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-7 Elevator Bellcrank Install Issue

mfleming

Well Known Member
Patron
I'm installing the F-635 elevator bellcrank assembly on my -7 QB fuselage.

The quick builders drilled the ?" bolt hole in the F-729A bellcrank rib and angle. They also drilled the hole in the F-728A bellcrank channel BUT did not drill the F-728B angle.

This seems like a critical hole to drill so the bolt is square with the structure.

My problem is how to drill through the angle and not get off center??

Here's the drawing.

dwg26.jpg


Here's the channel with the ?" hole but not in the angle.

not_drilled.jpg


I can get a long ?" bit through the rib hole but the there's nothing to help stabilize the bit and prevent a misdrilled hole.

Any thoughts would appreciated.
 
Drill bushing

Go to the hardware store. Buy one of each size brass tubing up to 1/4" OD.
Cut a length off each shorter than the bit that fits the smallest tube. Probably #41.
Insert them inside each other so the outer tube fits the hole. The inner tube holds the bit centered. Once you have the pilot hole, drill in incremental sizes up to 1/4".
Hope that helps.
 
Same idea

Use a square piece of aluminiun stock, drill the correct size hole through it using a drill press, clamp it in place between the rivets and use it as a guide. That?ll get you a square hole so to speak. ;)
 
Go to the hardware store. Buy one of each size brass tubing up to 1/4" OD.
Cut a length off each shorter than the bit that fits the smallest tube. Probably #41.
Insert them inside each other so the outer tube fits the hole. The inner tube holds the bit centered. Once you have the pilot hole, drill in incremental sizes up to 1/4".
Hope that helps.

Use a square piece of aluminiun stock, drill the correct size hole through it using a drill press, clamp it in place between the rivets and use it as a guide. That?ll get you a square hole so to speak. ;)

Thanks for the advice...both methods sound good.
 
Thanks for the help!

I'm installing the F-635 elevator bellcrank assembly on my -7 QB fuselage.

The quick builders drilled the ?" bolt hole in the F-729A bellcrank rib and angle. They also drilled the hole in the F-728A bellcrank channel BUT did not drill the F-728B angle.

This seems like a critical hole to drill so the bolt is square with the structure.

My problem is how to drill through the angle and not get off center??

Here's the drawing.

dwg26.jpg


Here's the channel with the ?" hole but not in the angle.

not_drilled.jpg


I can get a long ?" bit through the rib hole but the there's nothing to help stabilize the bit and prevent a misdrilled hole.

Any thoughts would appreciated.


Here's a look at how the troublesome hole was drilled.

I used a piece of ?" OD copper tubing. One end was squared off so it would fit in the small lip of the hole in the F-728A channel. The ?" tubing ID was perfect for a 3/16" drill bit.

So with the tubing in place, I had a nice square perfectly aligned jig.

Here's what it looked like just before drilling.

jig.jpg


And the final F-635 assembly in place.

635.jpg
 
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