Aruba

Hello All,
I need some help, I'm building a ZN Hydaway I installed the wing tube socket in the fuse and the former just in front of it.
I used Z-poxy 30min mixed with shaved glass. The problem is that that when letting it cure overnight the tube shifted (did not secure it good enough)and now there is a gap between the left wing leading edge and the fuse, and the right wing trailing edge and the fuse. My question is if there is a way to undo my boo boo without getting the dremmel out and start to grind away. I was thinking of tryin my heat gun but I'm affraid that will warp my fuse.
Also a question about drilling the cf wing tube, what is the best way I need to drill and tap for the wing attachment.
Anny help would be appreciated.

Thanks,

John

Flug

Be patient. Epoxy is tough to deal with once it's cured. Heat is one of the few things that work.....better for 5 minute epoxy than thirty minutes. The glass adds to the unlikelyhood that you can somehow chip it away.

I wouldn'nt use heat unless you can protect the area around it. How? I don't know. Maybe shielding it with something like foil. Otherwise your best bet would be the dremel.

On the Carbon fiber...There are different rake angles for bits used to drill composite materials. It helps to avoid the tendency of the bit to grab the last little bit of material....pulling itself through the last layers. This causes splintering on the back side. Carbon fiber is something you DONT WANT TO SPLINTER. It can lead to propagation of the damage through the piece. If it was me, I'd use a reamer on a low speed cordless drill. If you don't have a reamer and need to use a drill bit, start with a pilot hole(for reaming too.) using a small bit like a number 40 (appx .093 dia). Gradually work your way up to the size needed to tap it( or reaming). If you jump up in size too quick your bit will pull you through the hole. Literally, walk it up using each bit from an index.

The rake angle is the angle of the cutting edge on the bit. If I remember its a combined angle totalling 118 deg. A bit for composites I think, is 156....Much sharper!

Here, I found this..

Drilling CFRP

Unlike the easily machined aluminum it most often replaces, the low melting point of the resin systems in CFRP restricts temperatures of any machining operation to no more than a few hundred degrees F. Keeping the cutting edge cool is made difficult by the low thermal conductivity of the resin matrix. Unlike Aluminum chips, the cutting swath of advanced composites carry away very little of the heat generated by the machining process. Heat build-up in the cutting zone is much likely and must be avoided to prevent the resin from oxidizing and being degraded.

The widely different material properties of the fiber and resin also create changes. Slight dulling of tool cutting edges can cause separation and fiber pull out. Even modest cutting forces can separate lays causing delamination or leave residual stresses. The difficulty of producing quality holes with the abrasive nature of CFRP makes this and ideal application of Precorp's DiaEdge PCD tools.



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Recommended speeds and feeds for drilling CFRP

Two common cases are found for drilling CFRP, a stack up of CFRP over aluminum and unbacked CFRP. The stack up with aluminum reduces the problem of delamination and fraying and allows for higher feed rates. However, gaps between the aluminum and the CFRP can create a serious problem of chip counter boring as the drill retracts through the CFRP. A popular design is Precorp's Series 83 DiaEdge Drill. This eight facet point design helps breakup the aluminum chip and prevents damage to the CFRP hole wall. Additionally, the hole size with this point is held within a few ten thousandth of drill diameter.


Speed and Feed for
CFRP Speed and Feed for
SFRP with Aluminum Backing
Speeds: 300-600 SFPM Speeds: 200-400 SFPM
Feeds: .001 - .002 IPR Feeds: .002 - .005 IPR


Drilling CFRP without a metal backup requires a low thrust drill design for good hole quality. The Precorp Series 84 DiaEdge Drill is widely used in the aircraft industry. This drill yields over 3 times the number of holes as compared with a 118 degree veined PCD drill, six times that of an insert PCD drill, and 100 times that of a carbide drill. The relativity sharp point angle lowers the thrust of the drill and allows the cutting lip to cleanly trim fibers at the hole exit.

Drilling feed rates per revolution for CFRP need to be fairly light to prevent delamination. Excessive speeds will generate frictional heat and melt the resin. As with most machining operations, flood coolant is recommended when using PCD tools for the best tool life. However this is often impractical with CFRP and with sufficient speeds and a good vacuum system, drilling dry yields excellent results. For materials 1/4" to 3/8" thick, 400 SFPM is recommended for both wet or dry drilling.



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There's more info out there. Just take a little time and be patient.

John