I have an European print in which t

[Heming]

I have an European print in which there are two bores at 45 degree. By theory they should be aligned with each other (their center line in the same plane), but in reality they may not be that perfect. I want to know by the ISO, what tolerance I should have?

 

[greenimi]

Could you post a drawing? Or at least a partial and relevant portion of it

 

[Heming]

I marked two centerlines red. They are supposed to be in the same plane. But we machined them in two different setups. How much tolerance of centrality I could have? Print did not give any.

 

[greenimi]

If the print does not state, maybe there are some default tolerances such as ISO2768, or other notes that define or implies the coaxiality.
What the general notes read?

If not the drawing is underdefined.

 

[Heming]

That what I thought. I am just not that familiar with ISO. The general notes define like this: Precision: 2768-mH; Tolerance: ISO 8015.

 

[chez311]

Heming,

I'm not sure I can even tell what the second angled feature is supposed to be from this view, theres a diameter dimension and tolerance but no opposing side from which to measure a diameter? I do see some pretty terrible formatting, and a lone Datum Feature Symbol, but no geometric tolerances (ie: position). From the view you have shown, there is no requirement for these two features (or several of the features shown) to be at any particular orientation/location relative to each other unless as greenimi noted there is some applicable general tolerance/note which covers it.

 

[Heming]

I am sure ISO should have some kind of tolerance on the centrality of these two features. We hardly use ISO. Instead we follow military and auto industry standard all the time.

 

[juergenwt]

Just not enough info available from this print. For your own good: This unbelievable conversion (x25.4) will kill you.
Stay with metric only. You are taken a simple part print and are making a monstrosity out of it almost impossible to to make this part. If you are making parts designed in metric than stick with metric. Conversions like shown on your print will kill you.

 

[mfgenggear]

conversions from metric to English and vice a versa is common.
I would suggest to contact the originator or the customer and ask them the required true position.
the missing requirement is the true position on center line of the part. if that fails because the dimension .7559 has a +/- .0039 inch
total tolerance of .0078 . I would cut the tolerance in half and use true position of .004 held on center line.

 

[Heming]

Thank you, mfgenggear.
At least I can have something to refer to. I was thinking tighten it up even more <.003.

 

[Tmoose]

Precision: DIN ISO 2768-mH.
general tolerances are based on customary workshop accuracy, not part function.
The tolerance is the total width of the tolerance zone. Thus a tolerance of 1 mm is usually ±0.5mm

m = Middle tolerance. not Fine or Coarse- linear dimensions, angular dimensions

H = finer grade - straightness and flatness, circularity, cylindricity, parallelism ( numerical value of size or flatness/straightness, whichever is greater) , perpendicularity (H for 100 mm long features 1.2mm ± 0.6, symmetry , coaxially

 

[Heming]

Thank you, Tmoose (I always try to spot a moose where I was in Maine. Did not have any luck). 1.2 mm over 100mm. In my case, 19 mm would have .228 mm. It is kind of big , about .0089 of True Position. Half of it is still .004.

 

[Burunduk]

I agree with mfgenggear that the best way is to contact the customer and ask them what is acceptable.

I also agree with chez311 that the dia. 20 mm angled feature looks unclear. Is this some sort of arc in a true view? Can you even derive a center axis from it on the actual part?

If you want to go by the ISO general tolerances anyway, then the only location controlling geometric tolerances listed in ISO 2768 are symmetry and circular run-out. You may try to treat the deviation from axis-coplanarity that you want to control as symmetry (note that this is ISO symmetry, not the ASME Y14.5 kind of symmetry). The only value listed for the H class is 0.5, regardless of the length of the feature. You use the longer feature as the datum, but you have several to choose from. The M18 thread looks like a good candidate. This is from ISO 2768-2-1989 that remains the latest:

 

[Heming]

Hi burunduk and chez311,

The center line of the angled feature because it is how we machined it. There is only a small section of 20 mm diameter bore.

 

[Burunduk]

Hi Heming,
This also seems to be how it is dimensioned. The 20 mm "bore" is only a small curved surface of 10 mm radius. I don't think you'll be able to determine the axis of that thing to control its position. A proper print would have it defined by basic dimensions and a profile of a surface applied to it.

 

[Heming]

I got used to basic dimension and true position. But ISO seems or this specific customer have different way to define the relationship. What I don't like is that my CMM guy could not intersect the two centerlines then he converted 3D to 2D (project them into an artificial plane) to make them intersect. I told him we need the feedback how far these two centerlines apart of each other.

 

[chez311]

Heming,

Good luck with deriving a reliable axis from that partial cylinder. In ASME it would not be allowed to apply a position tolerance to this feature, as it is not a FOS and is lacking opposed points. Not sure about ISO, but the same issue will arise with deriving a reliable axis no matter the standard. Profile is what is needed to control this feature reliably.

 

[Heming]

That small section of bore has more than 72 degree sweep. I think it is enough (20% of the whole bore) to determine the centerline. I did not show the other view of the print.

 

[mfgenggear]

it's easier to machine than to inspect. however it should be doable with CMM, edit it takes a lot of hits, and proper programing