Subject: Tapers and Two Single Segment Profile Controls
Thanks for taking my call this morning. I'd like to continue our
discussion on tapers by sending you these hand-drawn pictures.
You'll notice the top half image represents the current dimensioning
of the taper. The bottom half represents the proposed changes based
on Fig 8-26 in your GDT 2007 book. Can you please review the
validity of these changes? I have a few more questions also.
1. How would I dimension the depth of this taper? Plus/minus or
2. Would the perpendicularity to A allow the taper to lean? Wouldn't
datum A move with the lean? I'm having a hard time visualizing this.
The proposed change looks good. The depth of the taper can be
dimensioned with plus and minus tolerancing. For this dimension, I
would recommend an arrowhead at the bottom of the taper and a
dimension origin symbol (a circle) at the top.
The perpendicularity control to A provided in the profile control
would allow the entire cone to lean .002. Datum A would not move
with the lean, since the profile control is measured from datum A
I don't have any suggestions, but I have questions. Will datum
feature B still be necessary on the drawing? If nothing is
referenced to B, it should be eliminated. Shouldn't the cone be
located to the rest of the part in some way? That would mean that
although datum B wasn't the proper location datum for the cone, the
cone still needs to be located somewhere on the part to other datums.
One option is to use more datums than just A in the upper profile
control (that uses .002). Another option is to lead in with a third
control that uses an even greater tolerance to A and other datums,
then refine with the two controls you currently propose.
Another option is to make the cone a datum feature and locate (with
position or profile) other features on the part to datum A and the
Just one more thought, Brian. Consider giving datum feature A a 3-D
form control of its own. If it is a planar surface, a flatness
control would be appropriate. If features are to be measured from
it, it should be well formed enough to make those measurements
Hope this helps.
Subject: GD&T in Kuala Lumpur
How would you like to go to Kuala Lumpur? Do you think these topics
are broad enough for 2-day workshops?
1st workshop: Intermediate level (Fundamental lessons in proper
interpretation of engineering drawings used in the design,
manufacture and inspection of parts; Measurement Applications; Also
a discussion on differences between the ASME standards and the ISO
ones, and trends towards simplification.)
2nd workshop: Advanced level (Advanced application and analysis;
Advanced Optimization strategies; Advanced Tolerancing; Implications
of GD&T on product reliability, cost savings and six sigma.)
Hi, Gene. I do think these topics are broad enough to sustain a
2-day course. And, no, I don't want to go to Kuala Lumpur. I'm
certain it's a very nice third world nation, but I have enough
trouble finding my way around Milwaukee. I don't want my body found
covered in Ox manure in a ditch in a country I couldn't locate on a
map with a flashlight.
If you ever need me to do a job in Disney World, let me know right
away. I'm here for you. I'm just not there for you.
Public GD&T Workshop - December 8-10 and 10-12,
“Tolerance Stack-Up Analysis”
with James D. Meadows
Course Details ...presented by nationally recognized GD&T
‘expert’ and dynamic communicator/instructor James D.
Course: Advanced GD&T [per ASME Y14.5M-1994] December 8-10,
2008 (2 ˝ days)
Course: Tolerance Stack-Up Analysis December 10-12, 2008 (2
Location: Radisson Hotel
Opryland . . . same location as last year
2401Music Valley Drive, Nashville, TN (across street from
the Opryland Hotel—minutes from Nashville airport; shuttles
Hours: 8 a.m. – 4 p.m. [includes lunch, except on December
●‘NEW’ text Geometric
Dimensioning and Tolerancing in 2007 © by James D. Meadows
●‘NEW’ workbook Geometric Dimensioning and Tolerancing in
2007 Workbook and Answerbook © by James D. Meadows
● text Tolerance Stack-Up Analysis © by James D. Meadows
●Certificate of Course Completion
JWinchell@geotolmeadows.com for registration; go to
details on the courses.
Subject: Just Grinding My Profits Away
I was consulting for a company, teaching them how to tolerance parts
and looking at their existing design drawings. At one point, I was
given a tour of the shop by the manufacturing manager. As we walked
through the facility, I could see assemblers putting piece parts
into the machines that make the packaging equipment. I noticed that
many of the parts simply didn’t fit. When that happened, which was
most of the time, I saw them making notes of the problems and then
taking the parts over to an area where a huge group of employees
were using grinding machines. These machines were throwing up such a
stream of sparks that it looked like a fourth of July celebration.
