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8/18/2019 Hob Length Effects
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Dear Edj~or:
Since we are a high volume shop, we were par-
ticularly interested in Mr. Kotlyar's article describing
the effects of hob length on production efficiency
which appeared in the Sept/Oct issue of GEAR
TECHNOLOGY. Unfortunately, some readers may
be unnecessarily deterred from applying the analysis
to their own situations by the formidability of the
mathematical calculations. I am making the follow-
ing small suggestion concerning the evaluation of
the constant terms.
The article's author adroitly recognizes that the ratio
alb
= =
sinrq) when he uses equation (2 .31 of the line
in reducing the three equations ,into one
polynominal in order to determine the length of the
roughing zone. That same relationship can be
employed in equation ( 2 . 2 ) of the workpiece
eclipse; that i s :
When the substitution for
X 2
is made by using the
above equality. the original constants of the fourth
degree polynominal are reduced to simple single
term expressions in four of the five terms:
K A cos
2
q
K8 -2Y
o
cos
2
q
KC
YQ2cos
2
q
+ (HO/2J2sin2q -
b
2
KD +2b2Yo
R
Mory
ProcessEngineer
Gear Development Department
Ford Motor Trans. Chassis Div.
Livonia Michigan
continued on p ge 4
l \TOTES FROM
truE
EDITOR S
DESK
The
last
t\YO
moI lChs
have been both a
t fme
c.IftcuIly and
growth
GEAR
TEO- fNOlOGY.
UnexpeaecIy,
ta.nd
myseI ' In th e
hospital.
hav ing
surgery. and
consequenUy cu
commission fo r SM 'a I
~. At
the s a m e
t ime two
IndIvIcIuaIS
on our
s t a r r los t
ta rnt ,
membe rs . and mos t
cI this per iod saw
us
ifttIng *'Yfa r thIS preshOw
I M T S
ISSUe whle be-
jn g s e ri o u Y ~
~ 3-1
J
1986 ,
the
IntematiOnal
Ma ch I ne
T o o f Show w m be held at McCormick Place ExposI-
1iCn Cerur
ThIs
show will be even Iafger than
In
years
past. ~
to
occ up y over
2 million
square feet w e
will see a
much needed
In 1prove-
ment . a ctJI f lJ
organIZadon
exhI:iIrJrs t ha t
wi
ptace ~ simi lar U n e s In o n e a r e a Mos t
G ear ~ Man~ will be Iocab d
t
the
new
M c C o Im i c k
l a c e
Notth
This
should make yru
v t s t t
to the ShoW eaSIer a n d
ITIOIe
procIuatve
A s an added c on v en ie nc e to o ur rea d ers, we have
Included a s p ed a lln d ex
ou r
advert isers with
boorh nurl t1ers and
bui lding
loc t ions
h s i ndex
wil l help you n n d th e
equipment
you ~
been
read ing about A prel im ina ry Index
w i.
appear In this
Issue,
and next Issue. M ak e your
travel
arrangements
to
Chicago
ea rly - th is cou ld
be
the biggest
show yet
Jul:y August 1986,
5
8/18/2019 Hob Length Effects
2/2
V I E W P O I N T
confil lued from page 5)
D ea r E dito r:
As
pointed l out by a reader. the value
of the helix angle in Table
I
of m iY arti-
cle o n ,h elic al
g e a r s
th e M a rc h fA p fiil
issue
of
G EAR TECHNOLOG Y should
have been 16.59467687. (helix angle
arc sin 1 1 /1 1 1 . T his . in cid en ta lly w as
a m ispr,int in the original publication in
M a c ,h in e D e sig n ..
A lso. p lease note that I am enclosing
Table 2 which was om itted.
Sincerely.
E liot K Buckingham . P resident
Buckingham A ssoc .. Inc.
Springfield.
v r
Absorbing End ThIust
Don t Make ,he
Cure Worse than the fIIness
A ll he lical gearrs develop an end
thrust that m ust be absorbed by a
thrust bearing. angular contact roller
b earfn g. o r ta pere d ro ller b ea rin g. ,If a
thrust bearing is used and the- gear
shafts tum in p lain journal bearings.
then a fr ee -b od yfo rc e a na ly sis s ho uld
be r na o e in th e ge a rr s to ensure that :h e
gear blanks do not tw ist and that the
shafts rem ain para llel. Th is analysis
m ust include all external forces on the
gear shafts and solid ly conneaed
elements. ,
o
overcom e the enects of end
thrust. the double-he lica l :tor herr-
[ngboneJ I gear w as develo ped. Here.
the thrust from one helix supposedly
balances the thrust from the other
h e lix . H o w ev e r. v n a sing le pair of
helica l gears is d ifficu lt to m atch, so
d ou ble h elic als la s ln a herringbone
drivel: are
v ir tu ally im p os sib le to m a tc h.
U sually. one gear lIthe pinion]1 is
allowed
to float
and
find it s own
cemer. But: sinGe t is g ea r ,ism ov in g a x-
Ia lly. tne loads. on the helixes cannot
b e e qu al.
In a h igh speed s e t th e m a s s of the
floating gear often prevents it from
p ositio ning . a nd o ne h elix ab so rbs th e
fuJ I load. This bad
si t u a t i o n
i s f ur the r
com pounded by the frequent use of
h igh helix angles increase the
num ber of teeth in contact. But th is
a lt era ti on d o es n o t n e ce s sa rily i n c r e a s e
lo ad c ar ry in g
capacity.
Table 2 HeUx Angles for Exact toads
Integer HeIlx Angle Integer
H e l i x . Angle
A
W
A
- , J t l
4 51 75751851 5 12 08950814
5 38 92617544 6 n 32357 8
6
31 57396132 17
10 64 944699
7 26 66665193 18
10 05147839
8
23 12254873 19 9 51739193
9
20 43018899 20 9 03742809
1
18 31006687 21 8.60372642
1 : 1 . 16 59467687 22 8 2 988341
iz
15 17685827
23 7 85062891
13 98459310 .24
7 52158526
4
12 96756767
25 7 219 8SS7
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Ally August 11986 43