Pos Tol applied to pattern (how to?)
Pos Tol applied to pattern (how to?)
(OP)
I have a X,Y grid pattern of holes laid out flat plate. Datum A is on the facing surface. Datum B runs through the part in the X direction. Datum C runs through the center of the part in the Y direction. (See the attached drawing.)
I wish to apply positional tolerance to the holes of the pattern.
What's needed, what's basic, what's reference?
I wish to apply positional tolerance to the holes of the pattern.
What's needed, what's basic, what's reference?
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
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RE: Pos Tol applied to pattern (how to?)
Arguably the 1.750 Dimensions are not required and if given should be either basic or reference (depending on if you really think you need them).
KENAT,
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RE: Pos Tol applied to pattern (how to?)
Paul
RE: Pos Tol applied to pattern (how to?)
"Equally spaced" is entirely redundant and should not be used. I would likely question the use of the mid planes as datum features for this application, without further insight. Tol on hole location vs hole tol? Seems tight.
Kenat,
You might want to rethink the 49X. I believe 7X in a vert and horiz direction to be more appropriate.
RE: Pos Tol applied to pattern (how to?)
The tol needs to be added for overall length of part, CL to 1st hole, each space between holes, then position of each hole.
To add these up and then equal 3.500 could be confusing for the machinist and inspector.
I agree that the equally spaced is redundent. I would use only the 7X. The 1.75 dim should be basic.
Which dimensions are needed is hard to tell without knowing the design.
Some examples: http
Here is a good site to find docs:
htt
Chris
SolidWorks/PDMWorks 08 3.1
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RE: Pos Tol applied to pattern (how to?)
I cannot get too much into function. The holes line up with an array that hovers over one whole row at a time. I will say that we are concerned with how the holes are located to each other and don't much care about the edges, per se. There are two alignment pins that locate the plate (I didn't model those for the example). One pin is the upper left, one in the lower right. The part is designed to be symmetric about the C datum for handling.
I don't see much issue with using the centers of the part as the datums, as this is not difficult for machinists to handle, though I may have to take additional action to allow the part to be more readily inspected.
Futher input is welcome.
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
If the hole pattern itself is more critical than where the pattern lies in the plate then consider composite position. Be sure to consider position at MMC if applicable. The only other thing I would change goes along with KENAT and that is making your .500 dimensions basic. Using equally spaced can become a bear but if your "equally spaced" is applied to basic dimensions, then most of the problems associated with it go away. I'm still not a fan of it though.
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RE: Pos Tol applied to pattern (how to?)
The secondary needs a size constraint and an orientation to the primary.
The tertiary needs a size constraint and an orientation to the primary and secondary.
The hole, countersink, and angle each need a tolerance.
The descriptions of the basics work ok as they are but could be improved by making them more universally interpretable by losing the English language and boxing the value. There are a number of ways to do that... try one and bounce it off this group and count the yeas and nays.
I don't see any problem with the opposing surfaces of the length and width being the secondary and tertiary datum features and referencing the basics from the center plane... if that mirrored function... but since you revealed that two alignment pins actually do the job of a pattern secondary (two round pins in two round holes) or a secondary and a tertiary (two round pins in a hole and a slot)... I would put the dimensional reference line at the center of the 2X pattern or the center of the 1X secondary... tolerance the pattern for position to A (which controls both orientation and spread) or the orientation of the secondary to A then the position of the tertiary to A|B. Then I would tolerance the edge profile "all around" from A|B or A|B|C which ever reflects function. Naturally the basic dimensions to the holes - countersinks would originate from that functional reference as well.
Paul
RE: Pos Tol applied to pattern (how to?)
I'm also been asked to completely disassociate the edges of the part from the pattern, without the use of locating pins or any other reference. The suggestion was to use "witness holes" to control the location of the datum. Am I completely off base by seeing this as trying to create a datum by using the very features created to mark the datum (chicken-and-the-egg self referencing).
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
Paul
RE: Pos Tol applied to pattern (how to?)
Paul
RE: Pos Tol applied to pattern (how to?)
The secondary needs a size constraint and an orientation to the primary.
The tertiary needs a size constraint and an orientation to the primary and secondary.
The hole, countersink, and angle each need a tolerance."
Why? Maybe the "straight line rule" is good enough. By the above logic, the holes should also have a circularity tolerance, and perhaps cylindricity as well...unless the block tolerances (unknown) are "good enough". More importantly, none of that really addresses fc's question.
