Doug Harris contributes a summary of responses to his question:

I found a plastic grocery bag full of old tennis balls in the dumpster behind my house a couple of weeks ago and am considering making some exerballs out of three of them. I figured I'd probably drill a small hole in them, fill with some sort of gunshot somethings, fill up the empty space with something somewhat lighter, and reseal with something like rubber cement. Has anybody out there every tried this (successfully or unsuccessfully)?

Specifically, I'd like advice about:

  1. what to use for the filling, I have no experience with guns and ammo and so don't even know what my choices are
  2. the best way to reseal the ball after filling
  3. what substance to use to fill up the space (millet? water?)

Jack Cunniff

Well, personally, I'd stay away from the buckshot - you really don't want to be responsible for all that lead - it's a health hazard, and might be too heavy.

One of my friends made exerballs from tennis balls - he filled them with pennies - crammed them full. No other filler (millet, water, sand) is really necessary - remember, if the ball has no give (because it's full), it'll hurt you over time more than it will help build strength.

Re sealing - stores selling athletic shoes frequently sell shoe repair glue, I've heard off "Shoe Goo" as a brand-name. This will nicely seal the ball. (you only need to make a slit big enough for a few pennies to fit through - any larger and it's more likely to break open during use. One other nice touch is to put the glued-shut tennis ball into a round balloon, I think the 10" round is the right size (uninflated, of course :-) That gives a nice surface to work with, as well as protecting the glued hole. A recent posting said that the balloon lasts longer if the balls are frequently used - skin oil replenishing the balloon or something like that?

Marty Sasaki

filling Because of concerns about lead in the environment, and lead shot in birds that are eaten, gun shops can offer steel or iron shot rather than lead.

resealing I would think that cutting a slit in the balls would be better than drilling a hole. With a slit, you don't have to replace any material, just close up the hole.

scott snyder

I made some of these this summer. I don't know much about guns either, but i looked around the local hardware store and found some boxes of lead air-gun pellets. These worked reasonably well, despite being non-spherical, but they did have one significant problem. The first time i went to the store, i didn't get enough, so i went back to get some more. There was a different clerk that time, though, and she informed me that one is supposed to have an ATF license to buy the things. Well, after explaining what i planned to do with them (and after mentioning that i had just bought a bunch of the things from the same store the previous day) they let me buy them, but that was a bit of a hassle. There was also a small amount of oil on the pellets, which made handling them a bit messier.

I've since discovered, however, that scuba shops often sell large bags of lead shot (for weight belts). If i were to do this again, that would be the first place that i'd look.

Actually making them was fairly easy: i used a razor knife to make a small slit in the balls, then filled them with pellets through a funnel. The last little bit i had to pack in by hand. I was able to get the packing fairly tight, so i didn't bother with any sort of filler. They've since settled a little, though it's not enough to be annoying. (I probably should have bounced them around a little, though, before sealing them.) I used epoxy to seal them up, by smearing it on the inner edges of the slit and along the outside surface and letting it set for a day. It came out looking somewhat sloppy, but so far has held up fine.

You should see people's expressions when i first give them one of my tennis balls to handle :-).

Steven M. Salberg

what substance to use to fill up the space (millet? water?)

Doug, I don't think you can leave *any* extra space because no matter what you fill it with (except more of what you are already using) the ball will be off-centered and it will fly through the air like a drunken trapeze artist and jump out of your hands like a clown caught in the lion's cage.

No scientific proof here, just speculation.

Allen Knutson

In my experience, this is only a problem if the weight is glued to the side and is a fairly small fraction of the volume. In particular, I made a great many very usable juggling tennis balls that only had 40 pennies per. BTW, nobody's mentioned putting TAPE around the ball to keep it from splitting.

Cloth tape works nicely, and doesn't change the feel significantly.

