tooth mesh when using Mechanism

When using Mechanism and setting up 2 gears, set the number of teeth etc.
done this. When drag rotation is done everything moves fine - HOWEVER - the
teeth don't mesh graphically - is there a trick to this to give a more
realistic appearance?

Using WF

TIA

 

: When using Mechanism and setting up 2 gears, set the number of teeth etc.
: done this. When drag rotation is done everything moves fine - HOWEVER - the
: teeth don't mesh graphically - is there a trick to this to give a more
: realistic appearance?
:
Steve, I'm not sure if I understand the problem. It sounds like you're saying that
they start out meshed okay, but when you define them as gears, with the ratios and
all, that somehow they don't stay meshed when you move them. Is that about it?

David Janes

 

wow hamei! Did this guy touch a nerve!? I was going to say that I've
seen some pretty decent involutes get drawn, but you're right... it was
a specialized 2D Gear application that knew about most of your points.
The graphics wouldn't really help too much if you didn't heed the other
warnings coming out of the software.

Actually, I think Steve was just trying to animate some gears that he
tossed approximate teeth on (nothing really wrong with that) and he
wanted to see them stay lined up. They didn't... because he didn't have
any real way to line them up. Probably an initial condition on the joint
would have gotten them lined up. I'll bet they were always the same
amount of mis-allignment, right? Not incrementally getting worse.

-meld

 

Sorry all - been away...
To answer a few questions..
Hamei...
The teeth were generated within Pro/E for the sole purpose of motion
representation only. I don't plan to do gear design or analysis in Pro/E. I
don't have the formulas I used in front of me presently - but if you need to
know then post and I'll post back. Your comment about modeling gear teeth -
depending on the business etc. modeling of teeth is required for drawing
purposes and thus will be in the assembly as well

David...
Yes you are correct ... If I assemble in assembly mode - you can use a
number of different items and configurations to simulate the gear teeth to
mesh in a reasonably accurate fashion. However when you convert to Mechanism
and create pin connections the orientation of the teeth from the 2 gears
doesn't match up as if they were properly meshed, movement is OK - however
if you are using this assembly as a presentation - it is noticeably not
correct.

TIA

 

I'm pretty sure there's a way to give one of the pin joints an initial
condition. It might take a bit to get it right but it's got to be there
somewhere -meld

 

i don't see what the problem with generating gear teeth is, we managed
to do this years ago using proe using proper involute curves,
compensating for correction factors, class, tooth root radius etc &
all done in accordance with iso6336 parts 1 to 5. Unfortunately we are
not going to be developing this into a commercial product, but it's
fast and easy to customise any aspect of the gears. Just a little bit
of hard work is all that is called for.

 

Right. Only problem is GIGO.

There is no such thing as a "tooth root radius." If you just want
to make a cute animation, fine. If you want to do analysis, forget
it. You are not including some of the most critical factors in an
analysis. Gear roots are *not* all created equal. The manufacturing
methods make a huge difference in the shape of the root. The roots
are *not* a simple "radius," either.

btw, there's no way in hell you could be "in accordance with iso
6336 parts 1 thru 5" when ISO Method A (which you erroneously call
part 1) "...requires precise measurements of actual test gearing ..."

GIGO.

 

iso6336 part 1 is "calculation of capacity of spur and helical gears,
basic principles, introduction and general influence factors"
iso6336 part 2 is "calculation of surface durablility (pitting)"
iso6336 part 3 is "calculation of tooth bending strength"
there is no part 4
iso6336 part 5 is "strength and quality of materilas"
Method A that you quote is used throughout this spec and relies on
physically measuring already produced gears. It is therefore pointless
to use Method A.
The "tooth root radius" is generated by the hob used to cut the gear.
All of our hobs are to BS978 part 1 fig.1. The tooth root radius is
accounted for in iso6336 part 3 section 5.
Our proe software does not use mechanica to do the simulation. All the
relevant data we require is generated using relations.

 

That's right. It is pointless unless you wish your results to
match the real world (tm).

Or the shaper cutter. And it isn't a radius, it's a trochoid
because, as you said, it's *generated.* The 'radius' is not
a copy of the tool radius because during the cutting action
the tool and part move relative to each other. That's what
generated *means*. This is not like milling with a form tool.

I'm sure you accounted for that in your software, right ?
the fact that the "radius" in the root is not in fact a copy
of the radius at the tip of the cutting teeth ?

And all your hobs use 'standard' dimensions ? Which 'standard' ?
DP ? Module ? Shaper depth ? Preshave depth ? Pregrind ? Split
pitch ? Old AGMA ? new AGMA ? Composite tooth ? What do you do
about tooth thinning for backlash, ignore it ? What about long
and short addendum gearsets, you don't do that ? Never compensate
for equal wear ? never run extra-depth teeth for smoother running
and less noise ? Never use full radius tip hobs for extra fatigue
strength ? You stick with a 20* pressure angle ALL the time ?
you're aware (no, probably not) that there is no such thing as
a "standard" tooth ? Nobody who is a professional gear person
sticks with "standard" tooth relations or "standard" proportions
which means that in gears there IS no "standard" except for the
convenience of buying off-the-shelf cutting tools for commercial
grade work. "Standard" cutting tools which one then uses at non-
'standard' depths to create non-'standard' teeth for the purpose
required. In a real gear design 'standards' are *starting* points.
For that matter,if you are doing production you don't even use
"standard" pitches. Go look at an automotive gearbox some time.
Or a set of plastic gears. Or timing gears. Or powder metal gears.
Or anything intended to be quiet. Or carry large loads with tip
and root relief. In fact, you can even buy off the shelf cutters
set up with protuberance for tip and root relief ... I suppose
you account for that, too ?

There is no such thing as "standard" in the gear world, except
for beginners who don't know any better.

That's really really nice. And I'm sure you know that shaper-cut
teeth are deeper than hobbed teeth ? And a totally different shape
in the root ? I'm also sure you know that the roots of even hobbed
teeth are NOT simple radii ? Did you know that a large percentage
of gear tooth breakage occurs because of cracks starting in the
corners of the roots ? And that often deeper roots with larger
curves are effective in increasing fatigue strength ? Usually by
around an 'insignificant' 15% ? Cut with 'standard' full-radius
(on the tip) cutting tools ? You're aware that there are *several*
'standards' for different gear cutting tools and *several* 'standard'
tooth depths so that just about every set of gears is *different* ?

You account for this in your software, do you ? unh-hunh.

As I said, GIGO.

Yeah, all the relevant information probably *could* be generated
using relations. It *could* be, but dollars to donuts in your case
it *isn't* because you aren't even aware of what the relations are.

And that was my initial point : this all *can* be done in software
(in fact some people are doing it in software, but not off-the-shelf
pro/e, that's for sure) but it's a lot more work than it sounds like
and if you don't know what you are doing the results won't match the
real world which is sort of the point of analysis, so in effect it's
meaningless. In fact, worse than meaningless because it gives people
who think they know everything just because they looked in a book
and pulled some numbers off a chart the impression that they know
what they're doing. Which, at the end of the day, could be very
destructive. My point was not that gear tooth analysis *can't* be
done, but that people asking the question "How can I model gear
teeth in ProE so I can analyze them ?" really *shouldn't* be doing
this because if they don't already know what they're doing they'll
get bad results. Unless, of course, they just want to make a pretty
picture to impress the boss, in which case it's fine (as long as
no one mistakes the results for accurate.)