Hole angularity mismatch

[Gary70]

I am doing an angularity mismatch study on determinant assembly holes between two composite parts. Both parts have two determinant assembly holes of .1285 dia. drilled. What is the allowable angularity mismatch (in terms of degree) between the hole center line on two parts if they are pinned together by cleco/pin ?

 

[KENAT]

ASME Y14.5M-1994 appendix B has some stuff on mating holes and the calculations to ensure they mate etc. Might be relevant.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[SWComposites]

What is the allowable angularity mismatch? - you will need joint test data (static and fatigue) for the applicable sheet materials and fasteners to answer that question.

 

[rb1957]

why would you drill finished holes in both parts ? i'd expect positional tolerances would be a bigger problem.

if the mating faces "mate", then drill both parts from the same face.

what's going in the hole ? a rivet ? a bolt ? clearance fit or interference ?

 

[WKTaylor]

IF these are pilot holes, in thin sheet or even moderately thick members, then probably no big deal.

Right-size [1/8-D, this case] "Clecos" have intrinsic ability to shrink small-enough to snake into significantly [0.016-inch or greater] mismatched/off-angle holes... and partially spring-back to hold/clamp alignment "good-enough" for match drilling/reaming surrounding holes up to final diameter where larger clecos can be installed [IE: 1/8, 5/32 or 3/16 D, etc]; then these pilot-hole clecos are removed and their bunged-up holes are drilled to final precision diameter (while the larger surrounding "right size" clecos maintain tightness and alignment).

NOTE. I have seen mechanics use next smaller diameter clecos [ie: 3/32-D this case] to punch-thru and sorta-align/hold/clamp significantly (1/32 or greater) misaligned holes, so that the surrounding holes can be step-drilled into common alignment/size for larger Dia clecos [5/32 or 3/16 1/4 D, etc].

Note.
clecos are a brand-name that identifies the family of temporary hole fasteners.

NOTE.
I real terms, modern tooling should be able to hold within +/-1-deg hole perpendicularity at any surface location. This should occur by a combination of digital definition [3D precision] and/or drill-head sensors that find/touch the surface location and instantly define the precise contour at that exact surface to "set" the best-fit drill-head angle.


Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[Gary70]

The two determinant assembly holes of .1285" dia on each composite part are used to index in order to drill the other holes from drill plate. They plan to install 1/4" bolts into those holes. The angularity mismatch is from .15 deg to .42 deg between the center line of the determinant assembly holes of the two parts. On each of the composite part, the positional tolerance for those determinant assembly hole is .028".

Thanks for all of your informative inputs.

 

[rb1957]

ok, what is the source of the misalignment ? by design ? (odd, i'd've thought that the surfaces would have been lofted together) by mistake ?

is the misalignment real (measured) or theoretical (dim'n'd from CAD) ?

will the misalignment be "resolved" when the fasteners clamp the details together (causing bending of the details) ? do the faying surfaces align ?

these holes sound like tooling holes, it's not common practise (in my experience) to join tooling holes together.

 

[Gary70]

Some manufacturing standards specify that the hole angularity between drilled holes on the parts should not beyond 2 degree when fastener are installed. Is this that maximum hole angularity that manufacturing must follow to ensure the surface flushness and joint fatigue life?

This is the case when the design install the same angle in multiple locations on the base part (contoured doubler) to reduce tooling cost.

 

[rb1957]

the holes (and the fasteners) don't need to be normal to the skin ... just makes our life easier if they are. we've been talking (haven't we) about mismatch between hole axis on mating parts.

if the fasteners are not normal to the skin then their load state is more involved (tension and shear).

 

[utspg1980]

Has anyone ever seen emperical data of joint strength values for non-normal fasteners? I never have. It seems like someone would have liked to back up our theoretical calculations at some point.

 

[holemaker888]

We are talking about DA holes here. I guess that it is important that temperary fastener could go through and hold the two pieces together. At the same time, we could not oversize the hole diameter too much which could cost the lost of the positional accuracy. By considering the two factor, you could calculate the mismatch yourself.