huangyhg

tolerance analysis books
hi all,
after we introlduced gd&t(y14.5) into our design requirements, our traditional worst-case tolerance stack analysis can't work(plus-minus system is our original system). could everyone suggest some tolerance analysis books for self-study?
note: we are investigating to buy vsa for our design jobs. this software seems powerful but is hard for us to understand if we are lack of tolerance analysis ideas.
thanks in advance,
ntuedutw
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"advanced tolerancing techniques (engineering design and automation)" by. hong-chao zhang
wes c.
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cetol is another program for tolerance analysis.
both cetol and vis-vsa are great packages.
we have both packages where i work.
we have engineers that are experts for each.
i have taught the basic cetol class for sigmetrix.
what products are you designing and with what cad system.
cetol is connected to pro/e or catia.
vis-vsa requires that cad data be sent thru one of their translators to bring the data into the vis-mock.
do you have any questions about either package?
tom rhodes, gdtp-s
the best book i've encountered for tolerance analysis is the dimensioning and tolerancing handbook (drake, et al, 1999).
the paul drake book is great.
has many contributions from authors and experts in the field. i enjoy my copy.
the adcats site has alot of good stuff.
too bad the adcats group is not current.
byu has provides sigmetrix with many excellent employees that make cetol the software i use.
the mech sigma package was shown to me by paul drake at one of the asme classes he teaches. it looked like a good 1d or 2d package.
tom rhodes, gdtp-s
the adcats program, i think, has accomplished what dr. chase wanted. sigmetrix has taken over the development and further enhancements of the program.
we used cetol where i used to work. the design engineers had a hard time with understanding the need for the program. the instructor from sigmetrix, a fellow byu grad, did a great job of explaining it, as he was a developer of the interface to pro/e.
"wildfires are dangerous, hard to control, and economically catastrophic."
ben loosli
sr is technologist
l-3 communications
has gordon c. or ted a.?
tom rhodes, gdtp-s
ntuedutw,
transitioning from a traditional ± tolerance system, to gd&t y14.5 is not always easy. many of the correct questions to ask are difficult, especially since you do not always know what to ask. this is especially true when choosing a tolerance analysis tool. should you choose vsafff"> (full blown 3d tool), cetolfff"> (vector based 2d-ish spreadsheet), or even an excel spread sheetfff">. all can do a good job, but all have advantages and disadvantages.
in essence you have to choose between ease of use (training time, time to perform analysis) vs. accuracy (extra effects of a 3rd dimension, depth of software "built in smarts").
other factors include what cad system do you use? cetolfff">works only with catia v5fff"> and pro/efff">. vsafff"> works with all - ug, autocad, catia v4 and v5, solidworksfff">, etc. some tools like tsvfff"> is only in ug nxfff"> . and of course, an excel spreadsheet works with all above, including manual drawings.
another factor is do you use embedded 3d gd&t in your designs / cad files, or nonparametric gd&t in a flat 2d drawing. some tools take advantage of the embedded "intelligent" gd&t and uses it directly as input to the tolerance analysis.
for more information, here is a great article in mcad cafefff"> on the above subject.
today's culture in tolerance analysis blocks real benefits
vsa operates inside vis-mockup.
vis-mockup handles the cad data for viewing and picking.
the cad data must be translated into a jt file for mockup.
tom rhodes, gdtp-s
technically, vis vsa needs two software modules. teamcenter's vis mockup and teamcenter's vis vsa. teamcenter's vis mockup handles the base 3d cad functions, then vis vsa does the specific tolerance analysis "on top of" the vis mockup 3d cad "engine".
all modern 3d tolerance analysis tools are "tied" to some form of 3d cad enginefff">. but to not be "loyal" to a specific cad system (i.e., catia v5, or ug nx, or pro/e), vis vsa uses teamcenter's vis mockup. vis mockup is the "cad neutral"fff">fff"> solution used in teamcenter pdm systems to view cad files from multiple cad systems.
using vis mockup is advantageous for a few reasons:
1 - you do not need a dedicated cad seatfff"> to perform tolerance analysis (vis vsa runs on windows based pc)
2 - you do not have to change the master cad filesfff">, when performing "what if"fff">fff"> studies, to improve results.
3 - for companies that run multiple cad systemsfff">, you only need one toolfff">fff"> to buy / train staff / schedule work flow through.
4 - other seemingly "stand alone" 3d tolerance analysis tools have a basic 3d cad system "built" in. since many of these products are primary tolerances analysis tools, the 3d cad portion is limited. teamcenter's vis mockup is improved annually, and get more functions added every year.
5 - if you already have teamcenter, you have access to all the cad files from all cad systems.
6 - if you do not have teamcenter, then vis mockup definitely less expensive to buy than a seat of a major cad system (see below).
to be "cad neutral", this does require some form of translation from the native cad system into a format that vis vsa and teamcenter's vis mockup can understand. for the ugs products (i.e., ug nx, ideas, sdrc), no special translator is required (see below). for other cad systems, there are iges, step and ones developed for each specific platform.
now the jt file format is a "tessellated" file, with nurb data. a "tessellated" file basically is the graphical representation of the cad file you see on your cad screen (this is why a hole sometimes looks like an octagon, instead of a circle). the real "cad" circle is within the math on the hard drive, but the octagon is displayed graphically on your screen. thus when you look at it, it looks incorrect -- but when you query the cad file, it looks at he hard drive and states this is a circle of xxxxxxxx precision. all modern cad systems use tessellation, to show graphics quickly on screen.
most modern cad files consists of many things - parametric parameters, nurb data, pmi information, "tessellated" data, and all other types of important stuff. the "tessellated" data is the bulk of the jt file, with the nurb data added for accuracy. for ugs products, the same "tessellation" is used throughout. thus ug nx a jt files have the same tessellated data. thus a ug nx file opens directly in teamcenter products. for all other cad systems, they use different form of tessellated data, and need to be translated.
typically, the jt file is 10-20% the size of the original cad file.
thus the bottom line -- if you are planning to do 3d tolerance analysis, do you want to "tie" it to a single cad systemfff">, or one that is can use multiple cad systemsfff">. both require a cad "engine" to run (i.e., vis mock, catia v5, etc.)
also beware, some "3d" tolerance analysis tools use the 3d cad system to generate "input" into an analysis tool that generates results outside the 3d environment in essence, creates a spreadsheet like analysis)fff">. this does not allow for true 3d geometry "effects", and may / will give misleading results. these tools seem "3d", but are more 1d / 2d -ishfff">
curtis desaele

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