The manager spoke on at length, obviously proud of the company. He
said, “We make products that are unique. We don’t make hundreds of
thousands of parts that have to interchangeably fit into any machine
we make. The parts just have to fit the one machine they will be
used in. Therefore, it not only seems to me that we don’t need to
know what you are trying to teach us about tolerancing parts, but we
don’t need tolerances at all. When we get a part in from one of our
suppliers, we just grind it until it fits into the assembly. What
benefit is there to us to learn to design and tolerance parts in
what you call the “correct way”?
I asked him, “Just how much time is spent grinding things to fit?”.
He answered by saying, “A lot. That’s why we employ all those people
over there. They grind and grind, until the parts fit like gloves.
The parts become dedicated to that one assembly and wouldn’t fit
another. It’s a great system. The machines work wonderfully.”
I asked, “Wouldn’t it be more efficient if you were able to just
take the parts as they come into your facility and assemble them
without all of that grinding?”
He looked blank, and responded, “Why would I want that?”
I plodded on, saying, “You could save a lot of money and you could
get rid of all those people that do the grinding.”
He face changed to a horrified expression and his voice went up an
octave. “I like those people. Why would I want to put them out of a
“Well,” I said, “You could always reassign them to do something
else, I guess.”
“Like what?” he responded, his voice even higher. “There wouldn’t be
anything else for them to do.”
I nodded, showing concern for the workers. Then I asked, “What if
one of your machines breaks down when your customers are using them?
How can you ship them a replacement part?”
His voice went back down into its normal range, and he smiled at me
like he was about to explain something to a small child. “We just
bring the broken part back to this facility and give it to the
grinders. They measure it, and grind another one that size. Then we
take it back and put it into the machine.”
I said, “Wouldn’t it be faster, if you could deliver to them a
replacement part that just fits, you know, without all that
He was dismissive about the idea. “I guess that might be better in
some cases. Let’s move on and I’ll show you the scrap area.”
He did, and let me tell you, it was impressive. It reminded me of
the time I was standing next to a general foreman on the shop floor
of another company, when one of his employees came running up and
said, “Boss, the scrap area is full!” And the boss responded calmly,
“Just build the walls higher.” I remember thinking at the time,
“This is a management decision? Wow, I could do that job.” It gave
me managerial aspirations.
It seems to me that although having parts fit interchangeably offers
many benefits to those making thousands of the same thing, it would
beat the heck out of all those “grind to fit” or “just throw it in
the scrap area” situations people are so satisfied with (or maybe
just so used to) even if they do make only one of each.
Recently, I was called by the design manager at that company and
invited back to take another stab at teaching them how to dimension
and tolerance parts that just fit together the first time out of the
box. He said he had to get permission from the manufacturing manager
first, since the money to pay me would come out of his budget. When
he called back, he said we would have to cancel the trip. The
manufacturing manager had told him that he just didn’t want to spend
his budget money that way. I guess he needed to hire some more folks
to work in the grinding area.
...James D. Meadows
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Subject: As cast bolt holes on W5A580 gear box case part# 449AA &
I have been having trouble holding true position on two as casting
assembly bolt holes ( thru holes) . I don't know why the general
rule for MMC can't be applied to these two as cast bolt holes? See
the areas painted blue below. The core holes have a dia 10.23 max,
with a min of 9.93 with the following:
The mating bell has these two holes drill and tap all the way thru
the bell. See the bell machining print below. Steve, our resident
engineer said that I don't have any bonus tolerance on these two as
cast thru bolt holes. I want your opinion on this.
Bell Machines Drill and taps two holes
Listen to Steve. There is no MMC symbology given in the control on
these holes. Without these feature positional tolerances being
referenced at MMC, bonus tolerance does not apply.
If the drawings had been created per the 1966 or 1973 versions of
the Y14.5 standard on Dimensioning and Tolerancing, then for
positional tolerances (only) the MMC symbol would be implied and
bonus tolerancing could be considered.
But in 1982's version of Y14.5, position without MMC, LMC or RFS
references is incomplete. One of them must be referenced.
However, these drawings appear to use 1994's revision of the Y14.5
standard wherein position is treated like all other geometric
characteristic symbology. It is implied Regardless of Feature Size (RFS),
unless the MMC or LMC symbology is used after the geometric
tolerance or after datum features of size. RFS controls allow no
The giveaway is that the international datum feature symbol is used
on these drawings. That symbol wasn't adopted by the ANSI approved
ASME Y14.5 standard until the 1994 revision was issued. In this
revision, RFS is implied for all geometric characteristic symbols,
including position. It is called Rule #2.
