Disc sander

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Well-Known Member
Oct 26, 2007
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heres a bit of kit I made years ago but is used (and abused) more than any other bit of kit I have. I Wrote an article about it and was published in several mags. I'll paste the entire original word doc and a few pics.

Hi there,
I thought I’d let you have a look at a bit of kit I made some years ago. I think it is the most used (and abused) tool I have in the workshop that has a part in just about every thing I make. Because it plays a part in just about everything I make I thought it might be useful if I wrote a short article explaining how it was made. It is so versatile and user friendly that if it ever packed up I would immediately build another. I cannot imagine my workshop without it or how I managed before its conception. The tool in question is a 9 inch disc sander. Originally it was built with woodworking in mind (and in the days when funds were short) but I quickly discovered that it would quite happily and swiftly grind metal as well. Everything from chisels to the 2 inch blades from hand planes. Just drifting off a little here I’ve enclosed a few pictures of a metal jack plane I made shortly after making the disc sander using only a pillar drill, the disc sander and hand tools. Many of the planes parts were shaped and ground on this tool. When I say abused I really mean it. Apart from the woodworking side of my hobbies this little sander can and does handle just about anything that I throw at it. It will of course sand wood, particularly end grain very well. It comes into its own when a fine amount needs to be removed when for example making boxes with mitre joints at the corners a small adjustment needs to be made to achieve a good and tight fitting joint. It will also remove stock at a fair old rate if a little more pressure is applied. I have made a few jigs that fit onto or slide across the table, 90 and 45 degrees are the most useful and commonly used in wood working with 90 degrees for metal. It’s quite a simple thing to clamp a fence to the table, a short length of wood or a piece of angle iron, at the required angle and feed the work piece into the rotating disc. Grinding metal is just as easy and with a relatively large and flat grinding surface and a large flat table as a rest (compared to a standard 6 inch bench grinder) its great for squaring up the end of flat, round and square bar when a fence is used at 90 degrees to the disc. If the fence is set using an engineers square off the disc face reasonably accurate results can be achieved and of course it grinds square and flat compared to the hollow grinding of the standard six inch bench grinder. It’s a lot quicker than setting up in the lathe or milling machine if absolute accuracy isn’t necessary. The sanding discs themselves are of the self adhesive type. I use a disc of 60 or 80 grit; these will happily cope with wood or metal. They are not expensive and last for ages if you clean the disc with an abrasive cleaner which is basically a lump of rubber you hold against the rotating disc. It’s amazing how well they work, bringing what looks like a worn out disc back to life. Axminster power tools (usual disclaimer) stock the discs for as little as £1.14 each and the cleaners from £2.82. I have used 12 inch discs before now as they seem to be more common than the 9 inch variety. They trim down to size very easily with an old pair of scissors.
So onto the construction of the sander. It was built before I even considered writing to magazines and before the days of owning a digital camera so no photographs of the original build exist so I can’t show it under construction. What I intend to do is dismantle it as far as is practicably possible, take photos and then rebuild it. With some simple drawings I think it should be enough for you to get a pretty good idea of how it all goes together.
The motor, which of course is the heart of the machine, came from a very old washing machine. You can see from the photos that the motor has oil cups for lubricating the bearings; they just don’t make them like that any more do they. It’s a simple thing with just two wires which makes the wiring up easy and gives the machine one fixed speed. As you can see from the photo the motor is rated at ¼ horsepower with a speed of 1425 RPM. This speed seems about right in use; it definitely doesn’t need to be any slower and whether any faster would be of any advantage I don’t know. Looking at the sanding disc the motor turns clockwise so all sanding and grinding is done on the right hand side of the disc. This has the effect of pushing the work piece down onto the table and not up and away from it. The motors from modern washing machines are multi speed and controlled by complicated circuitry usually built into the front control panel of the machine, not suitable really unless you’re good at electronics, although a sander with variable speed and reverse capability might be worth considering? The drawings I’ve included are very simple and include only basic measurements as the type and size of motor you use will dictate most of the dimensions so use them as a guide only.
