MacPara

MacPara

Well Known Member
I'm currently finishing the wingtip of the second wing and was looking ahead to the flaperon section 18 to see what's coming up. What I am confused about at this time - and I seem to be alone with this confusion as I haven't found anybody else talking about this - is how to correctly "match-drill" the stainless steel tube used as a counterweight through the nose ribs A-1204-L/R as requested in step 1 (I believe) on page 18-03.
Match-drilling until now meant to use an existing hole which was easy to access and drill through that hole into something else that didn't have a hole.
In this case though it appears that although there is a hole in the A-1204 nose ribs that you should match it is not easy to be accessed by a drill at all - at least not without canting the drill.
I read in blogs that most used a drill press to drill a straight hole which is fine and obvious but how did you make sure your hole was in the right place??
Did you just mark it using the hole in the A-1204's??? I'm really unsure about the best way of dealing with this issue and that heavy long stainless steel tube looks like it would be expensive to order after messing one up in the learning process.... so I thought I'd rather ask.
 
I was able to drill them in place using the holes in the skin. Be careful and understand that drilling stainless requires a different technique. Stainless is hard to drill and has a tendency to "work harden". Once this happens, you will have to relocate the stainless tube because you will not be able to drill that area. The tube will turn brown and will light up the end of your drill bit, rendering the bit useless also. Use a real good quality bit and take your time. Also, use a good centerpunch. If you don't have a good reference on the stainless, the bit will wander. Good luck and be patient, it will take a little while longer.
 
I first marked the skinholes on the left aileron counterbalance with a sharpie. Thereafter I unclecoed the assembly and prepuched the holes. Drilled the holes with a #40 and thereafter with a #30 drill in the drill press. Low speed, pressure and lube. If you try to matchdrill the parts with the skin in place you will end up with elongated holes for sure. The above mentioned method really works well if you take some time with the punch.

MyKitlog
 
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Wow, I'm glad I asked this question. Seems like I would have pretty much ruined the tube and my drill bit in the attempt to do it like other match drilling before!
I will use a sharpie for marking, then pre-punch the marked holes and use my drill press with a tube holder and set the drilling speed to the minimum the press allows.
Thanks for the help!
 
Cutting oil

Use plenty of cutting oil to keep the bit cool. You can mark a straight line on the tube by using a combination level-square.http://www.sears.com/shc/s/p_10153_12605_SPM2380556202P?prdNo=1
With the counterweight tube horizontal, place the square with bubble on top against the tube so that both sides of the square are touching the tube. Keeping the bubble centered, slide the square along the tube and mark the tube. It is hard to explain but easy to do once you get the hang of it. Having a straight line on the tube will help getting the holes drilled in the correct position.
Joe
 
Tony used the following tool. They are not expensive. When you can find one it make drilling tube easier. RVS drilling by hand is quite hard, with the drill press it was done in 20 minutes.

554868639_XFm9p-L-2.jpg
 
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