Thanks for the help I received
in figuring out what type of sandpaper to get. I've successfully made 2 of the things and it was so easy I almost wondered if I could make them and sell them...but the market is pretty low for such things. Anyway, my wife is a happier scroll sawer now and I've found a few good uses for them too.
This is all basically just a rehash of the excellent DIY sanding mop blog post
. Some things (like the bulk sandpaper) aren't pertinent anymore though, so maybe this is a little more up to date.
Start off with getting the correct parts. It can all be had at woodworkingshop.com
. I tried to get something for the mandrel at my local surplus store, but all they had was motor arbors. It would have taken making a shaft for the thing, and it added a lot of un-needed weight. So, the mandrels at woodworkingshop are exactly what you need. I ended up getting the XL one but in retrospect you probably only need the standard sized one since I ended up with close to an 1" extra threads when it was all done.
For sandpaper, get the cloth-backed roll, 2" wide
, whatever grit you're wanting. I agonized for a while as to what length to get, but I decided on 10 meter and it was just about perfect. I used the whole roll.
I made a template for cutting the slits in the sandpaper. Two pieces of 3/8" plywood worked great, 2" wide by 6" long. I taped them on top of each other with packing tape so I could cut both at the same time. I marked off 1/8" intervals on the end, and a line at 2" from the end. That will give me 2" of slitted sandpaper on each end and 2" of solid paper in the middle. I used the bandsaw for the slits. I set the fence so the blade was right at the mark on the end and then cut up to the 2" line. I then flipped the pieces over and cut the other side before moving the fence for the next mark. Quick work and very nice straight lines. Before taking the pieces apart, make sure and drill the 1/2" center hole for the mandrel.
Take the roll of sandpaper, measure off 6" and cut with scissors. Then, using that piece as a template, cut the rest of the roll into 6" pieces. It doesn't take long.
Stack up the pieces into 2 stacks. Sandwich them between the plywood and wrap it all with packing tape. Now take it to the bandsaw. You don't have to use the fence this time, just freehand the blade into the slots in the plywood. I got some occassional sparks from this, as the blade hit the sandpaper. I tried orienting all of my sandpaper so that the abrasive side was down, so that the blade was cutting from the cloth side...I think that helped.
NOTE: You are essentially sanding your bandsaw blade doing this....in other words, it will never cut wood again happily. So, only use a blade you don't care about (or find pre-cut sandpaper made for sanding mops...it's out there). You could also use a scrollsaw instead, as those blades are much cheaper and easier to replace.
Once cut, go to the drill press and drill through the stack for the mandrel hole. Then repeat for your other stack of sandpaper.
You end up with a big pile of 6" sandpaper pieces with slits and holes. You're almost there. Take the mandrel and clamp it upside down. Now, take 2 pieces of sandpaper and place them cloth-to-cloth, so you end up with abrasive on both sides. Slide it down the mandrel. Do it again, but the next set is 90 deg to the first. The next set is offset 45 deg and the next one after that is 90 to the previous again.
After doing that whole thing twice (so, 8 sandpaper sets), I added a washer for spacing. I couldn't find any washers big enough so I used a 1" hole saw and some 1/8" plywood, then drilled out a 1/2" hole in the middle. I think it took 4 for the whole thing. So, sandpaper X 8, then spacer, then repeat. When you're finally done, put the mandrel support ring and nut on the end and tighten down until the sandpaper on the top and bottom of the mandrel does not freely move.
If you're doing more than 1, take a nail and scratch the grit number into the top of the mandrel support ring so you can easily find the one you need.