SNX-W11-03 attach block reaming

[Sonex1243]

Getting ready to drill my second set of attach blocks and mate to new angles again since the 1/4" reamer I used in the drill press didn't provide the "tight fit" required. I experimented with a lower size letter "D" bit @ .2460 and found it to be too tight. Is there a way to slightly enlarge this hole size without the 1'4" reamer?

I am about to purchase a .2485 (.0015 under) reamer from MSC, or, the undersized 1/4" @ .2490 (.001 under) ream from avery to get it right this time. What have you folks done to get the "tight fit" that Sonex tech described as tapping in with a mallet?

Reading further in the plans, these assemblies are attached to the spars with "tight fit" AN3 bolt / MS screw hardware, what size ream, under 3/16" has worked for these? I have the pre-assembled spars and machined angles, so, slight reaming of the holes is all I would need to do to finish the spar assemblies.

I must be over-engineering this.. Thanks for the help!

Ken
Sonex KMT
Working the wings.

[Gripdana]

I plans built and used the drill bit from McMaster Carr to do the wing rigging as it is called out in the plans. I used 3/8 bolts in the main spars. The fit was very tight. If you would like to borrow the bits I used I'm happy to send them to you.

[lpaaruule]

I've found that the same AN bolts from different manufacturers vary in size by several thousandths. However, the same AN bolts from the same manufacturer have only varied by a couple thousandths in my limited experience.

Having said that, I used a .2470 reamer for the bolts you are referring to. It worked absolutely perfect for the bolts I have - 3 or 4 light taps with a mallet.

For the AN3 bolts, I use a different method. After I've enlarged the hole to a #30, I use a #14 to get close to the size. Then I use one of my custom ground #12 drills to get the "perfect" fit. While the hole isn't as round as a reamer, I've found it's as goods as I can make it without spending a fortune on reamers.

To make the custom #12 drills, I chuck one in my drill press then lightly sand the spinning drill with some 220grit or finer sand paper. Then I drill a #14 hole in some scrap 3/16" thick aluminum, then enlarge it with the ground #12. I then test the fit with one of my AN3 bolts. The first couple tries the hole is usually too loose, but I usually get it just right after the third or forth iteration of light sanding. It doesn't take much, and I've had to start over a few times because I sanded too much.

I've done this for tight and light drive holes, and all the different bolt sized I've encountered so far including the flush screw/bolts used in the main spars. I now have an assortment of custom ground drills in a bag in my toolbox. I take a yellow paint pen and paint the the non-cutting end, then use a sharpe marker to label what it is used for (AN3 Light Drive, AN3 Tight Fit, AN25, etc)

I'm in the process of joining my front and rear fuselage's together, and it's working great for the AN25 bolts.

Make sure that if you drill bolt holes without a drill press than you use a drill guide. If your like me, without a drill guide for at least the #14 hole, the hole will end up slanted, and the bolt head will never seat flat. Of course a lot of guys don't have this problem because they just use a #11 or #12 drill on all the 3/16" holes and don't give it a second thought. As you've probably heard, it's usually acceptable to use the next numbered drill size bigger than the bolt your using.

[kmacht]

You can buy adjustable reamers. That is what I did when I had an ovaled hole and wanted to go up to the next size bolt. I think I bought them from Enco for not too much money.

Keith
#554

[Sonex1243]

I plans built and used the drill bit from McMaster Carr to do the wing rigging as it is called out in the plans. I used 3/8 bolts in the main spars. The fit was very tight. If you would like to borrow the bits I used I'm happy to send them to you.

Thanks Dana, I may ask to borrow them later on, I'm no where near the wing completion / rigging stage. I'm getting whooped just attaching the blocks to the angles!

[Sonex1243]

I used a .2470 reamer for the bolts you are referring to. It worked absolutely perfect for the bolts I have - 3 or 4 light taps with a mallet.

For the AN3 bolts, I use a different method. After I've enlarged the hole to a #30, I use a #14 to get close to the size. Then I use one of my custom ground #12 drills to get the "perfect" fit. While the hole isn't as round as a reamer, I've found it's as goods as I can make it without spending a fortune on reamers.

Thanks for the information Paul!
I'll give it a try when I get ready to drill the "new" set of blocks and angles.
I'll also be looking at your method for the AN3 and MS screws when they get attached to the spars. When I looked at the pre-made spars, the attach blocks, lower angle and tie down holes are already drilled / reamed. Checking with Sonex tech to see if they are already set for the tight fit in which I just need to tap the bolts / screws in when the time comes.

Hopefully my hardware will be somewhat consistent as it is a wicks kit i bought several years ago.

[Sonex1243]

You can buy adjustable reamers

Thanks Keith;
I wasn't sure about them, but, have not pursued it any further. Are they complicated as far as setting a specific decimal size?

[kmacht]

If you have a micrometer or caliper you can set the size but honestly it is alot easier and safer to sneak up on the final size and use the bolt as the test to see when the hole is just big enough for it to fit. When I did mine I just kept adjusting the expansion nut a 1/4 turn at a time. It moved the blades very litle with each adjustment and I ended up with a perfectly fitting hole. You can practice with it on a piece of aluminum plate and get a feel of how much each adjustment opens the hole size up.

Keith
#554