Some guys were talking about various projects and we were sort of arguing
about tolerances in general. Is there any general chart listing parameters
for various types of work- Aerospace, automotive, farm etc. I know that
each part may have specific tolerances to adhere to, but I thought there may
also be some general categories sort of like various grades of fasteners.

"EdFielder" wrote in message
.net...
Some guys were talking about various projects and we were sort of arguing
about tolerances in general. Is there any general chart listing
parameters
for various types of work- Aerospace, automotive, farm etc. I know that
each part may have specific tolerances to adhere to, but I thought there
may
also be some general categories sort of like various grades of fasteners.



It's really about common sense. A bearing fit in a farm implement is no
less critical than it is in an engine for an aircraft. There are optimum
clearances or fits that perform satisfactorily----regardless of application.
Those that know and understand machining are able to work to tight
tolerances as needed, regardless of the application. Anyone that suggests
that it's for a plow, so it doesn't matter, is telling you more about their
ability and knowledge than they are about proper fits. The only charts I
know of are charts for specific type fits------and they are *not* job
category specific. A slip fit is always a slip fit.

There is no better way to improve one's ability than to work closely when
learning and even later when making widgets.. It becomes routine, so when
a tough job comes along, it's handled in stride.

Harold

Harold and Susan Vordos wrote:

"EdFielder" wrote in message
.net...

Some guys were talking about various projects and we were sort of arguing
about tolerances in general. Is there any general chart listing

parameters

for various types of work- Aerospace, automotive, farm etc. I know that
each part may have specific tolerances to adhere to, but I thought there

may

also be some general categories sort of like various grades of fasteners.




It's really about common sense. A bearing fit in a farm implement is no
less critical than it is in an engine for an aircraft. There are optimum
clearances or fits that perform satisfactorily----regardless of application.
Those that know and understand machining are able to work to tight
tolerances as needed, regardless of the application. Anyone that suggests
that it's for a plow, so it doesn't matter, is telling you more about their
ability and knowledge than they are about proper fits. The only charts I
know of are charts for specific type fits------and they are *not* job
category specific. A slip fit is always a slip fit.

There is no better way to improve one's ability than to work closely when
learning and even later when making widgets.. It becomes routine, so when
a tough job comes along, it's handled in stride.

Harold


I won't argue with you that the OP's question was oddly stated, but
consider the following cost equation:

Case 1: Bearing fails on a jetliner, airplane crashes into a cornfield
killing 300 people and ruining the corn crop.

Case 2: Bearing fails in a combine on the cornfield, farmer has a long
walk home (or more likely calls someone on his cell phone to come get
him), corn gets in a day or two late -- at worst he loses his crop.

So the worst-case scenario in the "farm bearing" case is that the farmer
dies from exposure on the way home, and you lose a corn crop. In the
"jetliner bearing" case it's 300 people _plus_ the lost crop.

Airplanes must be light, jet engines turn faster than diesels and run
hotter, joints must be much tighter to function properly, etc., etc.,
etc. To get light weight, reliability and high performance you design
expensive equipment that requires careful maintenance. Anyone who
designs farm implements that must be maintained like aviation equipment
should be made to purchase and maintain it for several years -- and if
that seems cruel and unusual you can take pity on them and use tar and
feathers.

I think it's more a matter of what's allowable (or prudent) to design
into the equipment that drives what you're likely to find, but I do
think you'll see a greater need for high precision work in aviation than
farming.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Tim Wescott wrote:

I think it's more a matter of what's allowable (or prudent) to design
into the equipment that drives what you're likely to find, but I do
think you'll see a greater need for high precision work in aviation than
farming.

The rule is quite simple: Do it as coarse as possible but as precise as
necessary.
But this rule doesn't help the OP.

For aviation: Most of the costs are coming from QC, the rest from QC.
Yes, it is true that they have tighter tolerances, but they need to have
very tight reproducable results. They get them from QC. :-)

Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige

"EdFielder" wrote in
.net:

Some guys were talking about various projects and we were sort of
arguing about tolerances in general. Is there any general chart
listing parameters for various types of work- Aerospace, automotive,
farm etc. I know that each part may have specific tolerances to
adhere to, but I thought there may also be some general categories
sort of like various grades of fasteners.



Ed,
There are a lot of standards out there. Most have already, and the rest
are being converted to ISO standards. You have a standard for fits, for
bolts, nuts, screws, shafts, bearings, and the list goes on and on.
These used to be, typically, one of three different standards, DIN
(European), JIS (Japanese Industrial Standard), and SAE (Society of
Automotive Engineers). The ISO organization is tasked with taking those
three standards, plus any others that exists and combining them into one,
world-wide useable standard.
You can purchase the book of standards for metal working. It is not cheap
though.


--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

"Tim Wescott" wrote in message
...
Harold and Susan Vordos wrote:

"EdFielder" wrote in message
.net...

Some guys were talking about various projects and we were sort of
arguing
about tolerances in general. Is there any general chart listing

parameters

for various types of work- Aerospace, automotive, farm etc. I know that
each part may have specific tolerances to adhere to, but I thought there

may

also be some general categories sort of like various grades of
fasteners.




