ISO TR 4467

[berto]

addendum modification coefficient
hi at all.
someone told me that this standard is the useful standard to
completely understand shift coefficient procedure.
i really appreciate if someone send to me the normative
and talk to me how is the procedure to define corrections.
thank you very much

 

[gearguru]

I do not have that standard, but you can look for the following very good article published in

Gear Technology Nov. - Dec. 2001:

"Profile Shift in External Parallel-Axis Cylindrical Involute Gears"
by
Phillips D. Rockwell.

Try to search for it on the

http://www.geartechnology.com

web page


gearguru

 

[JRCD]

Your quiz is very important.

You can buy the ISO/TR 4467:1982 standard directly of ISO (

http://www.iso.ch/)

or via AGMA (

http://www.agma.org/).

Also take a look at AGMA 901-A92 (R1997) and AGMA 913-A98 standards.

During the XIX century gears were manufactured with profiling tools at milling and shapers machines. Although conceived in 1856 by Schiele the first machine tool for the generation of gears was build near 1887. This process began to spread at the last decade of the XIX century. Soon the existence of tooth undercut on gears of small number of teeth was verified. This was overcome by profile shift. Only some years later the profile shift coefficient concept was introduced.

In the generation process the tooth thickness at the reference pitch circle may be equal (eventually somewhat minor to get the backlash) to half of reference pitch (p/2) or it may be different. If equal they are called x-zero gears, and if different they are called x gears.

A gearing pair can be formed by two x-zero, or two x , or even one x-zero with one x gear. The working center distance may be equal or different of the reference center distance [a = m.(Z1 + Z2)/2]. In the first case we have the so-called V-zero gearing (for the external gearing x1 + x2 = 0), otherwise we have the so-called V gearing (for the external gearing the sum x1 + x2 is different from zero).

The profile shift expresses the radial distance between the reference rack pitch line and the gear reference pitch line, expressed in terms of module (or diametral pitch) in the form ± x.m (or ± x/P). There is a positive profile shift if reference rack pitch line is outside of gear pitch circle, and negative in the opposite case.


The profile shift coefficient (x) has many influences on gears and gearing characteristics like tooth thickness, tooth undercut, bending strength, working center distance, length of approach and recess path, pitting resistance, noise and so on.

You can use gears books and standards recommendations. But if you want to optimize gears design it will be necessary to undertake full gearing analysis because there are always many possible solutions. For this we need more input data and knowledge of all requested conditions, like the transmitted power, angular speeds (reducing or increasing), load characteristics (including inertia), possibility of back transmission, gear materials and treatments, gear operation cycle, gear quality, maintenance and environmental conditions and so on.

 

[berto]

Dear Mr. JRCD
i have really read with lots of attention your reply. it is very interesting. a little flashback in the past century.
and thank you for AGMA normative number. i don't knew them before.
also DIN3992 talk about corrections they told to me.
i'm trying to get you another question;
an exemple to how do we arrive to define X factor.
where do i start with the calculation? diam pitch, pitch diam, other ..?
and which is the process to define the amount of X?
some questions? i'm sorry but curiosity is too hard for me ..
so, if you are agree to answer, i'll be very satisfy.
thank you very much
best regards
Ester

 

[gearguru]

The article I mentioned above will teach you everything what you need.
gearguru

 

[JRCD]

