Film-Tech Forum ARCHIVE: Assemblies falling apart after rebuilds

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Posted by Frank Dubrois (Member # 3042) on 02-10-2006, 04:58 PM:

I have rebuilt a few jackshaft assemblies for out Christie P35 projectors. I use the old casing, but new tolerance rings, new bearings, new shafts. The problem is, they work fine for a couple days, maybe....but after a while they start to make noise, and i notice that the bearing sometimes work themselves lose. We have had quite a few assemblies in the past get looked at and noticed that the bearings are bad and the shaft has been worn down to the point of uselessness. The bearings we use are the exact same size as needed for the assemblies. The only problem I can see is that I clean the housings and maybe dont let them dry enough?? I dont know though. We occasionaly have the same problem with the shutter assemblies, but to a lesser degree. Our problem there is we can get the bearings OFF the shaft. They seem almost frozen. The blades can be tricky to remove too. I'd prefer to rebuild these instead of buying rebuilds from Christie because of the extreme cost. Any ideas?

...and yes, the bearings are set into the housing as far as they can go....I check.

Posted by Greg Mueller (Member # 17) on 02-10-2006, 05:08 PM:

If the bearings are bad it is possible that they have been pounding around inside their bores and have opened those bores up just a bit. Also, everything has tolerances. Perhaps todays bearings are on the minus side of the tolerance and the old ones were on the plus side. You can get some goo from Loctite that you put on the OD of the bearing that will take up that slop and act like glue to keep the bearing in there.
As far as bearings on shafts... It's a common practice to heat the inner race of the bearing just a tad to get it to expand so it will slide on the shaft. Then it cools and it's stuck on there pretty good. You might try cooling the shaft to get it to shrink. It's kind of hard to do as the inner race wants to shrink along with the shaft.
Good luck

Posted by Mark Gulbrandsen (Member # 72) on 02-10-2006, 09:01 PM:

I bet I've rebuilt a hundred jackshafts and never had that happen. I generally don't replace the tolerance ring unless its been bougered up by some other tech. Do you have a proper arbor press and seating bushings to re-assemble them? Also what brand of bearing are you using and what grade... perhaps yours are not tight enough tolerance. I like to use ABEC 5 in that spot(and the shutter shaft) and they seem to last longer as well. I almost always use locktite bushing retainer compound on them, just a small drop on the shaft before pressing it in works well and gives some insurance.

Mark

Posted by Frank Dubrois (Member # 3042) on 02-10-2006, 11:10 PM:

I thought of using locktight, but I didnt want to make it any harder to remove the bearings than it is. As far as tools, we have nothing "official". I pretty much have to use whatever I can find to remove and set the bearings. I know they are seated properly, that is why I can't figure out why they keep working themselves loose. I looked at ABEC 5 bearings. They sell some on ebay, but they seem to be for rollerskates?!? They also dont list a size. I think we use something like R6-2RS as they match the orignal size exactly. We can get those fairly cheap as well. I don't know if there is a brand name or not. They look exactly like the older bearings, only much cheaper than what our tech place sells them for.

Posted by Mark Gulbrandsen (Member # 72) on 02-11-2006, 09:57 AM:

Ya really need to get ahold of a proper Arbor Press do do any job like this. They cost less than 50 dollars at Harbor Freight or similar stores. You also need to have the peoper bearing seats and backing plates to use with the arbor press so you can press tha bearings in place without putting stress on either the inner or outer race. These are strictly custom for each job being done... I made my own set for working on Christies on the lathe in our shop. Until you have these tools its doubtful that a proper rebuild of any P-35 assys. can be done peoperly. Just pressing bearings in any old way is a really bad habbit.

When pressing a bearing in place in its bore you press against the outer race and when pressing a shaft though the inner race that inner race needs to be supported so there is no stress on it, the balls, or the outer race. Not doing this may allow the balls or race to become indented fepending on how much forse you impose on them and needless to say a very short life spam will result. You must be pressing against the inner race with that race unsupported to have the problem you do.

