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Author Topic: Rebuilding Christie Ultramittents John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 04-02-2008 12:28 AM                     I definitely know zilch about lapping, but I'm a bit confused: Do you lap the star or the cam? It sounds like you're not lapping in-place? What significant difference is there between rubbing the cam with a piece of fine sandpaper, and "lapping" it with a piece of glass and some lapping compound? Presumably, Mark, you test after each lap of lapping, or you use a micrometer on the cam, or...? How do you lap a round feature (cam) by hand with a piece of glass in an even fashion? Just kinda curious... --jhawk  |  IP: Logged Randy Bowden Expert Film Handler Posts: 146 From: Portland, OR, USA Registered: Aug 2000 posted 04-02-2008 02:04 AM                     I will give a general rundown on how I do things. first off lets get something established here, when I say that a cam pin is oversized we're talking about a very slight amount. For instance today I did an Ultramittent rebuild. The cam fit the star perfectly out of the box. no problem, it ran nice and quiet. Later in the day I went to do a simplex rebuild. A test fit of the pin indicated right away that it needed work. It pulled through rather stiff, or shall I say pushed through. What I do first is clean the parts completely of the oil coating that Lavezzi leaves on. Then holding the star in one hand and the cam in the other I test the fitting of the pin through the slot. It it needs work, I clamp the cam in my vice and proceed to scrub the surface of the pin with 1200 grit. I use a narrow piece of sandpaper folded in half. The trick is to hit the surface as evenly as possible from all sides. If your starting off with a cam that just needs a new pin, then you can chuck the pin in a lathe or drill press and work it that way, the only real down side to that being that cam pins don't always want to press in strait, at least not for me anyway. Now I know my method may sound a little crude and quite frankly it is, but it works and with enough practice it works really well. The only Lavezzi cam that I never seem to have to do this with is the Pro-35.  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 04-02-2008 06:20 AM                     Sometimes pins depending how they are pressed ( preferred ) or "tapped" in will create a mushroom head that will require dress down. Lapping power is very fine and was more common when some make of projectors required lapping of shafts and sleeve bearings for fit.....I still have powder, stones in the shop with associated laps and tools.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 04-02-2008 09:53 AM                        We try not to disturb the surface hardening on the pin at all. The inside of the star is cross-hatched. It is that surface you want to reduce if you lap or run-in. Much more of a factor is "lack of squareness" on the majority of case halves, especially the XL and century. This will cause a binding when the pin engages if not corrected. This (& lack of oil) are the main reasons why intermittents fail in the first place. Louis  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 04-02-2008 10:20 PM                     JHawk, You lap out the slots in the star... on a piece of flat glass.. just keep track of how many strokes and above all don't go crazy.. it doesn't take much to loosen up the fit... but I like Randy's idea better and plan on giving it a try... I'll try your method next tight pin I come aross Randy... its interesting to say the least... I have a friend thats a knifemaker, he hardens his own steel!! He has a Rockwell hardness tester that we've tested alot of projector parts and the results are not always what you think you should find... generally not very good. Also, most cam pins which are nothing more than perfectly sized(not always) dowell pins are hardened completely through so a little scoring of the surface is totally irrelevant to its wear factor... its very good for oil distribution. You're right on about the lack of case squareness Louis!! Century's are especially bad... if you measure the squareness of the flat surfaces in relation to the bore for the bushings you will more than likely find they are off. I don't see this very often on X-L cases though... in general they are pretty good. Some century case halves have been so far off they are not even salvagable... I suspect the fixtures at the factory were worn out but they kept producing them anyway. Mark  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 04-03-2008 10:31 AM                        It is important to note that this is not a recent problem; it goes back to the very beginning. Strong, in fact, has done very well in terms of squareness. Louis  |  IP: Logged Randy Bowden Expert Film Handler Posts: 146 From: Portland, OR, USA Registered: Aug 2000 posted 04-03-2008 11:07 AM                     It's true, the century's can be a real pain. I have no problems with the simplex.  |  IP: Logged

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