Dimensioning stock extrusions
Dimensioning stock extrusions
(OP)
First of all, let me just say that after using many sites to find answers to engineering questions, I would like to give everyone on this site a big "thank-you" for being the most knowledgeable! Now on to my question.
I have been working in the aerospace industry for over seven hard years. The company I work for now, had no standards in place when I came on board. So I have been very hard at work trying to train people as to ASME and ISO standards. Everything has been going good until this new contract. One the the new people was designing a mount using stock extrusion. When he documented the extrusion, he told me that you don't dimension the extrusion parts that are not "toutched". I told him that just because you use it as stock, does not tell the manufacturer not to touch the areas. He them told me that he will just list the overalls as referance dims. Has any of you ever seen this done like this? I was tought to alwasy fully dimension the part. To me, I could then turn around and say to order stock sheet metal of a certain LxWxD and just dim the holes added?
So heres the questions:
1. Have you seen this done before?
2. Where in the standards would I find info about using stock extrusion to just put holes in?
3. Would I be correct into stating that "stock extrusion" is nuthing more than just that, a starting point? Because, if the stock extrusion is not readily available, without dims, one could not manufactur the part.
P.S. Example attached.
V/R
Nate
I have been working in the aerospace industry for over seven hard years. The company I work for now, had no standards in place when I came on board. So I have been very hard at work trying to train people as to ASME and ISO standards. Everything has been going good until this new contract. One the the new people was designing a mount using stock extrusion. When he documented the extrusion, he told me that you don't dimension the extrusion parts that are not "toutched". I told him that just because you use it as stock, does not tell the manufacturer not to touch the areas. He them told me that he will just list the overalls as referance dims. Has any of you ever seen this done like this? I was tought to alwasy fully dimension the part. To me, I could then turn around and say to order stock sheet metal of a certain LxWxD and just dim the holes added?
So heres the questions:
1. Have you seen this done before?
2. Where in the standards would I find info about using stock extrusion to just put holes in?
3. Would I be correct into stating that "stock extrusion" is nuthing more than just that, a starting point? Because, if the stock extrusion is not readily available, without dims, one could not manufactur the part.
P.S. Example attached.
V/R
Nate





RE: Dimensioning stock extrusions
Chris
SolidWorks 08, CATIA V5
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion
RE: Dimensioning stock extrusions
2.Basic dimensions missed on the positional tolerance callout.
SeasonLee
RE: Dimensioning stock extrusions
Your absolutly right about the lack of basic dims. He also did not properly align datum "A" eaither (flotting off the part).
So as I understand it, the stock should be dim'ed as referance.
I attachted an updated drawing with ref's and basic dims. Let me know if this is more copasetic to you all. I am going to use your replies to help teach him. As for his GD&T skills, they are inexistant, but thats just due to lack of training.
V/R
Nathan
CAD Technician/ISO Director
Compass Systems, Inc. ( http://www.compass-sys-inc.com/ )
RE: Dimensioning stock extrusions
2. 2X should be in front of the dimension .41. Please go to paragraph 1.9.5 of the standard ASME Y14.5M for more detailed information.
3. Please don't forget dim 1.00 (from datum B)is a basic dimension as well.
SeasonLee
RE: Dimensioning stock extrusions
The basic dimension value should be expressed with the same number of decimal place as the tolerance, please ref to the standard on paragraph 2.3.2 (d) page 25. On your case, the positional tolerance .005 has three decimal places, so all of your basic dimensions should be changed to three decimal places accordingly.
SeasonLee
RE: Dimensioning stock extrusions
Thank you for all your help. I was never fully tought GD&T myself, sort of self-tought. I have been learning a lot, and have no problem designing using it, but teaching others GD&T is not my strong side. I think I will have him take a GD&T course, and perhaps get myself into it for better clarification. The down side to the company I am working for, is that most people have the lack of pride in their work. Also, your right about the three place decimal. I cought that myself this afternoon, and was wondering as to how I missed it prior to then. I suppose it was after seeing it wrong so many times on all the drawings I am reviewing, it was wearing me out to the point that I was missing alot.
Drawings for review: 1541
Reviewed so far: 89
DWG's remaining: 1452
(progress takes time)
V/R
Nathan
CAD Technician/ISO Director
Compass Systems, Inc. ( http://www.compass-sys-inc.com/ )
RE: Dimensioning stock extrusions
You may want to re-consider using that point as a secondary datum. I would either switch datums B and C or change the FCF to callout the position WRT A, C, and B.
