Pocket Center Height or Centering; Citizen L20 & others



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Thread: Pocket Center Height or Centering; Citizen L20 & others

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    Default Pocket Center Height or Centering; Citizen L20 & others

    I work with an older Citizen L20. I had been concerned that the pockets were not locationally perfect, or course I can adjust my diameter centering on the pocket tools, being T22-22 and T31-33. Well, I have placed a 3/4" tool in each pocket, and I can run an indicator and tell that locationally, all these pockets are between .007-.009 above or below center. Since I've not been around these machines but for about 2 yrs, I am concerned that this is too much out of center. I would think not much more than .002, and I would probably live with .003 as what I should expect to see.

    Most of my smaller drills and such will walk up to center fine enough to make my part. I was using a .381 reamer though to ream a hole, and it gave me a hole .383, as you can imagine how solid a reamer of that size would be.

    I am concerned about the center height of these pockets, and adjusting them out in some way or another. My supervisor wants me to study out lifting the sub-spindle and pocket assembly, and placing some shimming underneath it to adjust to make all the pockets about correct. I am concerned about starting such a task because of my limited knowledge of the machine, and what might arise that I do not know of. I am also concerned about their knowledge at my shop, because as for what I know, I am the only one at the shop who knows much about these machines, nobody else really wants to mess with them.

    At one point, I knew a shop that was considering boring and placing a sleeve in their pockets to make them true for the machine, but I never heard the end of it. I'm thinking perhaps the lathe ways are worn out on my machine, and I'm hesitant about shimming the sub-spindle and pocket assembly because if the ways are worn, then I don't see my shimming doing any good, due to the inconsistency of the movement along the ways. I'd like to hear from some others on this. I'm certain I'm not the only one who has dealt with this thing. Thanks in advance.

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    Set aside a day to shim the subspindle and get those tool positions tuned in to .0002" or less.

    If your bores are off, your sub to GB is probably off too. Get the sub to GB dialed in first, check the bores on each side, get those to zero up and down and then comp the side to side in the X axis on the control. It's not a big deal to losen the sub and shim it, loosen only two bolts at a time. Measure meticulously and when you have it, take everything out, put it back and measure again. There is a keep relay to flip (at least on a fanuc) that puts the machine into alignment mode, which makes alignment much easier.

    These machines can be so accurate, it is a shame to run them with mis-alignments, IMO.

    Last edited by danrudolph; 05-12-2012 at 10:04 PM.


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    Sounds reasonable to me. It would probably take me 2 days though since I haven't ever cranked into anything of the sort, ha. I haven't had to hold a whole lot of accuracy on this machine with the pockets so far, but I definitely want to get the machine right, in case the occasion arises, as I don't want to be fighting it then. I do believe the sub-spindle is off also as I can tell sometimes by a noise that is sometimes made when it clamps to pick-off a part. I'm not too sure which 2 screws at a time to loosen. I'll have to look, perhaps theres pairs that are more evidently towards one side or the other of the assembly. It sounds like the main idea there is to not completely loosen the whole unit and try doing it, as you need your locational assistance while doing it.

    I am wondering if I correct this thing on the machine, can a simple crash throw it out again where someone would need to re-check that height? I used to think machining was interesting, but messing with these swiss style cnc machines with my low amount of knowledge already has made me somewhat dis-interested in the career. Thanks for the thoughts.



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    I learned how to do this from a Citizen tech. Crashed the machine, it was off about .002" on the sub to GB. Watched the tech do it once, now I can do it if I need to... knock on wood. We ended up adding a .001 or .0005 shim under one bolt.

    For your tool positions, use tightened down tool holders to align, do not sweep the bores. You'll be off about .0007-.001 right off the bat if you sweep the bores due to the slip fit allowance. I then engrave the tool position on the holder to minimize future errors.

    If your company can spare it, it would be good to have a tech in and go over the machine with you, probably show you enough to make you more confident with the machine in general.

    Machine should be quiet after the sub clamps onto the part, if I hear vibration after clamp, I know something is wrong. Good thing about your machine is that it should be able to only improve.



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    Quote Originally Posted by danrudolph View Post
    Good thing about your machine is that it should be able to only improve.

    Hahaha, you got that right. I'm pretty sure it's a late 80's model or such. We did have a guy out to work with me for a few hours one time. I found myself having to pound him for knowledge, because he didn't know specifically about my machine, though it's a common Citizen machine in my opinion. I had encountered the individual before in the industry and found out the same conclusion from speaking to someone else. He worked for a company that sells and installs some Citizen machines or whatever. I would've loved to actually have a true Citizen individual that knew what they were doing. I've discussed going to some training/education with one of my bosses, but I was hesitant as most of the numerous education programs I've seen and been through have failed to provide some important form of knowledge or another. Haha, sounds like I'd be pesimistic to some, but it is not wrong to consider the cons of a situation.

    I was just discussing the other day with some folks about the lack of workforce to back up the technology in our industry. It's very simple to see this fact to myself. Mostly the people that can't see it our blinded by some misunderstanding and not able to think past the surface facts when considering this thought. It's funny, people think technology is better, so they keep creating it, and still our educations and our workforces are not supporting it. Will be plateau'd in this situation for a while as far as I'm concerned, because nobody seems to think they should do anything about it.
    I'm very smart and capable and have encountered others that are also in this industry, but they are held back in ways by the circumstances the industry presents to them. Ha, I guess I'm saying this industry might be making me dummer, and I'm halfway not kidding when I say that. See there, I spelt dumber wrong, haha. There is a truth to what I say.



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Pocket Center Height or Centering; Citizen L20 & others

Pocket Center Height or Centering; Citizen L20 & others