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Fly cutter or Rotabroach for lightening holes?

C

Captain Sacto

Well Known Member


Question for the experts...

The rear spar for the vertical stab on the 7A has an eighth inch thick doubler that, according to the drawings, permits optional lightening holes. Two of the holes are 2" dia, and 5 are 1.5" dia.

It appears as though I have two options if I want to cut these lightening holes. I can buy the Rotabroach cutters from the good folks at Avery for $ 175; or, I can get an adjustable circle (fly) cutter from STS for $13.95.

My question is... do the Rotabroach cutters perform in a sufficiently superior manner to justify the >10X cost?

Any and all comments and suggestions welcome.

Thanks in advance! - - Tom from Sacramento

 
This is what I used.

On all my lightening holes on my six, I used a Malco HC-1.

I bought it from Avery in 98 and it works great.

It is a rotating cutter deal.

There site is http://malco.malcoproducts.com/products/shear/hc1.asp

and it shows a good picture of it.

The trick for nice holes is use the recommended rpm and let the cutter do the work. You must also not quite finish cutting and then stop at about 90% take the tool out an put heavy duty clear packaging tape on both sides of the inner biscuit before it moves, distorts or falls out.

Re install the tool and cut through the remaining aluminum slower than before.

it will come out round and with just the smallest bump where you finish the circle. Pull the tape off and do the next hole.

As with all things of this nature, practice first on something you don't mind throwing away

My experience with fly cutters and aluminum, RUN- AWAY!

I have seen people use them successfully before but one mistake and it's bandages and new parts. Believe me it can happen too fast. :eek:

Best wishes. :)
 
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I used Greenlee punches, since I had access to them and not to a flycutter. I have since borrowed a flycutter, then bought one. A flycutter would cut 1/8" aluminum like butter...
The two tricks are to clamp the work down tight (and keep clear if it decides to spin anyway). and to use the slowest speed possible! Don't remember offhand how slow my drill press goes - I think it's 370 RPM. At that speed it works great, and really isn't scary. That's my cheapo Harbor Freight floor model - my bench mount press only goes down to 750 RPM, and it scares me to think about using it in that!

Correction: Just checked my drill presses, and the actual slowest speeds are 170 RPM :cool: and 620RPM :eek:
 
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Or clamp them in a mill and use an indexable boring head. Of course its handy if you run a machine shop at your work :) Year of making pieces of metal into smaller pieces of metal and piles of chips have taught me a few things. As mentioned, flycutters, especially the single cutter ones, an notorious for hooking your part, flinging them about, often taking part of your hand or fingers with it. But only when used incorrectaly. It is very important to have your part clamped down well, for the doubler in question two 4" or 6" "C" clamps would be my minumim, there should be no need for your hand to be holding it. Put a piece of wood underneith it and pad the clamp face with a few strips of masking tape. Have the drill press table as high as you can get it and that it is tightened in position. If the cutting blade is adjustable, slide it up so there is very little stickout, perhaps 1/4" or so since your only cutting 1/8". The point is to keep the whole setup as ridgid as possable, you dont want the spindle of the drill press to be sticking down any farther than it has to be when cutting. Your cutting tool should have a slight angle on it so that the outer circumfrence of your cut is deeper than the inside. This way when it breaks through, it will seperate at a nice clean line on the edge instead of the whole swath of the cutter. Turn the cutter slow and use an aluminum cutting fluid like Tap Magic, A9 or even kerosene. Depending on the speed, cutter, and ridgity of the setup you will hopefully get a nice clean cut. Or it will chatter and make all kinds of noise. Just feed it in with steady, constant pressure and keep the lubricant flowing. An "acid brush" and a dixie cup make a good applicator.
 
Hole saw

I agree with Dan.
I did mine with a hole saw (bought the hole saw kit at Home Depot....Dewalt).
I think the kit was $29.95 or so. The holes came out slightly bigger than their nominal diameters (about 1/16"), but were totally acceptable.
There was a lot of noise,deburring and time, but for the cost I justified it.
Just make sure the piece is clamped down and secure and put the hole saw in a drill press.
Next time I will use some kind of lubricant. Duh
Jim
 
Fly-cutter

Nothing special on my -6. I did dozens of holes with the plain old cheap fly-cutter on the drill press.

