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Author Topic: What can cause a missing tooth on a sprocket? Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 02-07-2010 09:21 PM                     No, the entire sprocket is turned and cut from one piece of steel. Granted, it's an old "foxhole" sprocket where the steel is thinner than a VKF sprocket... could it be just metal fatigue that caused the tooth to break off? But, more looking at it, with the engouged area in the outside groove, it looks like the sprocket was cleaned with a blade in that groove, snagged on the tooth causing the tooth to break off. But, some guesses here .. -Monte  |  IP: Logged John Wilson Film God Posts: 5438 From: Sydney, Australia. Registered: Dec 1999 posted 02-07-2010 10:25 PM                     I've never known a tooth to just 'fall off'. Someone's jammed something into it to make that happen.  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 02-07-2010 10:55 PM                     I second what John said. Monte, that looks to be the VKF sprocket as the tooth profile on the tip is too rounded to be the older foxhole sprocket, and the teeth appear to be somewhat wide as well. Either way, that's NOT a normal failure or metal fatigue. Joe, time to seriously grill some employees as someone stuck something into that sprocket.  |  IP: Logged Joe Redifer You need a beating today Posts: 12859 From: Denver, Colorado Registered: May 99 posted 02-07-2010 11:42 PM                        Nobody's fessin' up. I don't know what or why anyone there would do. I talked to the guy who just happened to notice both teeth missing on the two separate sprockets, kind of wondering out loud what would cause such a thing hoping he would tell me ina roundabout way what happened, and he was "well maybe the pad rollers closed on it too hard". Uh, no way. He either is hiding something or honestly has no clue what happened. I will give him the benefit of the doubt.  |  IP: Logged John Wilson Film God Posts: 5438 From: Sydney, Australia. Registered: Dec 1999 posted 02-08-2010 12:59 AM                     Using titanium pad rollers? How many do you have on roster in the booth? At this point it seems you need to let them know (since no-one's 'fessing up') that obviously mistakes can be made and you don't want anyone's head...you just want to make sure it stops.  |  IP: Logged Ian Parfrey Phenomenal Film Handler Posts: 1049 From: Imbil Australia 26 deg 27' 42.66" S 152 deg 42' 23.40" E Registered: Feb 2009 posted 02-08-2010 02:09 AM                     At last a use for all those metallurgy classes at Tech School! Here's my take on this.... Monte is right in that a blade of some sort-possibly a screwdriver- was bought into contact with the sprocket tooth. Reasons for this assumption are -: Screwdriver blades are hardened and as such can deform hardened steels- depending of course on how hard the impact. The size, shape and position of the two indentations on the right hand side of the tooth base indicate a blade wide enough to bridge the groove in the sprocket. If the photo Joe supplied is enlarged sufficiently, it is possible to see on the side closest to the viewer a "rounding" of the broken edge of the tooth. This rounding effect indicates a "stretching" of the tooth as it was bent rearward. The tooth then tapers off to the rear following a line of least resistance (indicated by the sloping tooth wear on the following tooth) down to the far side of the tooth which is the fracture site. The ease at which the tooth fractures depends on the hardening process used, and to the level of hardness obtained. Very hard metal is usually very brittle. The tooth looks like it was struck from the front to the rear with a hardened blade in 2 if not 3 places (I'm not sure if there are other impact sites on the other two teeth) and this is the cause of the tooth fracturing. Age may have a bearing on the brittleness of the metal as will the level to which it was hardened and the rate of impact but it is difficult if not impossible to prove if metal fatigue has played a part without microscopic examination. Either way it seems the sprocket suffered blows strong enough to deform hardened metal. It's also my guess that the tooth either side of the broken one will also be a candidate for tooth fracture judging by the similar deformities on the tooth face. As to why a hardened blade was near a sprocket is anybody's guess. The forward groove appears to be cleaner that the rear groove which may indicate the blade was used to clean out the groove - possibly while the machine was running- the blade impacted the tooth and fractured it.  |  IP: Logged Joe Redifer You need a beating today Posts: 12859 From: Denver, Colorado Registered: May 99 posted 02-08-2010 05:40 PM                        OK, here's some facts: -The sprocket tooth was likely broken/damaged while it was in motion. -The Simplex XL and 5-Star soundhead has doors that everyone who operates in this booth keeps closed unless the projector is being threaded. Maybe a screw holding up a hinge or the little plastic light guard inside came loose and fell inside the projector at one point or somehow a screw from elsewhere found its way inside. That is the only thing I can really think of. I will have to look for missing screws on the inside next time I get a chance. I don't know why anyone would be messing around with a screwdriver near a running projector.  