James D. Meadows & Associates, Inc., will provide your facility
print review services and/or on-site training for courses 2˝ to 5
days in length---look at our generic course outlines for Basic GD&T,
Advanced GD&T, Tolerance Stack-Up Analysis, or Gaging (any of which
can be tailored to your design, manufacturing and inspection
requirements, if requested, and to your budget and time constraints)
I was looking through your geometric dimensioning and tolerancing
book trying to search for an example that references two different
size features that are used as co-datum. I was wondering if my
application of GD&T (on the attached drawing) is correct. We are
trying to establish a co-datum between the two holes that are placed
at a distance of 8.478 inches away. I have come across examples
where features that have share a co-axis but none that are not
aligned with each other. Could you please provide some information
about the how my dimensioning scheme would be interpreted and where
I can located the text and example in ASME 14.5 that explain my
Thank you for your assistance,
It is acceptable and common to make a compound datum pattern out of
two holes. First the holes must be positioned to each other. This
can be done by making one of the holes a datum feature and giving it
a perpendicularity control to the appropriate datum (such as H).
Then make this hole a datum feature (such as G). Then position the
other hole to the same primary datum (H) and to the first hole (G).
Then make this hole a datum feature (F).
Subsequent features on the part may then be positioned or profiled
back to H, G-F. It would be advisable to reference G and F at MMC in
these controls. We could then picture what we are measuring from
with a fixture that consists of a plate to simulate H and two pins
at virtual condition to represent G (MMC)-F(MMC). Once the part is
mounted on this fixture it is immobilized, making additional datum
features unnecessary. To do this, a basic dimension between G and F
is required. The datum axis formed by these two holes would be
perpendicular to H and halfway between the two gage pins.
If other surfaces are located from these datums, they would have to
use profile of a surface and use basic dimensions that would be
toleranced by the profile control. The profile tolerance can be
large or small as needed.
If widths are located from these datums, we would need to show their
relationship to the datum axis. If they are offset from the datum
axis that is formed by the common plane that runs between G and F
and the plane that is formed halfway between the two virtual
condition boundaries (embodied by the gage pins), the offset must be
given as a basic dimension. If they widths are centered to the datum
axis, then no basic dimensions are needed.
There are other methods open to you, but I can't easily explain them
without going on for pages. If you want to talk more about this,
please call me on Friday. It is my only day in the office.
Subject: Question on Wall Thickness
I attended your course Dimensioning and Tolerancing Principles for
Gages and Fixtures.
I have a question with a wall thickness calculation you apply on
your book Geometric and Dimensioning Tolerancing.
This is the image
What I’m looking for is the minimum and maximum wall thickness from
the right side of the part in the front view and the 4.0-4.3 hole
closest to it.
So in your book you use for your calculations only the pattern
4.3 = LMC Hole
+ 0.3 = Geo. Tol. At LMC
4.6 = Outer Boundary
+ 0.4 = Pattern Shift (B at MMC)
5.0 = Outer Boundary with Pattern Shift
The question is why you didn’t apply also the Position Tolerance of
B (which will increase another 0.4)?
Thanks and Regards,
The edge of the part is measured from B. B is not measured from the
edge. If B is out of perpendicularity to datum A, then the wall
could thin, but any out-of perpendicularity of the B hole would
negate an equal amount of pattern shift experienced by the profile
control. So, you could ignore the MMC symbol after the B in the
profile control and assign all of the impact on B being out of
perpendicularity to A, or you could assign all of the tolerance
given by B to the pattern shift for the profile control. But it is
one or the other, not both. Either way, the wall thickness is as
given in the book.
The full calculation and subsequent tolerance stack-up follows:
Subject: RE: Follow-Up Question
And what difference does the separated requirement label? Are all of
these changes are due to it?
If there was no separate requirement note, there would be no pattern
shift between the 21 hole pattern and the profile, because if either
shifted both would have to shift together and their relationship to
one another would not alter. However, with the separate requirement
note, the pattern shift of the 21 holes would be allowed to shift in
one direction and the profile would be allowed to shift in an
opposite direction. So, the pattern shift would be allowed for the
21 holes and it would also be allowed for the profile control. The
0.4 shift tolerance would apply to both (as shown in the calculation
in the above).
This question is different than your original question.
The question you've asked in this email gets asked a lot and is
addressed in many of the newsletters on
my website. Please take a look if you need further clarification.