ABEC 5 bearings are just tighter tolerance and they have less runout.... as a result they generally last longer. Another important thing to remember is to use bearings that have rubber seals in as many locations in the P35 as you can. Using any other type will allow two things to happen.... Belt grit will make its way into the bearings and or the grease in the bearings may dry out in just a couple years time... the latter is a bad problem out in this area of the U.S. with any type of shielded bearing in just about any situation. Any type of bearing is available through your local bearing distrubiter. On the R-6 the ABEC 5 version is about 4-5 times more expensive than a standard ABEC-1 bearing which is what you are using.

Mark

Posted by Frank Dubrois (Member # 3042) on 02-11-2006, 06:47 PM:

Ok thanks for the info. Our last Gm used a hammer and screwdriver to set the bearings..you can still see the screwdriver marks in the rubber seal. With lack of any proper tools, I've been using old bearings to set on top of the new bearings and pressing them into place. It works. Not as good as the correct way, but its better than a hammer and screw driver.

Posted by Greg Mueller (Member # 17) on 02-11-2006, 07:05 PM:

quote: Frank Dubrois
Our last Gm used a hammer and screwdriver to set the bearings.

Oh dear

Posted by Richard Fowler (Member # 893) on 02-11-2006, 07:30 PM:

Reminds me of a tech who used to buy scores of Century cam pins....I finally paid him a visit and saw the "sledgehammer" he was using [Roll Eyes]

Posted by Mark Gulbrandsen (Member # 72) on 02-11-2006, 09:15 PM:

The old bearing on top trick is ok for seating the bearing in a bore. But somehow you must be putting undue stress in the inner race when you press(hopefully not pound) the shaft home.

Mark

Posted by Steve Guttag (Member # 268) on 02-12-2006, 03:36 PM:

An ol' trick of mine is to use an appropriately sized socket to mate up with the outer race.

The "R6" portion of the bearing dentotes its dimensions but speaks nothing of its duty rating and such. For instance, the "R4" bearing is used on the Simplex as a P-3368, on the Century as a BG-259 and on the Christie centerfeed payout position sensor bearing (don't have that number memorized and it probably doesn't end in -001 since it is a "made by others part").

The duty rating of those bearings are not the same...the payout bearing, in particular is a lightweight bearing that should introduce as little frictional forces as practical. Going down to the "bearing shop" and just buying R4 bearings will not satisfy all of the above listed applications.

In bearings, you often get what you pay for as well. One reason we have decided to source most of our bearings ourselves is to control that quality level (increase it) to minimize faiures in the field. Like Mark, we have an Arbor press (good for making ribbon cables too), hydraulic press...in addition to the sledge hammers [Wink]

The right tools can definately make a tough job easier and frankly more successful.

Posted by Frank Dubrois (Member # 3042) on 02-13-2006, 02:32 AM:

I agre, the right tool for the right job...but they wont buy me the right tools, so I use what I can. I though that equal pressure was supposed to be placed on both the inner and outer portion of the bearing to press it in evenly. Are you saying that all I need is pressure on the outside to properly seat it?

Since I got you...how do you remove old bearings from shafts that they just DONT want to come off of? Assuming you have only the most basic of tools. I've had this problem with shutter blades and bearings. Once the shutter blades are off, they dont like to go back on any shaft. Best way to get one on? Bore out the hole in the shutter blade housing, ot grind down the shaft? If there is a 3rd option..I'd like to know also.

Posted by Mark Gulbrandsen (Member # 72) on 02-13-2006, 08:09 AM:

quote: Frank Dubrois
they dont like to go back on any shaft

You're probably mushrooming the ends of the shaft.... a bad thing!! If they won't get you a 50.00 arbor press Frank then I would not do the repairs. It IS about having the right tools.... The repairs you are doing are not lasting anyway so whats the point... let them go the expensive route, let them get the replacement assemblies from Christie. Based on what you've told us about your employer in previous threads if I was in your shoes I'd be looking for a new booth to work. [thumbsup]

.

Mark

Posted by Frank Dubrois (Member # 3042) on 02-13-2006, 09:09 PM:

I thought about the ends mushrooming, but when I try to time some of these projectors, I can't spin the shutter blade after loosing up the screws. When I take the assembly out, its impossible to ever budge the blade. Would some kind of anti-seize compound work? I don't understand why they wont come off. We can't even get old blades onto new shafts...it's impossible without hammering them on...but then if we do, we wont be able to time it anyway.