FC, you say the hole-to-hole pattern is what's important, and the outer form of the part could presumably be toleranced by +/- dimensions if you wanted to. My understanding of the best (least confusing) way to control the hole pattern is to call out one or preferrably two holes as new datums (say D and E), given position tolerance by whatever means you want (GDT or +/-), at whatever tolerance is required, to your existing datums A-B-C. The two new datum holes, perhaps one at each corner of the pattern, are then used to control position for the remainder of the pattern.
Callout would look something like:
64x 0.150 THRU (etc. for c'sk)
TP/0.5 dia/A/B/C
TP/0.001 dia/A/D/E
RE: Pos Tol applied to pattern (how to?)
I seem to be parroting Kenat in my first reply, and apologize, he said it better elsewhere in this forum:
"Were they a complete engineering drawing fully complying to the standards, no. However, when looking at illustrations on this site (as opposed to actual drawings/extracts of drawings) I wish we could treat them like figures in 14.5 and invoke paragraph 1.1.4. It even states "EXAMPLES ARE INCOMPLETE BY INTENT" in the top left."
RE: Pos Tol applied to pattern (how to?)
Yes, my picture was incomplete by intent. Some of the details added to my pics in your edits already exist on the actual drawing. I don't think I need to profile the edges to get the assumed perpendicularity or to control their size.
Regarding the first example, I misspoke before (a little bit). Although there are corner pin holes (as you drew), only one is engaged at a time (and it doesn't matter which one that is). The part is located with two pins, the second being in a slot across from the locating hole. So, I don't know if I could meaningfully reference the pin holes without making one arbitrarily important over the other. Your example would create two different datum B's, if I'm reading it correctly.
I guess the question on both your examples is whether the pattern itself should be basic? Also, your method of calling out the pattern is more intuitive to my needs, however Y14.5 says it this way "7X .500 (=3.5)" Even if I turn this basic, it concerns me that the .500 is the driving dim when I'm more interested in controlling the overall pattern of 3.5. Thoughts?
Blue,
"The two new datum holes, perhaps one at each corner of the pattern, are then used to control position for the remainder of the pattern."
The difficulty I'm having with this (and I've considered this) is that I cannot think of any way to logically fixture the part to the holes I would declare as the new datum while maintaining the symmetry of the pattern.
Both Blue and Paul,
In Paul's example two, what is the purpose of declaring the hole itself as datum B? I'm having trouble understanding how example two provides a complete callout.
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
In both mark-ups that I offered datum feature B is not one of the 2X locating pin holes at a time... or one of the 64X features. It is the entire pattern simultaneously either 2X or 64X.
paul
RE: Pos Tol applied to pattern (how to?)
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Pos Tol applied to pattern (how to?)
I guess where I'm confused is in how datum B is being used in each of the examples.
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
I was wrong, it's 56 X .500, 8 rows of 7 'gaps'. 7 X is just plain wrong to me because there's more than one row/column, unless you want to add the lines through the center of all the holes, which seems messy.
As to the centering 1.75 like Powerhound I believe the 'implied centered' is in effect so I'd probably leave it off. If you do put it though I'd prefer as reference but, I don't think making it basic is explicitly 'wrong' but is probably unnecessary and could perhaps be argued double dimensioning but I'm not sure that holds water. This is what I meant in my initial brief post.
Your concern over the total size of pattern 3.5 being more important than the individual .5 pitches doesn't seem too relevant if you are using position since there is no stacking of tolerances.
Given that you effectively 'swap' your primary functional datum from one hole to another during operation it does mean using the hole & slot as secondary and tertiary datum's gets a bit more complicated. Maybe making one of the holes in the pattern, or even the entire pattern the secondary datum makes sense and then using the common 'slot' as a clocking feature and relating the other 2 pin location holes back to this. This is getting out of my comfort zone though.
KENAT,
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RE: Pos Tol applied to pattern (how to?)
As Paul said, the datum is being defined as all of the holes together, i.e. the pattern. By defining the pattern as datum B, the profile tolerance then has something to work from.
"The difficulty I'm having with this (and I've considered this) is that I cannot think of any way to logically fixture the part to the holes I would declare as the new datum while maintaining the symmetry of the pattern."
