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RV-7 Wing Tie Down Bracket Question

Dave Taylor

Dave Taylor

Well Known Member
I've not used a tap and die set before so I'm not sure if I messed up my tie down bracket or not. Tonight I tapped my wing tie down bracket and the tie down goes in sloppy until it gets to the end. It tightens up when fully inserted and feels strong. Is this normal?

The plans call for 3/8-16 which I assumed to be 16 threads per inch. I counted the threads on my tap set and it was 16.
 
Aluminum is very not the easiest to tap. You need to drill the hole out with the correct size hole before using the tap and use a cutting oil made for tapping aluminum. The hole needs to be cleaned out frequently while tapping by removing the tap often and flushing out metal shards. You do not want your tapped holes loose as they may tear out and your beautiful plane may be damaged in gusty conditions. Best to replace the part and try again. Get some scrap and practice.

Roberta
 
A little loose sounds about right

or at least it sounds about like mine. I certainly don't need a wrench to install my tie down rings. I originally assumed that the tie down rings would stay installed out on the wing, but later learned that many folks just keep these in the plane for when they need them. Jamie Painter gets credit for an idea to insert a hex plug to force the tie down to bottom out at a desired depth.
 
robertahegy said:
Aluminum is very not the easiest to tap. You need to drill the hole out with the correct size hole before using the tap and use a cutting oil made for tapping aluminum. The hole needs to be cleaned out frequently while tapping by removing the tap often and flushing out metal shards. You do not want your tapped holes loose as they may tear out and your beautiful plane may be damaged in gusty conditions. Best to replace the part and try again. Get some scrap and practice.

Roberta
Click to expand...

You could helicoil if your threads are messed up. Rather get a pro to do it if you havent done it before. FWIW, the helicoil is way stronger than the aluminium thread.
 
I'd be reluctant to use a helicoil in this application. Yes, the steel insert is stronger than the aluminum, but the wall thickness left after drilling out for the insert may not be sufficient to carry the loads necessary for tie-downs or jack points. Just something to think about.
Terry, CFI
RV9A N323TP
 
Hi David....

......if you decide to re-make the tiedown, just take your time and be sure to be perfectly parallel to the tiedown. Only turn the tap half a turn or so and back up a quarter turn, then proceed another half a turn and back up a quarter turn and so on, until your done. Backing up loosens the chips and as Roberta pointed out, clean it several times during the tapping process.

Regards,
 
Thanks for the replies

Thanks for all the replies. I plan on reordering the part but I think I'll tap the other bracket before I order and see how it goes. I may need 2 :D
 
Tapping Tip

When tapping Aluminum place the hole so it will hold some IP Alcohol, Fill it up, tap it as far as you can without building up to many shavings / Chips.

Blow it out carefully, and fill it up again, Tap, Repeat, until you are satisfied with the results.

The Alcohol helps the tap cuts clean and keeps it cool.:)

Normally heat is developed in the aluminum, expanding it, the the aluminum shrinks around your tap, and all Hellpless breaks loose:eek:, but not the tap.:(

Best Wishes,
 
If you didn't already drill any screw holes to them yet, why just don't turn it "up-side-down" and make threads to another end? You could save some $$$...
 
Too late

Good idea but unfortunately I've already drilled the bracket to the spar. I'm going to play with a practice piece this weekend and tap the other bracket when I feel confident. Maybe I'll only need to order one. Thanks again for all the good replies.
 
I found a solution

philcam said:
Or you can just order them already tapped with nice powder coated tie down rings here:

http://www.cleavelandtoolstore.com/prodinfo.asp?number=RVTDK
Click to expand...

I had my buddy Bruce (an experience RV builder) come by and try to tap some scrap and we had the same results. He did not have this problem when he tapped his. We concluded that we may need to use a smaller drill bit. I used a 9/32 on some scrap and still had the same results. I went slow and cleaned often. I can only conclude I have a problem with my tap set.

I considered ordering the kit philcam posted but it seemed pricey considering I already had the tie down rings. His post prompted me to look around and I found this:

http://www.cleavelandtoolstore.com/prodinfo.asp?number=RVTD-AEX

This is a no brainer. I am one to want to do build as much of my plane as I possibly can but Roberta got me to thinking about it with her comments.

