A couple weeks back I posted an Instructable about needing a radius sanding device for my scroll saw.
I've seen other Instructables about similar ideas, but this was for a specific project that turned out better than I had hoped. I realized a few things though, both good and not-so-good, and I also came up with a final product which you'll see at the end.
For this relatively simple Instructable (the way I made it at least), you'll need:
- A set of cheapo Harbor Freight blades. After I bought better blades from Ryobi, I saved these particularly for emergency/experimental purposes
- Painters tape, but really any other type should be fine
- 5 pcs of ~11/16" thick plywood. 5/8" should work too
- Average can of WD-40
- Tape Measure
- Gorilla Wood Glue
- 3M Super 77 Spray Adhesive
- Zip Ties
- Some type of thin scrap metal bent at a loose right angle, about 1"x2" should do. Size isn't too critical
- (optional) Metal Lathe/Wood Lathe
- (optional) Milling Machine
I decided I wanted to elaborate on this mod and experiment with other shapes and sizes.
The first thing I realized with the original was that while it worked great for the small stuff, the blade flexed too much at the ends and the surface area was so small that the paper wore out too quickly. Having a good way to remove the paper and any excess adhesive is crucial, but can be kind of time-consuming by manual means. Otherwise you'll spend most of your time cursing and hating me for suggesting such a idea. One alternative which isn't too cost-effective is to make a bunch of them to store for other jobs.
The only real way to eliminate any flex in the blade is to make the dowel/drumstick/etc. nearly as long as the blade itself, so there isn't much room to wiggle about. I would suggest making the rod as long as the toothed area.
Once I had those variables in mind, I proceeded to find other ways to improve this concept and try out some different styles....
Step 1: Making a Square/Flat Surface Sander
Now, I'm not perfect, and now I know that it's probably just going to be better to use a flat piece of glass with spray adhesive on sandpaper to make a good flat surface. I tried to make a flat sanding block for the scroll saw, and upon its first use I learned some other points to consider.
The working surface was way too short, and the blade also had a lot of flex, but this time it also had severe rotational issues, as you can see in the video.
A way to fix all of this is to, again, make the height of the block taller so that there is very little play on the ends. A couple of factors led to the twisting: I should have used a wider kerf blade. I believe that one was a fine tooth for thin veneers and thin ply. Also for some reason that I have yet to figure out, there is another mount on my machine for a second blade, but it's rotated 90 degrees, luckily its center point lies exactly 5/16" from the normal blade. SO in theory, I could put two wide blades on one piece and it would be significantly more stable. I did not however, as you also should notice in the video.
Step 2: Trying Out a Slightly Larger Radius
This one worked out a little better. Thicker blade and a bit taller (but not too much, I still hadn't learned my lesson from the previous cube yet). I think in the near future I will take it to work and turn it down to a proper 1.5" diameter.
The wood came from a stool that I cut the legs off of.. No biggie. Again I zip-tied the wet sand paper to the form to keep it all tight together.
Results were nearly as expected, apart from not aligning the saw blade vertically, so all the surface I had to work with was about an inch, maybe less, which is sub-optimal.
Once I figured out that I needed a tall drum to eliminate flex and rotation, I began to wonder just how large I could make the drum as to fit in the hole without the guard...
Step 3: The Meat of the Story: the Final Product, Step 1
I measured the hole without the cover and the diameter is 2.75", so I figured 2.625" is a good safe maximum diameter for the drum. The safest maximum height for the drum should be 4.5", enclosing most of the blade.
I recently took home a section (8' x 2' x .687") of smooth finish 12-ply that I was able to get from work, a rare find at a sheet metal shop. We often do countertops at work out of 20ga #3 Brushed 304 SS, and this wood is usually what customers bring in for us to cover. All the bosses had no idea what it was for so they let me take it home.
Anyways, I used drops from a section I cut out for sign backboards and traced the bottom of the WD-40 can onto 5 cutouts. I then cut them and sanded them roughly to size, finding the centers for two of the discs which would be the ends. I then glued them all together, wrapped the circumference with the painters tape to keep them fairly aligned, and put a large object on top to keep them pressed well together.
The next morning I took it to work to turn on the lathe we have...
Step 4: The Meat of the Story: the Final Product, Step 2
(This step is necessary but it would also work on a cheaper wood lathe. I only have access to a metal lathe at work)
I turned it and sanded it to 2.25" diameter with the height at 3.25". I just wanted to make sure I had reasonable clearance on all axes. I did have to remove one of the covers on the underside to be able to fit it through completely. No biggie, just toss it aside.
Once I fit the blade through using needlenose pliers and some persuasion, I shimmed one end with slivers of scrap trimmings and wrapped the other end in painters tape to keep it plugged and in place. I had the blade fairly tight in the top so I was only able to get a few drops of glue in every couple of hours. once it dried enough to test, I tried it without sandpaper and it crazily shook the table at any speed... The only solution was to take it back to work again and drill out the core to reduce as much mass as possible.
Step 5: FINALE!!
(This step assumes that you have access to a milling machine. Although a hand drill would technically work, I don't recommend it.)
I loosely scribed out a 6-hole pattern and chucked it in the vice and drilled thru-holes with a 17/32" drill. It was a good drill with a decent tip. Most of our other drills are either gummed up with Aluminum or broken, waiting on me to resharpen (pfffft, fat chance).
Once I got home I wrapped it with 2 sections of cloth sandpaper, 7.312" x 1.5". The drill holes worked perfectly! I can't wait to try it out!
I hope this has shown you clearly enough. I usually only remember to snap pics at the last possible moment if at all, so if you have any questions or suggestions I'd love to hear them!
Thanks again for reading.
Never stop learning.