Portable 2in1 Disc & Drum Sander

#woodworking #electronics #mechanics #design

In this instructable - full in depth build of the Portable 2in1 Disc & Drum Sander. It has integrated 12V 7Ah lead acid battery and is powered with the model 895 12-24V DC motor. If I need more power or I have a lot of sanding to do, I can easily plug an external 12-24V power supply. Sander has two dust ports, one for the disc and one for the drum.

This project focuses on portability and convenience for very small workspaces. If you look for a powerful sander, you should look elsewhere. Realistic power while using the sander is ~30W @12V and ~100W @24V. But despite being low on power, it works like it should, only the sanding takes longer.

So again, this tool is more for the occasional woodworker with a tiny workspace.

FREE SketchUp 3D model - http://bit.ly/PortableSander3D

Provided Amazon links are affiliates.

Main Tools:

• 12V drill: https://amzn.to/2U5QQmL
• 20V drill https://amzn.to/2MY3GRt
• Jigsaw https://amzn.to/2rg4uXx
• Router https://amzn.to/2DVXXZC
• Rotary tool https://amzn.to/2MWaP4H
• Multimeter https://amzn.to/2MTl4Xs
• Tachometer https://amzn.to/2MtYmWW
• Clamps https://amzn.to/2YKWmRS
• Speed square https://amzn.to/2Ee6lDh
• Hole-saw set https://amzn.to/2pcizay
• Spade bit set https://amzn.to/2J8iPP3
• Combination square https://amzn.to/2oLYnwv
• Fretsaw https://amzn.to/33LcvVr
• Basic chisel set https://amzn.to/32xld9G
• Flexible drill extension https://amzn.to/2oZthBl
• Small drill chuck https://amzn.to/32y7yix

Main Components & Materials:

• 895 motor low-speed https://amzn.to/2BuIxsA
• Bracket for the motor https://amzn.to/2VZhuiG
• 12V 7Ah sealed lead acid battery https://amzn.to/2W1lfUL
• 8mm x 300mm shaft https://amzn.to/2P19ufG
• Bearings with holders https://amzn.to/31p91q4
• 20T 5B pulley https://amzn.to/2J1tjPV
• 60T 8B pulley https://amzn.to/2VXHyec
• Timing belts https://amzn.to/35QXSld
• ON-OFF-ON switch https://amzn.to/2quO6Fn
• Dust cap https://amzn.to/2oLYhVD
• Terminal block https://amzn.to/2MuDLle
• Spade crimp terminals https://amzn.to/2VY2jq5
• Power connectors https://amzn.to/2VWyFBo
• Power plug https://amzn.to/2VZfkjd
• Fuses https://amzn.to/2p1O0oj
• Optional 10A motor speed controller https://amzn.to/2N3DW6h
• 150mm/6inch sanding disc https://amzn.to/2VZpJeC
• Sandpaper roll https://amzn.to/31BliIh
• Threaded e-nut M4 size https://amzn.to/2MwI7s7
• Cold-weld compound https://amzn.to/35O9Yvv

Other Things:

Bolts, screws, washers, wires, heat shrink tube, right angle fastener, hinges, lock,

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Few photos of the build. If you want all the dimensions you can download the free SketchUp 3D model of this build - http://bit.ly/PortableSander3D

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Previously I cut my project pieces one at a time, immediately tested if it fits the others, and did another cut. But it takes way too long. So this time I tried to cut everything in one go. Meaning that I need to measure and cut very precisely. But is that realistic on the jigsaw table like mine? Well yes, later I needed to trim just a few pieces. It was much faster this way. With all the parts cut from a 12mm thick plywood, I placed main frame parts and made more cuts.

I glued parts one by one. It is time-consuming, but it’s easy to get perfect results.

With only one side glued, I made the hole for the dust port. The design of it is simple. As my vacuum connector’s outer diameter is 35mm there will be three pieces (including hole in the side) of the plywood with 35mm holes. And the last one will be with 25mm as this is the inner diameter of the connector. It will also act as a stop block for the max depth.

