades.I've been a welder for 30+ years and have a competancy in Workplace health and Safety, if your long sleeves may get caught in revolving blades your shirt could be to big and loose try a hair net if it is to long well as one person has already said Common Sense.

    Good luck

    That looks like an IBM Slectric typewriter motor. That mechanism on the shaft is a centrifugal clutch that lets the motor gain speed before engaging the load.

    2 replies

    Definitely not a Selectric motor, but possibly from another typewriter make.

    Same clutch as a Selectric, but, that same clutch was used on other makes as well...

    yes you are probably right, since I found one of those devices when I was young, and the motors remained years in my stuff :)

    Very crafty design! I notice a few makers commenting on safety. Brings to mind a sander, albeit somewhat larger than your mini-saw, that I made a few years ago, as an accessory to my wood lathe. While in a hurry, right after I made it, I was sanding a piece of wood, and it got caught between the disk and table. Lucky me, my grandson was in the shop to witness! I found it necessary to move the table very close to the disk (perhaps ~0.010" clearance), which seemed to alleviate this problem. If you decide to sand on your saw, you may want to lessen that gap.


    Oh come on you guys, ALL power tools are dangerous, you can spin your long hair or long sleeves into a hand drill which will pull you straight toward it; you can cut your toes with a lawnmower. Any power other tool that has a powerful spinning motion is dangerous and this one is no different.

    Great job for the author!

    5 replies

    actually this motor has a friction between crankshaft and gear, so it doesn't have power enough to pull your hair, and it's very safe.
    anyway you're right in general, power tool are dangerous

    well just saying, that if a 5-10yr old having 10-15 inch long hair would come close to see "how this works" from curiosity, and if the wind blows ( or for whatever reason ) the hair would get onto any spinning part ( in between the belt in the worst case scenario ) it would take less than a second ( ~10 rolls when spinning at 600rpm ) to pull the face on to the motor / spinning disc. even if there was no friction at the motor, the inertia of a spinning disc would be quite enough power to do that.

    I mean, yes it's in some sort an unlikely scenario, but I'm just saying, the we all have to keep our safety measures when using power tools, and this instructable does not say otherwise ;)

    But I agree, some kind of cover from the side would be great - so at least no finger could easily get in between the motor & the belt :) So take your own safety measures when building this!

    But I agree, some kind of cover from the side would be great - so at least no finger could easily get in between the motor & the belt :) So take your own safety measures when building this!