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Tool Talk Discussion Forum

Dial indicator setting

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Vern Iowa

11-30-2003 12:13:24




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When adjusting the slap in bevel gears on a transmission or rear end , do you measure the distance on the outside diameter of the ring gear or in the middle of the gear? I am working on the rear end of a Super H International. I sure would appreciat any information on the subject. Thanks to all.




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Fred OH

12-01-2003 08:20:54




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 Re: Dial indicator setting in reply to Vern Iowa, 11-30-2003 12:13:24  
I agree with others in that the ones that I have set up, I have used the outside part to set the dial indicator. If when you have set up the gear tooth spacing and you're still not sure of yourself because of inexperience...you might take a piece of paper such as a magazine sheet and run it through the teeth...it should JUST shear the paper in two at the tooth contact points. Another way of getting spacing right was to paint some teeth and then run it through and observe it...it should be uniform for the length of the tooth. These were methods used by mechanics years ago when dial indicators weren't in everyones tool box...taught to me by an old mechanic friend Forrest Barton...years ago. More important was the preload on the side bearings...using a small scale to pull test with. Fred OH

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Wayne

11-30-2003 20:34:33




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 Re: Dial indicator setting in reply to Vern Iowa, 11-30-2003 12:13:24  
It really doesn't matter wether you measure on the outside or the inside of the ring gear because it's gonna be the same measurement either way. What you are measuring is the clearance between the pinion teeth and the ring gear teeth. That clearance is gonna be the same all along the face of the teeth from the inside to the outside so no matter where you have the dial setup is's gonna register that clearance. That's the easy explination, and I know it doesn't make sense because you'd think that the larger OD would "move further" than the smaller ID would but in reality they both move the same. As an example take the tire/OD off a rim and make one revolution with it and it moves say 6 feet. Now take the rim/ID and do the same and it'll move maybe 3 feet with one revolution. But if you put the tire/OD back on the rim/ID and then make one revolution with it then the rim/ID goes 6 feet with one revolution just like the tire does, and by the same effect if you were to roll it one revolution on the edge of the rim the tire/OD would only go 3 feet just like the ID. By all rights this can't happen since mathmatically the OD has a larger circumference than the ID, but when two circles of different diameters are attached to each other logical mathmatics is thrown out the window. I read years ago that this problem is something that there is no mathmatical solution to and that some of the worlds greatest theoretical mathmaticians had tried to find a solution and failed. It is usually easier though to get the dial setup on the OD of the ring gear so that's normally where you see the reading made. Just my .02, I hope I didn't confuse you more.

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DaveWis

12-01-2003 16:49:46




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 Re: Re: Dial indicator setting in reply to Wayne, 11-30-2003 20:34:33  
I would guess the reason is that the center of the circle/s is not stationary but moving in the direction of rotation. Just a thought.



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Dennis Minn

12-01-2003 01:58:26




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 Re: Re: Dial indicator setting in reply to Wayne, 11-30-2003 20:34:33  
I beg to differ.I think given your example of a tire/rim,IF I am reading your writing correctly, that the ID of the tire rotated once, would equal a linear distance of three feet, that would equal the rim OD distance of a single revolution. If the measure being taken was rotational degrees, then all would be equal, but seeing we're usiing linear measurement, the rotation distance covered is dependent on the radius of the circle. Note, there is a difference in where the dial indicator is placed, but it may seem ever so slight due to the hyphoid/helical effect on pinion tooth engagement to the ring gear (more than one tooth engaged at a time). If the gears were sraight cut, then there would be even easier to see difference in dial indicator placement. Just my opinion, but have set a few ring/pinion sets for drag racing, trucks, turbines, and such. I have used the outer edge for all setup measures. Regards, Dennis.

