Shaft GD&T questions
Shaft GD&T questions
(OP)
Hello all,
I would appreciate some input on the following situation. I have a shaft with 2 bearing seats about 2.5 inches apart. The back bearing is pressed on to the shaft up to a shoulder and then the shaft and bearing are pressed into a housing up to a shoulder in the housing. Then the front bearing is pressed in against a shoulder in the housing. I am a bit confused about calling the GD&T for the bearing seats. What I have done is call out perpendicularity to the shoulder for the first and bearing seats and total runout to the centerline of the shaft. Does this sound proper?
SEE ATTACHED PIC FOR CLARITY
Recommendations welcome.
Thanks,BB
I would appreciate some input on the following situation. I have a shaft with 2 bearing seats about 2.5 inches apart. The back bearing is pressed on to the shaft up to a shoulder and then the shaft and bearing are pressed into a housing up to a shoulder in the housing. Then the front bearing is pressed in against a shoulder in the housing. I am a bit confused about calling the GD&T for the bearing seats. What I have done is call out perpendicularity to the shoulder for the first and bearing seats and total runout to the centerline of the shaft. Does this sound proper?
SEE ATTACHED PIC FOR CLARITY
Recommendations welcome.
Thanks,BB





RE: Shaft GD&T questions
ewh (Aerospace) 9 Apr 10 9:34
KENAT is pointing you in the right direction.
One thing that jumps out at me is that you need to identify which feature is datum A; an imaginary plane would be frowned upon, and a line may be the axis of datum A, but can't be A in and of itself.
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
KENAT (Mechanical) 9 Apr 10 10:13
Well, you haven't reposted so I'll try and give you some pointers.
1. What drawing standards are you working to? Most regular GD&T posters here, including me, work to ASME, mostly Y14.5-1994 though 2009 is increasing in popularity. So most responses will be based on those stds.
2. Your thread is not correctly specified. Should I believe be 1.2500-12 UNF-2A (or maybe -3A or something). You should also reference the relevant thread spec.
3. As ewh points out, you can't make 'center-lines' as such datum features. You need to pick a real feature from which the axis to be used as a datum is then derived. Also, depending on function using just one dia as -A- may not work well, you may want to pick up diameters at either end and have runout to the 2 datum features like in figure 6-49 section 6.7.1.3.2
4. Your perpendicularity call out makes no sense when referenced to A. Your cylinder is 'coaxial' to A, not perpendicular to it. If the perpendicularity is meant to be to the '0' face then that needs to be a datum feature and the FCF changed accordingly. You might actually want to put a runout control on the diameter relative to the '0' face, this is shown in figure 6-50 section 6.7.1.3.3.
5. Is the orientation of the flat at one end to the .281 cross holes significant? If so one of them needs to be a clocking datum feature and the other features related back to it. Also it looks like it should be 2X Ø.281.
6. You may not need total run out, but I'm no expert.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Shaft GD&T questions
Dave D.
www.qmsi.ca
RE: Shaft GD&T questions
I was using the C/L as Datum -A-. See attached picture for application info. Hope this will help.
Thanks,
BB
RE: Shaft GD&T questions
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Shaft GD&T questions
The intended feature is the shaft centerline. My mistake if this is not a viable option to use as a datum.
Thanks,
BB
RE: Shaft GD&T questions
This is what all 3 of us have tried to point out now. Do you have a copy of a drawing standard to look at?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Shaft GD&T questions
We do not have a copy of the standard to reference.
Regards,
BB
RE: Shaft GD&T questions
You need to read the ASME standard. Datums must be applied to real features so that fabricators and inspectors can reference everything off them. Your datums will be used to fixture your part. They must render it immobile.
In your case, the face at 0 (zero) would be a good datum_A, and the Ø2.5000_0/-.0005 next to it would be a good datum_B. If you have any rotation issues, the 2.500 flat face would be a good datum_C. Your second accurate Ø2.5000 would be located by a positional tolerance to |A|B|. In this datum configuration, concentricity is not meaningful.
Alternately, I would be tempted to make the first accurate Ø2.500 datum_A, the second accurate Ø2.500 datum_B, and the zero face datum_C. Your flat face would be datum_D, if required. The two diameters work together to define a centre. Your flat face must be perpendicular to |A-B|. Note how there is no need for a concentricity or true position tolerance.
I do not think your .0005 run-out specifications apply any control to +0/-.0005 diameters. Also, your 63μin finish is pretty rough. If the fabricator can achieve your diameter tolerances, the finish will be better than that.
RE: Shaft GD&T questions
You might try web-searching for some freely available material, perhaps you'll have more time to spend on it than I & might find something.
http://
http://www.draftingzone.com/ has a little to though most you need a membership for.
Some bearing suppliers actually given dimensioning information in their catalogs so you might get something there just be careful of any ISO V ASME differences.
Your second post actually starts to help with answering functional information, if you could maybe give a bit more description that might help too.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Shaft GD&T questions
RE: Shaft GD&T questions
Regards,
BB
RE: Shaft GD&T questions
Parts do not have conterlines, pls read the link below :
http://www.tec-ease.com/gdt-tips-view.php?q=130
SeasonLee
RE: Shaft GD&T questions
Examples are great, thanks for the confirmation.
BB
RE: Shaft GD&T questions
Frank