drafting methods 7

[palecactus]

hello,
im in a bit of a pickle. any help would be appreciated.is it standard practice to hold all decimal places in a dwg the same? if there are 4 views, for example, should all 4 have the same amount of decimal places or can they vary depending on the importance of the feature?
i know that if the dimension on a part is held at, lets say 3 places, the tolerance for that dim is held at 3 places.
i could be wrong.
one more, is it practical to call out dims on lets say a round part, such as a pulley, to be ordinate dimensions? do machinists and toolers read these easier rather than non-ordinate dims.
any insight would be appreciated.
thanx

 

[mechengdude]

All four views do not need to have the same number of decimal places. On the contrary, in most cases they won't. Thats why you typically have a title block tolerance that says something like three place decimals +/- .005 two place decimals +/- .020.

I would use the dimensioning schemes called for in the latest copy of ASME Y14.5 as a guide. Trying to guess what a machinist wants to see various from machinist to machinist.

 

[joebk]

I agree 100% with mechendude. Dimensions/tolerances on a single (or multiple) view drawing do not need the same number of decimal places. Grab a copy of the ASME Y14.5M-1994 handbook. I couldn't live without mine.

I have seen drawings from a customer of ours that carried ALL dimensions (inch units) to 4 decimal places regardless of the form/fit/function of the part. Even angles. Yuck!

 

[ewh]

One situation where the number of decimal places needs to be the same is when using basic dimensions. The number of dimension decimal places must be the same as it is in the feature control block(s).
Don't rely too heavily on the detailed examples in ASME Y14.5 for proper dimensioning of items other than the points that their examples are emphasizing. Do follow the printed recommendations.

 

[ewh]

forum1103 will get you better exposure for this type of question.

 

[Heckler]

I would highly suggest buying the specification and getting some training....like any lanuage practice makes perfect.

Section 1.4 Fundamental Rules: Dimensioning and tolerancing shall clearly define engineering intent and shall conform to the following.

a)Each dimension shall have a tolerance, except for those dimensions specifically identified as reference, maximum, minimum or stock (commercial stock size). The tolerance may be applied directly to the dimension, indicated by a general note, or located in a supplementary block of the drawing format.

b)Dimensioning and tolerancing shall be complete so there is full understanding of the characteristics of each feature.

c)Each necessary dimension of an end product shall be shown. No more dimensions than those necessary for complete definition shall be given. The use of reference dimensions on a drawing should be minimized.

d)Dimensions shall be selected and arranged to suite the function and mating relationship of a part and shall not be subjected to more than one interpretation.

e)The drawing should define a part without specifying manufacturing methods. Thus, only the diameter of a hole is given without indicating whether it is to be drilled, reamed, punched or made by any other operation. However, in those instances where manufacturing, processing, quality assurance, or environmental information is essential to the definition of engineering requirements, it shall be specified on the drawing or in a document referenced on the drawing

f)It is permissible to identify as nonmandatory certain processing dimensions that provide for finish allowance, shrink allowance, and other requirements, provided the final dimensions are given on the drawing.

g)Dimensions should be arranged to provide required information for optimum readability. Dimensions should be shown in true profile views and refer to visible outlines.

h)Wires, cables, sheets, rods, and other materials manufactured to gage or code numbers shall be specified by linear dimensions indicating the diameter or thickness. Gage or code numbers may be shown in parentheses following the dimension.

i)A 90 degree angle applies where center lines and line depicting features are shown on a drawing at right angles and no angle is specified.

j)A 90 degree basic angle applies where center lines of features in a pattern or surfaces shown at right angles on a drawing are located or defined by basic dimensions and no angle is specified.

k)Unless otherwise specified, all dimensions are applicable at 20 degrees Celsius (68 def F). Compensation may be made for measurements made at other temperatures.

l)All dimensions and tolerances apply in a free state condition. This principle does not apply to non-rigid parts as defined in paras 2.7.1.3(b) and 6.8.

m)Unless otherwise specified, all geometric tolerances apply for full depth, length and width of a feature.

n)Dimensions and tolerances apply only at the drawing level where they are specified. A dimension specified for a given feature on one level of drawing, is not mandatory for that feature at any other level.


