×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

root fillets of gears

root fillets of gears

root fillets of gears

(OP)
I seemed to misplace my equation for the max root radii fillet possible for a specific gear data.
And I am unable to retrieve it from my old HP 42 card reader. This was given to me about 30 years ago.

How ever In reviewing Gear Handbook by Dudley
Chapter 5 pages 5-24, 5-31 & 5-40
5-24
It depicts Eq. 5-33
Root Fillets

  rf=0.7[rT+ (ht-a-rT)  /(d/2cos2 helix)+ht-(a+rT)]
(super & sub scrpits formated correctly in word but does not format correctly here)



rs = mim calc fillet radius produced by hobbing or generating  grinding
rT = edge radius of generating rack, hob or grinding wheel
a= addendum of gear
ht=whole depth of gear
d= pitch diameter of gear
helix=helix angle (use 0 degrees for spur gears)
 then

easiest equation for fillet radius as shown 5-31 & 5-34
reprint from AGMA rf =fillet radius (in basic rack ) coarse pitch
.300/P = rf (20 & 25 deg Pressure Angle)

obsolete system
.157/P= rf  (for brown & sharp, AGMA 14.5 deg), & 1.33 x clearance (for full depth AGMA) will add more as time permits
Please comment for any suggestions or additions.
 

RE: root fillets of gears

You will find equations for the suggested minimum fillet
radius.  Machineries handbook used 1.333xclearance for 14.5 degree and 1.50xclearance for 20 degree teeth.
Each number of teeth will have fillet radii exceeding this
general guideline.  The fewer teeth, the greater the radii that the hob radius will generate.  As the number of teeth
approaches infinity, the closer will the part radii equal the hob radii.  These general rules applied to full depth
teeth.  I think FMC decided on using .295 for the clearance
as it would allow the maxiumum radius for a full fillet radius to be formed and it approached .44847 divided by the
diametral pitch which nearly matches the 1.5 x the clearance rule.
A theoretical approach for the max radius on the hob would be (C/CosAlpha) times the Tan((90 plus Alpha)/2) where
Alpha is the pressure angle of the gear or hob.  This gives a value of almost 1.52 times the clearance for a 20 degree pressure angle gear.  Does this sound familiar?

RE: root fillets of gears

(OP)
DimJim

Thanks for your reply :)

The equation I had, use the following gear data:

# Teeth
Diametral pitch
Pressure Angle
Major & Minor Diameter
True/start of Involute (TIF)
Actual circular tooth thickness

I may be able to purchased a used card reader
and reload the program & decipher the equation.

RE: root fillets of gears

If you check out my formula, the result for 14.5degrees
is 1.33 x the clearance, and for 20degrees is 1.519 x the clearance.  This was in agreement with the past Machineries handbook for external gears.
  
Internal gears cannot be hobbed and the radius is somewhat dependent on the number of teeth in the gear shaper cutter.

When you find your magic formula from your HP42 module, please post it here.  Do you think it came from the AGMA formulas for calculating the max bending strength?  I do remember a formula there in one of the AGMA standards.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources