Drilling into boom with 3mm drill bit

[curmudgeon]

The E5 will be my introduction to Synergy.   The E5 manual recommends drilling 3mm holes on both ends of the boom.  The E6/7 manual also recommends drilling similar 3mm holes.  It seems that the seasoned Synergy pilot should be familiar with these 3mm drilling steps.  I have 2 questions regarding these drilling steps.

1) I do not currently own a "metric" drill bit set.  I understand that I can purchase a 3mm drill bit; money solves most problems in this hobby.  The question:  Would a 1/8" (3.175mm) drill bit work just as well as a 3mm drill bit?

2) Considering that I do not own CNC equipment, is there a particular proven method or technique to assure that the 3mm holes will be aligned correctly?

[Chris Sexton]

Copied from HF:

I have always used a 3mm drill so I am not sure if a 3.1 would cause any real issue. I would say probably not. Pinning is a security to keep it from pulling off. The clamps are doing the real work.



As for alignment. I assemble the heli. I line up the tail box by sight. Doing my best to visually line the tail rotor and the main shaft. I could probably be more scientific about it but this method has always worked.



Once the tailbox is lined up i use a fine point silver paint pen to put a dot on the boom at each drill point. The front and rear boom clamps and the tail box both already have drilled and tapped locations for the pinning screws. I leave the paint to dry while I do the head setups.



After the pain dries I carefully pull the boom back of and drill at the dots. Simple enough.

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[RichL]

+ 1 to what Chris said.   Instead of paint i just ran the a screw / bolt in and out of the mounting hole a couple of times with the boom installed.  This will remove enough of the anodizing to mark the tube for drilling.  If you do the the front of the boom first and then install it into it's mounted position you can install the tail box and vertical fin and use a square to ensure the tail box and vertical fin is straight.  After you verify that all is square repeat step one using the bolt on the tail box. One other helpful hint, once you have drilled the holes in the boom and verified alignment install the torque tube into the helicopter's transmission box and then slide the boom over the torque tube.  I use silicone on the bearing retainers to help them slide into position.  Using this installation method ensures the the TT is fully seated in the front transmission, Rich

[flyalan]

Again +1 to what Chris said.  I use a 1/16 drill and wrap tape around it until it's just a bit smaller than 3mm.  I then use the bit in a dremel on slow to mark the hole position.  The tape keeps the bit centered and doesn't damage the threads in the hole.  I keep this bit handy for rebuilds. 

Cheers
Alan

[Ross Lawton]

Again +1 to what Chris noted.

I did mine slightly different in that i drilled the front hole first and got that installed and set then aligned the tail box assembly using the same method of a dot with silver marker, then removing everything and drilling the hole for the pinning the tail box.

Cheers,
Ross

[Rodney Kirstine]

So... I didn't pin mine and I have over 30 flights on it now with no issues.  The tail box hasn't moved at all and it hasn't moved at the front.  It sounds like the majority of you all pin yours, though?

[Darren Lee]

I pin the tail case only.  The boom has 3 clamps on it so I feel comfortable not pinning the front end.

[RichL]

Drilling the holes in the boom is considered and optional step but, if I remember correctly recommended.  When I drilled the holes for my E7 i didn't have a 3mm drill bit.  I used a smaller imperial sized drill bit and then used a extra screw / bolt of the same size and thread type to cut threads into the aluminum boom.  If you start with the front of the boom and make a mistake simply rotate the boom 180 degrees and repeat but make sure you are drilling the hole in the correct position closest to the transmission.  Drilling a hole in the in the second position closest to the rear of the helicopter frame will weaken the boom.  Using a 3mm drill bit gives you just a little wiggle room, because it is slightly larger and the bolt you are using to pin the tail.  Remember the only reason for drilling these holes to start with is to eliminate the possibility of the tail boom from rotating, all of the real support is provided from the clamping system on the frame clamping system and the tail box clamping system.
Rich

[Rodney Kirstine]

In the E7 TT upgrade manual it says it's recommended but in the E5 manual it just says "If you wish to use boom pinning feature you must drill 3mm hole! Follow these steps."  I've put some serious torque on mine, trying to get it to rotate or move, and it doesn't budge.  I may still end up going ahead and adding it, though, since the consensus seems to be for it.  I imagine it can't hurt, for sure.

[Jean-Luc Bolduc]

I carefully start drilling with  a 2.5mm drill to make a mark on the boom, then loosen the clamp, remove the box, and finish the hole. Then when I put back the box, the 3mm bolt will self-thread in the thin boom. Easy enough when you have proper drill sizes.

[GimpyGolden]

Could always grind a point on your pinning screws as well, they should punch right through the thin boom. I will go this route. My buddies Rush 750 came with pointed screws to pin the boom. It came with some spare I kept after I finished his build, going to use them.

My Compass 7Hv has two screws to help secure the tail case, manual suggest just thread them in and they'll punch through the boom and so they do

[Chris Sexton]

Could always grind a point on your pinning screws as well, they should punch right through the thin boom. I will go this route. My buddies Rush 750 came with pointed screws to pin the boom. It came with some spare I kept after I finished his build, going to use them.

My Compass 7Hv has two screws to help secure the tail case, manual suggest just thread them in and they'll punch through the boom and so they do

My only concern here would be the increased risk of stripping the tail box. Yes the boom is thin, but there aren't a LARGE amount of threads in the tail box.

If you do it this way, be very mindful of the threads on the tail box. Go slow :0

[RichL]

Could always grind a point on your pinning screws as well, they should punch right through the thin boom. I will go this route. My buddies Rush 750 came with pointed screws to pin the boom. It came with some spare I kept after I finished his build, going to use them.

My Compass 7Hv has two screws to help secure the tail case, manual suggest just thread them in and they'll punch through the boom and so they do

My only concern here would be the increased risk of stripping the tail box. Yes the boom is thin, but there aren't a LARGE amount of threads in the tail box.

If you do it this way, be very mindful of the threads on the tail box. Go slow :0

+ one to what Chris said.  It would be very easy to strip the threads from the aluminum on either end, use the pointed screw to mark to boom and then drill the hole.

Rich

[Greg Jackson]

Lol I guess to be safe I won't do the pinning.

[RichL]

Lol I guess to be safe I won't do the pinning.

You should do the pinning, it's not difficult.  Mark the boom using any method you like, drill the hole. Mount the boom (without the torque tube) align the tail box, mark the boom, drill the hole. Remove the boom install the torque tube into the front transmission.  Lube the bearings retainers (on the TT), slide the boom over the TT.  install bolt into the hole you just drilled .  Tighten boom clamps.  reinstall the tail box onto the boom install retaining pin, tighten pinch bolts. Check alignment, done.  There really isn't any drama involved in pinning the boom, just perceived drama.

Rich

Rich