Not clear what you mean. It sounded like you want the holes in a tightly controlled pattern (tighter than the rest of the part features), which makes any two holes a perfect place to drop the part over a couple of fixturing pins. Maintaining the symmetry of the pattern - pick a pair of holes that straddle the centerline if you want, or from corner to corner...the symmetry of the pattern is defined by the [7x 0.5], and the "lines drawn perpendicular are to be interpreted as perpendicular"...the pattern is symmetric because you drew it that way, not because of the location of the datum you chose to control it.
RE: Pos Tol applied to pattern (how to?)
Ah. Ok. Maybe I mistated something. First, I'm not going to use the profile. Second, the relationship of each of the instances within the pattern to each other is my main concern. In that effort, I arbitarily choose the part center of the datum to give these a common frame of reference. Is there a better way?
I was going to put a new example, but I'm not ready it, I think, until I get some clarity on this. Sorry if I'm being dense. Everyone's assistance so far has been very much appreciated. (Patterns suck)
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
KENAT,
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RE: Pos Tol applied to pattern (how to?)
Just to correct myself, the center datum was not arbitary, as I do want the pattern roughly centered on the part.
KENAT,
Yes. But now that you mentioned it, I guess its time for me to look it over again.
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
Let the actual functional features that are used to locate and orient the plate or the holes in the plate as they interact in their operation with other parts determine what should be declared as datum features! If that is not possible detail the most stable substitute DRF and divvy-up the allowable variation in the stack between the substitute DRF an the functional features.
Since we don't understand the function of the plate, the holes, and the interactions with other parts... any advice we offer is like target practice in total darkness.
paul
RE: Pos Tol applied to pattern (how to?)
Evan Janeshewski
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RE: Pos Tol applied to pattern (how to?)
I like your "no locating pins" concept. My primary concern about fcsuper's original drawing is that two of the datums are features of size, and the positional tolerances are very accurate. If the outline is not critical, it should be sloppy, and some other feature should provide datums. This is particularly important on something like a sheet metal part with all four edges bent up.
RE: Pos Tol applied to pattern (how to?)
I know the feeling. I knew that would be an issue, but I also know there's a lot of smart people on this board. :)
I've come to the conclusion (so far) that there are two competing interests in the location of the pin holes and the location of the pattern.
The locating pins are the common reference. The problem is that the part is symmetric about the datum B in my example, but the pins only engage one side of the part or the other, but not both simultaneously. The part is ambidextrous. It's almost as though I need the 64x pattern to be equally positioned in relation to each pin hole separately. This sounds like a lot of pitfalls.
The alternative I'm seeing is to keep the pattern and pin holes driven from a common datum (current the center of the part).
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
RE: Pos Tol applied to pattern (how to?)
This plate rests on a flat surface.
It is located by two pins which engage the pin hole in the upper left, and a slot in the upper right.
The part can be rotated 180deg and engage the same pins in the same manner, just with the other pin hole and slot.
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
RE: Pos Tol applied to pattern (how to?)
Yes, composite geo tols look like what I need. I'm just now conflicted about which features to use as the datums.
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
Like I said though depends if your function/tolerances can accomodate this.
I sometimes think a simpler approximation has benefits over a technically more accurate, but somewhhat more complex, solution.
Still reckon its 56X not 7X too
KENAT,
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RE: Pos Tol applied to pattern (how to?)
I was afraid you'd say that (if not you, then someone else). I am out of my depth in trying to apply a composite pos tol to a secondary datum based on a hole (and what would the tertriary datum be)?
BTW, it's not 56X, it's more like 1000X :) That comment was noted and accepted. The example I've give has be simplified.
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
I think I understand. Either one of the two locating pin holes could be engaged as the secondary datum feature depending upon 180 degree rotation of the part in the plane of datum feature A?
My recommendation then would be to detail it as I did making the 2X pattern datum feature B... and eliminate the slot in the mating part. You may have to restict the position tolerances of the 2X pattern in your part and the mating part 2X X.XX +/- .XXX |TP|dia. 0(M)|A| in both parts and then control the manufacturing variation and subsequent interference fit with the size tolerances on the pressed in pins and mating part clearance holes... or employ roll pins that are mallable to interference fits to account for that expected interference from manufacturing variation.
paul
RE: Pos Tol applied to pattern (how to?)
Two comments:
One, this is not a press fit scenario. It's a slip fit. These parts are frequently placed on two pins which are on the base plate and then removed.
