Thorp Air Command - T18.net

I am thinking about cutting a square inspection panel access plate in my fusalage under the stabilator. I realize a round access panel is an option, but I am curious about cutting a square one. How do you cut a straight line and what tool should be used to cut it out?

Ryan - two great additions to your library would be "Sportplane Construction Techniques - A Builders Handbook" and "The Sportplane Builder - Aircraft Construction Methods," both by Tony Bingelis.

The answer to your question really depends on what tools you have. I would
1) lay out the panel with a fine sharpie (bearing in mind the room you need for a doubler.)
2) drill generous sized holes in each corner, tangent to the lines, with a unibit
3) drill a hole inside the lines big enough to can get snips in
4) carefully snip out the majority of scrap, but no closer than 3/16 to the lines
5) carefully make a second pass no closer than 1/16 to the lines
6) carefully file out the remainder with a vixen file
7) just before you touch the lines, switch over to progressively finer files
finish off with fine sandpaper and/or scotchbright.

D

Pi' are squared ! A circle hole seems to be much simpler to do . If you have Muey' Grande hands then I suppose a "square hole" fits the bill . I used the Noah ARC-360 hole cutter to make my wing inspection holes on my S-18 . I also used to to make the cut out for the fuel tank sending unit . The tool is a bit expensive , but I believe in using the right tool for the job . Made a clean perfect hole with very little touch up . I do not have the inspection hole/plate below the stab. I may do it in the future , but right now I am still able to reach the bolts/nuts on the push pull tube and with a little "magic" I can R & R the bolts . When I lube the bushings on the push/pull tube I use a "long extension" that I attach to the red plastic tube that comes with the can of lube...point and shoot ! BOOM !

RB

yea, a round one is the easiest method for sure. Thanks for the tip Dick. I would have never thought of snips.....way to obvious.

You want to do the method that will distort the metal the least . If I was cutting a "square hole" I would use a Dremmel tool or a cut off tool after I drilled a corner radius using a step drill . File to the line or use an edge sander . As my Junior HS shop teacher use to say... " Mr. Brazell cut to the line , but don't cut the line away !" You know after 50 years those words still hold true ! Thank you Mr. Trone !

RB

One more thing I would add to the comments above is to drill radius holes in the corners. They will be less likely to crack out from the corner. Added plus is it makes a real clean look. Radius dia, is dependent on the size of the opening. Just my nickles worth, (inflation you know)
Skeet

Round hole NO! unless you want to remove the tail Ryan, geometry will tell you the you cannot get the backing plate in there if the hole is round. Mark the inspection panel size you want (preferably a rectangle around 5X7), drill a the corners with a step drill (.5 is good) then drill a foursome of .5 hole near the center, with a set of tin snips cut from each hole to the corners and then trim the rectangle out.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

I think if you have the top side removable access panels ( I like them ) you can install the round backing plate for the round access cover w/o taking the tail off . I plan to remove the tail during the next annual to inspect that aft bulkhead for "cracking." I may install an access panel (s) at that time...round ? Geometry ? Round holes ? Won't fit ? Pi' are squared ! Give that problem to a Navy Sailor and he will make it work ! BOOM !

RB

If you should decide to choose the easier round inspection hole, and it adequately meets your inspection/access needs, installing a backing plate is possible. After you have established the larger diameter of the backing plate, make a slice through the perimeter on one side. With a slight twist of the backing ring you can insert one cut edge into the access hole and then roll the remainder of the backing ring into the opening. It is even easier if you pre-drill and set the blind nuts before installing the backing ring into the interior.
I prefer to have as much access as reasonable so I only allow my backing plate to protrude into the access opening 1/8" on the perimeter, but make three bump outs to accommodate the nut plates.
I used a hole saw without a pilot drill to cut the perfectly round access plate. YMMV

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[b]Terry[/b]

Good point Dan! Although I personally think rectangles are easier

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

With the NOAH ARC-360 hole cutter I could cut a round wing access hole in less than 20 seconds ! No corner drilling , no snips , no filing . I used the same process for the backing plate . I have also used the HF large hole cutters (3" and larger) used for making holes in lumber/wood with good success in thin aluminum , however the teeth will not last long even at a slow speed . At $3.99 for a set I consider them throw away tools after 1 or 2 uses . BOOM !

RB

I stand corrected gents ... Cut that round hole!

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Lee: Thanks for coming over to the DARK SIDE ! "These are not the Droids you are looking for !"

RB

........options....and the experience of others to assist with guidance is good....at my age I don't have the luxury of re-inventing the wheel every time I come up against an obstacle. I made my fuel filler access door half round and half rectangle.
But, enough said, I must apologize for mis-directing this thread. It appears from the original question that "How to cut a square inspection panel" is the direction for this discussion. Some experts have already chimed in with excellent answers.
Well it is time for the annual condition inspection, no flying for a bit.

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[b]Terry[/b]

I used a fly cutter to cut the access hole for my fuel sender, but for some reason, I like the look of a square over a circle. So, I thought I would try a square access plate on the rear fuse. But, the fly cutter was so easy, its almost fool proof. The doubler plate was within arms reach for the fuel sender hole, so I would have to use Terry's suggestion for the rear fuse doubler.