Daniel J Mitchell

Given I'm in the UK and thus have more problems getting ammunition than the average US resident, I wound up using fishing weights; these are actually small lumps of (presumably) cast-iron (as lead's banned for fishing due to too many poisoned swans) which are certainly plenty heavy, and also a lot cheaper than buying the equivalent amount of shot. (why this should be is a mystery to me).

To fill the ball I wound up cutting a slit about 2" long in one side (down a 'seam', purely as it's easier to see what's going on there), and wedging the weights in place -- this required cutting some into smaller pieces to avoid large gaps, but your mileage may vary.

Once I'd wedged as many bits of metal as seemed sensible into the balls, I poured salt in until it started to overflow -- this isn't as much as could actually be fitted in with extra pressure to pack it down, but if I wanted as much weight as was humanly possible I'd be using shot. Next the slit needed cleaning up, then I used Araldite (epoxy resin) to seal it, on the grounds that it needed to be a strong glue which had at least minimal gap-filling properties.

(then rubber cement to seal it, then gaffer tape just to make sure; I've had the things split and spray salt all over the place too many times to risk anything less).

Note that the salt helps in two ways; firstly to stop the weights rattling around inside, and secondly as it pads out the corners somewhat, making it more comfortable to catch.

(though, of course, millet/sand/whatever would work just fine. Water is probably a bad idea, purely as it'd leak out very easily, and would be difficult to fill with.)

Phil Paxton

I dunno about the water -- if it leaked out so easily, why are tennis balls able to retain (air) pressure? I've come across several people who have injected water into tennis balls for weight. I think the preferable method was to use two syringes -- one for injecting the water, the second for allowing the air to escape as the water displaces it. A dab of sealant over the holes seemed to fix concerns about leaking.

Daniel J Mitchell

About the balance thing; I'll back up the claims that it really doesn't make much difference if they're not perfectly weighted -- even if they weren't to start with, unless it's filled with something very unyielding, the weight should even itself up somewhat as you juggle them anyway. It needs a /lot/ of off-centeredness to cause problems.

Dave Boll

about using water...

I've done this successfully quite a bit, with no double syringe or sealant used. I use a large sized (20cc) needle, and after pushing in a needlefull of water, the excess air pressure will cause air to naturally flow back into the needle. By being careful with the depth of the needle in the ball it is possible to remove every bit of the air. The syringe I use (which is labelled B-D 20cc Syringe) has a detachable needle - maybe they all do, I don't know - which allows you to refill the water without pulling the needle out, so you make only one hole in your ball. The ball will seal itself after pulling the needle out. A tennis ball takes between 3 and 4 injections with a needle of this size.

If you overfill with water, the ball will be ever so slightly damp for a while as the rubber contracts, but no biggie. The resulting ball is close enough to the size and weight of a lacrosse ball (which I also use) to be juggled or passed together.

I highly recommend these as a cheapie alternative to other balls. With a syringe, you can make one of these in under 5 minutes, the balls still bounce somewhat, they're a decent size for juggling, and the cost is minimal (assuming you got the tennis balls for free from a tennis player). One tip on getting free balls: I went to a college rec center that was close to some courts & asked if they had picked up any extra balls from the roof, or on the courts, etc. I was given a box of 50 or so. Some were kinda dirty, but I threw them in the washing machine and they came out fine. I filled half of them with water (it's still nice to have unfilled ones for indoor juggling) a while back and have had no leakage problems at all.

GReg Cohen

I've done this bit as well. I use a catheter needle which I insert at the seam (without the plunger!) I then put the whole ball under a running tap. By squeezing the ball and letting it relax, you can fill the ball with only one hole quickly. If your careful, and back the needle out while filling, you can get all of the air out. If this is done the ball will still bounce. (these can be fun if you play tennis, or just good for juggling). Let the ball dry, and you'll have a great ball. I put in a drop or two of chlorine to keep nasty things from growing. I have several that are years old.

Rick Moll

Note that steel shot is significantly lighter than lead shot. Also, if you're planning to use anything from the firearms supplies category, buy now to avoid the upcoming one *thousand* percent (no fooling) excise tax.

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