This article was published in the Spring 2008 edition of Woodturning Design.
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I’ve been spending a whole lot of time lately writing a book on Woodturning Accessories for All American Crafts, the publishers of Woodturning Design. I discovered while working on an expansion of an earlier article on Wooden Faceplates (http://www.davidreedsmith.com/Articles/WoodenFaceplate/WoodenFaceplates.htm) that I could use 2 mm Craft Foam and spray adhesive to build up a form and then use coarse abrasive to shape it however I liked. As the Guinevere pneumatic cushion ball sander had come out recently, shaping the foam into a ball was a pretty obvious step. All I had to do was figure out a way to cover the ball with abrasive.
Some “All”s are harder than others. I’ve lost track of how many different ways I tried. All of them worked, but I think the first version took about 5 minutes to change abrasive. I took several versions in for an extended show and tell at a Baltimore Area Turners meeting. When I was done, one of the guys asked me which version I liked best—and I couldn’t say. There seems to be an unavoidable trade-off between convenience and durability. Which approach is best depends on the application.
I really think the Foam Ball Sander has many advantages:
It’s not magic, but I do like the results. [Fig05 & Fig06] show a before and after of a 9” pear bowl I did with an early version of the Foam Ball Sander. I deliberately started sanding the interior after a rough gouge cut. Nine easy minutes later I had a better surface than I usually get.
This article will show how to make a Foam Ball Sander, how to modify abrasive discs to fit the ball, and three different ways to attach the abrasive. It’s a good idea to have at least some of the abrasive you intend to use on had before making the Foam Ball Sander. Where ease of changing abrasive is paramount, Velcro is used to attach modified loop backed discs. If you want to be more aggressive (or bought cheap loop discs that delaminate easily) you can add mechanical holding power by pinning the ends of the abrasive leaves between washers. If durability is paramount you can use modified cloth backed abrasive discs held between washers.
Plain for Velcro Only
If you want to make a Foam Ball Sander that has the abrasive attached with Velcro only, start by cutting a 3/8” plain steel rod to length. For bowl sanding you need the length to be about the diameter of the ball plus 1-1/2” (for instance about 3-1/2” for a 2” Foam Ball Sander). For sanding the inside of a vessel the length you need depends on the maximum depth of vessel. You can use drill rod, weldable steel, or the shank part of a long 3/8” bolt if you cut the head off.
Washer Backed for Mechanical & Reinforced Velcro
If you to use reinforced Velcro or a purely mechanical attachment, you need 3/8” rod that is at least partially threaded. 3/8” all-thread is the simplest thing to use, just cut to the same length you would for a plain mandrel. You will also need three 3/8” nuts and two washers. The size washer depends upon the size ball you want to make. I suggest using 5/16” plain washers (drill out to fit if necessary) for a 1” ball, and 3/8” fender washers for a 2” ball.
Prepare the washers. If you are making a Reinforced Velcro ball, cover one side of one washer with adhesive backed Velcro hook material. Cover the other washer with coarse (60 to 100 grit) abrasive. You could use PSA backed abrasive or spray adhesive with plain abrasive. A 3/8” hole punch will make this task much easier—lay the material hook or grit side down on the end grain of a scrap board, then whack the punch with a mallet.
If you are making a Mechanical Attachment ball, cover both washers with coarse abrasive.
Now assemble the mandrel. Spin a nut onto the all-thread about 2 inches. Drop the abrasive covered washer onto the all-thread with the abrasive away from the nut. Now add the other washer, so that the hook (or abrasive) side faces the abrasive of the first washer. Now spin two more nuts onto the all-thread.
The last two nuts will be locked in place by using two wrenches to tighten them against each other. For the 1” ball, lock them in place at the end of the all-thread [as in Fig07]. For the 2” ball, lock them in place ¾” from the end of the all-thread. Snug the other nut against the two locked nuts, holding the washers in place as in [Fig08]. You can cover the edges of the washer and last nut with a strip of masking tape to keep stray adhesive away [as in Fig08].
Foam & Shape
Mount the mandrel on your lathe with about ½” of mandrel plus the amount to be covered extending. A collet chuck is ideal for this, especially if you’re making a Foam Ball Sander for vessels, as you can choke up on the mandrel. You can also use #1 jaws on a 4-jaw chuck, or remove the top jaws from a 4-jaw chuck.
Spread some newsprint over your lathe bed to protect the ways, and spray adhesive on the mandrel while turning the lathe slowly by hand [Fig09].
The very nose of the Velcro only Foam Ball Sander will have a 3/8” hollow spot when applied. This doesn’t matter because the hollow will tend to close when shaping the ball, and because you should avoid using the nose dead on when sanding.
If you are using the Mechanical or Reinforced Velcro mandrel you will need to apply some foam to the center of the mandrel before winding the rest of the foam on. For the 1” ball, cut 4 circles of foam 5/8” in diameter. Spray adhesive on one side of the foam circles (hold them down with a finishing nail so the spray doesn’t blow them away) then stack them up on the end of the mandrel [as in Fig10].