If your part is sufficiently clamped down and held in place you can pretty much use any of the methods described above. If it isn't clamped down securely, make sure you have plenty of bandages handy ;) .

b,
dr
 
I also used my fly-cutter building the Val, and still have all of my body parts attached. See all of the notes above for safety tips though! I couldn't find a set of Greenlee punches in the correct size the day I was cutting my panel - they'd be the best for that if you can get ahold of them.

Paul
 
I prefer a good old-fashioned flycutter. Operated at 250 RPM in a drill press, I've never had a lick of problem using em. In fact, I sold my instrument punch early on because I discovered there are minute differences in diameter between various instrument manufacturers and the punch left shear marks that had to be filed away....tedious. I could more precisely cut in each burr free custom hole for all those steam gauges using the flycutters shown. The waste llustrated in the photo represent the total of lightening holes I cut out of my vintage 2000 pre-matched hole RV-6A kit.

Just make sure the work is securely clamped to the press and use a slow RPM with cutting oil and you shouldn't experience any problems. If you hurt yourself or experience other problems, it is a virtual certainty the problem can be traced to poor technique.

fuselageassembly07015ob4.jpg
 
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250 rpm is still pretty fast for a fly cutter. Back in the "old days" we had to cut ALL holes including lightening holes in the ribs and bulkheads. I never use over 170 rpm with a fly cutter. Like said before, make sure everything is clamped down and gloves are worn.
 
Fly cutter

I used a fly cutter for the VT spar holes. No problem...just took my time.
 
Still I prefer the rotary cutter.

Maybe I'm just overly cautious.

I tried a fly cutter in the beginning and even with clamping had poor results.

I believe now that it was an RPM thing as my drill press only goes down to 400 rpm or so.

When it went bad on a practice piece all I could imagine was injury and destruction.

The rotary tool is the safest way I see, and speed of process is not that important to me. I don't like buying new parts.

One thing that the rotary tool can do is cut holes up to 12"

http://malco.malcoproducts.com/products/shear/hc1.asp

I can't imagine that with a fly cutter or hole saw.
 
A true confession...

Also, in addition to the excellent posts in this thread, make sure you read the print correctly, and cut the holes as designed. My configuration went through the Material Review Board, and even though it doesn't meet print, it was dispositioned "use as is." :eek:
Don
P.S. (And yes, I am a Mechanical Engineer.) :eek: :eek:
 
Ahhhh the good 'ol days.

This may be old news but just in case...

The good 'ol days of cutting lightening holes in the vertical stab spar doubler seem to be over. My RV-8 emp kit came, (04/07) with the lightening holes already cut out. :)

(The plans still show the measurements and they're still listed as optional.)

You can almost hear the sound as thousands of fly cutters cry out as one....

Peter
 
RVF-84 said:
This may be old news but just in case...

The good 'ol days of cutting lightening holes in the vertical stab spar doubler seem to be over. My RV-8 emp kit came, (04/07) with the lightening holes already cut out. :)

(The plans still show the measurements and they're still listed as optional.)

You can almost hear the sound as thousands of fly cutters cry out as one....

Peter
Click to expand...

My six is a slow build kit, I cant imagine the work it took to make a plans only plane :eek:
 
How much weight saved versus the effort?

For those of you that have taken the time to cut the lightening holes, what is the weight saved for your model RV and would you do it again based on the time, effort, and slight chance of an emergency room visit?
 
Weight

Mhead said:
For those of you that have taken the time to cut the lightening holes, what is the weight saved for your model RV and would you do it again based on the time, effort, and slight chance of an emergency room visit?
Click to expand...

Depends on the model, if you look at the pic in post 5 I would guess about 2#

I like the lightening holes also because the allow me to see structure during inspection. Think of the flap hinge brace that goes from the top trailing edge to the rear spar. With no lightening holes here it would be difficult to see the condition of the rear spar as well.

They also allow the for less trapped moisture. with Aluminum its ok to get wet, you just don't want ANY of it to stay wet.

The subject of lightening holes might make a good "Poll" thread. :rolleyes:
 
Mhead said:
For those of you that have taken the time to cut the lightening holes, what is the weight saved for your model RV and would you do it again based on the time, effort, and slight chance of an emergency room visit?
Click to expand...

If all you do is save 1oz a month, you'll save 2 or 3lbs by the time you're finished. That's 1/2 a gallon of gas. It's amazing how tiny, insignificant weight savings add up. On tail heavy models, it will also help with balance. A couple of ounces back there is lots of ounces up front.

I guess it's just part of the build-it-light philosophy...you just don't let even an ounce slip by! :D
 
My drill press slowest speed is 400 rpm. No problems. I certainly do clamp the part and go slow!

