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I have had just one projector that I had to replace the upper / lower constant speed sprocket because of grinding. Aside from that, do your normal maintenance things.

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Your comments about the types of gears (straight vs round) is interesting.

In all probability Christie is purchasing their gears in bulk from a manufacturer such as Berg.

Now the types of gears/belts that Christie uses are in fact timing belts. The problem lies with poor engineering with the jackshaft-shuttershaft assemblies.

Berg does in fact make 3-D and twist o flex pulley/belt drives. I have not done any engineering research, so I do not know if they would be approperiate for this application--timing, rpm and torque are definate factors.

Another possible option would be the use of brass/bronze to Delrin gears. Delrin is a self lubricating engineering plastic that is commonly used in gear manufacturer. Once again, torque and rpm is a definate factor.

I was also thinking about a sealed bevel gear box/drive to replace the existing system--but I have not put anything on paper yet--just an engineering idea that I have.

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>Your comments about the types of gears (straight vs round) is
>interesting.

This was one of the fixes Strong did to the 5 Star Sound head. It made a huge difference. They have used round tooth metric belts on them for quite a number of years now. The difference in W&F is definately measurable in this case. I have measured the difference myself.

>In all probability Christie is purchasing their gears in bulk from a >manufacturer such as Berg.

You're right except it is a company outside Chicago. Another problem is the extensive use of alumnium pulleys. They should be all Steel. Alumnium is cheaper...using these makes Christies profit margin increase...Oh well....

>Now the types of gears/belts that Christie uses are in fact timing >belts. The problem lies with poor engineering with the jackshaft->shuttershaft assemblies.

I agree to some extent on this. However Christie used to use a 90 degree gear box with hardened steel helical gears. The only problem with the gear box was that the gears were about the diameter of my small finger tip. One would have gear box failures from time to time but 5 years was a normal lifespan for these. Increasing geear size would have been a better fix than to eliminate the gear box for a belt.

>Berg does in fact make 3-D and twist o flex pulley/belt drives. I >have not done any engineering research, so I do not know if they >would be approperiate for this application--timing, rpm and torque >are definate factors.

These are unique belts. In fact I made use of one of the miniature Berg Ladder belts when I built the crystal motor drive for my VistaVision camera. The outer perifery of these is a pair of stainless steel cables. They do last along time and do not shed at all either. A Christie made completely out of these would probably run forever, and very quietly too. These belts can also easily be made to any length in the field.

>Another possible option would be the use of brass/bronze to Delrin >gears. Delrin is a self lubricating engineering plastic that is >commonly used in gear manufacturer. Once again, torque and rpm is a >definate factor.

Not for this applicaton as lubricant is then required due to the rpm involved here. Mr Murphy also enters here...It will leak out and not get replaced. This is the case with many Christie movments I've opened up in past years. The last one had about a half ounce of lube in it!

>I was also thinking about a sealed bevel gear box/drive to replace >the existing system--but I have not put anything on paper yet--just >an engineering idea that I have.

To relace which existing system? If it is to replace the shutter drive this type of gearbox is already a minor neusance on other brands of projectors. So this option is out. Remember, this is supposed to be a no maintainance machine other than once a year servicing. Using spiral bevel gears is also the more efficient route for a 90 degree gear box. This would add to the price too.

>As far as bearings are concerned. Sure, the name brands such as >Timkin still exist--but for the most part, bearings are not US made >anymore and their quality will vary depending on were they are made. >Sure, you might order a Timkin bearing with a certain part no, but >you will not know where that particular bearing is made until you >get it! In fact, the same bearing might be made is several countries >whose quality will differ.

There is a brand of bearing made here in the US, Barden. They are a high end bearing company of the highest quality. There were Barden bearings in my surface grinder spindle to give you an idea of the stuff they make. There are other high end bearing companies in Europe and Scandanavia as well. Also just because of where the bearng is made has nothing really do do with its quality. You just have to spec and order the right version of a given bearing. A cheap bearing is a cheap bearing. I have sucessfully used Barden bearings in many Christie intermittemt overhauls to great sucess. The Bardens I bought to replace in the Ultramittents cost me 60 bucks apiece! And they last, so the higher price is not really much of a factor here. However, I believe the real problem lies in the fact that the bearings used in the Christie movement are way to small to begin with. Also the outer star and cam bearings rely solely on their internal factory grease for lubrication. This in itself is another major problem. In dry climate areas the grease evaporates and the bearing fails. In humid areas like the midwest, the cheap fibre shield on the Christie bearings allows moisture to build up in the bearing from either condensation or just from creeping in and and mixing with the grease itself. This causes the bearings, especially the outer cam bearing to fail rapidly. Larger bearings are needed, especially in the cam end of the mmovement. Perhaps doubling up the inner and outer bearings would work in this case. In the Motiograph AA the outer bearings were double row if I remember correctly and they last forever and in the Ballantyne Pro 35 they used double stacked bearings on the outer cam position as it was getting the drive off of the V belt. Also the Christie cam bearings need to be in the lubricant. In a Christie movement, this would be an easy modification to do in a normal shop. Move the bearing in slightly and install the shaft seal outside of the bearing as on a Ballantyne. My hell now, we wouldn't want them to last too long would we?
Mark @ GTS

Thanks for the info about Barden--I'll look into them. Actually I had gone to several bearing suppliers looking for high end domestic bearings. No one ever mentioned Barden. The info I posted about bearing quality is what I recieved from these suppliers. Please post an address/ph for Barden!

I am glad to hear you made good use of the Berg 3-D belt/pulley system. I was not sure if these would be approperiate for a timing application, and I also think that rpm is another engineering factor.

Christie has replaced the aluminum jackshaft and shuttershaft pulleys with steel ones. You may be able to get these for free via an even exchange?

When changing pulleys, remember that Christie used Locktight on the pulley set screws!

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

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