Unilateral VS Bilateral Tolerancing
Unilateral VS Bilateral Tolerancing
(OP)
I am wondering if there is any type of drawing that would require the designer to use both Unilateral and Bilateral tolerances in the same drawing? If so what would be an example of one?





RE: Unilateral VS Bilateral Tolerancing
Bilateral = variation permitted in both direction.
I'm not sure if I'm missing the question completly, but it wouldn't make sense to limit the drawer to only one or the other?
EX: Sometimes interference between two pieces is a big nono, so you are forced to specify a unilateral tolerance. Other times you dont really care about the direction, you just specify the tolerance to have something more specific than the offered machining tolerances.
RE: Unilateral VS Bilateral Tolerancing
Any case where some features require one type of tolerance and others a different type.
RE: Unilateral VS Bilateral Tolerancing
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Unilateral VS Bilateral Tolerancing
If we were working on drafting boards, this may be a meaningful question. I believe all of us are designing on CAD, mostly 3D.
We have to decide how to transition from the CAD model to the dimensioned drawing. On parametric 3D, features on one part are used to drive features on the adjacent part. I like to set everything to nominal dimensions, e.g. If a 40mm shaft goes into a 40mm hole, I model both pieces at 40mm. If I have a minimum clearance, notice how we must wind up with a +/+ or a -/- tolerance somewhere.
On diameter dimensions, I reset the dimension to limit style tolerances. This is largely because people are rattled by +/+ and -/- tolerances.
Increasingly, people are using Model Based Definition (MBD). This makes the relationship between the nominal model size and the as-displayed dimensions, nasty and critical. The limit dimensions, noted above, actually conceal information. If I show a shaft at 40-0.05/-0.15mm, I am showing the as-modelled size, as well as my required tolerance.
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JHG
RE: Unilateral VS Bilateral Tolerancing
(FYI if you want hardcore drafting advice in future you could try posting in Drafting Standards forum.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Unilateral VS Bilateral Tolerancing
-handleman, CSWP (The new, easy test)
RE: Unilateral VS Bilateral Tolerancing
The way a part is toleranced can affect the way it is manufactured. Consider the length of a part that is produced from bar stock with a required length between 4.750" and 5.000". It must be less than 5.000" to fit the assembly, but as the length of the part decreases, it does not function as well. Below 4.750", the part will not function properly. If the length is expressed as 4.875 +/- .125", you will find the output is centered around 4.875 as the impression is that 4.875" would be "perfect". If, however, you express the length as 5.000 +0/-.250", you will find the output centered as close to 5.000" as the variation of the process will permit. Now, the OD could be 3.625 +/- .031", particularly if the design was based on 3.625 and history has shown that a +/- .031" tolerance was appropriate.
rp
RE: Unilateral VS Bilateral Tolerancing
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Unilateral VS Bilateral Tolerancing
http://eng-tips.com/viewthread.cfm?qid=332690
In my experience it's most common, especially on complex/high tolerance parts, that machinists (especially on non-CNC) aim for MMC and sneak down inside the tolerance to be safe. It's always easier to cut a little more metal off than to add it back on. You definitely don't want to scrap $500 in material and 35 machine hours because you cut a few extra microns out.
-handleman, CSWP (The new, easy test)
RE: Unilateral VS Bilateral Tolerancing
-handleman, CSWP (The new, easy test)
RE: Unilateral VS Bilateral Tolerancing
Bilateral = variation permitted in both direction,
or high limit & low limit
example: linear length .350-.300. I use the nominal anyway regardless of the tolerancing method.
Max or Min type tolerancing can be dangerous. because it is human nature to hit close to max or min dim.
I do not Give a plus or minus on my work instruction. I only give high & low limit.
But on the engineering either way is acceptable.
the prefered is Bilateral
HTH
Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.
RE: Unilateral VS Bilateral Tolerancing
.0005" tolerance and closer. Outside diameter the the high limit is held.
Inside diameters the low limit is held. standard practice for OD & ID grinding.
this because it is very easy to deviate size. examples are if it is an OD," in the undersize condition " or if it is an ID "the oversize condition".
The dimension as drawn by the designer will be held regardless.
the point to this. is for your information. there's more than one option.
and it depends on the type & size of the part, mfg method, fabrication, machining, assembly. all have their methods.
to say one way is better than an other is probably experience or can be very subjective.
HTH
Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.
RE: Unilateral VS Bilateral Tolerancing
Software For Metalworking
http://closetolerancesoftware.com