BTW, a fly cutter will sure tell you if your work table is not level.
 
GAHco said:
Maybe I'm just overly cautious.

I tried a fly cutter in the beginning and even with clamping had poor results.

I believe now that it was an RPM thing as my drill press only goes down to 400 rpm or so.

When it went bad on a practice piece all I could imagine was injury and destruction.

The rotary tool is the safest way I see, and speed of process is not that important to me. I don't like buying new parts.

One thing that the rotary tool can do is cut holes up to 12"

http://malco.malcoproducts.com/products/shear/hc1.asp

I can't imagine that with a fly cutter or hole saw.
Click to expand...

I'd often use the rotary tool for lightning holes, as shown in the link, since I use this tool often, in my HVAC business. 4", 6", 8" holes are a breeze and quite safe.

For those 3 1/8" panel holes, my preference is the fly cutter. The holes are perfection without cleanup, and don't distort any metal, such as a punch might do.

I'd drill the pilot hole, then spin the fly cutter by hand, a few revolutions on the top surface (unplug the drillpress), then flip it over & power cut from the bottom. No oil, and a bit of jabbing motions work great. Have done two panels this way.

I'll also use some hole saws for small holes such as 1".

L.Adamson
 
RVF-84 said:
This may be old news but just in case...

The good 'ol days of cutting lightening holes in the vertical stab spar doubler seem to be over. My RV-8 emp kit came, (04/07) with the lightening holes already cut out. :)

(The plans still show the measurements and they're still listed as optional.)

You can almost hear the sound as thousands of fly cutters cry out as one....

Peter
Click to expand...
Pete....Here is a thread I started to document exactly how much weight was saved by cutting in the optional lightening holes in that doubler. My particular weight savings was slightly increased over the plans callout because I very slightly increased the diameter of two of the middle holes in the pattern. BTW, I used the tried and true fly cutter.
http://www.vansairforce.com/community/showthread.php?t=2445
 
Mhead said:
For those of you that have taken the time to cut the lightening holes, what is the weight saved for your model RV and would you do it again based on the time, effort, and slight chance of an emergency room visit?
Click to expand...

It's maybe 0.1 lbs. If it weren't all the way at the back end of the airplane, I might not have bothered. So far, though, I think I cut every optional lightening hole I've encountered...and then more than made up for it by adding all sorts of not-in-the-kit stuff!

I clamped the heck out of the part, and was reasonably confident I'd emerge unscathed.
 
Thanks muchly!

I appreciate the excellent suggestions and comments.

I just ordered a fly cutter from ATS, so I'm going with the cheapest solution first.

Duly noted are cautions re safety. I've got a full face shield, gloves, body armor (not really), a first aid kit, and maybe I'll put 911 in my speed dialer.

As a sidebar, I have little option other than to cut every possible lightening hole. I have some serious "mass" issues ahead. I've been priming everything (no such thing as a "light" coat with the rattle cans I've been using), I plan a CS prop, and I have this odd passion for servos, switches, and every conceivable avionics gadget.

Regards all - - Tom from Sacramento
 
Fly Cutter, hole punches and hole saws

I used them all in the order shown above. I thought the hole saws from the local hardware store were the best. One caution - don't even think that after the hole is cut out that you can go back in there with the hole saw and clean up the edges. Once you loose the centering function provided by small center locating drill it will eat surface material outside the hole. This can be especially disturbing when you are cutting a hole for a new instrument in your completed airplane. The MRB may disposition use as is but the pain remains.

Bob Axsom
 
hand flycutter

I have no idea why Vans instructions dis hand drill fly cutters. Mine work perfectly. The only difficulty is finding hand drills. They turn up in garage sales.
 
Mhead said:
For those of you that have taken the time to cut the lightening holes, what is the weight saved for your model RV and would you do it again based on the time, effort, and slight chance of an emergency room visit?
Click to expand...

I did not cut the VS lightening holes. I recently weighed my 9A which is equipped with an 0-320 and Hartzell CS. The c of g calculations work out pretty good. However, I am a relatively light pilot at 76 kg and if anything, I would actually prefer a little extra weight in the tail.

Fin 9A
 
RE:Flycutter Worked for me

Captain Sacto said:


Question for the experts...

The rear spar for the vertical stab on the 7A has an eighth inch thick doubler that, according to the drawings, permits optional lightening holes. Two of the holes are 2" dia, and 5 are 1.5" dia.