Two, for me to apply your recommendation about datum B, I would have to understand it. I'm not sure, at this point, how to explain my use of the 2x pattern as reference to others. In using both pin holes, doesn't this create rather complex geometry in trying to calculate the position of each instance in the 64x pattern?
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
This kind of registry is done daily (repetitively) in automotive valve body calibration test fixtures and in the actual assemblies. The DRF origin is in the center of the 2X pattern with slight interference if the spread between the holes and pins are alternately long... short... if they are the same there may be slight freedom to shift.
The 64X holes would be controlled symmetrically from the plane of A and the center of the 2X pattern... what is so complicated about that?
paul
RE: Pos Tol applied to pattern (how to?)
Thanks!
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
I'm calling out the pattern with "56x [.500] (= 7x 3.5)" I am using a delta note similar to "For Reference: this is a 7 x 7 = 49 pattern with 8 x 8 feature instances" to make make sure the pattern callout is clear.
I'm locating the 2x pin holes with TB|.002m|A|B|C and making the 2x pattern Datum D
For the 64x pattern I'm calling out TB|.001|C|D.
See attachment
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RE: Pos Tol applied to pattern (how to?)
In the spirit of 1.1.4 I'll assume your 2 slots are defined elsewhere
KENAT,
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RE: Pos Tol applied to pattern (how to?)
"Also, if you aren't relating the holes to B & C I dont' know if you get the 'implied centered' anymore."
KENAT,
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RE: Pos Tol applied to pattern (how to?)
Point 1: Yes, that was a typo. The hole should read tb|.001|A|D
As to the rest of your questions, I am still looking into the Y14.5 standard and cannot find where datum D would be the center of the part and not a plane between the axes, yet. Beyond that, I still have to put this on the real drawing in a way that is readily interpretable, which means I may have to consider another way about this anyway.
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RE: Pos Tol applied to pattern (how to?)
I had trouble getting my nogging around it so my solution was to quit following the thread!
KENAT,
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RE: Pos Tol applied to pattern (how to?)
OK, I understand the usage of the pattern as the datum. I'm still not clear on how rotation of the pattern to the datum is controlled. Does using a "mid-point" assume the existance of unstated perpendicular planes (where B and C would be), and assume a reference to those?
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
Composite TB|dia.002M|A|D
Composite TB|dia.001M|A|D
Matt Lorono
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RE: Pos Tol applied to pattern (how to?)
It would be a mistake for you to propose some new way of dimensioning if you couldn't fully defend your reason for doing so! I looked at your new sketch and read your typo capitulation to referencing the 64X holes from A|D rather than C|D but... I am confused as to why there are slots??? in your sketch if the plate registers on two round pins in the two round holes D whether rotated right-side-up or up-side-down 180 degrees while still on surface A? What do the slots do???
As for your questions about using composite FCF's... Why??? The lower segment of a composite... controls pattern integrity to itself and just orientation of the pattern to the datum features... what is its benefit with this design where the 64X pattern needs to be repeatable and 180 degree reversible at its approximate 40 degree angle to the 2X secondary pattern???
Sorry for the delayed response. I had to go play racquetball with the younger-faster-more agile engineers in our old league... Old age and treachery struggling to overcome youth and determination kinda stuff! I lament... I took off the whole winter block to ski and teach little rascals to ski... golf is beckoning... oh my knees, oh my back... it's hard engaging again!
paul
RE: Pos Tol applied to pattern (how to?)
KENAT,
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RE: Pos Tol applied to pattern (how to?)
Paul
RE: Pos Tol applied to pattern (how to?)
It appears that I misunderstood a great deal of this exchange if your insights are correct. I think that I clarified my assumptions 14 posts ago!
Paul
RE: Pos Tol applied to pattern (how to?)
I thought you were proposing replacing the slot with a hole, or something like that. Or else relating the pattern to the 2 holes, even though only one hole is used at a time functionally, as an approximation.
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RE: Pos Tol applied to pattern (how to?)
OK Paul, so does this change your impression of how to properly control the pattern? ..cuz I think both KENAT and I have questions about your proposal (which I did try to implement).
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RE: Pos Tol applied to pattern (how to?)
