Tips on drilling aileron bracket holes through aileron spar?

[Draker]

Well, after conferring with the mother ship, I've decided to bite the bullet and re-do both aileron spars on my '7 build. Fortunately I have not riveted the skins on yet. Here's the result of match drilling the bracket through to the spar without properly securing the workpieces:



This is the left one. The right one is a little better but still way larger than the acceptable diameter for AN3 bolts.

Problem with drilling these is that there are only two holes, so while drilling one hole, there's only a single cleco securing the parts together. I tried additionally holding the workpieces in place with a c-clamp and a small piece of wood, but obviously the bit still walked around unacceptably. Anyone have a good method/tool for match drilling these correctly?

[Walt]

I would suggest using a piloted double margin drill.



http://www.panamericantool.com/doubl...s-nas-937.html

•Designed for close tolerance drilling in titanium, stainless, heat treated material and aluminum alloys. When the drill point penetrates enough for the second margin to contact the wall of the hole, the point is stabiized and true cylindrical geometry is established. Smooth accurate holes are produced and reaming can often be eliminated.

[wirejock]

Use some sort of drill bushing. Pieces of brass tubing inserted into each other or a true bushing.
Other option is transfer punch. Drill the punch mark small and increase incrementally.

[rapid_ascent]

I'm not sure if it would work in this specific location but I find that small C clamps can be useful for holding pieces together. The 2" or 3" ones can be found at Lowe's or Home Depot for not much money. I think the ones I have are Irwin. I have about 8-10 of them. I put painters tape on the clamping surfaces to limit the scratching. These small clamps are light weight enough to be useful in many places were a larger clamp doesn't work too well.

Don't worry about this type of mistake. I've ruined several parts by not having them secured well enough.

[BillL]

So that is why my ailerons are low! I suggest a 6" C-style vice grip clamp (no feet). Then take the ends and grind down the tips to fit within the hinge. The 6" frame is narrow enough to fit. That's my process for redrilling my hinges for a heavy wing.

[rzbill]

I can't tell you how I did my bracket drilling because it was too long ago for memory.

BUT.....

For a pre-drilled 2-hole assembly, only one 1 hole needs match drilling. You may choose the 'first' hole and open it up accurately on both parts, one at a time, not as assembly. Bolt it together using that hole. Clamp as appropriate. Match drill the other hole. The only positional error possible is then rotation around the first hole. For an aileron bracket, if you are able to not egg the second hole, position will be essentially perfect.

[Draker]

Thanks everyone, I’ll give these tips a try. I remember having to use a lot of force on these holes too, my bits may not be sharp enough.

[wirejock]

Originally Posted by Draker

Thanks ever, I’ll give these tips a try. I remember having to use a lot of force on these holes too, my bits may not be sharp enough.

The enlarged hole is a common symptom of a dull bit. I lost a side skin that way. If a but doesn't feel right, toss it. Replace with new, start small and incrementally enlarge. Use light oil on steel.
High speed on aluminum. Low on steel. Let the bit do it's job.
BTW. When you get to stainless, buy several. It will dull a bit quickly. I replaced every 10 or so holes.

[az_gila]

Originally Posted by Walt

I would suggest using a piloted double margin drill.



http://www.panamericantool.com/doubl...s-nas-937.html

?Designed for close tolerance drilling in titanium, stainless, heat treated material and aluminum alloys. When the drill point penetrates enough for the second margin to contact the wall of the hole, the point is stabiized and true cylindrical geometry is established. Smooth accurate holes are produced and reaming can often be eliminated.

Neat, but it's a pity the minimum order is for 6 of any one size.

[Walt]

Originally Posted by az_gila

Neat, but it's a pity the minimum order is for 6 of any one size.

Is it worth $25 to drill reamer quality holes, I guess not for everyone.