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 02-08-2010 09:08 PM                     I deal with a lot of students who don't know much about projection, much less anything else. One thing I always tell them is my policy on damaged equipment. I always tell them, if something breaks... even if it breaks because they fucked up... they will not get in trouble as long as the damage is reported to me right away. The worst that will happen is that I will cuss about it. Then we'll fix the problem and make some more movies. However, if they break something and try to ditch it and I find out about it they will get in trouble TWICE! Once for breaking it and once for lying about it. The exception is for gross negligence or willful acts. I have had this policy in place for almost 10 years and I have only had one or two big disasters. The last time I can remember was when one student was breaking down a print. One of those stupid plastic Technicolor film reels broke in two and the whole reel got dumped on the floor. The student called me on my cell phone just minutes after the film fell on the floor. I said something like, "Aw Shit!" Then I told him to just pick the film up as carefully as he could and leave it on top of the rewind bench so I could come in and fix it in the morning. It turned out that the damage wasn't too bad. I carefully untangled the film and gave it a coat of film guard using the bench winder and it was as good as new. I often get notes left in the booth or phone calls at night apologizing because they didn't know how to solve a problem. It's always something minor. The worst thing I ever said was something like, "That was a stupid thing to do." I believe that one reason I don't have very much damage is because of this policy. The thing is that it is probably a lot harder to enact this policy with people who already work for you. It's a lot easier if this policy is in place right from the start. It's not going to work for you in this situation because the damage is already done. Whoever it is who is responsible is obviously covering it up. A "Don't get in trouble" policy isn't going to work in this situation. That's a kind of policy you would have to work on for the future but you also have to have the right kind of atmosphere for it to work in the first place.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 02-09-2010 01:33 AM                     I just thought of something to add .. wonder if the eccentric shaft came out on that pad roller arm striking the rotating sprocket...for you know, them things love to work loose at times.. ..or worse, it snapped off and found its way in the rotating sprocket... ..just guesses - Monte  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-09-2010 09:30 AM                     I'm amazed you are rrunnig CS type sprockets, especially one that even has undercut teeth. Those undercuts actually make the teeth weaker. Those are tiny film damaging teeth there! CS type film and perfs went the way of the garbage dumpster several decades ago... even though CS type perfs are actually stronger than KS type perfs. VKF sprockets are a must these days because of booth mongers like the ones you work with... Note the circled area which is undercut or also known as a hooked sprocket! Causes alot of extra dirt to accumulate in the projector. You should call in a booth tech and get these projectors updated! Mark  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 02-09-2010 11:52 AM                     Mark, I doubt the owners will buy Joe new sprockets, but Joe can certainly reverse them to use the other side of the teeth.  |  IP: Logged Joe Redifer You need a beating today Posts: 12859 From: Denver, Colorado Registered: May 99 posted 02-09-2010 01:19 PM                        If you look at the picture, the missing tooth is on the soundtrack side. The "hook" that Mark points out is on the opposite side that pulls the film since the sprocket rotates clockwise. That means this sprocket was already reversed some time ago unless the sprocket was initially manufactured like this like Mark kind of alludes to.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-09-2010 04:10 PM                     Ya know Brad, I had thought of that... In fact I flipped the photo around and took a look at the other side of the tooth... almost worse than the side Joe showed... The pisser is that the case hardening at the base of the tooth is now gone... worn away... and the wear will only be accelerated by the estar film itself which is much harder on sprockets than acetate was. Sprockets are not all that expensive, especially at Brads normal highly discounted pricing!! They'll also be the last ones that projector will ever receive... Mark  |  IP: Logged Joe Redifer You need a beating today Posts: 12859 From: Denver, Colorado Registered: May 99 posted 02-09-2010 04:24 PM                        LOL, Mark! Even you should know that flipping photos doesn't move you around in 3D space to see the other side of the sprocket!  |  IP: Logged John Wilson Film God Posts: 5438 From: Sydney, Australia. Registered: Dec 1999 posted 02-09-2010 05:15 PM                     Joe, I think you just fell for something you shouldn't have.  |  IP: Logged

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