It's really about common sense. A bearing fit in a farm implement is
no
less critical than it is in an engine for an aircraft. There are
optimum
clearances or fits that perform satisfactorily----regardless of
application.
Those that know and understand machining are able to work to tight
tolerances as needed, regardless of the application. Anyone that
suggests
that it's for a plow, so it doesn't matter, is telling you more about
their
ability and knowledge than they are about proper fits. The only charts
I
know of are charts for specific type fits------and they are *not* job
category specific. A slip fit is always a slip fit.

There is no better way to improve one's ability than to work closely
when
learning and even later when making widgets.. It becomes routine, so
when
a tough job comes along, it's handled in stride.

Harold


I won't argue with you that the OP's question was oddly stated, but
consider the following cost equation:

Case 1: Bearing fails on a jetliner, airplane crashes into a cornfield
killing 300 people and ruining the corn crop.

Case 2: Bearing fails in a combine on the cornfield, farmer has a long
walk home (or more likely calls someone on his cell phone to come get
him), corn gets in a day or two late -- at worst he loses his crop.

So the worst-case scenario in the "farm bearing" case is that the farmer
dies from exposure on the way home, and you lose a corn crop. In the
"jetliner bearing" case it's 300 people _plus_ the lost crop.

Airplanes must be light, jet engines turn faster than diesels and run
hotter, joints must be much tighter to function properly, etc., etc.,
etc. To get light weight, reliability and high performance you design
expensive equipment that requires careful maintenance. Anyone who
designs farm implements that must be maintained like aviation equipment
should be made to purchase and maintain it for several years -- and if
that seems cruel and unusual you can take pity on them and use tar and
feathers.

I think it's more a matter of what's allowable (or prudent) to design
into the equipment that drives what you're likely to find, but I do
think you'll see a greater need for high precision work in aviation than
farming.

I don't have an argument with that, but I see no difference in failures when
a little care can avoid them. We were not discussing the cost of the
failure, only the fact that failures occur. That's my point, and always
has been. I'm the guy that twists the handles and makes the product (or I
should say I used to be. I'm retired now). Those that used my services in
the past reaped huge benefits because of my work ethics. I've always said
that if you are interested in used oats, they come cheaper than nice, fresh
ones. I sold only new oats. I see no difference in machining and oats.
You get what you pay for. How slop work on a combine would make it work
more reliably is not something I see clearly. I still suggest to you that
one should use good work practice, regardless of application.

Harold

What the others said. My personal ax to grind is using a 'one size fits
all' approach to tolerances on a given assembly. I used to get prints
for thin tube weldments (twin cylinder exhaust headers) with a block
tolerance section calling for +/- .003" on a WELDMENT. Holding that on
the flange was tough but necessary. Holding that on the tube 8" from the
engine block was rediculous.

EdFielder wrote:

Some guys were talking about various projects and we were sort of arguing
about tolerances in general. Is there any general chart listing parameters
for various types of work- Aerospace, automotive, farm etc. I know that
each part may have specific tolerances to adhere to, but I thought there may
also be some general categories sort of like various grades of fasteners.

On Wed, 7 Dec 2005 17:36:30 -0800, "Harold and Susan Vordos"
wrote:




I don't have an argument with that, but I see no difference in failures when
a little care can avoid them. We were not discussing the cost of the
failure, only the fact that failures occur. That's my point, and always
has been. I'm the guy that twists the handles and makes the product (or I
should say I used to be. I'm retired now). Those that used my services in
the past reaped huge benefits because of my work ethics. I've always said
that if you are interested in used oats, they come cheaper than nice, fresh
ones. I sold only new oats. I see no difference in machining and oats.
You get what you pay for. How slop work on a combine would make it work
more reliably is not something I see clearly. I still suggest to you that
one should use good work practice, regardless of application.

Well my personal take on it works this way.

It depends on what part of the plow you're talking about. If you're
talking about the spindle then it needs to be pretty close. Not to
tight where you can't get the wheel on and off but tight enough that
the bearing won't wear out the spindle. In other words I usually shoot
for between 1/4 up to 1 thousand undersize. This is better than the
factories are turning out now days (I've seen some factory spindles
that are way to loose). The hub on the other definitely needs a press
fit.

On the other hand when I thread a plow shaft I always make the
threads loose. Usually I'll get a good fit and then got about 0.010"
under that. The reason being that I've spent well over a hour more
than once just trying to get the nut off a shaft before. After they
run in the dirt and rust they won't be to loose for long.

Most everything else on a plow falls under welding type tolerances.
Never try to make a precision fit on a product that's going to sit out
in the dirt and rain. It'll freeze up in short order. I learned this
early on in my life working on the farm and repairing equipment.

Common sense combined with a little experience will get you a long
way to knowing what tolerance you need to work to. I get complaints
from customers that I make some things to tight. Like pulley bores and
bearing fits. They want it to just slide on but many of these need to
be tight or they'll wear the shaft and/or bore out. Other things like
gate latches need lots of clearance. Nothing worse than trying to open
a gate to find the latch is froze up.


