Thorp Air Command - T18.net

Supporting Owners, Builders and Pilots of the Thorp T-18 and its variants.
It is currently Thu Oct 31, 2024 6:30 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 6 posts ] 
Author Message
SHIPCHIEF
PostPosted: Fri Mar 23, 2018 3:27 pm 
Sr. Member
Sr. Member

Joined: Tue Nov 29, 2011 9:05 pm
Posts: 471
Location: USA
I'm getting ready to drill the H beam to the spar angles and web of the outer wing panel.
The plans call for drilling these holes with a #12 drill and installing NAS 178-6-8 "Hi-Shear" rivets with NAS 179-6 Collar.
'Feisty' was built with AN-3 bolts in these locations.
A #12 drill is too big to fit in the original holes of the H beam. A standard 3/16" (.1875") drill will not fit either, but it's close.
The used AN-3 bolts mic'd @ .185" give or take, a #12 drill is .189"
What say the experts? Should I drill #13 (.185") or drill #14 (.182") and ream ream up to .185 or other value? The #14 bit is a little loose in the hole and centering would be in doubt?
I understand a drill will not make a round hole, more like a hole with lobes...or is that just when drilling sheet-metal?
I'll be drilling down thru the original holes in the H beam, through the new parts using a drill press and support blocks to minimize damage to original holes in the H beam.

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE


Top
 Profile  
 
James Grahn
PostPosted: Fri Mar 23, 2018 10:22 pm 
Hero Member
Hero Member

Joined: Sat Oct 24, 2009 7:16 pm
Posts: 1459
Images: 0
Location: USA
I would drill small and ream. Although that is hard to do accurately with that many holes. Get good, American made split point drills and they don't make the triangular hole you mentioned.
I use a mill with a DRO, but not too many folks have access to those.
Cubes


Top
 Profile Personal album  
 
1albee
PostPosted: Sat Mar 24, 2018 4:04 am 
Sr. Member
Sr. Member

Joined: Sat Oct 31, 2015 6:58 pm
Posts: 172
Images: 0
If you accidently have a oversize hole, a close tolerance bolt (cup head) is .001 - .003 larger in diameter for a tight fit.
Phil
118BC


Top
 Profile Personal album  
 
TonyNZ
PostPosted: Sat Mar 24, 2018 4:10 am 
Full Member
Full Member
User avatar

Joined: Thu Oct 22, 2009 10:25 pm
Posts: 106
Images: 8
Location: New Zealand
Agree with Cubes. AN bolts are always undersize by 3 to 4 thou. Mic all your AN 3 bolts and replace any that are not within a thou of all the others. Select a drill (it may be metric) that gives the closest size to bolts. A light tap through with soft faced hammer is the aim. You will need to do the same exercise withe the wing joint fittings.
Cheers
Tony Schischka
ZK-VMS


Top
 Profile Personal album  
 
SHIPCHIEF
PostPosted: Sat Mar 24, 2018 11:14 pm 
Sr. Member
Sr. Member

Joined: Tue Nov 29, 2011 9:05 pm
Posts: 471
Location: USA
Thanks All;
Plus phone calls with Bruce F & Gary J.
I have a 3/16" split point drill that mic'd the same as my bolts. By carefully setting up my drill press and installing AN3 bolts as I drilled, I got a very snug fit on all and it turned out very well.
Maybe I got my self all worked up over a small issue, but the original H beam fit would be hard to duplicate to the center section clevis, Serious Pressure to get it right!
I then took the assembly to the airframe and installed it, the original bolts were a nice snug fit. I'm satisfied that I can continue with the clean-prime-rivet & bolt together part.
Then to drill/celco on the ribs and rear spar...
I'll be flying to Sedona in Brand X again this year, but I'll bring some progress pics to share around the wine table at the Sky Ranch.
:P

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE


Top
 Profile  
 
James Grahn
PostPosted: Sun Mar 25, 2018 9:35 am 
Hero Member
Hero Member

Joined: Sat Oct 24, 2009 7:16 pm
Posts: 1459
Images: 0
Location: USA
Excellent. Looking forward to pictures
Cubes


Top
 Profile Personal album  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  

[ Time : 0.114s | 10 Queries | GZIP : On ]