Gear Inspection - MOW, Tight Mesh CD, Test Radius

[SwaggingIt]

I've been researching this but sometimes you just need an expert to give a straight answer. I'm at a small aerospace design shop where I dont have access to gear mfg, so its difficult to understand some of these inspection methods without the firsthand experience.

If our gear drawings define MOW, should they specify test radius too?

On the flip side, if the gear mfg is doing double flank inspection for TCE and TTE, then they can measure tooth thickness too so MOW wouldnt be necessary. However, if we define test radius or tight mesh center distance on the print, then we need to also include the master gear details which, I assume, might further increase lead time and cost if the mfg doesnt have that master gear available?

The Gear Technology white paper on double flank testing implies that tight mesh CD is better than test radius. Do you guys agree, or what do you see more commonly used?

Furthermore, our gear SME is saying that test radius doesnt need a tolerance, but everything I'm reading says it should. Could someone clear this up for me or point me in the right direction? We often do a profile shit to balance forces, how is that accounted in the test radius?

Sorry for a list of questions - a lot to unpack here. Any advice/help is greatly appreciated! Please let me know if I need to clarify anything.

 

[mfgenggear]

OP
Most but not all, gear shops have cnc gear checkers, master gear rolling machines. Lead and involute inspection machines.
I will specify usa AGMA gear requirements.
I am bias with standard measure over wire or balls for externals and measurement between wires or balls for internals. For small to medium lots a gear inspection checker can do it all involute, lead, total index error, tooth to tooth error., gear cutters and gear grinder operator machinist prefer to inspect their parts while machining with a master gear. Since gear checkers can be tied up.
Once upon a time master gear verification with a master gear was a fast method to inspect gears . A test radius verification would be a quick fast verification of size.
But that master gear has
to be for a specific gear. Test radius is mfg at basic size, but has a high and low limit for the gear size. To verify the correct gear tooth thickness inclusive with all attributes.
AGMA class specifies either analytical to be inspected by cnc checker or by master gear. Give the gear shop option to use either.
Again a tight mesh mater gear for verifying tce and ttce is a standard cut master gear. A test radius test is a master gear designed with a basic test radius but is given a limit to hold size. A standard master gear will or could give the correct size for a test radius.
A test radius is rarely used any more unless the gear shop prefers it.

 

[mfgenggear]

Op
The AGMA will specify the recommended gear attributes.
AGMA quality class will address the require attributes.
If the requirements need to be none typical it can be specified on the gear table. Minimum is number of teeth, DP or Mod. Pressure angle, measurement over wires or balls.
The wire or ball diameter. Major diameter, minor diameter, true involute form diameter, TCE, TTCE, lead, involute chart. Degrees of roll at major, pitch diameter TIF, high velocity gears require a modified involute, a low rpm can be standard involute. Lead or parallel.
Of course the gear design is more complicated.

 

[spigor]

For MOW, no test radius should be specified as wires will touch the flanks on a radius they choose to. That radius depends on many factors, including gear basic data, wire diameter and tooth thickness. You have influence on the test radius by choosing the wire diameter.

 

[3DDave]

MOW (measurement over wires) is what I would expect is to tell the guy running the hob that the teeth are deep enough and should stop.

For those stopping by:

"TCE" stands for "Total Composite Error" and "TTE" stands for "Tooth-to-Tooth Error"

Probably CD (Center Distance) is for measuring backlash; if so that should be as accurate as possible and needs no tolerance. The tolerance is in the backlash measurement.

 

[mfgenggear]

MOW OR MBW inspection measures the correct CTT for external and CSW on internals. Test radius or center distance specified on a master gear setup test is not the same as tested on a cnc gear checker.
Master gear check was a procedure before we were born. It is the fastest method for inspecting gears. While a cnc checker can measure pitch diameter and CTT. To my opinion it is not as accurate as a mow check or a master gear check.
That can be debated.

 

[mfgenggear]

Master gear can and normally is used at tight mesh , means no back lash. It verifies the TCE and TTCE, a gear checker will measure Total Index, and Tooth to Tooth index error.
That is a fact.

 

[mfgenggear]

An operator will inspect all the attributes of a gear as he or she machines it as a first article. Master gear is a very quick fast and easy check. It is preferred. An MOW check is preferred as well , then a test radius is not required. For a design and fabricated for master gear for test radius.
Again a master gear designed to be inspected with a test radius is only for that specified gear. How ever it is a fasted method to inspect gears.

 

[mfgenggear]

https://www.geartechnology.com/ext/resources/issues/0114x/double-flank-testing.pdf