trochoid & involute
trochoid & involute
(OP)
what is the difference?
why the root fillet of a gear teeth is generated by trochoid
and not by an involute?
someone help me ..
thank you very much
why the root fillet of a gear teeth is generated by trochoid
and not by an involute?
someone help me ..
thank you very much





RE: trochoid & involute
RE: trochoid & involute
RE: trochoid & involute
From the Base diameter out to the
od is the unrolled involute form.
Below the Base diameter to the root
of the gear is a fillet formed by
the method of cutting. If it is generated
by a hob cutter or pinion style shaper
it forms a trochoidal fillet radius.
If the trochoidal fillet radius is formed
by a hob style cutter any gear with the
same pressure angle and form can operate
with that cut gear without having involute
interference although it may have been
undercut by the hob style cutter if there
are very small number of teeth in the pinion.
This is the large advantage of hobbed gear
teeth.
RE: trochoid & involute
Just to clarify that the interference I was referring to was generating interference - which probably most people call undercut. My trouble is that I use the Maag gear handbook all the time, and it's translated from the German.
RE: trochoid & involute
1_diamondjim: what is "hob style cutter"?
2_so, trochoid exist only when i got interference or undercut becouse of the small number of teeth. Right?
becouse if i have no undercut, trochoid and involute blend toghether.
to clarify, they have the same origin, straight lines that
rollin on a circle.
RE: trochoid & involute
If gears are generated,(which includes "Hobbing"), you will always get a trochoid in the root, and an involute on the flank. If you try and generate a standard gear with too few teeth (seventeen or less) you will get "undercut" or "cutter interference", and the trochoid will not blend properly with the involute.
I'm going to leave this to Diamondjim to clarify! He can probably recommend some good books too.
RE: trochoid & involute
Yes you are right in that when the gear teeth
are not undercut you have a tangent trochoidal
fillet radius.
As English Muffin said hobbing
is the correct term for a rack type
or hob cutter. He is also right in
that the lowest number of teeth
without undercut is dependent on the
pressure angle and is 17 for a full depth
tooth form and 14 for a stub tooth form for
a 20 degree pressure angle system.
The lowest number of teeth without undercut
is listed in almost all gear books as well
as Machineries Handbook which is a nice
gear section to start out with. Many basic
gear formulas are there and it is a good
reference book.
Module gearing is full depth form and can be
stubbed by truncating the addendum so can be
formed by using the same tooling.
There are so many things good about the metric
system.
RE: trochoid & involute
i write just now becouse of a little holiday ..
best regards
RE: trochoid & involute
Is there an equation based on given gear data such as base circle, pressure angle, addendum modification etc.?
RE: trochoid & involute
Is it a cycloid, curtate cycloid, prolate cycloid or something else entirely.
RE: trochoid & involute
of the gear or pinion is
X = r x sin theta
Y = r x cos theta
where theta is the vectorial angle from
the vertical centerline.
keep substituting theta values from 0 to
about 45 degrees to get different coordinates.
You want to use small angular interval differences
from 0 to 2 degrees and progressively larger
intervals thereafter.
RE: trochoid & involute
I am trying to construct a trochoid along with an involute. Involute is fine but to consruct a trochoid what r is to be used. Is it the Base dia of the gear?
RE: trochoid & involute
the hobbing of the trochoid. The trochoid is
unique for each number of teeth hobbed.
Any hobbed tooth will operate with another
hobbed tooth if both are external gears.
The trochoid can be generated with a shaper
style cutter as well but then you need the
full shaper cutter details.
If you give me the number of teeth in the
pinion and gear I can send you the hobbed
gear teeth acad drawings for each.
330 678 0226
In Dudley's book there is a program that will
allow you to created the coordinates of the
trochoid.
You should become familiar with the term SAP Diameter
(Start of Active Profile Diameter). Also learn
about undercutting in small number of teeth that
are generated by a hob or shaper cutter.