Intro: Very Cheap Wood Sanding Machine From an Angle Grinder
I make objects from recycled pallet wood. The main problem is the recycled wood is very rough and sometimes dirty. I can't afford a drum sander or a planer thicknesser but had a dying angle grinder that was itching to become something better. I decided to design a box to run the lengths of wood through. In the bottom I wanted to fit the angle grinder fitted with a flap wheel so that it took a set amount off the wood as it passed through. Now that I have expertly and succinctly described my wondrous invention, you had best look at the pictures instead.
The only outlay was for an offcut of 13mm plywood £2.00, a length of m5 threaded rod £2, and some wing nuts and t nuts @ £1.
as I already had the angle grinder and the flap wheel. I have included dimensioned Sketchup diagrams and these were based on a 115mm grinder and with sufficient depth for 20mm thick wood. You may have to adjust your dimensions but none of this was rocket science.
Step 1: Getting Started
The width of the boards is determined by the width of the flap wheel. I didn't want any gaps between the uprights and the flap wheel so that the unsanded board could miss being smoothed. I was using 13mm plywood so the width was wheel diameter + 13mm x2.
I didn't want the box to be too long as the wood generally comes out at 80 to 100 cm and as it would be fed by hand, it needed to emerge from the end of the box before the end of the wood entered the front of the box. I decided 500mm would be adequate for this purpose.
Once cut to length and width I cut the hole for the wheel with a router, this could easily be done with a jigsaw but I was lucky enough to be able to peg the router in the centre of the circle through a hole in the router mounting plate and the bit tracked out at the right circumference to cut the hole.
Step 2: The Rest of the Box
The top board is dimensioned the same as the bottom. A hole was centred above the flap wheel and made to accept the dust extraction pipe. There is going to be a lot of dust and I didn't want it clogging the box and stopping the wood from sliding through.
The sides were simply made to the accept the maximum thickness of wood I planned to sand plus 15mm to allow for the combs to be fixed in place. More on them later.
The sides were glued and clamped in place on the bottom board, the top was set aside for later on.
Step 3: The Infill Piece
As the unsanded wood is fed through, it will reduce in thickness after sanding. Without raising the receiving side of the bottom board this would cause an uneven pass. So to remedy this I glued a piece of 3mm ply to the receiving side. Once dried I routed the end overhanging the flap wheel hole flush. The grinder body would be set at an angle to receive the wood at the lower level and rising to be level with the raised receiver. The theory would be that the length of wood would be in contact with the bottom board throughout the operation giving a consistent thickness throughout the pass.
Step 4: Mounting the Angle Grinder
The next step is to make and fix the pillar blocks. Please note, I had to change the dimensions of the blocks as I miscalculated the bore required to hold the grinder, I used a 75mm hole cutter , The width and depth of the blocks were suitable increased.
So using some scrap 18mm ply scrounged from the wood bin I cut a 75mm hole in the centre of the block (twice). Once the hole was cut, the blocks were cut in half on the bandsaw, giving two sets of halves. The two halves that would be mounted to the bottom board had a bit nibbled out of the bottom to accepted the M5 Tee nuts. (This wouldn't have been necessary had I been able to source some M5 countersunk bolts to go through the whole assembly and then drilled through from top to bottom to allow the threaded bar to go through. The pillar blocks were then screwed and glued to the bottom board at a suitable distance to securely hold the angle grinder. The photographs show this better than my description. The M5 threaded bar was then screwed through the blocks ready to accept the grinder and then the top blocks. Wing nuts would keep the grinder secure but easily removable. A large self tapper was mounted in the rear to allow the grinder to be adjusted for angle.
Step 5: The Combs
The design would require a method of holding the wood down as it passes through the box, this is necessary to ensure an consistent pass and to stop the wood bouncing about like a demented frog as it meets the flap wheel spinning at 10000rpm.
After considering bearings and spring loaded mechanisms I decided to keep it simple. I often get plastic drums from the local car wash, they get through loads of them and are happy to give them away. I had one that had been used to hold an engine part that needed cleaning. This was cut into strips with a saw, then scored with a dremel at the halfway point. After this the comb was bent through 90 degrees and a soldering iron was used to weld it into a permanent angle. The teeth were then cut out. This was then screwed into the top board before and after the hole for the flap wheel. In the photograph you will see three combs but on my test run it provided too much friction and didn't really add anything in downward pressure so the third was removed.
Step 6: Connecting It All Up
Now it is just a case of setting it all up. The grinder is fitted into the pillar blocks. The adjusting screw is turned up and down to enable the lower end of the flap wheel to be flush with the lower bottom board and the top of the flap wheel to be flush with the top of the bottom board. Finally ensure the the flap wheel is laterally square in the hole so it sands evenly across the width. This can be quite fiddly, in fact a fair bit of patience was required before it was set correctly.
The top is mounted onto the box I decided to use more M5 Tee nuts and threaded rod. So I drilled all the way through the bottom board, uprights and out the top board. This was then fastened down with wing nuts. It would be just as easy to use self tappers but I am wary of the longevity of using self tappers into the end grain of plywood. During testing I did use self tappers but this was because it was quicker to unscrew them with a drilldriver than to unfasten wing nuts with arthritic hands. Once set the wing nuts will be used exclusively.
I cut a block of 18mm ply to the dimensions of the total depth of the pillar blocks with angle grinder in place to allow the box to be clamped to the bench, the was then glued and screwed to the bottom board.
Finally I cut a old dyson vacuum pipe and stuck it in the dust extraction hole so I could attach my vacuum cleaner to it. Sorry no shop vac yet, a free used and unloved Dyson is as good as it gets for now.
There are two pictures of it in operation, the first is a close up of the raw wood and the second after it had taken two passes on each side.
The result was very pleasing, the sanded wood is splinter free and quite smooth, certainly smooth enough to use for my garden furniture products. All in all this is a cheap and easy way to very quickly prepare recycled wood for its' next life.
I hope you enjoy and if you find it useful, all the better.