For the 2” ball, cut a strip of foam that is ¼” wider than the distance from the last nut to the end of the all thread (1” if ¾” of all thread is exposed [Fig11]). Spray adhesive on the strip. Then wind the strip onto the exposed all thread until the level of the foam is equal to the diameter of the nuts [as in Fig12].
Now cut a strip of foam to form the bulk of the ball. For the Velcro only mandrel this strip should be ¼” more in width than the intended diameter of the Foam Ball Sander. For the Mechanical or Reinforced Velcro, this strip should be the width of the distance from the washer to the end of the filler foam you just applied. Wind the foam onto the mandrel by turning the lathe by hand in the direction it normally runs (top towards you) [Fig13 & Fig14]. Keep winding the foam on until you’ve built up the foam to a diameter slightly greater than the finished Foam Ball Sander is to be [as in Fig15]. For larger balls you’ll probably need more than one strip. Take a coffee break now to let the adhesive cure a bit.
Now prepare to shape the ball. Remove the newsprint from the lathe bed so turning on your dust collector will be less exciting. To prevent the ball from unwinding while it’s being shaped, do half of the ball at a time, protecting the other half with tape. Wrap masking tape or a narrow ripped strip of duct tape all the way around the tailstock third of the foam [Fig16]. Turn on the lathe at a moderate to fast speed and also turn on your dust collector. Use coarse abrasive (80 or 100 grit) backed up with a wood scrap to shape the back half of the ball [as in Fig17]. First bring the un-taped portion of the ball to round, then shape the back of the ball [Fig18].
Stop the lathe. Gently remove the strip of tape protecting the tailstock end of the ball. Apply another strip around the headstock end of the ball. Restart the lathe and shape the front of the ball [Fig19 & Fig20]. Now stop the lathe again and remove the protective tape.
Check to make sure the ball is a diameter that will work with the abrasive you have (I suggest 3” discs for the 1” ball, 6” discs for the 2” ball). For the Velcro only mandrel, just make sure that a disc bent around the ball covers most of it [as in Fig21]. For a Mechanical only ball, check that the disc can extend over the washer on both sides of the disc. For the Reinforced Velcro ball you have to be more finicky, as the thickness of the Velcro hook layer will throw the measurement off. Cut a ¼” wide strip of Velcro hook material as long as the diameter of your disc. Leave the backing on, but attach it via the hooks to the loop side of your disc. Now wrap the disc around the ball so that the Velcro strip is against the ball, and make sure that the both sides of the disc can extend over the washer. If necessary reduce the diameter of the ball by sanding some more. You should be past the stage where the foam might tend to unwrap under power, so you don’t need to tape and shape half at a time.
Now cover the foam with duct tape to protect it. For the Velcro only mandrel I suggest starting with a couple of strips that extend on to the metal mandrel [as in Fig22] just to make sure the mandrel doesn’t starting spinning freely within the foam. Finish up with a strip wrapped around the middle; other than that you can apply the tape in what ever fashion you like as long as it covers all the foam [Fig23]. Remove the mandrel from the lathe.
Unless you’re making a Mechnical only ball, now you can cover the ball with Velcro hook material. It doesn’t matter what pattern you use, so long as most of the ball is covered in an un-wrinkled fashion [Fig24]. Punched out circles seemed to be the most esthetically pleasing, but that probably isn’t the highest priority.
The Foam Ball Sander is now complete. [Fig25 shows a Velcro only 1” sander. Fig 26 shows a 1” Reinforced Velcro sander. Fig27 shows a larger Mechanical sander].
You can start with any source of abrasive you like, but it makes sense to start with discs because they are readily available and the pattern is round.
I’ve included two kinds of patterns for two sizes (1” and 2”) of Foam Ball Sanders [see Drawing1 and Drawing 2]. To conserve space the patterns are combined. To cut the abrasive with leaves that overlap, follow the black lines. To cut the abrasive with leaves that don’t overlap, follow the black straight lines and the red curved lines. The non-overlapping version looks a little neater, the overlapped version will last a little longer perhaps, and protect the underlying Velcro better.
The abrasive discs have to be modified to fit the ball. If you don’t have a scroll saw, then you’ll have to use trash scissors. Copy or print out the appropriate pattern [in Drawing 1] and attach it to thin cardboard with spray adhesive. Cut out the pattern. Use it to trace the cutting lines on the back of your abrasive and cut it out by hand.
If you have a scroll saw you can cut more efficiently. Copy or print out the appropriate pattern [in Drawing 1] and cut it into a circle. You may wish to write the grit with marker in the center of each disc for easy identification. Arrange the abrasive discs you wish to cut out into a stack (you can probably cut a ½” stack at one time) with the abrasive facing down. Tape the stack together at the edges with masking tape [as in Fig28]. Now tape the pattern on to the top of the stack [Fig29]. Adding a plain paper disk on the bottom of the stack will make sliding the stack on the saw easier. Take the stack over to your scroll saw and mount a medium (#5 to #7) blade that you don’t mind ruining. Cut out the pattern [Fig31], then remove the pattern and any tape from the top and bottom pieces [Fig32].