My first mark-up of your picture had only 2 round holes "upper-left and lower right" as datum feature pattern "B" omitting the slot that I assumed was "lower right." It wasn't until I saw your re-sketch tonight that I questioned the difference in our assumptions! If you re-read my comments in that light you will understand my advice to make the plate 180 degree reversable and repeatable with the least marginable shift or interference.
paul
RE: Pos Tol applied to pattern (how to?)
This stuff isn't all science... there is a lot of art and communication in it.
paul
RE: Pos Tol applied to pattern (how to?)
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RE: Pos Tol applied to pattern (how to?)
Are you now saying:
1. Use a 'conventional' hole & slot secondary & tertiary datum using one set of hole & slot. Make the tolerances on the other hole & slot close enough so they still provide adequate location when the part is reversed and they become the functional datums.
Or:
2. Make the 64X pattern the second & tertiary datums per 4.5.8 & figure 4-22 of 14.5M-1994 then relate the 2 hole/slot pairs back to this datum. While this is 'backward' from a function point of view to me it's equivalent and allows the different hole/slot pairs to act as the true functional datums in the 2 different orientations.
I think both options have been suggested by several people now but we got lost due to some misunderstandings. Option 2 seems more technically correct to me, however depending what tolerance is really required 1 may be adequate and perhaps simpler to understand.
I think anyway
KENAT,
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RE: Pos Tol applied to pattern (how to?)
I was advocating leaving off the (=7X 3.5) bit or variations there, on as it's confusing to me too, just have the [56X .500].
([] indicates basic for anyone feeling picky
KENAT,
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RE: Pos Tol applied to pattern (how to?)
I'll upload a new example tomorrow. Once we get this sorted out this may be a good topic to make a FAQ.
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RE: Pos Tol applied to pattern (how to?)
No!!! my advice was to loose the slot!!! that I thought was "lower right" and replace it with a round hole... In doing so... the pins "roll pins or solid... each with chamfered ends" will interfere slightly or substantially restrict rotation and shift of the plate to the fixture or mating part that it assembles with.
Paul
RE: Pos Tol applied to pattern (how to?)
fcsuper, when you talk about rotating 180° and engaging in pins, is this tiff something like what you're talking about? I added a chamfer on one corner to try and understand the orientation better.
If this is correct then Paul, [pretend the slots are holes, and the pins have some give if need be] and answer 1 or 2 per my above options or something else, if you have the time to try and educate a dullard like me.
KENAT,
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RE: Pos Tol applied to pattern (how to?)
I just looked at 4-22 "hole pattern as a datum feature" and I understand your apprehension in employing it (as others in this forum have lamented in previous posts)... Where in fact is the origin of an imperfect geometric pattern???
That is not "so much" a question with a tightly toleranced 2X patterns "round dowels fitting with round holes with slip-fit or interference fit clearances" where 90% of the variation is dissipated in a straight line between the dowels. These assembly locators win wars, help us travel through space, taxi us through the air at 400+ miles/hour, and enable us to get groceries in the blink of an eye, yada, yada, yada.
No matter whether the CAD designer, draftsman, or detailer depicts the "two round holes and two round pins" as "secondary and tertiary" or "pattern secondary" they operate the same way! When one spread is long and the other short they tend toward interference... no matter what the size differences are!!! A slot naturally eliminates the potential interference but... we consistently design precision assemblies with "two round holes and two round pins" to achieve the least possible variation in location and orientation of one feature to another, hence my advice for your plate.
paul
RE: Pos Tol applied to pattern (how to?)
Yes, that's what've I've been saying. :)
Paul,
So, my last example is OK now if I continue to use the pattern secondary?
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RE: Pos Tol applied to pattern (how to?)
Do you
Option A: Arbitrarily pick a pair for your secondary/tertiary datum and rely on the tolerances on the other pair giving adequate relation to the main hole pattern when in service they are providing alignment.
Option B: Make the main hole pattern the datum (all 64 holes) and relate both sets of alignments holes (or hole-slots) to that pattern.
Option C: something cleverer/simpler I haven't listed.
I never meant to argue that hole-slot is better than hole-hole if you can use it - you convinced me of that on an earlier thread some time back.
KENAT,
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RE: Pos Tol applied to pattern (how to?)
RE: Pos Tol applied to pattern (how to?)
If his part can be redesigned to accomodate your scheme great. Howevever, if he's stuck with 2 separate sets of alignment features, dependant on orientation as per my sketch, which I've got a feeling he is then what?