To make the 150mm and 100mm discs for the sander, I used a router. This can be done with a jigsaw, but later you will need to do a lot more of sanding, to get a perfectly round circle.

You can see how the back of the disc should look like. 150mm and 100mm discs glued together, 8mm hole drilled not all the way through, in the end a 2mm hole, four holes and two groves in the 100mm disc.

I deliberately cut the 150mm disc in a bigger piece, that later I could use it for the bottom of the disc. I also routed the edges of the pieces for the wires from the battery to go through.

These parts won’t be disassembled in the future, so gluing makes perfect sense, as you can precisely place and adjust it how you need it. Back and top support parts will be permanent too. All these glued parts is the key to the perfect alignment of other parts.

I made the hole in the top part for the 60T pulley and the 200mm length belt to go through.

Other parts here are two bearings integrated into the holders, 300mm long and 8mm thick shaft, 20T pulley, motor holder with bolts and the model 895 12-24V DC motor.

This is the “low-speed” variant, which means that you will get 3000RPM at 12V instead of 6000RPM on the “high-speed” variant. Max voltage for the motor is 24V and at this voltage, you will get ~7000RPM.

To make the drum, I cut 7 pieces of ~40mm diameter with a hole saw bit. For this, you better have good bits to avoid the struggle. When I had all the pieces, I stacked them on the shaft. I used a spare short one, but you can easily use the main one. Even when drilled with an 8mm drill bit, they fit snugly onto the shaft. I sanded it until I get a nice and round surface.

To finish the drum, I cut one smaller piece and drilled a hole into the side. When glued on top of the drum, it will be a spot for the threaded e-nut. Just make sure to drill big enough hole and clamp the parts while threading in, that the nut wouldn’t split the plywood. With a small bolt in, now I can tighten the drum to the shaft.

Only one thing is missing – the sandpaper. To secure it to the drum, I just made a groove. The sandpaper goes inside and wraps around the drum. And the end of the sandpaper, I just glued with a double side tape. Very simple and effective. Only one condition – you need to start wrapping sandpaper in the opposite direction that the drum spins.

On the end where the disc will be, I roughen the shaft as much as I could with 60-grit sandpaper. Then with a rotary tool, I cut out small grooves vertically and horizontally. The rougher it looks the better it will bond to a “cold weld” type bonding compound.

This type of compound has a very bad and strong smell, so better do this in a well-ventilated area. You can see that the routed circle is for that the compound wouldn’t spread too much. It should cover the 8mm hole and a little bit around it. Without that smaller hole in the end, you won’t be able to push in the shaft, as the compound is very viscous. It also usually has a very short set time, so I had to set everything square quickly.

I finished securing the shaft to the disc with four extra screws and washers. Just try not to drill into holes, which were previously made in the disc.

I started making holes in the parts, where the shaft with the drum comes out. Three holes of 62mm, bottom one of 10mm and top one of 50mm. Then, I rounded inside edges of the top part for the best airflow.

I made similar dust port like before and glued the parts. When glue completely dried up, I made a hole that directly goes into the 62mm hole where the drum will be. Inside edges should be sanded as round as possible, again to minimize restriction of the airflow. And then, that part just glues to the back cover.

To mount the shaft, I marked and drilled pilot holes for the bearing holders and secured the parts, which won’t be disassembled later. After securing the bearings, don’t forget to tighten all the screws on them, and on the big pulley.

When mounting a motor, it is important that the shaft of it will be parallel with the 8mm shaft. It will give even tension across all the width of the belt, which will minimize the wear of it. As the bracket has wide holes for the screws, you will still be able to adjust it slightly with a trial and error method, after you drill the pilot holes.

Also, it’s a good idea to grind a flat spot on the motor’s shaft for the pulley, as here the motor transfers full force to it. The belt should be neither loose, neither too tight. In the last photo is an example of how it looks when the motor is instantly powered with 12V. Not much play, but also not too tight.

Next, I really wanted to finish the disc, so I added extension wires for the motor, put on the belt and clamped the top. I powered the motor with the 12V battery and sanded edges with a chisel to get a perfect balance and reduce all vibrations.

