Grinding two flats question

[Ineedto5s]

I have a quick question... I have a process sheet with the GD&T similar to the one above. The process is a fine grinder. We grind one side, and then flip it and do the other side.

From what I was taught the bottom is how we are supposed to call it out. Also, both of these don't seem to address the perpendicularity...

Thanks

 

[3DDave]

How about including the full file name? So there's a file type?

 

[Ineedto5s]

I'm having a hard time uploading files... the first one was a PNG, this one is a JPG..

 

[3DDave]

Filenames cannot contain special characters. For some reason people like to embed the "&" which doesn't work.

 

[Ineedto5s]

Thank you sir!

 

[chez311]

Ineedto5s,

The bottom scheme addresses flatness of the datum feature A while holding the referenced opposite face parallel to A and indirectly controlling flatness of that face. In this case neither surface can have a form deviation of greater than .001

The top scheme is technically redundant since the .001 parallelism indirectly controls flatness to the same tolerance (think of it as flatness with an orientation requirement). In that case now the flatness of the datum feature A is uncontrolled and can vary the entire amount of the size tolerance .01 while the opposite face is still limited to .001

As far as which one "should" be used - that depends on your requirements but typically your datum features should be held to tolerances sufficiently tighter than the features it controls.

 

[greenimi]

Also, both of these don't seem to address the perpendicularity

Well, yes, I am curious to the perpendicularity too.....is the default title block tolerance (assuming one exist and has angle tolerance) addresses perpendicularity?
How you guys are seeing this?

 

[chez311]

If we're talking about perpendicularity of the faces 2.000 apart to datum feature A, I sort of glossed over that since there is no orientation control and additionally I took the parenthesis to mean it is a reference dimension. As it stands I believe it is technically uncontrolled - it would of course need a size tolerance (or at least not be a reference dimension so a title block/general size tolerance can apply) and some sort of orientation requirement added (or at least again not be a reference dimension that some sort of general orientation tolerance, if included in a note or title block, can apply).

 

[Ineedto5s]

Thank you Chez311! Greenimi the top system is how it currently. There is no call out for perp. currently the flatness and parallel are the only things on the print. I would say I would need a perpendicularity call out in order to avoid the grinding to push down unequally on the part causing a large angle, but consistent flatness/parallel

 

[Ineedto5s]

This was my fix...

 

[Ineedto5s]

Oops forgot the Datums.

 

[greenimi]

Ineedto5s,

Do you know which side is which, because the part looks symetrical? Which side is datum fetaure A?
Or the part should be good from both sides?
So the inspector will choose one side to be datum feature A, check the opposite side for GDT (parallelism, perpendicularity, flatness etc). Then will choose the other side of the part to be datum feature A and will check again the opposite side?

Is my understanding correct?

 

[Ineedto5s]

The part is symmetrical, even the other features. Datum A can be either side. I also included the parallel call out on the 2 inch ref dimension.

 

[greenimi]

Again, if the part is good on one side (datum feature A be randomly choosen one side and the opposite side being the controlled GDT surface) does the inspector has to go to check the other side (to switch the control surface with the datum feature) or not?

 

[chez311]

Ineedto5s,

You have added a perpendicularity tolerance to a face which is parallel to A. How exactly do you imagine this working? This is confusing at best and really not allowed - its been discussed before about putting perpendicularity tolerances on a feature which is not perpendicular to the primary datum it references, but I don't think thats pertinent as I don't think thats really what you're meaning to do. Presumably this perpendicularity tolerance should actually be applied to one (or both) of the faces making up the 2.000 dimension.

Additionally the (2.000) dimension is still technically uncontrolled. I'll copy-paste below what I said previously, with bold added for emphasis:

As it stands I believe it is technically uncontrolled - it would of course need a size tolerance (or at least NOT be a reference dimension so a title block/general size tolerance can apply) and some sort of orientation requirement added (or at least again NOT be a reference dimension that some sort of general orientation tolerance, if included in a note or title block, can apply).

 

[Ineedto5s]

Sorry I'm at work, so I'm trying to be quick with my responses...

Greenimi: The inspector picks a random side to check, as they would have no way of knowing which side is which on this particular part from operation to operation. They check one side for flatness, and then put the part on that Datum. They then check for parallel using a surface plate and indicator. So we want to generate Datum A and then tie the opposite face to Datum A.

Chez: I fixed the Perp. by adding it to the reference dimension. I want the cylinder walls to be perpendicular to datum A. I am creating a manufacturing Operation not a part definition. At this operation we are only grinding the top and bottom face (datum A and the face that's parallel to it). the 2 inches will not change at this op, and it was generated at a previous lathe operation. Do I need a size tolerance in order to be able to use the 2 inches as a datum? Does that make sense? I'm new to this...

Thanks for the responses guys.

 

[chez311]

Ineedto5s,

Well your datum reference for the perpendicularity is to A which is the opposite, parallel face. If your intention is to make it perpendicular to the face(s) which make up the 2.000 dimension you would have to set either one of the faces or the width (FOS datum) as datum B and set perpendicularity to that.

As far as utilizing a reference dimension for this purpose, I guess its fine as long as its controlled on another drawing. Maybe someone else can chime in.

 

[Ineedto5s]

Awesome, again thank you for all the help!