Having acquired your motor you will need a flange of some sort onto which is mounted the 9 inch disc. Mine was pressed from an old car water pump but anything with a flange that will fit the motor shaft will do, the pulley that came with the motor might suffice. The flange I used had to be drilled and tapped to take a grub screw (1/4 Whitworth) to secure it to the motor shaft. The shaft itself having a flat on it means once the grub screw is tightened it can’t slip. The motor is mounted onto a base board. The base board, the box and the shelf are all made from 15mm white conti-board. If you can get hold of an old kitchen unit or even better the doors you will have all the board you need. You can see from the photos that my motor has a three bolt rear mounting and a support at the front of the motor. I won’t go into to much detail here as all dimensions depend on the type of motor you are using. The most common type of motor mounting that I have seen is the foot mounting type. The base board is mounted on three rubber mountings, two at the front and one at the back. The mountings are old shape mini exhaust mountings. (Take a trip to your local exhaust centre). The stud part of these mountings is not long enough to go through the conti-board so the holes must be counter bored with a forstner bit. Construct the box to the approximate dimensions shown and simply screw together. You will notice a couple of 1 inch holes in the sides, these are used when moving or carrying the machine. Just use a couple of screws in the front piece for now as it will have to be removed and refitted a few times. To make the disc draw a circle on a piece of the conti-board the same size as the flange, this will make lining up the disc and flange easier later on. From the same centre point draw another circle of 9 inch diameter, (4 1/2 inch radius). Roughly jig saw out the 9 inch disc. Using the smaller circle drawn on the disc as a guide mount the flange. I used fat course thread self tapping screws, these bite hard into the conti-board. The next bit is a bit tricky. Mount the motor on its base board and clamp the base board to the bench. Wire a plug onto the motor. Rig up a temporary fence close to the edge of the disc and clamp this to the bench or if possible clamp the motor close to a bench vice like I did and use the vice to hold the rest. Grind up an old wood chisel, turn on the motor and then with chisel supported on the rest ``turn`` the disc to a true 9 inch. This works really well and what you end up with is a perfect 9 inch disc running true centre on the motor shaft. Loosen the grub screw on the flange and slide the disc back along the shaft towards the motor. Mark and drill three holes in the bottom of the box for the rubber mounting studs to fit into and counter bore the bottom of the box underneath so that the nuts will fit into the recess and not protrude so that the box will sit flat. When lining up the base board for marking out of the mounting holes try to get the motor shaft just touching the front of the box and line it all up by pushing the disc along the shaft so that it touches the back of the front of the box. This will ensure the disc runs true to front. With the motor secure on its mountings push the disc up to the front of the box and draw round the disc with a pencil. Remove the front of the box (that is only held in with a couple of screws) and drill a hole into the waste side large enough to take the finest jigsaw blade you have and carefully cut out the marked circle. Refit the front of the box with a couple of screws and from inside the machine push the flange back along the shaft until the disc is just proud of the front by about half a millimetre. Turn the disc by hand and carefully check and mark where any adjustments to the hole might be needed. Once you are happy with the clearance tighten the grub screw in the flange making sure it tightens onto the flat on the shaft. Time for a test run. Plug in and switch on. If alls well it will run smoothly without the disc fouling the hole and be free of any vibration. The photos show two types of abrasive disc that I have. The black ones are 9 inch and will therefore stick straight onto the disc. The red ones are 12 inch and have to be cut down, a fairly easy job of drawing a 9 inch circle on the back and cutting out with scissors, but use old ones not the best kitchen scissors unless you want to face the wrath of her in charge! The adhesive on the discs is powerful stuff so when fitting a disc take great care to get it on dead centre first time; you can’t peel them off if you get it wrong without trashing