Heckler
Sr. Mechanical Engineer
SWx 2007 SP 3.0 & Pro/E 2001
XP Pro SP2.0 P4 3.6 GHz, 1GB RAM
NVIDIA Quadro FX 1400
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_`\(,_
(_)/ (_)

(In reference to David Beckham) "He can't kick with his left foot, he can't tackle, he can't head the ball and he doesn't score many goals. Apart from that, he's all right." -- George Best

 

[palecactus]

IM GETTING MY COPY TODAY. THANX. TOO MANY HEADACHES.

 

[drawoh]

palecactus,

ASME Y14.5M-1994 specifies that trailing zeros are not to be shown on metric dimensions, and that they are to be shown on inch dimensions.

Other than that, I agree with everything above.

JHG

 

[fcsuper]

[green]drawoh,

You went and mentioned the difference with metric without explaining why. Simplified explanation: in metric, the tolerance is presumed based on an overall spec that refers to a standard tol table, in conjunction with the part/feature size itself. The standard tol table is part of the international tolerance standard.[/green]

[blue]Pal,

Look into blueprint reading class or drafting classes locally or online (if haven't done so yet). Having the standard in hand helps, but understanding it may be an issue without some training. Also, I do not recommend using Ord dims on a round part unless there is some logical feature which can serve as the 0,0 location (a rare occurance).[/blue]

Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA
sw.fcsuper.com
Co-moderator of Solidworks Yahoo! Group

 

[KENAT]

fcsuper - the table you refer to is only applied if you invoke it. Most of the metric drawings I worked on didn't, they had a tol block on the drawing. The europeans seems a lot keener on it than the Brits.

 

[palecactus]

the reason i brought these questios here is because my boss for some reason disagrees with all of us and he is right. im a certified draftsman w/ 2 yrs work experience and 3 yrs education.i seemed baffled when he told me these things and knew better. but he signs the check so what the heck.

 

[ewh]

Keep your resume up to date, and try not to pick up too many of his bad habits. I know it is frustrating to do as he asks, but at least you have the knowledge that it is only his personal preference, not an industry standard.

 

[fcsuper]

ditto, ewh. What city do you hearld from, palecactus? One of use might know of some opportunities for you.

Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA
sw.fcsuper.com
Co-moderator of Solidworks Yahoo! Group

 

[Heckler]

Palecactus - when you run into one of these drafting standards problems with your boss......place your reference data on your desk for him to see if he walks by. Sometimes the indirect way works.

Heckler
Sr. Mechanical Engineer
SWx 2007 SP 3.0 & Pro/E 2001
XP Pro SP2.0 P4 3.6 GHz, 1GB RAM
NVIDIA Quadro FX 1400
o
_`\(,_
(_)/ (_)

(In reference to David Beckham) "He can't kick with his left foot, he can't tackle, he can't head the ball and he doesn't score many goals. Apart from that, he's all right." -- George Best

 

[KENAT]

Question,

Do your drawings say on them that they are in compliance with ASME Y14.5 and/or do you have a company policy to follow ASME Y14.5?

If not then you can effectively do what you like/what the boss tells you, just no guarantee anyone else (e.g. vendor, customer etc) will understand what you're doing.

On the other hand if you say you are following Y14.5 and your boss asks you do something that goes against it you have a few options, although non of them is likely to make the boss happy. One option is to remove or strike through the note from the drawing that says you follow 14.5. Another is to ask in writing for permission to deviate from the standard.

If you claim to follow them then He'll probably hate having a paper trail of telling you not to follow company standards. It's up to you to judge if this will make him change his ways or get you canned!

 

[palecactus]

im betting that id get canned so my resume is on monster and i have another job lined up. our templates have the ansi y14 disclosure and some of the stuff we (or should i say I)put out arent up to snuff.
irrigation in central california is a cut throat bussines.
thanks you guys.

 

[drawoh]

fcsuper,

I did not know that that was the reason for deleting trailing zeros from metric dimensions. I always assumed that they were trying to make them look different from inch dimensions. I could use either dimension system at any time. This has to be obvious.

JHG