Gear Measuring - Determining when a gear has had too much wear
Gear Measuring - Determining when a gear has had too much wear
(OP)
Hello all,
I am trying to find out when a gear has faced too much wear. In other words, I want to be able to determine whether or not a new gear is necessary for an assembly. I would assume there is a standards chart or something that would let me know what the standard backlash is for certain gear sizes, or if some gears have a standard tooth thickness, but I have been unable to find any kind of document/link online. I have been researching gears, finding out about their nomenclature and how to measure them using a Vernier Gear Tooth Caliper, without much luck.
In summary, is there any way I can learn more about gears and their standards, if they have them? Or knowing when a gear is shot?
Thanks for the help!
I am trying to find out when a gear has faced too much wear. In other words, I want to be able to determine whether or not a new gear is necessary for an assembly. I would assume there is a standards chart or something that would let me know what the standard backlash is for certain gear sizes, or if some gears have a standard tooth thickness, but I have been unable to find any kind of document/link online. I have been researching gears, finding out about their nomenclature and how to measure them using a Vernier Gear Tooth Caliper, without much luck.
In summary, is there any way I can learn more about gears and their standards, if they have them? Or knowing when a gear is shot?
Thanks for the help!





RE: Gear Measuring - Determining when a gear has had too much wear
RE: Gear Measuring - Determining when a gear has had too much wear
A properly designed gear set should not experience "wear" in the classical sense. While a new gear set may produce a small amount of debris during an initial run-in period from shearing of microscopic surface asperity tips, once the gears have been fully run-in they should experience no further abrasive wear under normal operating conditions.
Properly designed gear sets are usually limited by tooth bending or surface contact fatigue life. By the time your gear set has accumulated enough abrasive tooth wear to produce any measurable change in tooth thickness or backlash, they are definitely "shot". But simply replacing the gears will not likely resolve the root cause of the problem. If your gear set is experiencing abrasive tooth wear, you need to address the problem by modifying the design of the gears and/or lube system. As Jboggs noted, the AGMA documents provide an excellent reference for designing gear systems.
Good luck.
Terry
RE: Gear Measuring - Determining when a gear has had too much wear
RE: Gear Measuring - Determining when a gear has had too much wear
@Jboggs- I have checked with the AGMA, and is one of the reasons I posted in the first place. There's a broad spectrum of standards they offer, but I didn't want to make a choice and end up wasting money on a set of standards that don't pertain with what I need.
@tbuelna- you can see from what I said about the company above, that is precisely what we do. We see what causes a gearbox's wear, then we fix it. What I need to know is when a gear is still usable, or if we need an entire new one.
@Brian Petersen- Our applications vary greatly, but a basic RPM range we work with is 1100-1700 (we are certainly not limited to that). As for strengths/ratios, we typically work with steel and paper mills, which also tend to vary (hence the medium speed on the RPMs). We've worked with gears with high enough ratios that the output hardly even moves when the input is rotated.
I hope all this helps. Thanks again!
RE: Gear Measuring - Determining when a gear has had too much wear
You presumably wouldn't have the gearbox in for repair unless something broke. Broken stuff inside a gearbox tends to send metal shrapnel everywhere inside, which can end up jamming itself between gear teeth and getting into bearings and wrecking all sorts of parts that weren't directly involved in the original failure. If maintenance is as per usual - keep going until you absolutely cannot go any further - I'm sure you've seen the results.
I'm working on a motorcycle transmission in my own shop right now, in which an engagement dog broke off and ended up in the oil pan without damaging anything else, and there was no outward indication of any fault with it because the other two continued to carry the load! Those are the exceptions. I've had the same type of failure result in the bike having to come in on the recovery truck (at a track day).
RE: Gear Measuring - Determining when a gear has had too much wear
That's a valid point. For some gearboxes, however, things like backlash and tooth length aren't as critical as other gearboxes correct? So we could trim down the teeth on the gear to remove blemishes, while shortening the teeth to make the teeth stronger (or at least the torque on the teeth less). Obviously we would not be able to remove much, but for minor abrasions that could save money. Would that be possible?
You lucked out there, we've seen what one missing tooth can do, I can tell you!
RE: Gear Measuring - Determining when a gear has had too much wear
Other methods are oil samples.
No matter what the condition: if it stable under the applied operating conditions, it is good.
"better" is only relative.
RE: Gear Measuring - Determining when a gear has had too much wear
My company does this too. Our basic approach is: new or like new gets full warranty, slight wear gets much shorter warranty, worn stuff gets no warranty. Customer gets to choose.
The real answer always depends. What is the failure mode of the gearing? Is it surface failure? Are your customers sensitive to noise and vibration, or do they only care that there are enough teeth intact to keep the output shaft turning?
David
RE: Gear Measuring - Determining when a gear has had too much wear
A substance to do this with is Technovit 3040, but there are more, and they all do the job