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Author Topic: Straightening bent intermittent shaft? Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 01-17-2007 11:59 AM                       You guys think I'm kiddin'. The proof's in the pudding; I have witnesses. I've done this successfully no less than three times with single-bearing intermittents (again, it's just a temporary solution until a replacement can be procured). Only once was I unable to save it because the movement had other problems from being dropped to begin with (though I still improved the vertical unsteadiness). It takes a keen eye (which I no longer have, unfortunately, due to middle age setting in) and/or a dial gauge. quote: Steve Guttag 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. Very well said, Steve. That's exactly my point - it is an emergency situation, which I think I clearly stated in my first post. The unit is already shot and unacceptable on the screen. You can try to make it better and save the show -- you have nothing to lose -- or leave them down. Although, it does take a measure of finesse to do successfully.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 01-17-2007 09:02 PM                     Tim... We believe ya man.... I just HAVE to razz you about that though. Also... those crapo machines got what they had comming!! MArk  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 01-18-2007 12:45 AM                       "Metal wants to return to its original shape" said a wise old machinist who had straightened any number of motor shafts that had been dropped to within .002., by imparting a good whack with a hammer and drift punch. Strange but true.  |  IP: Logged Matthew Taylor Expert Film Handler Posts: 186 From: Essex, UK Registered: Mar 2004 posted 01-28-2007 12:59 PM                     Well I the thing measured and it was spot on. It was as true as he could measure - down to about half a thou. BUT.....it goes from bad to worse........................... in either taking the shaft out or putting it back in, the bearing casing seems to have been damaged. Now I can't run the damn thing without a small amount of oil leaking out from around the shaft as it exits the unit. It is right near the film path so I can't use the projector at the moment. I'm assuming it's been scratched or something. Is there any way out of this or does it require a rebuild?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 01-28-2007 05:22 PM                     A new busing can easily be made by any competant machinist. If the original is cast iron then stick with cast iron. If it was bronze then stick with bronze. Leave oilite for the dummies to use! Try to locate an age hardened piece of cast iron to make it from if possuble. Check the original to see if it is offset at all. Some radius clearances are set by rotating the star bushing! But in brief....Machine the O.D. and any shoulder required AND WITHOUT REMOVING IT FROM THE COLLET drill it out several thousands undersize. Then using an expanding reamer ream the new bushing to just slightly undersize a little at a time. BE sure not to stop the reaming operation with the reamer in the bushing . Then it can be removed, reversed in the collet and machined to length if needed. Some can just use a cut off tool and get it to the correct length. Fix it inplace in the movement housing and then use a barrel lap to lap out to just the required fit with fine lapping compound mixed with oil. Clean very well before use or the lapping coumpond left over will ruin both the new shaft and bushing in just a short time. If there is an oil spiral in the bushing that complicates it a bit but its not that hard to cut a spiral with a tiny boring tool and fast feed in the lathe. Sometimes I do this cutting by rotating the lathe spindle by hand allowing the tool to go completely back and forth the length of the spiral. This allows you to stop just before the outer edge of the bushing if needed. Make the spiral deep enough to hold the weight of oil your using and then with the the consequent reaming and lapping operations the spiral will look very nice. I made a couple of new inner star bushings from some old seasoned cast iron for a JJ movement a couple of weeks back and threw the cheap oilite in the trash that LaVezzi provided. Man does it run nice, it will also live very long! Mark  |  IP: Logged Matthew Taylor Expert Film Handler Posts: 186 From: Essex, UK Registered: Mar 2004 posted 01-29-2007 12:11 PM                     Thanks Mark. I think I'll take the intermittent unit to a good machine shop and get them to do it. A question though, how do these types of bush work - I mean, how do they stop oil from seeping out from between the shaft and bearing in the first place. Is it that the tolerences are so tight that the oil molecules can't escape?  |  IP: Logged Will Kutler Phenomenal Film Handler Posts: 1506 From: Tucson, AZ, USA Registered: Feb 2001 posted 01-31-2007 12:33 AM                     So, lets talk Speeds: Cutting speed for reaming depends on the type of material being reamed, the amount of stock to be removed, the tool material being used, the required finish and the set-up rigidity. A good starting point is to use 1/3-1/2 the cutting speed used for drilling the same material. The use of carbide reamers may allow you to increase cutting speed. The biggest limiting factor in reaming is the absence of set-up rigidity. Also, chatter, often caused by too high a speed, will usually chip the edges of a carbide reamer. Feeds: Feeds in reaming are usually 2 - 3 times greater than those used for drilling same material. Too low a feed may "glaze" a hole and may result in material work-hardening, occasional chatter and excessive reamer wear. Too high a feed will reduce hole accuracy and surface finish. Stock allowance: Too small a stock allowance will result in burnishing instead of cutting. Burnishing is a sliping or polishing action. It can also wedge the reamer in the hole causing excessive reamer wear or breakage. Drilled hole surface finish also plays a part. The rougher the hole, the more greater the