If something doesn't seem right it probably isn't and I don't want my plane blown away by a freak storm. It would probably never happen but I'm not willing to take that chance over such a cheap part. YMMV

Much thanks for all of the replies.
 
Make it easy on yourself

Dave Taylor said:
I had my buddy Bruce (an experience RV builder) come by and try to tap some scrap and we had the same results. He did not have this problem when he tapped his. We concluded that we may need to use a smaller drill bit. I used a 9/32 on some scrap and still had the same results. I went slow and cleaned often. I can only conclude I have a problem with my tap set.
snipped
Click to expand...

David,
If you have access to a drill press, use it. Mount your tie down extrusion into the vise on the table. Use a level to ensure that your extrusion and the drill bit are parallel in both axis. Draw an X across the tip of the extrusion to find it's center. Center punch this spot. Drill a 1/8" pilot hole first to a depth of about 1.75". Now drill again using the correct 5/16" bit (or a letter N for a slightly tighter fit). The finish drill bit will not wander when using a drill press in combination with a pilot hole.
Remove the finish drill. Insert your 3/8" 16 tpi (national coarse) tap in the chuck of the drill press. Chuck the tap along it's round surface. USING ONLY YOUR HAND (no power) on the chuck, lower the quill of the drill press until the tap contacts the hole in the extrusion. Turn the chuck with your hand to start the tap into the hole. This will ensure that the tap is started straight. Using the turn and back out method described by others. Get the tap at least three full turns into the extrusion using hand power on the chuck. Loosen the chuck on the drill press and finish tapping by hand.
Charlie Kuss
 
Charlie's advice for aligning the tap works perfectly. One of the best lubricants for drilling, taping or other machining of aluminum is kerosene. The other important thing is to clear the chips as others have said. One quarter of a turn with the tap cutting, then a half turn back to break the chip. Make sure you clear the chips occasionally. I don't recommend compressed air however, it can send razor sharp chips flying back into your face. (I'm a retired high school machine shop teacher, I can't stop stop making safety references.)
 
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Tap advice

mdoyle said:
Charlie's advice for aligning the tap works perfectly. One of the best lubricants for drilling, tapping or other machining of aluminum is kerosene. The other important thing is to clear the chips as others have said. One quarter of a turn with the tap cutting, then a half turn back to break the chip. Make sure you clear the chips occasionally. I don't recommend compressed air however, it can send razor sharp chips flying back into your face. (I'm a retired high school machine shop teacher, I can't stop stop making safety references.)
Click to expand...

Mike,
That's good advice. However, since he won't want to disturb the extrusion in the vise once he has it parallel, air pressure can be used with caution. Use a blow gun with the air pressure reduced to about 20 or 30 PSI. Cover the extrusion with a shop rag. Lift one end (facing away from your face) of the rag and blow out the chips. Always wear glasses to protect your eyes. The rag will deflect the chips away from you.
The only thing positive about getting older, is that I no longer have to look for my safety glasses. I'm always wearing reading glasses for close work now. :(
I used a taper tap to do my initial tapping. It is much easier to get a taper tap aligned with the hole properly. However, it won't cut threads near the bottom of the hole. I usually use a plug or bottoming tap to cut holes down to or near the bottom of a drilled, blind hole.
Charlie
PS If you chip, dull or damage a taper tap down along the bottom third of it's length, don't throw it away. Cut the damaged area away with a die grinder and cut off wheel (remember the glasses). Dress the sharp edge on the bottom thread with a bench grinder and you've just made yourself a bottoming tap.
 
Good advice

chaskuss said:
David,
If you have access to a drill press, use it. Mount your tie down extrusion into the vise on the table. Use a level to ensure that your extrusion and the drill bit are parallel in both axis.
Click to expand...

Charlie,
Sounds like that would work better than what I did. I went ahead and ordered the parts from Cleaveland but I'll practice your method so I'll be able to tap if needed again.

Thanks,

-David
 
Hey guys. I know this thread is pretty old, but I'm having this same problem.

