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True position with Perp control
- Thread starter Precise
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To refine what tunalover posted, the perpendicularity must be smaller than the position tolerance, and have an appropriate datum reference. Other than that, no problem.
Jim Sykes, P.Eng, GDTP-S
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Jim Sykes, P.Eng, GDTP-S
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CAD-Documentation-GD&T-Product Development
One could have a positional tolerance in which the reference datum was only the surface reflecting features within the pattern and perpendicular to the surface. It depends upon the situation.
One should not have a positional tolerance of 1 hole to the surface as I have seen on many drawings to qualify the secondary datum. In this case the drawing should have reflected a perpendiclarity rather than positional tolernace.
Dave D.
One should not have a positional tolerance of 1 hole to the surface as I have seen on many drawings to qualify the secondary datum. In this case the drawing should have reflected a perpendiclarity rather than positional tolernace.
Dave D.
Dave, interesting second point, but I don't fully agree. It is definitely easier to understand a perpendicular control symbol, but a positional tolerance with only one datum reference does denote orientation. The question arises then whether it is parallelism, perpendicularity or angularity ... the datum reference tells you that. It's definitely not as easy or direct as using the perpendicularity symbol directly, but it is valid.
Jim Sykes, P.Eng, GDTP-S
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CAD-Documentation-GD&T-Product Development
Jim Sykes, P.Eng, GDTP-S
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CAD-Documentation-GD&T-Product Development
Jim:
Positional to 1 hole relative to a surace reflects perpendicularity or any other angularity symbol which is the orientation. Why place positional when the appropriate symbol should be perpendicularity, parallelism or angularity? Doesn't make sense to me.
This is just something that I have seen over the years - pet peeve.
Dave D.
Positional to 1 hole relative to a surace reflects perpendicularity or any other angularity symbol which is the orientation. Why place positional when the appropriate symbol should be perpendicularity, parallelism or angularity? Doesn't make sense to me.
This is just something that I have seen over the years - pet peeve.
Dave D.
- Thread starter
- #7
The reason I am using Position and Perpendicularity control was to control the holes location to within 2 thou and the hole needs to be perpendicular to within .0002 tenths.
Position does control perpedicularity however not tight enough so this is why I used both. I assume I am correct but was just checking.
Position does control perpedicularity however not tight enough so this is why I used both. I assume I am correct but was just checking.
Precise: precisely. You have the right controls for your application.
Dave, I'm not fussy about which way it's put on drawings because I understand that they are the same thing. I was doing it for a while a few years back because some German engineering colleagues had been taught that way in their technical programs, and their shop people had a bit of a time recognizing the perpendicularity, angularity and parallelism controls as being applicable to holes rather than just edges/faces. We trained it into them in time. The shop people that I was working with over here had no fore-knowledge of GD&T whatsoever for the most part, so it was easy enough for them to accept and understand the equivalence of the two methods, though they also indicated that it was easier if we just used the three orientation controls.
I'm a firm believer that only 5 controls are actually needed; position, profile of a line and profile of a surface, runout & total runout. Everything else is just a special case of these fundamental or "primitive" controls. Unfortunately, most users of GD&T (engineering or manufacturing side) don't have enough knowledge and experience to appreciate it. It is, of course, far quicker & easier to break these down into the special cases that each of the other controls represents, and teach or learn it on that basis rather than understanding how it all relates back to the "primitives".
Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development
Dave, I'm not fussy about which way it's put on drawings because I understand that they are the same thing. I was doing it for a while a few years back because some German engineering colleagues had been taught that way in their technical programs, and their shop people had a bit of a time recognizing the perpendicularity, angularity and parallelism controls as being applicable to holes rather than just edges/faces. We trained it into them in time. The shop people that I was working with over here had no fore-knowledge of GD&T whatsoever for the most part, so it was easy enough for them to accept and understand the equivalence of the two methods, though they also indicated that it was easier if we just used the three orientation controls.
I'm a firm believer that only 5 controls are actually needed; position, profile of a line and profile of a surface, runout & total runout. Everything else is just a special case of these fundamental or "primitive" controls. Unfortunately, most users of GD&T (engineering or manufacturing side) don't have enough knowledge and experience to appreciate it. It is, of course, far quicker & easier to break these down into the special cases that each of the other controls represents, and teach or learn it on that basis rather than understanding how it all relates back to the "primitives".
Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development
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