07-19-2017 10:11 AM - edited 07-19-2017 10:12 AM
Probably not the right place to ask this, but there are so many brilliant people on here -
I have a stepped cylindrical part and want to apply a perpendicular tolerance relative to a plate that it is welded to.
If I attach the geometric tolerance symbol to just one section of the cylinder, does that imply the remaining sections are included ?
Or should I attach it to the axis centreline of the cylindrical part - which makes more sense to me but I'm not sure it is correct.
Every example I can find shows only a plain cylinder, with the symbol attached to the cylindrical surface.
07-19-2017 10:39 AM
I would expect it to need to be attached to each feature , so if stepped, each cylcindrical step would need it's on FCF.
07-19-2017 11:23 AM
Hi @beachcomber
without having a draft or picture it isn't that easy to give the right answer, but IMHO and depending on the length of those cylindars, I would like to say that either You take the longest cylinder as datum or You put all (or some) of them into a common datum base A-B
The only wrong method AFAIK is to use the center axis itself.
This is something what isn't defined any more (this was possible before 1998 or 2002)
07-19-2017 11:23 AM - edited 07-19-2017 11:27 AM
I tend to agree with @KennyG. Since a centerline is virtual it's not really appropriate since you're trying to control the cylindrical faces. I suppose it might be legal to apply it to one face and attach a note saying it applies to all cylindrical features.
Just my .02
07-19-2017 11:38 AM
HI @beachcomber
sorry, it seems as I have confused the situation.
You want to have the plate plane as datum and the cylindars as target?
Then You have either to put a geometrical tolerance to each of those cylindars, or - what I suppose as to be better - give them a common zone, that all of them have to be in one and the same tolerance area.
07-20-2017 03:50 AM
Thanks for all your input - you have pretty much confirmed what I thought. I was sure that in the past you could apply the tolerance to the axis - as @hawcad indicated.
The image below shows the assembly in question.
The problem for me is that the important bit is the end indicated - this is where a mating part locates.
It is only a short length of the part (dimensions only shown for your reference) and I have been given the tolerance value of 0.4mm. The 19 & 56 long sections do not really matter.
I think the 0.4 is a bit loose for the short length, but as time is tight on this job its going to be a case of JFDI here.
07-20-2017 08:37 AM
Not sure if it applies here for you but a projected tolerance zone can help to keep a short feature's effective nominal tolerance tighter.
07-20-2017 09:13 AM
@bshand - just looking on the 'net and I don't think the projected tolerance zone can be appled here.
It seems to be applicable to holes into which a stud is inserted. We don't use GT all that often, other than positioning of multiple holes, so I'm a bit behind the times on the subject and hadn't even heard of this.
It could, I think, be applied to the hole in the plate to maintain that perpendicular to the datum face.
07-20-2017 10:38 AM - edited 07-20-2017 11:21 AM
It can be applied to male features as well. Example, a dowel pin. Or even a stud.
It's a theoretical zone so agnostic regarding feature type.
(I think. I was wrong once.)
You have a possible point about using it for holes only. Though I can't find any prohibitions about using it for male features I can't find any examples of that use online.
07-20-2017 01:55 PM
Hi @beachcomber
is it possible to indicate the mating cylinder faces on that image?
Will the mating part fit on the back only, the front only or on both cylindars ?
If both then You should use a common tolerance zone for that indicating the two partly cylindars to clarify it clearly for every manufacturer.