Help with Spur Gear Specifications 1

[Trukker]

Hi Folks

I urgently need to replace a current 14 tooth pinion with a 17 tooth one with no change to the 52 tooth mating gear.

I tried reading up some stuff and though I could decipher the basis for the specs and translate that to the 17 tooth pinion required, but realized that I have quite some ways to go. I hope I can get through with it this one time with your help.

Current Pinion
Z=14, OD = 20, Pitch Diameter=17.5, Module =1.25,
Pr. Angle = 20
Mating Gear (Will remain unchanged)
Z=52, OD = 67.50, Pitch Diameter = 65

Detailed Specifications

Pinion Gear
Basic Rack:
Addendum = 1.0447 x m; 1.0224 x m
Dedendum = 1.2053 x m 1.2376 x m
Tooth Thickness= 1.5708 x m 1.5708 x m
Base Diameter=16.4446 61.0800
Correction factor = - 0.0446 -0.0424
Norm. Tooth Thickness = 1.9229 1.9249
Base Tangent Length = 5.742 - 0.034 21.170 – 0.042
No of teeth spanned = 2 6
Dim over 2 pins = (20.827 -0.074) (68.451 -0.110
Pin Diameter = 2.300 2.300
Tooth Quality: DIN 58405 Class 9
Composite Method
Composite Error = (0.050) (0.063)
Tooth to Tooth error = (0.018) (0.022)
Run-out at Tip = 0.042 0.053
Tooth Alignment Error0.018 0.016
Tip Diameter utilizable=19.722 62.885
Root Dia Utilizable=16.467 62.805
Centre Distance 41.25

New Pinion will have Z = 17 & Center Distance = 43.125

I need detailed specs for the new pinion.

Thank you very much

JohnLouis

 

[israelkk]

First of all I do not think that this is the forum to do engineering work it is for guidance.

Secondly, you can not use 17 teeth gear without a major negative gear correction which will create a large undercut which will reduce the gear strength.

I think you should seek a consultant that will check the complete gearbox. You will probably will have to change the mating gear too and the module too.

 

[dimjim]

If the pinion and gear was modified
as shown in your calculations,
you cannot use the standard
center distance without making the
pinion a short addendum which as
israelkk states without some undercutting
of the pinion. It is a good design practice
to make the correction factor of the pinion
greater than the correction factor of the
ring gear which would require a greater
center distance than the standard. Yes, you
are over your head unless you do a lot more
study of correction factors and their effect
on center distance and also understand why
small pinions may be undercut unless you
you use a correction factor.

 

[gearcutter]

Zp = 17
Zg = 52
Center Distance = 43.125
Xp = +0.0424
Xg = -0.0420
Span accross 2 pinion teeth = 5.832 (includes 0.04 backlash)
Pinion O.D. = 23.86

As israelkk suggests, the pinion will be undercut. Along with the existing minus correction on the gear, this gear train will end up with a Balanced Specific Sliding Ratio of 3.77 (should be around 1) and an efficiency of 96.75%. It will end up being noisier than the existing geometry along with a weakened pinion tooth profile because of the undercut. Not a good idea to use this design for anything permanent albeit it should get you out of trouble for the short term only.

 

[Trukker]

Many Thanks, gearcutter.

Can you tell me how to obtain tooth thickness for pinion & gear

This will help me to muddle through this time.

I am trying to get comfortable with all this. Just downloaded AGMA 913-A98 from the AGMA website.

This is actually a very low load kinematic application. The big gear only oscillates through a max angle of 20 degrees.The torque on the bigger gear would about 8 to 10 Nm.

Regards,



JohnMLouis

 

[gearcutter]

What do you need the tooth thickness for?
If you're cutting this gear then all the gear cutting data is there. You won't need the tooth thickness as the span across teeth is given. This is far more accurate than the method of using gear tooth verniers and measuring the tooth thickness. The span is measured across the given number of teeth using verniers or disc micrometers.