I applied few coats of hard varnish, as I will be using sanding pads with a sticky back, rather than with a Velcro hook and loop system. It will give more consistent sanding results.

Finally, it is wiring time. I made the hole for the 3-position switch. It is important that it could handle at least 10A. The design of the circuit is pretty simple here.

When the switch is at the first position, the motor is powered from the internal 12V sealed lead-acid battery. When the switch is at the OFF position, the battery and the power supply are disconnected. When the switch is at the second position, the motor is powered from the external power supply.

Circuit connection:

• First, the battery charge port’s positive and negative wires connects directly to the battery, it is just an extension of the wires for easy access.
• Next negative wires from the battery, external power supply, and the motor connects together.
• The positive wire from the motor goes to the middle connector of the switch, and positive wires of the battery and the power supply to the outside contacts.
• Also, it would be a great idea to add a 10A fuse from the outgoing positive wire from the battery for safety in case of a short circuit.

Where I could, I added crimp terminals and heat-shrink tubing for the insulation.

Finally, I secured the top with four screws in each corner. Then, the hinges and the lock to the door. It’s nice to have quick and easy access to all wiring and charging port when needed.

You additionally can grind a flat spot at the end, to add even more grip, if the drum slips from the shaft.

Now, not much left to do. I just need to secure the backside with four screws, add the drum and tighten it, add the top cover to neatly hide bearings and the shaft, and finally add the battery cover.

Make sure that the battery is not fully sealed inside the box and there are some gaps, as sealed lead acid batteries can produce hydrogen gasses (which isn't toxic, but is flammable) when you charge them.

I also put on a dust-proof cap to the switch, as it should be. And now, how I like to say it, the build is complete.

The only thing that I additionally made, was this abomination. It’s a cable, that plugs into the socket for charging the internal battery. But it additionally has soldered 6A fuse and different length contacts. Safety over looks, right?

While you read this instructable, I bet you had a question, “how the hell he will sand with the drum without tipping the whole thing?” So, as the battery weights almost the same as a whole construction, it gives a lot of mass to the bottom and prevents it from tipping. But of course, you should clamp it while sanding. I clamp it to my jigsaw table’s rip fence. And when I am super lazy, I just sand while it lies on the table.

Sanding with the drum takes some time, but not too long, considering this is hard plywood and I need to remove relatively a lot of material.

Meanwhile sanding with the disc is a lot faster. But what’s the most impressive, is that all of this works from the 12V battery.

For a lot of sanding more quickly, I just need to plug the external power supply. But I think, I should talk more about that. At 12V, starting the motor from a standstill, there isn’t too much starting current and force to be worried about fast wear of the belt and the bearings. But at 24V there will be way more forces and especially high starting current (my measurements aren't fully realistic, as multimeters usually shows value with some delay. Realistic start/inrush current without power supply limits should be around the value as the motor's stall current - last picture).

So to eliminate that, you can use a motor speed controller like in the first and the second photo.

Every time you start a motor, you rotate the potentiometer until you reach the desired speed. Personally, I just like to do this trick – I start the motor with an internal 12V battery and then switch to a higher voltage like 24V from a power supply.

If anyone knows a very simple DC motor soft start circuit, please post it in the comments. I would appreciate that.

Realistic power while using the sander is ~30W @12V and ~100W @24V.

If you will be running the sander at 24V, make sure to make some sort of cooling for the motor. I just added 4000 RPM 12V 60x60x25 fan with the LM2596 buck converter. The fan wires goes to the converter, and wires from the converter goes on the motor's positive and negative contacts. The module will reduce the voltage for the fan to ~12V even if the motor will be powered with 24V.

Overall, I call this project a huge success! It allows me to sand outside and inside curves with one tool, much faster and way more precisely than I ever could do it before.

For a tiny workspace like mine, it is a very convenient tool!

I hope this instructable / video was useful and informative.
If you liked it, you can support me by liking this Instructable / YouTube video and subscribing for more future content. Feel free to leave any questions about this build. Thank you, for reading / watching! Till next time! :)

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