Straightnes/Flatness requirement.
Straightnes/Flatness requirement.
(OP)
We have a part, which is the shape of a large washer. Its a steel disc with a sintered material (9 in. OD x 6.5 in. ID x .575±.015 thickness). The disc is then cut into multiple sections of equal size. The manufacturer is having difficultly maintaining the default straightness of ±.015 (Rule #1 of GD&T). We don't care how warped the disc becomes, as long as the straightness/flatness within a 4 in. area is maintained.
Any suggestions on an appropriate GD&T callout for the drawing to maintain what is required.
Thanks,
Rich
Any suggestions on an appropriate GD&T callout for the drawing to maintain what is required.
Thanks,
Rich





RE: Straightnes/Flatness requirement.
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RE: Straightnes/Flatness requirement.
Or, does it have to be cut from a 'washer' shape? Why not have the dwg show the final part and let the vendor cut it to the shape from whatever stock they please?
Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP3.1 / PDMWorks 05
ctopher's home site (updated 06-21-05)
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RE: Straightnes/Flatness requirement.
Do you mean they are chopped up into pie slices?
JHG
RE: Straightnes/Flatness requirement.
gk
RE: Straightnes/Flatness requirement.
I previously looked at ASME Y14.5M-1994, section 6.4.2.1.1 as MadMango mentioned, but I am not sure that solves the problem. Per the specification, does the part not have to be straight within ±.015. We can allow as much as they need (Warp), so long as they can control the straightness or flatness to within ±.015 in every 4 in. length. The only way to override the default straightness is to place a straightness on the FOS or add a note "Perfect form at MMC not required". I am no GD&T expert, but if appears that section 6.4.2.1.1 of the spec, would not allow for addition straightness or flatness deviation, which the manufacturer requires..
I need to allow the plate (Washer shaped) to deviate like Fig. 6-5 if section 6.4.1.1.4. If I add a straightness callout of ".015 / 4.00" to the thickness dimension, would that do what I am trying to accomplish?
Thanks,
Rich
RE: Straightnes/Flatness requirement.
RE: Straightnes/Flatness requirement.
Does the entire part still not have to maintain a straightness of ±.015 by default? Flatness callouts in zones sounds good, but if the part is straight within ±.015, that would be permissible per our requirements. But like I mentioned, this is not possible by the manufacturer.
The parts seems to warp from one end to the other. So long as the change is not drastic within a 4 in. length, the warping is of no concern.
If a centerplane or surface has a straightness callout, is that straightness implied in all directions?
Sorry for all the questions and comments, but I am just trying to understand.
Thanks,
RE: Straightnes/Flatness requirement.
Parallelism (top surface to btm plane datum A), Flatness, or Straightness (point to surface in one front view with a tol, and point to same surface in right view with a tol...2 direction tol).
A call out of straightness AND flatness may be too hard or confusing for a sheetmetal part.
Just a thought.
Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP3.1 / PDMWorks 05
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716
RE: Straightnes/Flatness requirement.
So in short, we need a large tolerance window over the length of the parts, but a smaller one within any 4 inch segment (While maintaining the ±.0075 thickness tolerance).
I am not sure if I am conveying this info in an easlier understandable manner.
Thanks for all the comments... its really appreciated.
Rich
RE: Straightnes/Flatness requirement.
What actually is the problem here? Is the manufacturer unable to meet your flatness specifications, or is he unable to understand your drawings?
As per ASME Y14.5M-1994, you can specify straightness as an absolute value, or per length. See section 6.4.1.1.4. In your case, you would specify .015/4.
Flatness may be specified per area -- .015/4X4. See section 6.4.2.1.1.
JHG
RE: Straightnes/Flatness requirement.
A. If you are exempting the "boundary of perfect form at MMC" requirement of Rule #1 then you should add the note PERFECT FORM AT MMC NOT REQUIRED.
B. ASME Y14.5M-1994 permits flatness per unit area or flatness per unit length. Take a look.
Tunalover