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Author Topic: Straightening bent intermittent shaft? Matthew Taylor Expert Film Handler Posts: 186 From: Essex, UK Registered: Mar 2004 posted 01-15-2007 12:37 PM                     On my Prevost P70, I suspect the intermittent shaft is bent only very very slightly (probably due to heavy handed tightening of the sprocket). It's certainly not visible by the eye but it is visible on screen if you look closely for the movement. I'm currently having an engineering friend check it out with a needle gauge. If it is bent, Is it possible to straighten it, perhaps by machining the bent end?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 01-15-2007 02:59 PM                     No, For it to be correct a new shaft will need to be procured to replace the bent one. On most Italian machines the actual star and the star shaft are two seperate parts. So in many cases just the shaft can be replaced. The star and shaft are pinned together with a taper pin. The only other option is to heavily plate it with hard chrome and then re-grind its O.D. in order for it to be completely true. BEtter yet look around for another parts machine and just swap the movements out. What ever you do it needs to be +/- .0005 or better in tolerance for it to be considered true for this application. BE sure he has a 4-1/2 digit dial indicator or one at least one that reads to .0001". Mark  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 01-15-2007 04:06 PM                       You have to be VERY GOOD to do this with any success, or else you worsen the trouble... or take the machine down permanently. IN AN EMERGENCY SITUATION ONLY, I have done this on Cinemeccanica V5 movements that were bent due to film wraps. Find the high spot, put a big, flat screwdriver on that outer screw head, and whack it with a hammer. This is, of course, until you can get a loaner movement and have the other rebuilt.  |  IP: Logged Matthew Taylor Expert Film Handler Posts: 186 From: Essex, UK Registered: Mar 2004 posted 01-15-2007 04:10 PM                     So would you shave off the outer part of the shaft on a lathe until the diameter was reduced enough so the end was true, and then plate that part until it's diamter matched the rest of the shaft?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 01-15-2007 07:44 PM                     Remember that some movements have a very long broonze bushing and you may damage it trying to straighten the shaft  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 01-15-2007 08:47 PM                     quote: Matthew Taylor So would you shave off the outer part of the shaft on a lathe until the diameter was reduced enough so the end was true, and then plate that part until it's diamter matched the rest of the shaft? Thats correct. It may be best to plate the entire shaft and then re-grond it completely true. This is how a shaft in a film camera would be restored. Personally a new shaft...even if it included the star wheel itself would be less expensive to procure and replace. quote: Gordon McLeod Remember that some movements have a very long broonze bushing and you may damage it trying to straighten the shaft Gord is correct! And in fact if the shaft is bent far enough you can damage the bushing just by pulling the bent shaft back through it. If it won't slide out easily then either cut the end of the shaft off so it slides right out, or remove the star wheel from the shaft and pull the shaft out towards the operating side. Vic 8's are built this way and I'd bet your Prevost is also made this way. Tim, Bang on a movement with a hammer . NEVER! Mark  |  IP: Logged Russ Kress Expert Film Handler Posts: 202 From: Charleston, WV, USA Registered: May 2000 posted 01-15-2007 08:57 PM                        Save yourself some heartache. Order yourself a new shaft. I'm sure that everyone that replied is capable of doing everything they claimed. I for one, do not have my own machine shop, and really enjoy seeing my wife and kids every-now-n-then! Call the manufacturer and order the part. They'll be more than happy to send it to you ready-made. You'll be back on the screen and your wife will be glad to see you this weekend!  |  IP: Logged Will Kutler Phenomenal Film Handler Posts: 1506 From: Tucson, AZ, USA Registered: Feb 2001 posted 01-15-2007 11:16 PM                     Someone asked about returning the shaft on a lathe. First, is the shaft case hardened (heat treated). If it is, then forget it. I would save headache and buy a new shaft. K  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 01-16-2007 12:22 AM                       quote: Mark Bang on a movement with a hammer [Eek!] . NEVER! Not the movement, the outside end of the shaft. Like I said, you have to be very good to be able to pull this off. I would've never done it to begin with, but (in addition to the film wrap bends) I got so tired of theatre personnel opening my replacement V5 intermittents when they arrived, dropping the movement, and my discovering the bent star shafts when I installed it. Out of exasperation one day, I said to heck with it, I'm gonna bend it back! To my astonishment, it worked well enough that they didn't lose any shows. I figured dropping the unit was a lot worse than what I was (very carefully) doing, and it was gonna be shot to hell anyway... so I had nothing to lose and shows to gain.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 01-16-2007 08:16 AM                     quote: Will Kutler Someone asked about returning the shaft on a lathe. First, is the shaft case hardened (heat treated). If it is, then forget it. Overplating and re-grinding on a center grinder would be the only way to save it.  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 01-16-2007 05:27 PM                       Or whack it with a hammer.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 01-16-2007 06:14 PM                        We returned to service a customer's XL that made bumping noises. Turned out to be a bent cam shaft. We took an iron rod, 5 feet long and milled an opening into the end to exactly fit the offending shaft and carefully bent it back. It apparently wasn't hardened. The 5 feet gave us a measure of control. The run out gauge showed it to be sililar to a non-bent one from Lavezzi. Bottom line, you have nothing to lose! Louis  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 01-16-2007 08:57 PM                     I have successfully unbent a cam shaft (Simplex XL) and to the best of my knowledge it still is in use 22-years later. A star shaft would be more difficult to be passable. That is, it is one thing to do what you have to to save a show(s) it is another thing to expect it to have the same stability. you can get away with more on the cam shaft but a star shaft (intermittent sprocket shaft) will show ALL of its problems in the picture stability. The sad thing is...most people won't know the difference and most prints wouldn't be able to show it either.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 01-16-2007 10:46 PM                     Louis, I can believe the 5 foot shaft idea but I never beat on mine with a hammer ! Mark  |  IP: Logged Matthew Taylor Expert Film Handler Posts: 186 From: Essex, UK Registered: Mar 2004 posted 01-17-2007 05:38 AM                     Well, thanks for all the advice. After reading some of the posts, I wasn't really convinced about the hammer whacking solution so I contacted Mr Paolo Prevost himself and he gave me an estimate of the repair cost for the shaft which was very reasonable conisidering, so if it it is bent, I think it will end up winging it's way to Italy.  |  IP: Logged

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