stock allowance. When materials that work harden are reamed, it is extremely important to have an adequate stock allowance. Proper cutting fluids are also critical. Reaming problems: Insure adequate set-up rigidity by reducing speed to eliminate chatter. Also increasing feed, putting a starting chamfer in the hole prior to reaming, using a reamer with a pilot, or reducing clearance angle on the cutting edge. Oversized holes and "bellmouths" worn machine tool bearings, misaligned machine tool, bent reamer shanks, etc, etc. When reaming, there are charts that should be consulted to ensure that you are using proper sppeds, feeds and stock allowance. Kutler  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-01-2007 08:48 AM                     quote: Will Kutler Proper cutting fluids are also critical. Actually fkluids are very non critical and normally not needed when it comes to working cast iron in small quantities. I always cut cast iron dry and it cuts extremely well and with a very sharp cutting tool you can get almost a mirror finish. Since the main objective of cutting fluids is to prevent a build up of particles at and on the cutting tool... and cast iron does not tend to build up on a cutting tool the normal fuids can be dispensed with unless you're going for production quantities and tool longevity. In fact there are very few fluids that will work well with cast iron since most fluids will tend to cause it to surface rust extremely rapidly. The thing I agree with Will on is cutting allowance... there HAS to be sufficuent material for the reamer to remove or the bore will just end up being burnished. Too much material to remove will just cause alot of wear on the reamer. Since the final bore is lapped out with fine compound using a barrell lap it will normally end up being mirror finished when you're done. Lapping is the most difficult part for most and many machinists have a tendency to go at it too fast and enlarge the bore to far. Mark  |  IP: Logged Matthew Taylor Expert Film Handler Posts: 186 From: Essex, UK Registered: Mar 2004 posted 02-01-2007 10:01 AM                     Since I first mentioned the oil leak problem, I decided to take apart the mech again and see if I could see any obvious grooves in the bushing. I couldn't but I noticed that there's a rubber collar at the end of the bush that seals around the shaft. This didn't appear to be damaged in any way so, as I hadn't noticed it when first reassembling the unit, I decided to put it all back together but more carefully - easing the shaft through the tight-fitting rubber seal. Lo and behold, the thing doesn't leak at all now. All that fuss and it seems it was only a case of not being careful in putting the shaft back The movement really purrs nicely. So now I know the shaft is ok, I think the next suspect for the very slightly shaky pic is the intermittent sprocket itself. I have tried out several new ones but they look like cheap chrome-plated copies rather than the well made case-hardened Prevost ones. I suspect that they might be causing a problem.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-01-2007 11:58 AM                     Actually I have yet to be impressed by any Prevost sprockets... pretty ragged things! Since there is no slot like on a Cimemecannicca and its just the expansion of the shaft that holds the sprocket in place try to get yourself a nice Kinoton sprocket instead... like fomr an FP-20 or such. Its the same bore. Might require a little careful lateral alignment but they work beautifully and last much longer. Mark  |  IP: Logged Matthew Taylor Expert Film Handler Posts: 186 From: Essex, UK Registered: Mar 2004 posted 02-01-2007 12:19 PM                     Mark is it possible the cheapo chrome plated sprockets would cause a problem even though they are new?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-01-2007 01:59 PM                     They are just not of the quality that the Euro or LaVezzi sprockets are up to. The Italian sprockets in general have a much rougher finish and they seem to be counting on the hard chrome to take the wear.... while whats underneath that is pretty soft metal. The Kinoton or LaVezzi sprockets don't depend on a hard chrome layer... the metal is hardened before the final grind operation eliminating the need for any hard chrome plating. The resulting sprockets are much smoother and generate less film dust. PLace the two side by side and its quite easy to see the difference. Mark  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-01-2007 04:52 PM                     The dual 35/70 sprockets are always a lighter weight material than the straight 35mm ones never had any major issue with cinemecanicas sprockets  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-01-2007 05:46 PM                     Gord, Actually if you weigh a combo 35/70 alumnium sprocket you'll find it to be almost the same weight as a 35mm only sprocket. In my experience Italian sprockets have never been of the high quality manifacture that LaVezzi sprockets have been and thats probably why LaVezzi makes all of Cinemecaniccas intermittent sprockets today... including a hardened steel 70mm only sprocket for the Vic 8&10. Nothing else compares to a LaVezzi sprocket in terms of quality of finish and fit as well as longevity of life. Installing a short lived alumninum 35/70 sprocket is the equivelent of throwing $$ in the campfire so going with a 35mm only sprocket makes more sense these days. Keep the old 35/70 sprocket to run 70mm if that ever happens again. The Prevost sprocket is probably the easiest sprocket to switch out on the planet. Mark  |  IP: Logged Will Kutler Phenomenal Film Handler Posts: 1506 From: Tucson, AZ, USA Registered: Feb 2001 posted 02-01-2007 11:12 PM                     I once spoke to Lavezzi about their manufacturing processes. I was stold that their entire shop is proprietary and that they have developed their own special machine tools and process over a period of decades. I was also told by them that they do not give shop tours. K  |  IP: Logged

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