To load a Velcro only Foam Ball Sander, put the center of the abrasive on the top of the ball and press down the leaves of the abrasive one by one. If you are using an overlapping pattern you may have to tuck the last leaf under the first one.
To load a Reinforced Velcro Foam Ball Sander, first back off the nut and washer. Put the center of the abrasive on the top of the ball making sure it is centered well enough that all the leaves will overlap the Velcro covered washer. Press down the leaves one by one making sure the tips are pressed down on the Velcro covered washer. Tighten the nut so that the abrasive covered washer locks the abrasive in place even if the abrasive/loop delaminates.
To load a Mechanical Foam Ball Sander, first back off the nut and washer. Place the center of the abrasive on the top of the ball and hold it in place with one hand. Wind a rubber band around the middle of the ball to keep the abrasive in place [Fig33]. Now add another rubber band closer to the washer to bend the leaves inward [Fig34]. You can tug the leaves snug at this point. Drop the washer into place and tighten the nut to hold the abrasive in place [Fig35]. Even if it looks a little loose it will probably work just fine.
You can use a small Foam Ball Sander to sand the inside of a vessel. I wouldn’t suggest doing so when the wood is still wet, but if you sand the outside first the inside will probably be dry enough not to overly clog up the abrasive. You can also let the vessel dry and remount it on the lathe. Turning the lathe on at a very slow speed will make up for any wood movement while drying.
You can use the back third of the Foam Ball Sander to sand under the lip of the vessel [as in Fig36]. The side of the ball will sand the bulk of the sides of the vessel [Fig37 & Fig38]. Try to avoid straight on contact with the nose of the ball as much as possible except for the very bottom, as this will make the Foam Ball Sander unstable in the same fashion as a foam backed disc is all the time. Stop the lathe and blow out the interior regularly, and make sure any defects you can’t tolerate are gone before moving to a finer grit.
I think you’ll find that sanding the interior of a vessel with a Foam Ball Sander will go much more quickly—whereas before it was almost only possible for those with Obsessive Compulsive Personality Disorder. I’ve heard that in the realm of artistic turning, if you can, then you must. If so, sorry about that.
Sanding a Bowl On the Lathe
Subjectively the Foam Ball Sander feels much nicer than a disc when sanding a bowl on the lathe. The only problem is that the chuck may prevent you from sanding the near the foot of the bowl and that you can’t sand details with a radius less than the radius of the ball.
When sanding the outside of a bowl it helps to have the bowl turning in reverse to maximize the speed of the abrasive relative to the wood [Fig39]. Avoid contacting the very nose of the ball.
Use the side of the ball as much as possible when sanding the inside of the bowl [Fig40]. Have the lathe turning forwards. Angle the ball when sanding the bottom to avoid contacting the very nose of the ball [Fig41]. You can stop the lathe and angle the ball to sand with the grain on the bottom of the bowl after each grit.
Use the side of the ball to sand the edge of a bowl. If the lathe is turning forward, sand at the front edge of the bowl [Fig42].
You can also stop the lathe to do spot sanding of defects. Since the Foam Ball Sander is so stable, you don’t have to lock the lathe spindle, but instead hold the bowl in place with one hand and the drill with the other [Fig43].
Sanding a Bowl Off the Lathe
If you reverse turn a bowl using a tailstock center for support and leave a small nub which is then cut or broken off, the Foam Ball Sander will almost instantly erase all the evidence. It’s easier to see what you’re doing with the 1” Foam Ball Sander.
You can use the Foam Ball Sander to sand the inside of a bowl off the lathe that has been finish turned while green and dried. Ordinarily I’m not a fan of finish turning bowls while green, as once you build up a stock of green rough turned bowls you don’t have to. But sometimes you need to hurry—maybe a thank you bowl for donated wood from someone with delayed gratification problems. I also don’t like sanding wet wood on the lathe—it tends to be slow, frustrating, and have high wastage rates for sandpaper. In my basement a finish turned from green bowl will dry in a week. If that’s not fast enough, a thin bowl will microwave dry easily. Try giving the bowl 2 minutes at 30% power (enough to make it warm) and let it cool. Weigh the bowl, then repeat until no weight change is seen.
You can mount the Foam Ball Sander in a drill chuck in your lathe [Fig 44] if you use a draw bar. The only drawback to this method is that it’s hard to see what you’re doing. You could consider mounting the Foam Ball Sander on your drill press if you can rig up dust collection. I’ve heard that lateral stress is not especially good for a drill press though. Since the Foam Ball Sander is so stable in use you can also just hand hold the bowl and drill while standing near your lathe’s dust collector [Fig45]. The Foam Ball Sander isn’t especially efficient on the outside of a bowl when hand held, but you could use a pneumatic cushion drum sander, or apply the same foam trick in this article to a drum, or wait for the book…[Fig46]
Materials & Tools
David Reed Smith is a Basement Woodturner and tinker living