Wayne Cook
Shamrock, TX
http://members.dslextreme.com/users/waynecook/index.htm

Anthony,
Thanks, you were the only responder who grasped the question and gave an
answer without a " my way " speech. Any idea where a person could find the
book online? I tried a google search under ASME and ANSI, but the
engineering crowd protects this info like the CIA.
"Anthony" wrote in message
...
"EdFielder" wrote in
.net:

Some guys were talking about various projects and we were sort of
arguing about tolerances in general. Is there any general chart
listing parameters for various types of work- Aerospace, automotive,
farm etc. I know that each part may have specific tolerances to
adhere to, but I thought there may also be some general categories
sort of like various grades of fasteners.



Ed,
There are a lot of standards out there. Most have already, and the rest
are being converted to ISO standards. You have a standard for fits, for
bolts, nuts, screws, shafts, bearings, and the list goes on and on.
These used to be, typically, one of three different standards, DIN
(European), JIS (Japanese Industrial Standard), and SAE (Society of
Automotive Engineers). The ISO organization is tasked with taking those
three standards, plus any others that exists and combining them into one,
world-wide useable standard.
You can purchase the book of standards for metal working. It is not cheap
though.


--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

EdFielder wrote:
Some guys were talking about various projects and we were sort of arguing
about tolerances in general. Is there any general chart listing parameters
for various types of work- Aerospace, automotive, farm etc. I know that
each part may have specific tolerances to adhere to, but I thought there may
also be some general categories sort of like various grades of fasteners.

I think you may be thinking about the standards for limits and fits.
Machinery's Handbook and most other handbooks have tables with standard
ANSI preferred sizes and limits and fits. Most specs. include these
standards for designing equipment.
Bugs

"EdFielder" wrote in
.net:

Anthony,
Thanks, you were the only responder who grasped the question and gave
an answer without a " my way " speech.

Probably because I design and build stuff for a living


Any idea where a person could
find the book online? I tried a google search under ASME and ANSI,
but the engineering crowd protects this info like the CIA.

http://www.iso.org/iso/en/CatalogueL...eList?COMMID=0
&scopelist=PROGRAMME

Tiny URL for above:

http://tinyurl.com/chdpa

IIRC, DIN, ANSI, SAE, ASME, JIS are in the process of being depreciated,
meaning they are being phased out. ISO is the new standard and is under
active, continuous development.
That page provides an index of published standards and committees. There
should also be links to where you can obtain the standards.




--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

Nick,

It seems you are right on!

However, from the little bit of aviation work I was exposed to, it is really
one of the better toleranced fields.
It seems they truly follow the 'form, fit, function' concept of geometric
tolerancing.

As to QC costs, there is a saying that you cannot inspect quality into a
part. What I observed is that the buyers of
aviation products do indeed inspect their incoming purchased goods, often
100 percent inspection!

As to the OP's question about tolerances: I have observed that most job
shops (contract manufacturing) have developed
their own set of 'standards' covering the basic machining operations. These
often are taken from 'Industry standards' such
as the typical sizes resulting from a drilling operation. This procedure
lends itself to a relatively uncluttered drawing,
where only deviations from accepted practice is desired. Hence the standard
tolerancing note on most drawings.

These standards are then incorporated into their contracts. Consequently,
it is the buyer's responsibilty to obtain and
review these standards to see if they satisfy his requirements. Then upon
reciept of purchased goods, their is a basis
upon which to base a valid inspection criteria.

To paraphrase what you said, it is all a matter of economics. More
precision costs money. Essentially it boils down to
return on investment. You can quote lower hourly rate using a standard
drill press as opposed to a "Devleig jig grinder.

I guess the OP should be looking for some good literature on the economics
of manufacturing methods.


""Nick Müller"" wrote in message
...
Tim Wescott wrote:

I think it's more a matter of what's allowable (or prudent) to design
into the equipment that drives what you're likely to find, but I do
think you'll see a greater need for high precision work in aviation than
farming.

The rule is quite simple: Do it as coarse as possible but as precise as
necessary.
But this rule doesn't help the OP.

For aviation: Most of the costs are coming from QC, the rest from QC.
Yes, it is true that they have tighter tolerances, but they need to have
very tight reproducable results. They get them from QC. :-)

Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige

Ace wrote:

These standards are then incorporated into their contracts. Consequently,
it is the buyer's responsibilty to obtain and
review these standards to see if they satisfy his requirements. Then upon
reciept of purchased goods, their is a basis
upon which to base a valid inspection criteria.

Generaly, you have a note on the plan that sais something like
"untoleranced sizes according to DIN/ISO blablabla".


To paraphrase what you said, it is all a matter of economics. More
precision costs money. Essentially it boils down to
return on investment. You can quote lower hourly rate using a standard
drill press as opposed to a "Devleig jig grinder.

Yes. That's what the phrase "only as exact as necessary" says.
For every job, there are accepted tolerances.
For weldings, they are easy to be within. If this ain't enough, add
tolerances. And the prize goes up.
For bearing-fittings, they are quite small, but that's what is required
for them to work well.


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige