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I've seen people specifically mention they use automatic shufflers with easily replaceable cards, but what about if it matters if the cards get damaged?

What are the drawbacks to using automatic shufflers? Does machine shuffling cause any more damage than would occur through a normal riffle shuffle? I've also seen some mention that automatic shufflers don't truly randomize the deck. Is this true?

  • 1
    One drawback of auto-sufflers is that you don't get a truely random distribution. I don't remember the exact math, but if you cut a deck perfectly even and do a perfect 1-1 riffle shuffle, after so many iterations you end up back where you started. – DForck42 Oct 28 '11 at 14:35
  • @DForck42 Mechanical shufflers are designed to randomize the deck using different shuffle sequences — not just repeating a perfect riffle X times. For example, this shuffler has two settings, fully random setting is 1 riffle, 1 strip, 2 riffles, 1 strip and 4 more riffles. – ghoppe Oct 28 '11 at 15:42
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    @DForck42 If you can do 8 perfect shuffles you can restore a deck to it's original state youtube.com/watch?v=7lNk7bfkFq8 – AlexC Oct 28 '11 at 15:58
  • possible duplicate of Card shuffler for many sizes – Dave DuPlantis Oct 29 '11 at 2:36
  • as well as Please recommend a good shuffling machine – Dave DuPlantis Oct 29 '11 at 2:37
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Mechanical shufflers come in several types. The simplest are the hand cranked gravity fed multi-wheel versions... and are the only ones I've much experience with, having owned two. (Both inherited.)

These particular ones both use a wheel to throw cards into the central bay from two elevated bays.

  • some cards end up face up - I've averaged 1 face-up per 3 shuffles or so.
  • cards can get scratched on the metal surfaces
  • can't handle anything that's not "standard height" - it'll do bridge and poker decks of the 3.5" tall variety, but it won't do larger cards, as they get stuck, nor smaller, as they don't stack up in the center bay.
  • crunches over-thick cards badly. In other words, 110# cardstock won't work well, as home cutting results in being too thick to work.
  • Kem and other solid plastic cards don't grip right - increased flipping, and more manual downpressure required
  • older machines' rubber wheels lose tackiness, and don't drag cards as effectively
  • not quiet.

All the automated ones I've seen have the same issues plus

  • not stopping if a jam occurs
  • needing a source of electricity
  • being even noisier.

I've not used it enough to determine edge wear effects, but Kem used to note that shuffling machines voided their warrantees.

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For a deck of 52 cards, 8 Perfect Riffle shuffles to get back to where you started with the deck. Getting back to where you started is different based on how many cards you are dealing with. For 24 cards, it takes 11 perfect shuffles (like euchre).

For mechanical shufflers, it depends on the type you have. If you have split the deck in half, then the top of one will always be the top in the final deck. And the bottom in one of the halves, will always be on the bottom. Thus, a cut should always be done to further randomize the cards.

One or two shuffles (mechanical or manual) is not sufficient to randomize a deck of cards. At least four is required. Beyond 5 or 6 is a waste of time.

Unless properly done (several shuffles) you will not get the cards randomized.

  • Every analysis I've seen on the subject suggests that 7 riffle shuffles are required to properly randomize a 52-card deck. Four definitely isn't enough, and it's not a waste of time to go beyond 5 or 6. Not sure what the point of your second paragraph is, as it's the same for manual shuffling - when doing a riffle shuffle, the top card of one of the two piles will be the top card of the shuffled deck. This answer doesn't seem to address the question at all, as it doesn't mention anything that's unique to automatic card shufflers. – Nuclear Wang Jan 11 at 15:44

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