25T 1.0 Mod Gear came out wrong. How to measure 'over the wires'? 1

[MonsterMaxx]

I've made this gear before with these specs (10+yrs ago), but with a new vendor I'm having to explain how to check it and I'll be darned if I remember. It's way undercut but it's mating gear they did right.

The spec is:
Spur Gear
1.0 Module
20° Pressure Angle
.001" of backlash
Hobbed on a standard 25T diameter.

I've looked up several resources on the net on how to measure this and am not getting answers. I'm getting bits and pieces, but not the whole picture.

Proper methods for 'measuring over the wires'?
How do I choose the wire diameter?
What calculator should I use?
Where do I find the 'standards' to compare it to?

Any help would be greatly appreciated.

 

[mfgenggear]

MonsterMax

do you have any of the previously made gears in stores or laying a round. have the gear supplier take measurements.
the sketch supplied is in adequate for manufacturing. see spec

https://members.agma.org/ItemDetail?iProductCode=1103-H07&Category=STANDARDS

hire a gear engineer to help out with design. and to document because you are not experienced in gears.

 

[spigor]

How about

https://global.ihs.com/doc_detail.cfm?document_name=AGMA 231.52&item_s_key=00005739

And

http://www.geartechnology.com/issues/0987x/Reece.pdf

 

[MonsterMaxx]

Hmm, not sure how to take that mfgenggear.

However, I sense your reluctance to offer a complete picture of the answer here...nothing for free, right? I get it.

Perhaps you'd be at least willing to confirm or deny if a Ø.083" pin would be suitable for measuring over the wires on the above gear. If not, perhaps a table that shows what pins would be appropriate for this gear?

I drew the gears in my cad system and the Ø.083" circle (my gauge pin size) seems to land nicely on the face of the tooth.
Further, when I measure over the wires on the gear from the gear pair that looks properly made, it's almost the same as cad says it should be.
When I check the other gear (the one we are discussing, it's off by 1.5mm (too small.)

It would be great if answering my vendor I could include a table of suitable pin sizes and dimensions.

TIA.

 

[SwinnyGG]

Your gear vendor makes and QC checks gears all day, every day- let them tell you how they measure.

 

[3DDave]

I am a bit confused - module is typically a metric value but backlash is given in inches?

The pins should sit near the pitch diameter.

https://evolventdesign.com/pages/gear-measurement-over-pins-calculator

has a calculator. It uses profile shift rather than backlash.

There is a lot more to gear design. Capturing dimension over pins doesn't do the entire job of telling if the gear is going to perform well, but that's where a gear designer would come in handy.

 

[mfgenggear]

Monstermax

lets go over some basics, the reason I am reluctant is this
not sure of the fit form or function, is there a safety issue, will some one get hurt if it fails.
some of the small details are important, are the pinions enlarged and profile shifted, so the small gear (pinion) will have a larger tooth thickness.
the gear will have minus tooth thickness to adjust the correct backlash. are the gears are designed for the correct module. pressure angle for the given.
torque, horsepower. and RPM. there are many factors for wear, tooth bending , and fatigue. the type of material, heat treat required, and case depth.
1.728 or 1.92 series Van Keuren pins, 1,728/25,4 (1 mod.) = .06803 gear wires. 1.92/25.4 = .0756 gear wires, the trick is to get the wire as close to the theoretical
pitch dimeter. and the wire must clear the root. to add I don't know if the gear is a standard gear. follow what is in the machinery hand book. here is a tip

https://evolventdesign.com/pages/gear-measurement-over-pins-calculator

 

[mfgenggear]

profile shift is to strengthen the pinion, and to adjust for wear by changing the profile contact. a gear must still have the correct backlash for the given module or diametral pitch, and pressure angle.
if not enough backlash the gears will self destruct. or wear prematurely. better to have to much backlash. one must follow the AGMA or other similar specifications as a guide. or buy a good gear design program.
that lets one crunch numbers to optimize gear trains. efficiency, wear, tooth bending safety factors. are in reasonable design parameters.

 

[spigor]

Hobbed on a standard 25T diameter.

Is the O.D. 27 mm? Is it not truncated? Taking 0.001" backlash I get wire size 1.502 mm and M.O.W. 26.45 mm. That is less than the O.D., so wire dia.>1.65 mm should be used.

 

[MonsterMaxx]

Yes spigor, the OD is approx. Ø27mm. It's the cut of the tooth that's wrong. Even with my gauge pins (Ø2.1mm) being way bigger than you recommend, on the 'bad' gear, the pin fits all the way down into the root of the tooth. On the good gear (it's mating pair) the pin is sitting on the tooth pretty darn close to the pitch diameter.

The pinion is a 27T. The facewidth is 6mm. RPM is low to 5k. It's an aftermarket gear so we are fitting an existing housing.

As for having the backlash in inches on a metric gear...my bad. These were some of the first gears I ever made and they date back 15+yrs. The design of these gears were to replace plastic with something indestructible. I took a WAG at the material and best heat treat back then. It worked.

I'm going to get some smaller pins and see if my ##s line up.

I think I understand this well enough now to update my vendor. Thank you all for your help.

 

[spigor]

For pin dia. Ø2.1 mm I calculate M.O.W 28.52 mm.
If the 27T pinion has been designed with the same philosophy, then its O.D. would be at 29 mm and the center distance would be 26 mm. The M.O.W. Ø2.1 mm would be 30.54 mm.
Do these numbers make sense to you?

 

[gearguru]

If the "backlash" means "clearance" between two gears in mesh, then we need to know the meshing gear data (tooth thickness); or am I wrong?

 

[spigor]

gearguru

Backlash only exists in a mesh with a mating gear and with a defined center distance. A single gear never can have backlash.
Many gear cutting companies inaccuratly use the term as meaning that you take half the backlash value and reduce the tooth thickness by that amount from half its circular pitch. Its a very dangerous practice.

https://www.eng-tips.com/viewthread.cfm?qid=252168

I looked at the pitch and at the backlash value as specified (0.001") and, out of the experience, I reduced the tooth thickness 0.001" measured on the base pitch (not on the circular tooth thickness).
One way to explain that would be to mount the gear to be inspected at correct centre distance with a master gear (made to full theoretical tooth thickness) and set a dial indicator normal to the tooth's flank - it should show 0.001" backlash.

 

[mfgenggear]

gears are designed according to the requirements. it is not uncommon to to control span measurement or measurement of wires. and the attributes of the gear inclusive, EG lead error, Tooth to tooth, total composite error. pitch diameter runout. with a master gear or with a CNC gear checker. which controls back lash. and the designer controls the center distance tolerance. with .001 backlash the question is to what AGMA tolerance does a gear required. the rpm is low to 5K what does that mean exactly. that means at 5k RPM this must be a close tolerance gear.
a lot of loose gears are manufactured as I had stated above. the major diameters of gears are base on the total involute form diameter (TIF) of the mating gear. at a set center distance.
as not cause interference. and both major diameters clear. go back to the gear box and look at the center distance. and have the gear shop measure the mating gear.
from that data the measurement over wires from circular tooth thickness can be defined.