What is the best way to hang a 50lb punching bag from the celing, I used a 1/4 inch eyelet screw screwed into a wood beam, but the mag moving back and forth works it out of the wood. what is a better way to do it?
Are the rafters exposed? If they are you could just loop a chain over the top and hang it from that, and then put a bolt through the link on top (or any of them for that matter) to keep it from sliding around.
First off, do you own your own house? Any method of securing a heay bag to a ceiling will probably violate any lease.
Second, how is your home built? What is above your ceiling; a second floor? solid wood floor joists? attic trusses? I started to make a long ranbling reply,but I’d rather that you got an answer specific to your home (BTW, it may take a while for me to reply. I’ll follow up, but others may give a good answer before I get back.)
I do own my home. the rafters are not exposed, it has a sheetrock ceiling. Not sure about the terminology, but in the attic there are realy long boards about a foot apart(ie you have to laydown plywood over them to store stuff in the attic, otherwise your stuff might fall through the sheetrock.)
Cut an 8" square centered under a joist, wrap a chain around the joist, hang the bag from the chain.
The reason is that you want to keep from damaging the egdges of the drywall so that when you take it down you can easily repair it.
If drafts are a problem, use tape to seal the hole.
Good. It sounds like your attic was stick framed with dimensional lumber. The joists should easily support a heavy bag.
A chain wrapped around a joist will probably hold the bag, but it will look pretty bad. IMHO, the ideal way of doing this would be to make a strongback, using the same size lumber as the ceiling joists (the long boards that the sheetrock is attached to.) The bag will mount halfway between two joists, and the strongback will need to extend far enough beyond the adjacent joists so as to either spread the load onto several joists or to reach a bearing wall (i.e., it needs to lay atop the outside or a center wall if you run out of joists.)
I’d mount the bag to a 1/2 inch eyebolt that goes through a hole in the flat part of the strongback, and use fender washers, flat washers and two nuts on both the top and bottom of the bolt (run the bottom bolts down to the eye so that the bolt can’t rock back and forth in the wood.) The top nuts can be locked together, and the bottom ones can be used to take out any slack if the wood compresses.
Finally, to dress things up, you could use some spare wood to box out the hole in the ceiling, then tape and paint. This will leave you with a clean hole in the ceiling which can be covered with an air conditioning vent if you ever need to hide the hole (such as if/when you sell the house.)
All of this is overkill, but I’d consider it to be the cleanest and strongest way to attach the bag. You might also be able to get by with using the hanger that Joey P linked to, but I would attach it to two lengths of lumber that is lag bolted on both sides of a joist and remove any sheetrock that it might bear upon.
Planning on suspending a piano from the thing? 
I can’t help but think of S & M!!!
Sure, it’s probably overkill, but I’d rather overdo things than underdo them. Even if the owner doesn’t pack a young-George-Foreman-like jab, heavy bags tend to be used at some time or another as either: 1) a kick bag, or 2) a swing for children or young adults. Even with regular use, the repeated blows will transmit some force to any sort of a screw eye and can either work it out of the wood to which it is attached or split the wood that it runs through. With an eye bolt and fender washers, the weight would bears on the top of a board, and there is a fair amount of meat on both sides of the hole to prevent splitting.
S&M? So what is this, some sort of… lumbertorture? 