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Access panel perimeter gap?

SabreFlyr

Well Known Member
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I'm cutting the top skin of my forward fuselage for my (OP-43) access panels. I used a step drill to cut near the corners of the first hole and a cutting wheel in a Dremel for the straight edges initially. I then switched to a milling bit with a steel ruler clamped in place to limit the bit and finished with a file. I'm at the point where the straight edges clear the panel by precious few thousandths. My question is, considering that there will eventually be paint on both skin and panel, how many thousandths are adequate? I thought I'd check one of the access panels on my wing where the panel and hole were cut by the factory. I was surprised to see that the gap is much closer than I would have expected, barely more than I've got already. However, the panels I'm cutting will be much more visible and I'm hoping they'll look decent after painting.

Any thoughts?
 

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1/16” (.064”) is a good rule of thumb for a paint gap.
 
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Most paint is only 4-5 thou thick. However, due to surface tension, paint tends to get pretty thick on sharp edges. I would probably go with 1/16" as mentioned above.
 
Much appreciated guys! I've got a little ways to go. Just got out my feeler gauges and I'm currently varying from .019" down to less than .0015" (my thinnest feeler gauge).

Freehanding the corners is going to be a slow, tedious process! Expecting to use the milling bit and then straight to a sheet of aluminum oxide paper. Any suggestions most welcome!
 
I would use a little drum sander in my dremel tool for the corners. The larger diameter the better. These cut slow enough that doing it freehand shouldn't be a problem.

My access panel kit is still on the shelf so I haven't started mine yet.
 
I did these a while back. I rough cut the hole with an air nibbler, then cleaned up the edges with a drum sander on a dremel with a straight edge clamped on the line to prevent excursions. Did the corners freehand with the same drum up to the line and then finished with a 1/2 round fine tooth vixen file and they came out ok.

Also, some food for thought;

I've seen quite a few of these that are puckered up between the screws. I think that what's happening is that people are laying down a bead of sealant to make a gasket per instructions, and then cranking down on the screws to try to bring the panels flush with the surrounding skin, causing them to pooch up between the screws. If you look at the relative material thicknesses, they would be flush with zero sealant or gasket material, but if you get anything else in between the nut plate rings and the panel, then, the panel can't help being high by the thickness of the gasket material.

With this in mind, I made additional .020 spacer rings that go between the inside of the skin and the nut plate rings that vans supplies in the kit to recess the rings a little more. In theory, this will let me have a .020 thickness of gasket material without deforming the cover panel.

I say in theory because I haven't got it all put together yet, so we'll see.
 
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I've seen quite a few of these that are puckered up between the screws. I think that what's happening is that people are laying down a bead of sealant to make a gasket per instructions, and then cranking down on the screws to try to bring the panels flush with the surrounding skin, causing them to pooch up between the screws. If you look at the relative material thicknesses, they would be flush with zero sealant or gasket material, but if you get anything else in between the nut plate rings and the panel, then, the panel can't help being high by the thickness of the gasket material.

With this in mind, I made additional .020 spacer rings that go between the inside of the skin and the nut plate rings that vans supplies in the kit to recess the rings a little more. In theory, this will let me have a .020 thickness of gasket material without deforming the cover panel.

I say in theory because I haven't got it all put together yet, so we'll see.

I would think that this issue would be resolved by the sealant that Van's suggests putting on the nut plate ring before riveting.

For those mentioning the Dremel sanding (grinding?) drums: I've always been a little unclear about the proper drums to use. The gray ones seem a bit soft and I suspect are less aggressive. The tan(?) ones seem a bit more aggressive but I don't believe too much so. Are those the right ones to use?
 
Vans suggests you make a panel gasket with a bead of pro seal with a piece of saran wrap on one side as a release agent. Once it cures, you are supposed to take the panel off and remove the plastic wrap and you're left with a perfect gasket. That's clever, but I feel like its got to be quite a bit thicker than a skim coat of pro seal around the nut plate ring.

All I know is that I've seen several of these that are puckered up above flush between the screws. My reasoning was that I could lower the nut plate ring a little and leave myself room to make a .020 gasket without puckering the edges of the panel.

I dunno, it makes sense to me, but I've been known to be wrong before.

Re the sanding drum, I just used the red ones because thats what I had on hand, but I went through 2 or 3 of them.
 
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In regard to the sanding drums I bought a kit of them on Ebay or Amazon, can't remember which. They have like 20 mandrels and 100 sanding drums that slide on. Most are fairly fine sandpaper 240ish. These are small sanding drums.
 
Looking at Dremel bits on their website, I think the right ones to use aren't the sanding drums that use a mandrel but the red(?) aluminum oxide grinding stones.

Terry, it's been a few days since I've looked at the access panel kit instructions but I'm thinking that Van's also had you put a bead of sealant between the skin and the access ring that would serve the purpose of spacing the ring somewhat below the skin.
 
The problem with the grinding stones is that they develop grooves which can then round your edges. That is why I prefer the little sanding drums for something like this. If you use a new grinding stone that may work fine, but just be aware.
 
In my experience the Dremel stones load up with galled aluminum very quickly and become unusable long before they are worn significantly.

It's too late to help me much since my build is done, but I'm curious if there is a "gouge" / trick to prevent this from happening.
 
In my experience the Dremel stones load up with galled aluminum very quickly and become unusable long before they are worn significantly.

It's too late to help me much since my build is done, but I'm curious if there is a "gouge" / trick to prevent this from happening.

I’ve been using a file card but with only very limited success.
 
Keeping your stones clean

A really slick way to keep dremel stones from loading up with aluminum is keep the ones that you plain to use for aluminum soaked with a light oil like “Tap Magic “ or “ PB Blaster “ and re-dip or re-wet them often during use . Just leave a few soaking in a pill bottle for the next use.
 
Is that 1/16 all the way around or 1/32 on each side?

I followed the suggestion as 1/16" all the way around (actually aimed for slightly less: chose .057" arbitrarily) and I'm very pleased with the result. However, and of course, this is without paint. No idea how it will look then.

Maule, sounds like a neat trick I'll have to try! Thanks!
 
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