It appears as though I have two options if I want to cut these lightening holes. I can buy the Rotabroach cutters from the good folks at Avery for $ 175; or, I can get an adjustable circle (fly) cutter from STS for $13.95.

My question is... do the Rotabroach cutters perform in a sufficiently superior manner to justify the >10X cost?

Any and all comments and suggestions welcome.

Thanks in advance! - - Tom from Sacramento
Click to expand...

Made that first 3 1/8 hole in the panel today for the Trio EZ Pilot instal. I had used the flycutter in the past with some success.....but...Dan C. got me thinking.......The punch $$$$$$$$$$$$$$ tools do look great for the job. But having droped mucho grande denaro on stuff this past week I decided i would give the fly a try.

1. Measured the spot to have the hole about a zellion times. 2. Drilled an 1/8 starter hole and increased it to 1/4". 3. Installed the flycutter in my drill press. Put the panel on a wood panel sized to the instrument panel. 4. Clamped the wood/panel to the drill press base and adjusted until the fly center bit lined up perfectly with the 1/4 inch hole in the panel. 5. Set the diameter of the flycutter to cut the 3 1/8" hole and rechecked it about a zellion time. 6. Before turning the press on I lowered the flycutter to the panel and slowly turned the drill chuck with my hand a number of revolution to both begin the cut and to check for accuracy. 7. Double checked to make sure all of the set screws on the fly cutter were tight and that the drill press base was tight. "YES TO BOTH" 8. Turned on the drill press and slowly lowered the flycutter to the panel and slowly but surely added pressure. 9. Turned off the drill press and had to admire one fine flycut hole. :D

So my experience is........use the flycutter......save the $$$$$$$$$$

But I also think that new hole saws from Lowes Aero or Home Depot Aero would also work great. I think the key is to use a drill press and make sure the part being drilled is absolutly 100% clamped down!!!!!!!

Frank @SGU RV7A "NDY" PANEL/ELECTRICAL ....engine being built @ America's Aircraft Engines Inc.
 
Here's a neat tool to flare your lightening holes. Just add a little lubricant.

tool001if4.jpg


A form block with a hole is best for clamping. Pic is an example.

Ron Jennings of EAA 21 came up with this.
 
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I agree with Bob Axsom. I bought the cheap hole saws from Menards and they worked like a champ. Each diam blade cost me about $3. Aluminum is so soft, the hole saws intended for wood work fine, given the few holes we have to cut. I too won't go within 20' of a fly-cutter.:D

Terry
 
one extra step...

fstringham7a said:
.......

1. Measured the spot to have the hole about a zellion times.
2. Drilled an 1/8 starter hole and increased it to 1/4".
3. Installed the flycutter in my drill press. Put the panel on a wood panel sized to the instrument panel.
4. Clamped the wood/panel to the drill press base and adjusted until the fly center bit lined up perfectly with the 1/4 inch hole in the panel.
5. Set the diameter of the flycutter to cut the 3 1/8" hole and rechecked it about a zellion time.
6. Before turning the press on I lowered the flycutter to the panel and slowly turned the drill chuck with my hand a number of revolution to both begin the cut and to check for accuracy.
7. Double checked to make sure all of the set screws on the fly cutter were tight and that the drill press base was tight. "YES TO BOTH"
8. Turned on the drill press and slowly lowered the flycutter to the panel and slowly but surely added pressure.
9. Turned off the drill press and had to admire one fine flycut hole. :D

So my experience is........use the flycutter......save the $$$$$$$$$$

But I also think that new hole saws from Lowes Aero or Home Depot Aero would also work great. I think the key is to use a drill press and make sure the part being drilled is absolutely 100% clamped down!!!!!!!

Frank @SGU RV7A "NDY" PANEL/ELECTRICAL ....engine being built @ America's Aircraft Engines Inc.
Click to expand...

I also use the steps above, but found one extra item helped keep things aligned...

ADDED A NEW STEP

7 A. Remove the 1/4 inch drill from the fly cutter and replace it with a short length of smooth 1/4 rod.


This helps keep the fly cutter centered in the pilot hole... if the 1/4 inch drill bit is used, the drill bit can wallow out the hole and loose centering if your drill press is not perfect.

I may add (flame suit definitely on...:)...) that this method lets me use the fly cutter in thin materials used in a hand held slow turning cordless drill...[/flame suit] ...Such as making the tank filler hole...
 
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