Drilling holes in carbon fiber

[Brass_Machine]

So I work with carbon fiber quite a bit. I end up drilling a lot of holes. Looking to see if there is a better way of doing it. Right now if I am drilling a hole in CF, I tape the area where the hole is and use a regular drill bit. Works OK most of the time. Occasionally the epoxy chips... is there a better way? Or better tools to do it with?

Eric

[spuddevans]

I will preface this by saying that I have exactly ZERO experience with CF, but would a lip-and-spur drillbit work? I've always found them to be good on non-metal objects that are a little more troublesome.

Tim

[Bernd]

Eric,

Try a brad drill that's used for wood. It's close to what Tim suggests. Don't know how long they'll last though. Isn't carbon fiber a bit tough on HSS?

Bernd

[Sorekiwi]

I've drilled a gazillion holes in carbon-fibre (20 odd years as a racecar mechanic).



From your comment about chipping the epoxy, I gather that these are visible holes where appearance is important (as opposed to a hole that for example a bolt and a washer are going through it). 

The cleanest hole I think comes from a Rotabroach tool - its a piloted cutter.  I have them down to 5/16" but they may come smaller than that.  It will give a nice clean edge.  Uni-bits (step drills) can give a clean cut when sharp, but dont stay sharp with carbon for very long.  Normal drills work OK when sharp for normal bolt holes and rivet holes, but its easy for them to give a ragged edge on the back side.  Backing the piece up with a piece of wood helps a lot with this.  If you are making a big enough hole, a sanding barrel in a ginder will clean up the fuzzy edge pretty well. 

Carbon can also cause the drill to wander a bit.  I dont really know why, I've always suspected that the weave of the fabric can pull the tip of the drill over a bit.

Normal countersinks work OK when they're sharp, but again the material blunts them really quick.  I buy solid carbide ones now, and they seem to last a few years.

Carbon Fibre can vary a lot depending on the application.  Stuff thats made to look pretty has a lot of epoxy so it gets the fancy shiny appearance.  Things that are functional tend to be a lot "drier" where a lot more of the epoxy is drawn back out while vacuum bagging and has a matt, greyish finish.  The material itself is ridiculously expensive, so they tend to use the minimum amount of material possible.

[Brass_Machine]

Wow. That's some good info. Hopefully I will have the part I will be drilling soon. I am getting ready to layup the mold in the next day or two. The part will be vacuum bagged BUT is mainly a cosmetic piece for a motorcycle. Though it does have some function, it is not a structural piece.

Thanks for the info!

Eric

BTW... what race team? My buddy works for Brumos DP race team in the Rolex series.

[No1_sonuk]

Would drill bits made for glass or ceramics work?  Drills for tiles should be available from a local DIY store.

[kellswaterri]

Carbon can also cause the drill to wander a bit.  I dont really know why, I've always suspected that the weave of the fabric can pull the tip of the drill over a bit.

I worked with the stuff in the aircraft industry for a long time, the drills we mostly used were akin to a ''Masony drill''  Tugsten tipped, sometimes we used pure Tugsten ...depended on how the material was laid up///formed and type of material ie. Kevlar...in most if not all cases a ''JIG'' was used when boring thus no wandering of the drill...in some cases a Diamond drill or diamond rota cutter may have been used.
John.

[Sorekiwi]

BTW... what race team? My buddy works for Brumos DP race team in the Rolex series.

I've always done open wheel cars.  In the US it was Indycar as well as the various feeder series - Indy Lights, Formula Atlantic etc.  I've never done much sportscar work, but a lot of my friends have started doing that in the last few years.

I got sick of all the travel, and spending every weekend over the summer working, so at present I'm doing something else.  But I do miss it, and may go back  

[Lew_Merrick_PE]

I do a fair amount of work with carbon fibre structures.  We normally use a coated "reamer" to "size" holes after they are pilot-drilled with a carbide drill.  We start with a hardened piece of drill rod with a diameter that will be correct once the cubic boron nitride (Borozon -- brand name) abrasive (purchased by size) is applied (plasma bonded).  The end is tapered (7.5° of taper) so that there is a "lead" of abrasive to open up the (undersize) pilot hole.  The shop that has been doing this work for me (since the late-1970's) has a broad array of such "reamers" now in stock.  These are not inexpensive tool bits!

One thing to remember about carbon fibre is that it has nearly zero resistance to abrasion.  Some of the early carbon fibre antenna and solar array supports failed rather spectacularly due to the abrasion from rotating about (aluminum-bronze) pivot-clevis-pins.  (You may remember some embarrassing satellite failures in the early-/mid-1980's.)  A bit over a year ago, I qualified the use of a carbon fibre leaf-spring for a (classified) military application.  The "trick" was to place lubricant-impregnated acetal rollers over the "pins" that the leaf-spring drove to prevent abrasion.  Without the "rollers," the spring failed in less than 20 cycles!  We passed 10,000,000 cycles with the "rollers."

I know that on highly-stressed aerospace and military structures that they make "wound" carbon fibre inserts that are placed in the lay-up tool with the "cloth" punched for a close fit.  Extra resin is laid in around the inserts before curing in the autoclave.  The inserts provide an accurate hole size in the form of a flanged bushing with an "invar" (a nickel alloy with a 0.0 coefficient of thermal expansion) insert/inner bushing.

None of these as implemented are appropriate to the home shop type, but they might give you ideas.