the disc. Removing an old disc is a bit of a game, patient scraping and cleaning with thinners to remove all traces of the old one. Any bits left on the face of the disc no matter how small will result in a high spot on the new disc so its worth taking a little extra time and care. I use mine a lot but only have to change the abrasive disc once or twice a year so it’s not much of a problem. The table is another piece of the conti-board mounted on two sturdy shelf brackets. The brackets are held onto the front of the machine by four coach bolts pushed through from inside, nuts and large washers enable fine adjustment of the table to get it square to the disc. The table must be mounted on the machine so that its top face is exactly on the centre line of the disc. As can be seen from the photos an engineers square is used to align the table and disc at 90 degrees to each other, adjustment being made via the four nuts in the shelf brackets. The table must be removed for abrasive disc changing. Wiring up is straight forward. The motor I have still had a short length of its original wiring attached so I simply attached a 3 pin plug. Mounted on top of the machine is a single switched socket wired to about two metres of cable with another three pin plug attached. The motor plugs into the socket on top of the machine and the cable plugs into the wall socket. This gives an on/off switch on the machine and with two metres of cable gives some flexibility as to its position in the workshop and can be used outside sat on a workmate type bench. I’m quite happy with this method of wiring up as all the power sockets in my workshop are trip protected but a no volt release switch would be a good addition. In use the machine behaves itself very well and I have to say it’s probably the safest machine to use that I have. Having said that common sense must prevail wherever a power tool is concerned. For example when sanding or grinding very small parts they are best held in something like mole grips or a hand vice as it is capable of snatching it out of your hands and giving you a very quick manicure! When sanding wood wear a face mask as a fair amount of dust is kicked out. If I have a lot of sanding to do I rig up the vacuum cleaner underneath the table as that is where most of the dust exits. When grinding metal always wear some form of eye protection. If you are interested in building one for your self I would like to make a couple of suggestions. Firstly I’m sure the motor I have used would be powerful enough to drive a 12 inch disc. Obviously the bigger the disc the greater the working area. How many times have you said to your self “I wish I’d bought a bigger one”. If a 12 inch disc proves to be too much for the motor all you would have to do is turn the disc down to 9 inches and make a new front panel for the box with a smaller 9 inch hole. Secondly the table could be mounted to the box front on a couple of sturdy hinges and held in position by a couple of drop front cabinet stays on studs with wing nuts, (the curved sort with slots would be nice) this would make setting the table to disc a lot easier and give variable angles. The table itself could have a slot routed in to take the mitre fence from your band saw or circular if you have one. With the moveable table and a mitre fence compound angles could then be achieved. Well there you have it, a well used and abused bit of kit that I’m sure would be a valuable addition to any workshop and what’s more won’t cost a lot to build and will give many years of faithful service.

The sander


Inside the box with the motor removed


The motor mounted on its own board


The motor back in the box


The disc mounted on a car water pump flange


Yours truly squaring up the end of some angle iron


here are more photos available if any one wants more info.

Hi there Firebird,

Great job on the sander! I'm glad to see it's successful with the 1/4 hp motor as that's what I have "in stock" to build up one for myself. It's a 1725 rpm though; I guess that's due to the 60 cycle AC power over here in the colonies.

I posted a question about disc size over on another forum and most people there said don't bother unless it's a 12" disc and 1 full horsepower. I say horsepoop, 1/4 hp will do for my needs, especially since the motor is free. An internet friend sent me an 8" disc off an old sander he parted out so I'm anxious to get started as soon as I finish a couple more projects.

The motor on mine is plenty powerful enough. If I try really hard I can stall it but you gotta push a length of 2 X 2 into it very hard.

Before I bought a disk sander I made 10" disks from 3/4" MDF
I glued 60 grit on one side , 100 grit on the other side. Made two more disks, 180 Grit and 220 , then the third disk 320 and 600 wet and dry paper for metal sharpening. I still use them once in a while on a cabinet saw.

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