TORSION BAR - spring

[twistedneck]

Two pronged question about the hex end of a torsion spring.

I understand what a profile tolerance is, normally w/o the phantom lines it implies equal bi-lateral profile.

However, what if the profile points to a surface that is also a datum? (i.e. A datum of a torsion spring is the hex flat) does this imply a unilateral profile only or is this still equal bilateral?

to complicate further, there is a max and min flat to flat distance or feature of size - if that dimension is -0 / +5 .. how does this all work out?

GD&T, never fails to confuse me!!!

 

[dingy2]

twistedneck:
Profile of a surface is a range of a bilateral tolerance unless it is shown with a phantom line on the inside or outside of the object line.

When it is shown on a surface and that surface is a datum, it means that the surface must meet the profile requirement to become the datum.

The profile of a surface tolerance can be used if you have 2 surfaces sharing the same plane. One would assume one plane and set up the plane using 3 points and performing more or less flatness on both surfaces.

The last part to your question gets a bit complicated. From the created datum, we could dimension another surface with a +/1 tolerance. No problem there.

Dave D.

http://www.qmsi.ca

 

[twistedneck]

dingy2.. i finally got the 2003 gd&t spec..

its got that new to me U for unilateral.. also the 'O' for outside..

i can't understand how the datum A, can actually have a profile tolerance. i mean, its a theoretical perfect plane! anyway, the profile is 0.35 U-O.. so its pretty tight.

Thanks for cleaning it up!

 

[dingy2]

twistedneck:

What 2003 GD&T spec are you talking about? GM maybe? Their specs are a bit different from the ASME standard. The ASME Y14.5M-94 does not use "U" and "O" but phantom lines as I stated.

If you send me the drawing or somehow post it and I will confirm what I stated.

Dave D.

http://www.qmsi.ca

 

[powerhound]

You're probably talking about ASME Y14.41-2003. It uses a different way to spec profile using a U in a circle and a tolerance zone on either or both sides of it in the feature control frame. I personally think it's a better way to do it but 14.5 hasn't adopted it yet. It eliminates the use of phantom lines to indicate which way the tolerance zone is disposed which can be a problem on less than perfect prints or prints with excessively heavy lineweights. The O that you're talking about is more likely a 0(zero) which indicates the tolerance zone is unilaterally disposed (one direction only).
The plane is theoretically perfect but not in real life so the amount of error allowed should be stated. If the profile is applied to a plane only and not referenced from another plane then the callout is illegal unless I'm misunderstanding what you're describing. Flatness is the correct callout for this situation.

Powerhound
Production Supervisor
Inventor 11
Mastercam X
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Taji, Iraq OIF II

 

[dingy2]

Powerhound:

Flatness is the correct call out on a single feature but if you have 2 or more features (surfaces) that lie on the same plane, flatness may not be appropriate. Profile of a surface would be correct in this situation.

Dave D.

http://www.qmsi.ca

 

[powerhound]

Dave,
I agree with your reply. Flatness only applies to a single surface at a time. From what I understood about the OP, there is only a single surface involved in his question. He mentioned one hex flat, not one flat located with respect to another whether opposed or co-planar. If that were the case then yes, profile could be appropriate.

Powerhound
Production Supervisor
Inventor 11
Mastercam X
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[twistedneck]

Thanks everyone. Its a hex end on a torsion bar. the a-datum is called out via GM GD&T (as dingy2 noted). I am a bit confused by the zero. I understand the circled U = unilateral - but the zero is a bit tough to visualize.

Powerhound said "The O that you're talking about is more likely a 0(zero) which indicates the tolerance zone is unilaterally disposed (one direction only)." I understand, but i though the U indicated unilateral? if zero indicates it, then what tells us 'outside'?

Finally, the plane is called out with a circle meaning 'all around' however what really confuses me.. there is an adjacent frame that references profile tolerance back to A, B and C datums. this other plane has some 'single stacked' tpye callouts for profile, here is the odd part:

in the top frame two individual proflie call outs (3 over 1) both revert to A datum only. below in the same frame a second ref to the 0.35 profile circle U, 0 (but without the A datum plunger.) and sketch will come shortly.

 

[powerhound]

Twistedneck,
The U does not mean unilateral, it's the modifier for this type of callout. Here's how to interpret the FCF:

The first number (to the left of the "U") is the total tolerance zone. The number to the right of the "U" is the amount that the tolerance zone extends OUTWARD from the surface. In your case you should have a value to the left of the U which is the total tolerance. The 0 to the right of the U says the zone extends a distance of 0 outwards of the surface. This means all the tolerance goes inward of the surface. This is unilateral. If you had a value of .030 to the left and .030 to the right of the U then that means that out of a .030 tolerance zone, .030 of it goes outward of the surface and 0 inwards. This is also unilateral.

If your tolerance zone is unequal then you could have .030 to the left of the U and .010 to the right which means that the zone is .010 outward of the surface and .020 inwards.

Just remember that the first number is the total tolerance zone and the second is the amount that the zone extends outwards of the surface.

Powerhound
Production Supervisor
Inventor 11
Mastercam X
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II