8/18/2019 Hob Length Effects

1/2

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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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B ro ok fie ld , W I

5 3 0 0 5 .

Phone

4 1 4 - 7 8 3 - 7 6 0 6 .

 

C IR CL E A -4 O N R EA DE R RE PL YC AR D

Ally August 11986 43