This is topic Starwheel, Cam & Pin ? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Erkan Umut (Member # 330) on 01-28-2001, 10:34 AM:
Dear Experts and Handlers:
*Why the face of cams is larger than the face of starwheels generally, except the ones of Cinemeccanica & Bauer?
*Some pins are short and some others are long in length.
=Are there any specific reasons for them, or?
Thank you for your reply 
Posted by John Eickhof (Member # 323) on 01-28-2001, 04:44 PM:
The size difference is mainly due to machining standards, the face of the cam will be slightly wider to accomidate differences in final machining of castings that may place the star at different aligments to the cam thus a little lee-way is allowed in case the star is laterally closer or further away from the cam when the unit is assembled. Pin sizes were basically up to the maker, also, the fact that Cinemechanicca & Brenkert intermittent parts, (stars, cams)are not case hardened like other makes provides that the cam pins be larger diameter, also with the advent of 70mm the cam pins were enlarged and stars were webbed for extra durability. Non hardened stars & cams in a constant oil bath will last a long time! They are also more quiet when operating! But you know right away when one has a problem!!------------------
John Eickhof President, Chief Slave
Northwest Theatre Equipment Co., Inc.
P.O.Box 258
Wendell, ID. 83355-0258
208-536-5489
email: jeickhof@nteequip.com
Posted by Mark Gulbrandsen (Member # 72) on 01-28-2001, 05:09 PM:
One must also be very careful in instances of webbed starwheels to be sure to use the correct length cam pin or serious damage will most likely result from the pin striking the web. Personally, if you take the time to blueprint a movement on re-assembley the cam pin should engauge the entire ground depth of the slot in the star. This will result in the least wear to both star and pin, and more area of the pin cranking the star to its next position. Also most people do not realize that cams actually do not really wear out. The shafts can wear and seize ups can also destroy the face but in general the face of a cam does not wear at all when the clearance is set properly and usually only a new cam pin is needed.
Mark @ GTS
Posted by Bill Purdy (Member # 202) on 01-29-2001, 11:24 AM:
Have you ever opened up the intermittant from a Hortson 16mm machine? Very interesting. The cam is more than twice the height of the pin because there is another mechanism that moves the cam shaft longitudinally such that the pin engages the star every other revolution of the cam. This means that the pull-down is very fast.------------------
Bill Purdy
Component Engineering
Posted by Gordon McLeod (Member # 33) on 01-29-2001, 11:34 AM:
The reason for the hortson design is to allow for a 8 tooth sprocket not a miniscule 4 perf one that the normal geneva would require.
Also Kalee used a roller for there cam pin
Posted by Jeff Stricker (Member # 224) on 01-29-2001, 01:09 PM:
I can hear a very slight "tick" when the pin on one my Brenkert BX-40's just starts to engage the starwheel (just as pulldown starts). I can hear it on all 4 positions of the intermittent equally. You can hear it just as the machine is coming to rest after coasting down at end of reel, or when cycling through by hand (not real slowly, but about as fast as you can spin the motor shaft by hand). The picture is excellent - good and steady, nothing seems abnormal at all, plently of oil being thrown around inside. The other machine doesn't seem to have this slight "tick". Is this just the effects of a little wear that I'm hearing?
Posted by Paul G. Thompson (Member # 655) on 01-29-2001, 03:39 PM:
Jeff, the slight "tick" is probably due to wear, or maybe a little binding of the star shaft. There is a cam pin roller on the cam pin, and it might be starting to get a little sloppy, and the star wheel webs themselves may be wearing a little. I really would not worry to much about it at this time. Is the "tick" also present when you start the machine with no film in it? If not, check your gate and shoe tension, as the movement might be working a little harder than normal during pull-down.
Roll the machine forward by hand, and see if it is nice and smooth at the start of the pull-down. Do this with and without film in the trap, and with the film trap open and closed. Then compare it with your other machine. It might tell you something.
Posted by Jeff Stricker (Member # 224) on 01-29-2001, 04:00 PM:
Hi Paul,It sounds the same to me with the gate and shoe open. Rolling it over by hand seems very smooth, can't feel a thing as the pull down begins. Both machines seem the same to me by hand. I'm running "real Brenkert Oil" from Wolk, but, like you say, maybe someone ran some thicker stuff in the past!!
I'm not gonna' worry, I expect with the amount of use they will get here, they are gonna' outlast me!!
Jeff
Posted by Paul G. Thompson (Member # 655) on 01-29-2001, 04:06 PM:
Jeff, they are good machines, and will serve you well. I have heard some Brenkert movements that sounded like they were ready to self distruct, but they just keep running and running and running...
Posted by John Eickhof (Member # 323) on 01-29-2001, 08:32 PM:
It sounds like a little slop in the roller between it and the cam pin, it should be ok and since it is on all four quadrants, it indicates wear is equal! The Brenkert cam pin is soft, yet has a hardened steel roller on it. Just keep the oil fresh! (once a year change) I should last for years to come!------------------
John Eickhof President, Chief Slave
Northwest Theatre Equipment Co., Inc.
P.O.Box 258
Wendell, ID. 83355-0258
208-536-5489
email: jeickhof@nteequip.com
Posted by Bill Purdy (Member # 202) on 01-31-2001, 09:29 AM:
Note to Gordon: Well, I went over to my warehouse and looked again at the Hortson, and while I didn't take it apart, I have to disagree with you. Yes, it does have an eight frame pull-down sprocket, but no, that is not the reason for the every-other-time star and cam arrangement. Think about it, you have to have one slot in the star for every sprocket position. If you had a four slot star and an eight frame sprocket you would have to have gears and then what good would the cam be? I stand by my original statement that the idea was for a rapid pull-down. This is further supported by the fact that when this projector and I first became acquainted it had a three bladed shutter in it. As I turn the machine over with the one-revolution-per-frame pulley it is easy to see that the pull-down occurs in far less than 90 degrees.------------------
Bill Purdy
Component Engineering
Posted by Gordon McLeod (Member # 33) on 01-31-2001, 10:52 AM:
The first hortson I had had a 8 point starwheel and it sounded like a tractor when running. I will be takeing a newer one apart in the next couple of weeks so I will take some photos
Posted by Bill Purdy (Member # 202) on 02-01-2001, 09:32 AM:
Well, mine sounds like a threshing machine, maybe we ought to mate them and see if we could get a reaper.Noisy, yes, but a really solid picture.
Posted by Gordon McLeod (Member # 33) on 02-02-2001, 01:27 PM:
In the Hortson service notes they refer to a red dot on the intermitent sprocket that has to be lined up with one on the shaft and if you do that they have a very steady picture if you don't they dance all over the place.
The older type "G" machines were less steady than the later ones