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Old 05-11-2017, 05:07 PM
Louavul's Avatar
Louavul Louavul is offline
Join Date: Jan 2005
Location: Rio Communities, NM
Posts: 119
Default Drilling HS-714

Guys: Looking for some ideas/suggestions/help in match drilling the holes in the HS-714 angle, that was installed during the horz stab SB, with the previously located and drilled longeron holes, as they existed with the old angle, before the horz stab SB.

It's too tight of a space to crawl back there so, I'm thinking maybe a strap duplicator or.....?

Figured I'm not the first one that has had to do this.

With the lack of adjustability for this application I'm a little gun shy in trying "what might work".


Steven Hild
Rio Communities, NM USA
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Old 05-11-2017, 06:14 PM
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CubedRoot CubedRoot is offline
Join Date: Sep 2013
Location: Ooltewah, TN.
Posts: 525

This looks like it would be a good use case for a strap hole duplicator. Get the horizontal stab all lined up and squared up with the fuselage and then use a strap duplicator to make sure you have good edge distance. Adjust things until you do have good edge distance and use the duplicator to mark and drill your holes.
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Old 05-11-2017, 07:20 PM
Mark H Mark H is offline
Join Date: Jul 2011
Location: Indianapolis, IN, USA
Posts: 29

Back drilling up through the deck would be the best option. I don't think you need to crawl back there. The access through the holes is pretty good but does require the use of a mirror and some careful positioning and the right bits/attachments. I know from performing the SB on mine, HS-714 is not an easy peace to remove/replace. I would be very hesitant to drill from the top with anything. You might possibly be able to make some sort of template using the old HS-714.
Old 05-11-2017, 08:31 PM
BillL BillL is offline
Join Date: Sep 2007
Location: Central IL
Posts: 4,236

Mine were drilled by the previous builder, but the holes are very tight on the bolts.

The alignment of the axis of the holes has to be correct to ensure they are tight in shear. This is a consideration before just marking and drilling off the airplane. I use a 3/16 piano wire as an alignment pin and one with a conical point as a center punch through existing holes. I would agree that experimentation is not a good way to go.

You might first ensure the holes are square to the structure, if so it makes choices easier.

If I was doing it, I would take the old angle, make a drill template ( 1/8" minimum thickness) that can be flipped and used as a guide. Use it to drill a practice piece, and see if the holes are aligned. If they are, then make a center punch from 3/16" piano wire (hardened rod), mark the finished HS through the fuse holes after getting it aligned. Then, align the drill guide over the HS and drill the final holes.

If you use a drill press for the drilling and the alignment works on the test piece, all is good. If not, an angle drill from the bottom is the only way left (I think). Just be sure the bit is aligned when drilling as to maintain hole size.

My 2 cents - good luck.

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Last edited by BillL : 05-11-2017 at 08:34 PM.
Old 05-11-2017, 09:33 PM
Bevan Bevan is offline
Join Date: Sep 2007
Location: BC
Posts: 1,523

If it were me, I would use my angle drill adapter and drill up from the bottom (by reaching in through the large access holes).

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Old 05-12-2017, 12:26 AM
tgmillso tgmillso is offline
Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 566

It is possible to crawl up the back and match drill these holes of you want to badly enough. When I drilled mine initially, I drilled the holes into the aft deck from the top so I could place them exactly where I wanted since I knew the edge distances on the Longerons were critical, then crawled up the back and match drilled those holes to the HS. Even if you find it too awkward to drill the hole all the way through, you can at least get it started, then take the HS off and finish it. I wasn't comfortable reaching through the holes in the aft deck to drill these because I wanted to see what I was drilling for something so critical. Being 5'10" and 150lb sucked when it came selection time for football at college, but it's sometimes handy when building an aircraft. If you don't meet a similar physical criteria or less, then I'm sure there's a builder near you that for dinner and few beers would be happy to drill them assuming you lay down an adequate working surface (I used slabs of polystyrene between the bulkheads with a big sheet of plywood over the top).
Old 05-12-2017, 06:10 AM
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bret bret is offline
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Location: Gardnerville Nv.
Posts: 2,760

Like mentioned above can you get a mini 90 deg drill adapter in there, looks like it will be close to the bulkhead, in that case can you use a 12" drill and flex it to get a straight shot at it doing a match drill from under the deck?
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Old 05-12-2017, 05:42 PM
tgmillso tgmillso is offline
Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 566

Bret brings up a good point. For the outboard holes these were so close to the side of the fuselage that I just spun the drill between my fingers to mark the hole, then removed the HS, marked a cross at this point and drilled those two holes as accurately as possible to #30. I put the HS back in place put two drill bits down through these holes to align the components, put my clamps back through the aft deck to hold things in place. I then drilled up through the F-710B/C for the inboard holes to #30 up into the HS, then opened these #19 and finally #13 before finishing with a 3/16" ream, all from below. The outer holes in my case were then drilled down from above using 6" drills to #19 then finally #12 (as I didn't have a long enough reamer), using a try square against the HS to ensure that these holes are dead-nuts straight. In the case where you are retrofitting and your aft deck holes are already drilled to final size, then I'd probably want to be drilling up from below with a slightly undersized drill and a brass drill bushing using as long a bit as possible to ensure straightness, then finally opening this to final size after the initial hole has been drilled. I don't envy your position having to do this as a retrofit. Good luck.
Old 05-24-2017, 05:34 PM
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Louavul Louavul is offline
Join Date: Jan 2005
Location: Rio Communities, NM
Posts: 119
Default Drilling HS-714

To wrap this up for anyone faced with a similar challenge; Considered the options offered here but, continued to search the google for ways to drill holes that couldn't be seen and ran across tools called "Transfer Punches". Located an assortment of these punches at Harbor Freight for $10.

Was able to mount and square the horz stab, clamp it in place, reach under thru lightning holes, inserted 3/16 inch punch thru the angle piece as well as the spacers, allowing for a fairly wobble free insertion. Gave the punch a wack with a bucking bar, removed the stab and witnessed the centered punch mark.

Drilled the inboard bolt holes first then repeated the process for marking the outboard holes.

Drilled all holes incrementally until the final size was achieved.

I'm pleased with the outcome.

Many Thanks to those that offered ideas and comments, holding my hand so to speak for this part of the "repair".

Steven Hild
Rio Communities, NM USA
RV-7, FWF/Fiberglass, N590SC res

Contributing annually since January 2002
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