Obscure Perpendicularity Callout Help

[cjohnso0]

Hi all,

I am trying to decipher a GD&T perpendicularity requirement we have run into.

This is a requirement while repairing a commercial CFM56-7B turbine engine accessory gearbox. The bores in question are bearing bores which locate the gears in the gearbox.

Each of the bores has a perpendicularity callout to a surface, but where we would commonly see a decimal number, there is a percent (0.10%). I have attached a sketch of one of the callouts and associated datum's (dims in inches).

Has anyone ever seen anything like this? Is this something I can rewrite into current GD&T so we can actually manufacture? We have no way to get info from the original manufacturer to discuss.

I did find one old related thread, but it was for a face to an axis I believe, and the consensus was to ignore the % sign. This is not possible in this situation, as there is no way the bores can be out more than a few thousandths of an inch to continue to function. Similar parts run around .0004 in/in between bore diameter and datum surface on other engine types.

Thanks in advance,

Chris

 

[pmarc]

Is there a reference to any dimensioning and tolerancing standard on the print? Maybe there is a reference to a corporate document, spec. or something similar, where this method would be described?
For sure this is not standard callout per Y14.5-1994 or -2009.

Or maybe this is percentage notation of decimal 0.0001?

 

[pmarc]

By the way, "%" symbol is not the only issue. Lack of diameter symbols preceding tolerance values in both feature control frames (especially in concentricity FCF) is another story.

 

[CheckerHater]

Is original drawing manual or CAD?

Sometimes GD&T symbols don't come out right, especially when convertig between CAD systems.

Just a thought

 

[cjohnso0]

Thanks for the replies.

Is there a reference to any dimensioning and tolerancing standard on the print? Maybe there is a reference to a corporate document, spec. or something similar, where this method would be described?

There are no references whatsoever. This is directly from the CFMI engine manual repair. I can find nothing in the remainder of the manual, or in any related manuals, like the Standard Practices Manual.

Is original drawing manual or CAD?

Sometimes GD&T symbols don't come out right, especially when converting between CAD systems.

Just a thought

This is taken from a repair manual for this engine. I do not have access to the original drawings. There are several pages (12 or so) that have this requirements for different areas on the part.

Definitely a stumper so far...

 

[CheckerHater]

OK, another theory:
Surveyors use percent to measure slope. 1%=1:100 incline.
So your perpendicularity is 0.1:100 or 1:1000 of the length of the housing, or rather distance between datum A surface and place where DIA 1.0000 bore is locating.
If your picture is to scale, the length is about 2.5 in, so perpendicularity is 0.0025.
Does it look realistic to you?
And also, is your machine big enough to use theodolite?