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Wayne
12-12-2003 16:25:54
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Re: dial indicator (dead horse here) in reply to Dennis Minn, 12-11-2003 23:35:04
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Hey Dennis, I don't mind discussing this, I enjoy a good discussion, but it seems like no matter how I explain it nobody (not meaning just you..) seems to understand it. True if you were to set the dial up in the exact center of the ring gear and let it stick out 6" and then 8" and measure to a fixed degree of arc then it would be further at 8" than at 6" I haven't disputed that yet. However, although this may seem like what is being measured, in reality it is, and it isn't all at the same time. I tried in the last post to explain it in an even easier way than I have before, but let me try again like this. First, knock the whole circular way of thinking with arc lengths, etc. out of the picture and think about it is like this. Dealing with high speed turbines and gearsets like you do, and like I did too when I was in the Navy, you know that gear teeth have to be cut where matching faces are parallel to each other otherwise you won't get proper tooth contact, Right????? Ok, when we measure a clearance like this, we are measuring an arc length, I won't dispute that but we are also measuring the clearance between two parallel sufraces. Why the "arc length" part of it doesn't actually matter is all part of the tire/rim theory. Try it and you'll see what I mean.... because of what happens there we can measure the clearance we have independent of "arc lengths" because, again, what is being measured is actually the clearance between two parallel surfaces. Now by definition, for two surfaces to be parallel, they have to be the same distance apart at all times, correct???? So that means if on the OD the teeth are .010 apart, then they are also gonna be .010 apart at the ID, Right??? Otherwise the teeth wouldn't be parallel to each other and wouldn't mesh properly which would cause massive amounts of wear on the "high point" until they seated in and became parallel by default, Right????...Following now??? OK, now if there is .010 of clearance at the OD and ID, which there has to be if the teeth are parallel, then if you set the dial on the OD at 0 and opened the gap as far as it would go then it would read .010...Right?? Same goes if you set the dial on the ID at 0 and opened the clearance, then it would read also read .010....Right??? If the teeth are parallel, which they have to be, then for the ID clearance to be smaller than the OD clearance, then when the OD went back to 0 then the ID would have to become an interferrence fit, or less than 0, which we've already established is isn't and can't be, Right?? By the same reasoning if the ID went to .010 then the OD would have to be greater than the already established clearance of .010, which we've established already that it can't be, Right??. Neither of these things is gonna be possible with two gears that are designed to run in mesh. Like you said, in high speed operation, you have to be dead on everytime or it won't work. If a mfgr. were to cut teeth not parallel and use them in a high speed application, how long do you think they would last???? Ok, that's the last way I know of to explain it, I'm tapped out. Dennis, next time you set one up get two dials and set one on the ID and one on the OD and see if they don't read the same..... For Fred--- I don't want to sound like a smart a$$, but in response we aren't "married" to anything here, this is a simple discussion about a complex theory/problem/or whatever you want to call it. My Grandpa always used to tell me "Every day you don't learn something new is a wasted day". It's this learning new things that makes mechanics, and anybody else for that matter, be confident and not drag their feet when it comes to doing a job. In this example, I have run into gear setups where you couldn't do it exactly like the factory says because I'm in the field and not in some multi million dollar engineering facility. Knowing what I know I can always find another way to do it that's just as acurate and many times alot easier and faster, and I have never had a machine come back to me because of something I screwed up. (Something I can't say about "factory mechanics" which I go behind all the time) I can say this and "toot my own horn" because I am good at what I do, and that is mainly because I;m not afraid to ask questions, and because I never stop learning.
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