What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Drilling a clean properly located hole

RV-Ogler

Active Member
I’ve been fighting one hole for the last 24 hours. Drilling the 1/4” bolt holes for securing the horizontal stabiliser to the aft fuselage on my 14 tail dragger I elongated the bottom one and Vans told me to upsize to next bolt size (AN5). Well I screwed up that too. I believe I have the edge distance to upsize to an AN6 but I’ll check with mother ship first .

So if I can upsize to an AN6 I dont want to F it up again. What would you do to stack the odds in your favor of successfully upsizing this hole and have it be clean and perpendicular?
 

Attachments

  • 592E6577-31BF-4FBC-B74C-340FAB87B9B5.jpg
    592E6577-31BF-4FBC-B74C-340FAB87B9B5.jpg
    341 KB · Views: 189
A good way to get it perpendicular is to use a long drill bit and a visual guide block on the part. Some drill bits tend to grab, so test out the bit on some scrap first, or use a reamer.

p.s. another suggestion is to have the parts clamped together tight while drilling. In the photo it looks like the VS spar may be binding on the socket for the tail wheel spring and is preventing the parts from being in close contact while drilling.
 
Last edited:
Drilling holes

Drill bits or reamers?
Reamer is best. Drill bits don't make round holes.
Go up in tiny increments. Like no more than 10 numerical at a time. Five is even better. Sure hope Vans approves. Best of luck.
 
The bit did grab that’s how this mess got started. I’ll try a reamer. Also the parts are flush and clamped tightly and the spar is not contacting the tail wheel spring it’s just the angle of the picture makes it appear that way
 
Up-size the drill bits slowly, especially when getting close to final size. I have a good collection of fractional bits, so generally use those, going up small increments at a time. Bit before final size will be ~1/32" smaller than final size.

Practice on scrap is the age-old bit of wisdom. Rather learn a technique doesn't work on a 10c piece of scrap than the real airplane.
 
Good advice already:

  • reamers;
  • increase size slowly;
  • make sure the drill is spinning very fast.

I'd also check with Van's on going to a -6 - my TLAR indicator says that there won't be a problem, but always better to confirm.
 
I feel your pain, been there. You're not alone.


I use a very high quality (NOT HF!!) step drill bit. Before I use it, I drill a 1/16" hole, then a hole up from that (sorry, just got my wakeup call and head is fuzzy) until it's ready for the step bit. Put a piece of blue tape at the size you want to stop at.

Something like this. https://www.amazon.com/Neiko-10169A.../138-6534215-5462826?pd_rd_i=B09VZV4Q7B&psc=1

My building mentor turned me on to them. Now I wonder how I ever built anything without them.
 
Try a drill bushing

Use a snatch block drill bushing.

Centre it on the existing hole, with the drill bit you previously used providing alignment. Clamp it firmly in place, using screw Clecos if possible, or any other clamping arrangement that fits. Swap the bushing to whatever is required for the upsized hole, then drill or ream. If you need to open the hole out a lot, step up slowly through multiple bushing sizes.

I used this on my elevator horns as shown, to ensure the holes were precisely positioned and square.
 

Attachments

  • empennage_2017-07-22_01.png
    empennage_2017-07-22_01.png
    648.1 KB · Views: 149
For squareness, make a drill block to suit the job. Some are just a small block of aluminum, some are larger. A block lined with a steel tube can be clamped in place to move the hole center if necessary.

Think of a drill block as transferring the squareness of your drill press or mill to a portable tool.
.
 

Attachments

  • P1140004.jpg
    P1140004.jpg
    33.8 KB · Views: 95
  • P9210002.JPG
    P9210002.JPG
    71 KB · Views: 97
Last edited:
Vans suggested I go with a NAS6205-5X or 6X the X means its oversized by 1/64” , if I can find one. I called Genuine Aircraft Hardware and they did not have any in stock and could not get a quote, but said they would pursue it further.

I showed the hole to an experienced RV builder and he said it’s not that bad and would just leave it if it were him. My A&P also thinks it’s ok but if I can get an over size X or Y bolt to go for it and use a reamer

So anyone here know where to order 6200 series X or Y bolts?
 
I like the idea of upsizing to a -6 with a step drill or reamer. Very round hole, and easier to control. Making a drill jig like Dan suggests is better, and a twist drill bit won’t walk in a jig like that, but I like the round hole you get with a step drill or reamer too. They don’t grab and mess up your hole like a twist bit can do when drilling it free hand, especially on larger drill bits - and you’re running out of room to keep upsizing.
 
Drills

Standard protocol for reaming is to drill 1/64 undersize and then ream. Something like what Dan showed is fine for a guide. Separate hole in guide for drill and reamer.
I have best results with high speed steel straight flute reamers.
 
Back
Top