KENAT,
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RE: Pos Tol applied to pattern (how to?)
RE: Pos Tol applied to pattern (how to?)
I think I can justify using the 2x pattern because both directions need to be symmetric, and this forces symmetry. So even though both pin holes are not engaged in the fixture, both can be engaged individually to provide common results, as long as I control the adjacent slots well enough.
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
RE: Pos Tol applied to pattern (how to?)
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
RE: Pos Tol applied to pattern (how to?)
RE: Pos Tol applied to pattern (how to?)
Only thing I'm a bit unsure on is given your 64 hole pattern now reference A and D, is there a clocking/orientation issue as the D planes are at an angle to the outline. Should an angle be given for the pattern to the plane between the 2 D hole axis?
I think you'd get what you need but I'm not totally sure it's bullet proof.
KENAT,
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RE: Pos Tol applied to pattern (how to?)
Since the distances between the holes are basic and orthogonal to the part, the specification is complete. However, I did talk to my contact at an inspection house about this scheme and he did ask that I add the angle as a reference.
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
RE: Pos Tol applied to pattern (how to?)
KENAT,
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RE: Pos Tol applied to pattern (how to?)
I don't think that is the issue, the pattern is drawn and dimensioned perpendicularly to the datum hole "pattern" if you will. But, the location of the two datum holes "D" are not completely defined relative to the pattern...I think...the dimensioning scheme Matt is showing works, because the centerline implies the "D" holes are located halfway between two columns of the pattern. But long ago I got beaten about the head and shoulders rather severely in this forum about implied datums and implied symmetry. My shampoo bottle still hasn't recovered...
'Twere me, I would dimension the x-y location of the datum "D" holes from the center(s) of one of the pattern holes, using basic dimensions (looks like two each [0.500] dimensions would suffice). The extra basic dimensions may arguably be redundant, but redundant basic dimensions are allowed and even encouraged elsewhere in ASME Y14.5M (remember the circular bolt pattern
arguementdiscussion awhile back...:)RE: Pos Tol applied to pattern (how to?)
As to the implied center, I vaguely recal that incident. Generally there is no such thing. However, in certain situations i.e. when using datum feature center planes it seems it's allowed. I couldn't find the text that backs it up in 14.5 but figure 5-4 shows it (yeah I know 1.1.4 is inplace
However, I wonder if the horse needs me to keep beating it.
KENAT,
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RE: Pos Tol applied to pattern (how to?)
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
RE: Pos Tol applied to pattern (how to?)
You have Datum A as the top of the part. When I was taught GD&T, from a Y14.5 committee member, we were taught to think of the datums as the inspection setup planes.
To inspect your part, the inspector would plase the countersunk hole side down on the inspection device, then work from there.
Do I have that right or am I missing something?
"Wildfires are dangerous, hard to control, and economically catastrophic."
Ben Loosli
RE: Pos Tol applied to pattern (how to?)
I would say yes.
Is the committee member still a member and still teaching?
.
RE: Pos Tol applied to pattern (how to?)
KENAT,
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RE: Pos Tol applied to pattern (how to?)
I cannot discuss design intent to that degree.
Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
RE: Pos Tol applied to pattern (how to?)
Yes, I'm saying you do it the other way around. Fcsuper has said, repeatedly, that the outer profile is less important. If that's so, then the D-datum holes would be held to tight tolerances relative to the pattern, and loosely to the outer boundary. If I was inspecting the part, I'd look at the tightest tolerances, and start my inspection there. If I read the drawing, and was making the part, I would grab any old sheet that had enough room, punch/drill/laser/waterjet the hole pattern, and then indicate off the hole pattern to lay out and shear/cut/trim the edges of the plate.
In reality there is not any preferred "order" to the datums, you can design, fabricate, and inspect, in any order you please, as long as you satisfy the requirements...
RE: Pos Tol applied to pattern (how to?)
I then restrained myself to looking at the scheme fcsuper came up with hence the request for clarification on what you were saying.
I do agree that people sometimes get too caught up in following the datums during manufacture etc. The important thing is to meet the final intent - that doesn't always mean manufacturing in the order of datum precidence etc.
KENAT,
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RE: Pos Tol applied to pattern (how to?)
My reply "Yes, I'm saying you do it the other way around. "
I now retract. I shoulda said, 'you do it in whatever order you want, but meet the requirements nonetheless.'