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RE: Dimensioning stock extrusions
And for the reference dimensions for stocked, or purchased items. We here do use that method as shown in your second attachment. Only thing i meant do different is call the stock size out in the BOM and just dim the two legs as reference.
Solid Edge V20
RE: Dimensioning stock extrusions
I would only reference the lengths of the legs, and that would only be to define the part envelope. If this had to be made from scratch, the standard from which it was chosen would be used for any dimensioning. To show all dimensions is an unnecessary cluttering of the drawing.
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Dimensioning stock extrusions
Yes, I think you are right
SeasonLee
RE: Dimensioning stock extrusions
I agree with Cadman1964, although I'm not sure that having the 3 dim.s is incorrect. It just seems to make more sense to have it as he specified. Personnally, I'd leave the 1.00 dim on the right as a reference dimension (as long as it's not cluttering the drawing) and add the overall dimension.
Also, would the 1.00 dim from datum B need to be basic? To me, it would seem that the hole spacing is the critical aspect, and the excess on either end doesn't need to be held to the positional tolerance shown. I'm guessing without knowing the function of course. For example, if the title block tolerance were +/- 1/32... I'm guessing that if the LH was 31/32, there was 7.53 between the holes, and the RH was 1 1/32, the part would still function. By making the RH 1.00 dim basic, you are increasing the accuracy required without any benefit.
Is it required that all dimesions from a datum to a feature with positional callout be basic? If so, could the centerline of the LH hole be used as datum B to allow the 1.00 dimension to have the looser tolerance?
--MechEng2005
RE: Dimensioning stock extrusions
I've attached a image from the ANSI standard (Page 85), hopefully this will help a little. Basically you GD&T feature tolerance is your hole position tolerance up and down and all round, understand??
Solid Edge V20
RE: Dimensioning stock extrusions
1 Your dimension from Datum B does need to be basic
2 the file.....
Solid Edge V20
RE: Dimensioning stock extrusions
Feel free to comment.
V/R
Nathan
CAD Technician/ISO Director
Compass Systems, Inc. ( http://www.compass-sys-inc.com/ )
RE: Dimensioning stock extrusions
Chris
SolidWorks 08, CATIA V5
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion
RE: Dimensioning stock extrusions
Chris,
That statment is very true. Thus for our reasoning as to fully "constraining" the final part. I for one would rather fully check a part that was made from stock and find errors rather then just say "it was a stock dim, so ref it". I personnaly have found cases that the stock material was not within tolerance of our required finnished part, but they never knew that till it was too late. I beleive that one incedant cost the company over ten thousand dollers to have every part re-manufactured to be within spec. Talk about a bad delay.
V/R
Nathan
CAD Technician/ISO Director
Compass Systems, Inc. ( http://www.compass-sys-inc.com/ )
RE: Dimensioning stock extrusions
Also I think you want 2X.063, or you're missing a dim.
Mecheng - the matching decimal places is in ASME Y14.5. Also yes, the 1.00 from B needs to be basic. Essentially all dimensions locating features toleranced bye Position have to tie back to the datum with basic dims. (can be stacked basic dims as basic dims have no tolerance)
As to the idea of changing the dimension scheme and/or datum there are several options such as making the holes the secondary & tertiary datum or making the pattern a datum but this would have to be decided based on function and there's no point using a more complex dimension scheme if no one understands it, even if it is more 'correct'. If what they have adequately meets function and is adequatly understood it may be OK.
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RE: Dimensioning stock extrusions
1. As for the 2X .063, your right. That will need to be defined.
2. As for using the hole pattern as the datum, I look at that myself, until the designer stated that the distance between Datum C was important for fit, more so then the other end. Also, ther is another part that gets made out of this one as a "mod" that needs the Datum C. So we are leving it to allow one part to be used to make the other. I personnaly don't care for there method there, but just getting people to used GD&T is hard enought. Thus we are trying to keep it more basic untill they get the hang of it. I would rather have satisfied customers and gradual training, rather then the other way around.
V/R
Nathan
CAD Technician/ISO Director
Compass Systems, Inc. ( http://www.compass-sys-inc.com/ )
RE: Dimensioning stock extrusions
I am not quite sure is it allowable with basic dimensions on the rectangular coordinate dimensioning, some dimensions (.41 and 1.00) without dimension line while the other (7.53)with dimension line, it looks very strange for me, expect someone who can give the right guide.
SeasonLee