Span deviation / Spur gear / ISO 1328

[DocSergey]

Please, help me
I'm from Russia and everybody here is working according to GOST standard, but right now i need to build a spur gear according to ISO 1328 and i've got one problem: i can't find information about span deviation, i mean minimum and maximum. For example in GearTrax (gear generator)for pinion m=1.25 z=18 x=+0.5 - span measurement: teeth to gage over = 3, max=9.968, min=9.912 (cant remember what tolerance class in this case).

so, how i can find this minimum and maximum values?
(sry for my english)

 

[mfgenggear]

Doc

The maximum and minimum will depend on the center distance, and the amount of backlash required.
the tolerances held will depend on the fit form and function of the gear train.

example if the back lash must .006-.010 then the tolerances of the center distance and the measurement over wires or spam measurement must be tighten to maintain the backlash.

Mfgenggear

 

[DocSergey]

thank u mfgenggear, but it is kind of obviously
what i meant before is that i can't find information about how to calculate upper and lower deviation for span measurement.
ISO 21771 describes how to calculate it, but there are some stupid things:
for example 2 formulas from page 67 (BS ISO 21771:2007)

sbn.amax =sbn.max −cosβb(FrtanαtM +FpkcosαtM);

sbn.amin=sbn.min+cosβb(FrtanαtM +FpkcosαtM).

i can calculate sbn (tooth thickness on base diameter), but dont know min and max (even tolerance) to know that, i need to
look into DIN or AGMA ("This annex includes the technique for calculation of the tooth thickness test dimensions using the
nominal system, but does not include calculations for the predicted backlash range. See DIN 3967 for such calculations.").
lol

i mean, i do not have a lot of money to buy standards only for 2 values. maybe smbdy can just tell me how i need to calculate
or where is information about that :c

Many thanks for considering my request.

 

[mfgenggear]

Doc

You start with standard circular tooth thickness. then modify it to suit your needs.
most gear programs inputs are as follows.
# teeth Mod or DP and pressure angle.
input would be CTT or span or M.O.W.

The starting factor is circular space width based on the center distance required.
the tooth strength required will be the DP or mod & pressure angle required.
it's that simple. it's being a while since I calculated that but most gear books address that.

whats even more important is the tooth strength, contact ratio, gear efficiency.
the tolerance on the set of gears is based on the back lash required.
For example if a tooth thickness is thinned out by .003 your standard ctt -.003 = high limt ctt.
now high limit - .001 = low limit ctt. it's that simple.
now use the formula to calculate the span measurement from those CTT.

but do your self a favor get professional help.
there are to many factors in gear design i not even addressing.
that it takes years and years of experience.

Good Luck
Mfgenggear