Pattern Locating Tolerance Zone 1

[ringman]

Why is it that rarely, if ever, a rectangular tolerance zone is used when compound positional tolerancing is required on a drawing? Assuming for the moment that the outline is of a rectangular configuration. I know of no examples in the Y14.5 illustrating this.

 

[ctopher]

Why do you think it is "required"? Depends on the design.
can you show a pic of the detail of what you are referring to?

Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-05)

 

[looslib]

When you say "rectangular tolerance zone" are you refering to what you would get if you used +/- dimensionsing?

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli
Sr IS Technologist
L-3 Communications

 

[ringman]

looslib,

It would replace the "rectangular zone", as once allowed and described in the Standard. The benefit is that by using the RECTANGULAR or SQUARE zone for the Pattern Locating Tolerance Zone, it would provide the 'BONUS TOLERANCE' and more directly establish the minimum edge allowance for the pattern or holes.

(I should have mentioned Pattern Locating Tolerance Zone in my initial post, but failed to do so.) Hopefully this will clarify my original question.

 

[drawoh]

ringman,

Are you talking about a tolerance zone for a hole that interfaces with something like a slot?

JHG

 

[ctopher]

A pic would help.

Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-05)

 

[ringman]

Not sure how to post a picture. But will try to describe my intent. Suppose a rectangular plate with a 4 hole rectangular pattern in the plate. The hole to hole relationship requires, lets say, a .028 dia positional tolerance. However the pattern of holes may be located to a much looser tolerance, on the order of .o6 dia. If we elect to use composite tolerancing, why must the PLTZ or pattern locating tolerance zone be expressed as a diameter?
(no slots or square fasteners involved) :>)

Hope this will help to clarify

 

[ctopher]

How Can I Show An Image In A Post
faq559-1100

Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-05)

 

[Heckler]

Try reading faq1103-1185 on how to upload an image.

If you want to know the rectangular tolerance from composite TP Tolerance then just calculate it. I usually design around rectangular tolerance scheme then convert that to TP once the design and manufactureability studies have been completed. One more thing, If you concerned about limiting the tolerance zone then research bidirectional positional tolerancing of features.

Positional Diameter = 2*SQRT(X^2 + Y^2)

Best Regards,

Heckler
Sr. Mechanical Engineer
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Never argue with an idiot. They'll bring you down to their level and beat you with experience every time.

 

[ringman]

I will try again using a little different approach.

Using the example FIG. 5.19,in the Y14.5 1994, on page 96. Relative to the 4 hole pattern in the plate: why does the pattern locating tolerance of 0.8 have to be a dia? A square zone of 0.8 on a side would provide the 'BONUS TOLERANCE'.

 

[drawoh]

ringman,

I see two possibilities here.

You could replace the diameter symbol with a square so show a square tolerance zone. This is not shown anywhere in the standard, but I see no reason why it is not valid. I also cannot see why you would do it.

Your composite tolerance could look something like the following...

POS .05 A B
POS .15 A C
POS DIA .028 A

Datum_A would be your base. Datums_B and_C would be edges. Your tolerance area is rectangular, as opposed to round or square.

Does this make sense?

JHG

 

[thundair]

Just take the dia symbol out, and it then means +/- in Cartesian Coordinates

We do that all the time for slotted bushings, as one direction is critical and the other wide open.
So really its +/-.010 side to side and +/-.040 top to bottom. this is shown with a positional tol without the dia symbol

Cheers

 

[looslib]

By using a diameter for the tolerance zone, you get the bonus of a larger value than if you used a rectangle or +/- tolerancing. If you have a +/- of .007, then the extreme diagonal corners are really .010 away from the target. If you can have .010 in the corners, why not allow .010 all around the target, whgich is what you can use when you switch to a diameter tolereance zone.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli
Sr IS Technologist
L-3 Communications

 

[ringman]

Looslib,

I have suggested that the square zone behave sides equivalent to the diameter that is most usually used. The resultant area would then be greater that the dia.
Therefore the BONUS TOLERANCE.

Thundair,

Do I correctly understand that you have used composite positional tolerancing without any symbol for the PLTZ?
If so, that is a new one for me. I think I would have some reservations on that one.

 

[drawoh]

thundair,

Ringman's example was a composite tolerance requiring accurate location between holes and a much less accurate positioning of the entire pattern. I assumed a rectangular pattern partially because this is what Ringman asked about, and partially because, as noted above, a square pattern is usually not very useful.

You are describing a scenario in which the hole-to-hole positioning is not critical, in which case, I would have left off the last (the third) part of the composite tolerance.

JHG

 

[drawoh]

ringman,

Answering your original question more precisely...

My standard rectangular tolerance problem involves sheet metal. Holes can be punched in sheet metal to within around +/-.005" from any edge. They can bend the sheet metal to a tolerance of around +/-.015". My solution to putting tapped holes in such a part is to use the PEM floating nuts, which correct some of the misalignment.

With the PEM nut, I still require the holes to be located inside a diameter. The manufacturing errors are likely to be distributed in a rectangle or ellipse, but this does not affect my requirement.

If I wanted to use +/- tolerances, I could specify a rectangle, but I would accomplish very little. A GDT positional tolerance of .030"DIA works out to around +/-.01". If I stretched that into a rectangle with a +/-.005" tolerance in one direction, the othogonal one would be +/-.014". Every possible combination of this is allowed by the .030"DIA positional tolerance, which is why people here keep advocating it.

JHG

 

[Tunalover]

ringman-
Seems like a lot of discussion on a fairly simple question. The answer is that you can locate feature patterns using rectangular tolerance zones established using two positional tolerance feature control frames (fcfs). One provides control in one direction and the second provides control in the second direction. One or both fcfs can be composite.

One useful situation is when you have a pattern of slots (with all of the slots running in the same direction) where something attaches to them. In the widthwise direction you can have a composite fcf to provide a loose pattern-locating tolerance but a tighter feature-relating tolerance (to insure fit). The feature-relating value can be calculated using one of the two fit formulas. In the lengthwise direction you can simply use a single-line fcf (non-composite) with a coarse tolerance providing both pattern-locating and feature-relating control.


Tunalover