Run out help

[thebiglad]

Guys,
Can you help i have a shaft with a dia in the middle greater than the shaft.
the drawing states one end of the shaft as datum A the other end as datum B.
the run out between datum A and B must be no more than 0.0005" the shaft is .3" in dia and 1.5" long.

one end and dia of the shaft are produced on a differant machine.
i then clamp this end in nice bored soft jaws and turn the other end.
my problem is when i locate the end i have just turned in a vee block put a dti on the other end and spin the part the run out reading is very good no more than 0.0003" however when i turn the part aroung locate the dia i didnt turn in the vee block and check again the reading is now 0.0015"???
both parts are round and straight i cant see where the error is coming from any advise? i cant turn the end in the same set up.

 

[Belanger]

Runout readings will be a combination of location, form, and even orientation error. I'm thinking that the differences may come from form.

When you hold the datum feature in order to check runout, it should be a device that grabs the highest points around the circumference (such as a chuck or collet). Are you checking in a vee block? A vee block is susceptible to error because the part can rise and fall slightly as it is rotated for runout verification.

The end opposite the datum -- the one being checked for runout -- may be perfectly centered but if it is not a perfect circle, that will contribute to the reading.

So grabbing a diameter for the datum doesn't factor in form (roundness) but checking a diameter for runout does. Perhaps this accounts for the different readings.

Not sure if this helps answer the question, but I thought I'd toss in these preliminary ideas.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[dingy2]

I am going to assume that your machine shop or tool room has a chuck on a granite table. If not, circular runout is going to be really difficult to achieve.

Each time you place the part in a chuck (no V blocks please), it will contact on different surfaces. Make sure you have enough depth of contact that the part is stable. If one only had a small amount of contact on datum A, the other end could move all over.

Now zero out the dial indicator (with stand) at the high point across the diameter on the other end (will be datum B). Make sure that you have the indicator vertical (down). Once you have the indicator zeroed at the high point (centre of the feature), rotate the part 360 degrees and take the TIR. Don't spin the part!

Now you have confirmed the runout on datum B relative to datum A.

Hope this helps.

Dave D.

http://www.qmsi.ca

 

[powerhound]

When you say the drawing "states" the requirement, does it state it in words or in GD&T symbols with a feature control frame. I'm just trying to make sure you're checking what the drawing is asking you to check. I can think of a similar case where someone was trying to check pretty much exactly what you're trying to check but that's not what the drawing was requiring.

Powerhound, GDTP T-0419
Production Manager
Inventor 2010
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[thebiglad]

Its in proprt GDT symbols powerhound a arrow drawn from bottom left of box to top right specifing .0004" in the next box

 

[powerhound]

I was thinking you might have a specification that looks like the feature control frame in the drawing shown in this link.

http://www.tec-ease.com/tips/march-03.htm

disregard the subject of the tip. It's the feature control frame that's the point. When you said the runout was between A and B I thought you might be seeing this symbology.



Powerhound, GDTP T-0419
Production Manager
Inventor 2010
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II