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Wayne

12-01-2003 19:52:02




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 Re: Re: Re: Dial indicator setting in reply to Dennis Minn, 12-01-2003 01:58:26  
I used the tire/rim example because I didn't know of a better way to explain it, and looking back that was a bad example, I apologize. Reading your response though made me think about it more and I think we actually we have both explained it. In this instance where the dial is placed will not make a difference because the measurement taken is not "linear" at all, because it doesn't rely on either the ID or the OD of the ring gear. Like you said with this cut you get more than one tooth meshed at any given time for the same diameter/# of teeth than you would with a plain straight cut gear. Still no matter how many teeth are meshed the clearance is gonna be constant wether it's between the fully meshed ones or between the partially meshed ones. If it were different then you would never be able to set it because when the partially meshed ones came into full mesh they could be tight/loose and when the fully meshed ones became partially meshed they would be the same way. The clearance between the teeth is the same all along the tooth face wether the tooth is straight or hyphoid so no matter where you put the dial, inside, outside, middle, wherever, the dial is gonna show the same movement of the gear because all it's measuring is that clearance which WILL NOT change no matter where you measure it. Does that make sense now???. For "linear movement" to have an effect you have to have a fixed point and a movable point. If you were measuring something like seeing if a 6' long piece in a lathe was true between centers or not then the linear part would come into play because the further you get from the chuck/fixed point the more the dial would indicate. For instance .010 at the chuch may be .100 6' out. In the case of the ring gear there is no "moving" point, there is only a fixed clearance. Does it make sense now?????..... ..... Ok, I used a bad example for the question, but here is my point in the tire/rim deal I gave. If you rotate the tire 360 degrees on the OD/tire the the center line moves in a linear motion 6 feet, but if it rolls 360 degrees on the rim/ID then the center line only moves 3 feet. When you rotated the rim/ID 360 degrees the centerline moved 3 feet but the tire and rim BOTH make one 360 degree revolution so why doesn't the tire/OD make the centerline move 6 feet just like it did the first time it made a complete 360 degree revolution instead of only 3 feet??? Try it, when two circles, or more, are attached together like this linear measurement becomes fluid at the center line in relation to the OD being used. So 360 degrees can mean 3", 3', 6', 12' of linear movement for the center line for each circle no matter what the actual diameter of any of them. Another example, if you measure the RPM of an object with a photo tach or a mechanical wheel type tach, wether your 6 inches from the center of the flywheel (say 50FPM) or 12 inches from the center (say 100 FPM) the tach is still gonna show the same speed even though the FPM is different. Think about it even more, the exact center isn't actually moving at all, but .00000 01 out is still gonna show the same speed/RPM as the OD would 2' away. Like I said logic and math both say it shouldn't happen, but it does.

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Vern Iowa

12-02-2003 11:58:39




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 Re: Re: Re: Re: Dial indicator setting in reply to Wayne, 12-01-2003 19:52:02  
All I know is when traveling down the road on the Super M the axle movement does not look like it is going as fast as the top of the tire, it is making the same amount of rotations but if you put a dial indicator at the top of wheel and measured 1" the axle sure didnt move 1" with that being said I really dont think there would be that much of a difference in measureing the back lash at the top of the tooth or at the middle of the tooth. Probably the best way would be with the paper shear suggestion, or the paint suggestion. Very interesting as they say. Thanks for the responses.

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Dennis Minn

12-02-2003 02:01:34




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 Re: Re: Re: Re: Dial indicator setting in reply to Wayne, 12-01-2003 19:52:02  
Wayne, I am not quite following your example, and I truly want to be enlightened if I'm wrong. First off, a good discussion between me and anyone else remains that,no arguing over the keyboard for me. Now that being said, the ring/tooth engagement regardless of hyphoid/helical/straight cut will have clearance, as you stated correctly. My understanding is that the ring gear dial indicator measurement IS affected by where it's placed on the tooth, relative to axis of the ring carrier. The reason I say that is the ring gear dial indicator is alongside the ring, actually measuring the DISTANCE the ring moves, and this distance is affected by the arc of movement, and the arc length is dependent on the radius. I am trying to figure a way of stating what I think without coming across as some sort of smart aleck. Heck, lets go with an equal-sided teeter totter, the left side being limited in travel representing the pinion clearance, the right side being the dial indicator measurement, and the pivot point being the center axis of the ring gear carrier. Now, don't change how far the left side moves, and measure from the ground to the board on the right side.This measurement(arc length) will change the further I am from the pivot. That's all I am trying to say with the dial indicator placement, the further the measure is made from the rotational center of the ring the greater the measurement will be (assumiing the same clearance on the pinion). The pinion clearance does not change yet the reading of the indicator does,dependent on location. As far as the tire deal, I got some homework to do, because I have seen that explained in my applied physics book as to why, and if I can scratch it up, I write you back and try to reference it for you. Try this take your tire ID/OD dilema and put it on a tire balancer(off the ground), now use some string or a tape measure and record how far things travel per 360 degrees. I think the problem with the tire on the ground is that the tire travel causes the center point of the RIM to "slide", but the center point of the TIRE is spot on. That being said, great thought provoking stuff, and I appreciate the back and forth. Regards, Dennis.