I followed the normal tapping guidance (1/2 turn in, 1/4 turn (or more) back out). Repeat.

Things were great until I got my tiedown rings and they are sloppy until the very last 1/4 turn.

Is my tap set not truly 3/8-16? Not sure about the older kits, but the newer tiedown stock comes predrilled.

Any recent thoughts on this? Am I doomed to order the cleveland kit?
 
N999ZA said:
Hey guys. I know this thread is pretty old, but I'm having this same problem.

I followed the normal tapping guidance (1/2 turn in, 1/4 turn (or more) back out). Repeat.

Things were great until I got my tiedown rings and they are sloppy until the very last 1/4 turn.

Is my tap set not truly 3/8-16? Not sure about the older kits, but the newer tiedown stock comes predrilled.

Any recent thoughts on this? Am I doomed to order the cleveland kit?
Click to expand...

All of my tiedown stock came drilled but not to the correct size to be tapped. I went to the chart and pulled the correct bit and then drill them all up to the correct size for the tap... worked pretty well for me.
 
LifeofReiley said:
I went to the chart and pulled the correct bit and then drill them all up to the correct size for the tap...
Click to expand...

I didn't drill them up...

Would that have made the tap cut too much?

This morning at work, I grabbed a better quality tap (4 flutes) and threaded it in by hand. That tap was loose. I have a feeling my Harbor Freight tap was a little oversize.
 
I know this wasn't my thread, but I did learn a little last night:

After some thought (and a trip to work), some of the guys were convinced that 1) I didn?t ruin the part, especially since I had only tapped the 1″ shown on the plans (and the rings are like 1 1/2″ long), and 2) it must be the tap quality.

They lent me a really nice tap (as opposed to the $7.99 tap and die set from Harbor Freight.)

I screwed in the nice new tap, and once I got past the first inch, I immediately felt a difference. When I turned 1/2 turn in, the tap felt like it was cutting, instead of just pushing material out of the way. There was significant resistance at the end of the 1/2 turn. Once you start the 1/4 back out, there is some more resistance, then a ?release.? I could tell immediately that the release was the cutting of little chips from the material.

It was like I heard angels. This is what tapping is supposed to feel like.

(The old one was just steady increase in resistance in, then decreasing resistance out.)

Just one more reason why I should have bought the $80 tap and die set, instead of the $8 tap and die set.

Lesson learned.

From the following picture, you should be able to tell that the thread cutters on the left are nice and sharp, and the apex of each blade comes to a point. The one on the right is not sharp, and the apex is kind of rounded.

http://n999za.files.wordpress.com/2011/07/20110713-003-large.jpg

So now, I have about 1″ of slightly loose threads, and 1/2″ of perfect (remember the angels?) threads. I am okay with at least four threads perfectly engaged, and 16 threads mostly engaged. If my airplane blows away, you all get to say "I told you so."

Hope this additional information helps someone.
 
I can confirm this about the Harbor Freight tap/die kit. I was trying to make some threaded rod using the kit I got there and simply could not get it to work. It just wouldn't bite into the metal. It made a very nice single ring. I took the rod stock to a friends house and he made my threads in no time at all with his 15-year old craftsman kit.

Seems you get what you pay for in tap/die kits. Lesson learned for me, too.
 
Chinese threads are like that; we get odd threading when using Chinese hardware (nuts/bolts) in the RC world.
 
Buy American Taps!

It's hard to make SAE threads on metric machines. They never convert over just right. Thats why China threads are just a tad off. Just find a local Ace hardware and get some Irwin Taps. I bought a Harbor Freight Tap set for some non airplane related stuff. What a waste of money. The tap handle was junk.
 
It's hard to make SAE threads on metric machines. They never convert over just right. Thats why China threads are just a tad off. - Wingtime -
Click to expand...

Huh? I don't believe anyone is making SAE threads using "close" metric pitches. SAE taps made on metric machines can and should be exact.
 
The problem with "cheap" taps is not thread pitch!

It's burrs! Look at the cutting threads on a cheap tap. You will likely see large burrs. These burrs cut the threads too deeply.
Taps are one of the many places you shouldn't cut corners on price. You get what you pay for.
 
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