Contraction of holes in composite post-drilling?

[RPstress]

Does anyone have experience of this occuring?

We had a hole which wound up at diameter 5.75 mm after being created by sinking a 6 mm end-mill through a UD carbon/epoxy laminate.

 

[saksmito]

I´ve been working with laminates of carbon-epoxi for a long time and never seen something like that, and less that amount.
From my own experience... have you checked the drills? maybe they are badly marked.
Other solution is that the worker has mistaken and didn´t tell you.
To me this is unprecedented.

Cheers.

 

[rstupplebeen]

I have seen this in aramid/phenolic and PE/epoxy composites. It was generally determined that the matrix was removed and the fibers created a fuzzy hole. I have not seen this in carbon/epoxy though. Hope this helps.

Rob Stupplebeen

 

[mapplem]

Like the previous post, sometimes you get "fuzzy" edges if you are using a standard drilling operation. For carbon/epoxy composites it is best to grind the holes (aka a diamond coated bit or hole saw). This will make it a much cleaner hole than if a rough drill bit is used.
M

 

[RPstress]

Thanks guys. Most helpful. Haven't bottomed out the problem yet; will let you know if we do.