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Wayne

12-02-2003 20:49:55




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 Re: Re: Re: Re: Re: Dial indicator setting in reply to Dennis Minn, 12-02-2003 02:01:34  
Hey Dennis, I'm the same way, I'm not into arguing. I like to learn and if I can learn something new here then I'm all for it, and if I come off like an smart alek, I apologize. Like you said it's hard to actually put what your thinking into words that can be understood by somebody else. Now we've both talked about linear movement, and you bring up the arc length, which if you think about it is the linear movement of the OD, (ie-- if it's 3' from 0 degrees to 90 degrees then it would be 4 times that or 12' from 0 back to 0 or 360 degrees.) I think the example your using about the seesaw is kinda like my example of a piece in a lathe. When you have a fixed and movable point on a flat plane then the measurement/length of arc does change as you get further aweay from the center/fixed point. When two circles are fixed together though as in this example that never comes into play. Think about it like this.... If the clearance between the teeth is .010 from the inside/ID of the tooth to the outside/OD of the tooth then the clearance will measure the same no matter where on the tooth you put the dial. If you placed the dial on the OD and it read 0 when the gap was completely closed then when the ring gear moved and opened the clearance it would show .010. When it moves back closed it will once again show 0. By the same reasoning if you put the dial on the ID the gear can only move .010 for the gap to close or open fully so if the dial is at zero and you open the gap fully it's gonna read .010, and if you close the gap it's gonna go back to zero. This is gonna happen no matter where on the toth you place the dial because the clearance determines the reading. I think the more we talk about this the more clear what we're trying to say becomes if not to each other then to ourselves which makes it easier to explain, right or wrong.... Think about the example I gave this time and see if it sounds right explained this way.----- ---- If you can find an explination for my tire/rim example and the movement/slip of the centerline in regards to the OD and ID, please do let me know because it doesn't make sense to me and like I said I once read that there was no mathamatical reason/logic as to why it happens.----- ----- - Just like you I appreciate the back and forth. I really enjoy a good discussion. In my expwerience being able to just discuss something is the best way to learn because you have to use your head and actually think about the subject, and that's the best way to learn. Take care, and I'm looking forward to any info you have. Wayne

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Wayne

12-03-2003 21:07:24




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 Re: Re: Re: Re: Re: Re: Dial indicator setting in reply to Wayne, 12-02-2003 20:49:55  
Hey Dennis, looks like I finally explained it right, or at least close. I feel like I'm "beating a dead horse" saying this, but I'll say it again, in this case the measurement is dependant on the clearance and nothing else. The thing I'm having a hard time explaining is why. How can I say this better where it makes sense? Man your making me think here...LOL... OK, I guess the best way to think about the gear teeth is to make them two normal bevel gears. Now take the fact that the teeth are on a gear and that it's round out of the equation and think about just the teeth. The clearance is the same on each end, so in effect they are simply two parallel lines, right? Ok, for two lines to be considered parallel that means they are equadistant apart from and to infinity so they never touch. So if the teeth are parallel then there can't be a line passing directly through the center point of the gear, there are actually two lines passing the center point equally distant from it. So they never cross/touch the actual center point, and therefore don't touch of cross or each other. Now for the clearance to change they would have to cross each other at the center point to give a pivot. This would bring about the condition your talking about with the measurement changing. The further you get from the line crossing/pivot point, the greater the arc angle/ dial reading would be. Without that pivot point no matter how close you get to or how far you get away from where the lines pass the center point the reading will be the same because the lines will continue to be parallel. Does it make anymore sense now? I wish I could draw all this out and post it, maybe it would be easier to explain and understand that way. I'm still stumped on the tire deal but this has made me see that it was a bad example. In it I was using a pivot point trying to explain this concept, when the lack of a pivot point is actually why it works like it does. The more I think about and discuss this the more I remember from school ..... .. Let me know how I did with this explanation. Like I said last night, your really making me think and taxing my education here. I was always good in geometry and dealing with this kind of thing but that was 17 years ago. I remember some of it, but not always enough. Take care. Wayne

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Dennis Minn

12-03-2003 00:42:27




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 Re: Re: Re: Re: Re: Re: Dial indicator setting in reply to Wayne, 12-02-2003 20:49:55  
Wayne: AH HA !!! I finally have an understanding of what you were getting to about the ring tooth/pinion clearance and dial indicator. I still have some trouble with the indicator position being a non-factor. Here's food for thought: run the ring gear teeth all the way into the center of the carrier, but only keep the pinion it's normal size. Now will the dial indicator placed .001 from the centerline of the carrier read the same as if it was placed on the outer edge of the ring gear? I think it may not but I'm willing to listen for more. Regards, Dennis.

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Loren

12-02-2003 19:57:41




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 Re: Re: Re: Re: Re: Dial indicator setting in reply to Dennis Minn, 12-02-2003 02:01:34  
You're correct Dennis. Think about if you measure from the same distance from the pivot on a casting rib that runs from the outside of the ring gear all the way to the center. Same measurement. It's the arc length you're measuring, not anything else. The only way that "it doesn't make any difference", is that the amount of change from the inside of the ringgear to the outside of the ringgear will still be with a good acceptable tolerance.

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Bob

11-30-2003 14:39:10




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 Re: Dial indicator setting in reply to Vern Iowa, 11-30-2003 12:13:24  
Every illustrated instruction I have ever seen for vehicles or tractors shows measuring the gear lash at the tip of the tooth nearest the OD of the ring gear.



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