[Paul Eastham]

So we all know that scratches are bad, right? What about scratches inside bolt holes (i.e. in thick stock)? On various assemblies, if the drill goes crooked a little, or after repeated match-drilling, I occasionally notice some lines inside the hole. Should I worry?

Sometimes the directions actually encourage this problem, I think...when they ask you to drill, then insert thick spacers and re-drill, often the angle of one of the layers is changed, leading to some off-angle gouging. Example: HS-to-fuse attach bracket spacers (7/9 models).

Next airplane (heh), I think I will try to get more undersize bits so that I can ream the holes to final dimensions.

Paul

 

[penguin]

There's any easy way around the problem - don't look into bolt holes. Drill, deburr, bolt-up, move to the next part and don't worry. No-one drills entirely smooth holes in thick stock. There are 4500+ RVs flying most built by amateurs ...

Yours, Pete

 

[Brockster]

Hi Paul,
Thanks for the response on the tailcone. Ditto for me on drilling holes. This is what I do now to help prevent this when drilling thick materials is, one, always drill pilot holes smaller than the finish diameter, two, use the drill press whenever possible, and three, step up in drill diameter sizes. For example when I did the horizontal stab attach bars on the F-711 bulkhead, I lined up the bars on the bulkhead and marked each hole. then I took the bars over to the drill press and put #40 pilot holes in each spot. Then I lined the parts back up on the bulkhead and used #40 clecos to hold them in place. Drilled with #31 and installed #30 clecos. Rechecked alignment finished with #30. Overkill maybe. Did get nice holes though. Someday I need to get some small diameter reamers too. On repeated match drilling, my method is to wait as long as possible and only final size until everything is in place.

Not to take away from the fact that we should always try to do the best job possible, it is inevitable if we are using twist drills we will get scratches in a hole. I also think Vans knows this and would have required reaming if drilling was unacceptable. Equally important is proper deburring and champhering to stress relieve the hole. Already had my share of waking up in the middle of the night thinking about something I'm doing on my plane with more to come I'm sure. Wouldn't have it any other way.

 

[Paul Eastham]

Yeah, I definitely drill progressively when I can, but frustratingly some of the parts that Van's supplies are already drilled full-size. And other times the instructions/build sequence get you into that situation.

 

[alpinelakespilot2000]

Yeah, I definitely drill progressively when I can, but frustratingly some of the parts that Van's supplies are already drilled full-size. And other times the instructions/build sequence get you into that situation.

Funny you mentiond this, Paul. Not sure how much scoring is OK, but just last night I drilled the VS forward spar attach bracket to the F711 bulkhead angle. Van's pre-drills the 2 holes in the bracket to 3/16" right from the start then you have to drill down through about 3 layers of angle and spacer stock. Well, how do you center a hole given the 3/16" pilot in the very thin bracket. The the point of the drill will start the hole, but there's no guarantee it will be centered in Van's pilot hole. Thus, on on of my holes I drilled and reamed a very nice round clean hole through all those angle and spacer layers only to find that it left Van's pre-drilled hole in the bracket slightly oblong. It was probably OK as is, but (since ordering a new bracket from Van's would not have helped me in this case) I added a 3rd bolt to the bracket just to make myself feel better and moved on. It would be nice if Van's would just drill the #30 pilots and let you drill up to 3/16 on your own.

 

[Brockster]

When you have a hole in some thin or even thick material and you want to drill down through several layers and have the hole centered in the pre-punched hole,use a sleeve with the same OD as the existing hole over a smaller drill bit. For example, you have a 3/16 hole in some .032 sheet and you need to continue that hole through two 1/8 thick pieces of aluminium stock. Place a sleeve over the drill bit that has a 3/16 OD and say a 1/8 ID. Put the sleeve in the hole and hold it firmly that it doesn't slip out of the pre-punched hole. Insert 1/8 drill in sleeve and drill pilot hole. Now using a uni-bit or step drilling you should be able to accurately transfer the original 3/16 hole through the material. Even if the uni-bit is not able to drill through completely before the next diameter, it will leave a deep enough hole as a guide to use a regular drill. I've used the brass tubing found at a hobby shops for R/C planes because so many sizes are available and they will telescope into one another. I've also made my own a lathe.