Staightness of a tapered pin.
Staightness of a tapered pin.
(OP)
Hi All,
have one more question on straightness.
How to control the straightness of a Tapered Shaft.
have one more question on straightness.
How to control the straightness of a Tapered Shaft.





RE: Staightness of a tapered pin.
RE: Staightness of a tapered pin.
On a CMM, take a number of readings on one end of the tapered shaft to arrive at a centre. Take the same number of readings on the other end and then create an axis. We now have eliminated the roundness of the feature. Take a readings perpendicular to the axis in a few cross sections and report the worst case non-straight situation. This is probably a 95% method but we need to take as many readings as practical.
Dave D.
www.qmsi.ca
RE: Staightness of a tapered pin.
RE: Staightness of a tapered pin.
RE: Staightness of a tapered pin.
The point is that per Y14.5 and ISO standards referencing any datum in straightness FCF is simply illegal.
RE: Staightness of a tapered pin.
To reflect the straightness requirement on a tapered shaft on the drawing, place a feature control frame with a leader line to the OD of the tapered shaft. In the feature control frame place a diametrical tolerance zone (reflecting centre line) and the tolerance. If the feature control frame does not have the diametrical tolerance zone, it would reflect the straightness of linear lines on the OD.
It is not necessary to show one end as datum A and the other end as datum B.
Dave D.
www.qmsi.ca
RE: Staightness of a tapered pin.
Frank
RE: Staightness of a tapered pin.
RE: Staightness of a tapered pin.
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Staightness of a tapered pin.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Staightness of a tapered pin.
Isn't there more to it than that? We would usually say straightness should have the FCF tagged with a size dimension in order to communicate that it's axial straightness. Consider Fig. 5-1 in the 2009 standard ... adding a diameter symbol would not instantly transform that callout into axis straightness.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Staightness of a tapered pin.
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Staightness of a tapered pin.
(With my luck, however, this will be something that ASME "didn't envision" when they wrote that paragraph!)
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Staightness of a tapered pin.
RE: Staightness of a tapered pin.
Well, I admit that there is not an example of straightness of the axis on a tapered round pin. I will also agree that it is best to show the straightness of the axis under the dimension but that is not possible here since the taper is made up with 2 dimensions - 2 diameters or a diameter and an angle. We cannot show a centre line with straightness but must shown the feature.
What does that leave us?
We could show the tolerance of a taper as israelkk stated but that is the taper and not the straightness of the axis.
Usually the leader line from a feature control frame to the OD means straightness of the linear line along the length of the feature when straightness is shown without a diametrical tolerance zone. With a diametrical tolerance zone, it does mean axis.
I agree that this is not perfect and might cause confusion out there but I think it is the best option.
Dave D.
www.qmsi.ca
RE: Staightness of a tapered pin.
"the zone" the pin has to be within indirectly defines a centerline.
RE: Staightness of a tapered pin.
However, for a cylindrical part (non-tapered), I will maintain that we can't point to the OD and simply rely on the diameter symbol (or lack thereof) to communicate which variety of straightness is being done (again referring to Fig. 5-1).
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Staightness of a tapered pin.
I agree that on a cylindrical feature, one must show the feature control frame with a diametrical tolerance zone on the straightness below the size tolerance.
Dave D.
www.qmsi.ca
RE: Staightness of a tapered pin.
This would be of course indirect control but as long as straightness and total runout cause troubles because it is not shown anywhere in Y14.5 how to technically apply them for that kind of situations, profile of surface at the end may be the only way to go.
Extended principles philosophy may work but not necessarily has to.
RE: Staightness of a tapered pin.
I could set up straightness of the axis of a tapered feature very easily in a chuck or CMM.
Now, profile of a surface, we measure the surface for any variation from the true (theoretical) shape of the feature which would be shown in basic dimensions. It does include straightness but also roundness and size variation.
I would still use straightness.
Dave D.
www.qmsi.ca
RE: Staightness of a tapered pin.
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John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Staightness of a tapered pin.
The OP is looking for straightness of the axis your answer seems to amount to "it can't be done". That is what some of us find so unsatisfying, beacause, it can be just not here.
IMHO, the simplicity of the ISO solution on is an elegant solution. If you want to check it as runout that is your business just let me specify what I wanted/needed. In the ISO standard they show it applied to the centerline of a something like a coke bottle. Does anyone here really not understand the intent when you see it?
Frank
RE: Staightness of a tapered pin.
I have no remarks to the set-up you proposed. What I just wanted to say is that since the method of defining straightness of median line for conical/tapered feature on a drawing is not clearly specified in Y14.5 you can have situation when one person may understand the method you proposed, while second one may not. Therefore you have to very clearly specify how to interpret 'your' straightness callout, otherwise at the end you will be probably forced to come back to the standard and face with the fact that this idea is just your private proposal of specifying one of geometrical characteristics.
J-P,
I was not thinking about combining profile of surface with directly toleranced dimensions. My point was that this situation is another one where 'classic' profile approach - with everthing basic - seems to have advantages over other tolerancing methods.
And Dave, I do not see a problem with including circularity (roundness) and size at the same time. If one wants to fully describe a conical feature, size, form orientation and/or position have to be somehow defined. Of course OP's question was about straightness only, but in reality straightness only is quite unlikely to happen, so other characterstics will have to be added anyway. Why not go with profile of surface which gives all that we need?
RE: Staightness of a tapered pin.
I agree that ISO method is an elegant one. But imagine what would happen if there where 3 or 4 or more coaxial features present. Would it be equally elegant?
I do not know exactly which drawing you are refering to (although I could promise I saw it somewhere), but if you take a look at Annex A of ISO 1101:2004 you will find out a clear statement that the method you are proposing is considered to be ambiguous and it should not be used any longer.
RE: Staightness of a tapered pin.
I agree that profile will be an easier method, but having a basic diameter would go beyond what the OP asked.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Staightness of a tapered pin.
Thanks, I only have the earlier (1984) version.
Frank
RE: Staightness of a tapered pin.
Peter Truitt
Minnesota