Sorry, this subject is so extensive that I can’t give here a full development.
You will find below only one preliminary example for external cylindrical gear drive design.
-------I-------
First of all start with estimated or imposed values for m, alpha(reference pressure angle) , z1 and z2.
1- Considering your (z1 + z2) value select the (x1 + x2) value recommended for profile shift on tables, graphics, articles or books.
For alpha = 20° you can start with:
a) If Z1>30 and z1+z2>60 than use Zero Gear Drive where a'=a=m[(z1+z2)/2)] and x1=x2=0 and so x1+x2 =0;
b) If z1<30 and z1+z2>60 than use Vzero Gear Drive where a'=a as above but x1=0,03(30-z1) and x2=-x1 and so x1+x2=0;
c) If z1<30 and z1+z2<60 than use V Gear Drive where a'>a and x1 = 0,03(30-z1) and x2 = 0,03(30-z2) and x1+x2 > 0;
d) If z1<10 use x1=0,6 and because of the insufficient tooth tip thickness in gears with small number of teeth the tooth height must be reduced to h = m (2,25 – k), where k is the tooth height reducing coefficient [k = 0,04 (10 - z1)] and adopt x2=(0,03(30-z2).
For best contact ratio (less noise) if (z1 + z2) > 60 select (x1 + x2) near zero, to improve the bending strength bring (x1 + x2) near 0,7 for increased load capacity.
2- Considering the gear ratio (z2 / z1) and also taking in account if it’s a speed reducing or speed increasing drive select separately values for x1 and x2. For this utilize information source above mentioned.
3- Compute the working pressure angle for this gear drive utilizing the under mentioned equation:
inv alpha’ = [2 tg alpha (x1 + x2) / (z1 + z2)] + inv alpha
where: inv alpha is the reference pressure angle (20° for example) involute function; inv alpha’ is the working pressure angle involute function.
4- Compute the working center distance from:
a’ = m (z1 + z2) cos alpha / 2 cos alpha’
5- Compute the working pitch diameter from:
d’1 = (2 a’ z1) / (z1 + z2) and d’2 = (2 a’ z2) / (z1 + z2)
6- Compute the root diameter resultant from the generating process and tool proportions.
df1 = m [z1 – 2 (1 + c* - x1)] and
df2 = m [z2 – 2 (1 + c* - x2)]
where c is the clearance and c* is the bottom clearance coefficient (c = m c*).
7- Compute the addendum (outside, tip) diameter from:
da1 = 2 (a’ – c) - df2 and da2 = 2 (a’ – c) - df1
8- Remember the profile shift don’t change the base diameter nor the base pitch of a gear, but change tooth thickness. For gear measurement with Wildhaber method (base tangent length) you need know the base tooth thickness:
sb1 = sb1zero + 2 x1 m sin alpha and
sb2 = sb2zero + 2 x2 m sin alpha
where: sb1 and sb2 is the base tooth thickness of gears with profile shift x1 and x2 ; sb1zero and sb2zero is the base tooth thickness of gears without profile shift (x1 = x2 = 0).
-------I------
Now eventually others geometrical parameters may be calculated like gears contact ratio, pinion tip thickness, etc. Thereafter you must check dynamics parameters like noise, bending strength, hertzian surface stress (pitting), scuffing risk (scoring), and so on. Eventually you must change pre-selected parameters like m, z1, z2 , gear material & tratment and make again the gear drive computation often and often as necessary. The gear drive design is an interactive process and for the same project there are as many different gear drives as designers.
You may find different calculation methodology and equations, for example you can employ the center distance modification coefficient , parameters B and Bv, but here I used the most understandable.

About the Nov/Dec 2001 issue of Gear Technology magazine you probably can buy it at

http://www.geartechnology.com/mag/gt-back.htm

I would be hope if fulfil your expectation.

 

[berto]

Dear Mr. JRCD
now i got lot of material to try.

and thank you very much for your patience.

0,03 factor is the right factor?
i've just seen a design of a pinion with 11 teeth, so <30, and z2 is 28 teeth so z1+z2<60.
the shift correction x is 0.747; it would be 0.57.
there is a big differce.

where do i find table and graphics about shift coefficient?
are there in any text?
or maybe in ISO/TR 4467 normative?

in point 6)you said:
&quot;Compute the root diameter resultant from the generating process and tool proportions.
df1 = m [z1 – 2 (1 + c* - x1)] and
df2 = m [z2 – 2 (1 + c* - x2)]
where c is the clearance and c* is the bottom clearance coefficient (c = m c*)&quot;.

the question is;
if c is the clearance at the root and c* is a value that depending from c, are there any formulas or standard to decide the amount of c?

so, today i'll try some calculation..

Mr. JRCD thank you very much
p.s.
as also Mr. gearguru told me about the article. i'm wait for a GEARTECHNOLOGY reply to buy.

best regards
ester

 

[JRCD]

Ester
a] 0,03 is the right factor for expression x = 0,3 [30 - z].
b] Okay, for z=11 result x1 = 0,57.
c] The preliminary [arbitrad] coefficient of profile shift can be accepted only with the knowledge of all requirements of power transmission and after the end of all calculation.You can adopt any value but if it's a good one you short cut the number of interactive loops for gear drive calculation.
d] Suggestion for shift coefficient must be searched in standards, books, papers and articles. Some were mentioned before but you have to take a look at DIN standard 3992, 3993 - 1 to 4, 3994 and 3995- 1 to 8. Also take a look at BP[British Standards], AFNOR (French Standards), UNI [Italian] and JIS [Japanese].
e] The clearance coeficient c* for root diameter calculation is determinate by generating tool proportion [c* = 0,25, per example].
Best Regards.