Tip: Jointing the Cowl Halves

szicree · #1 12-09-2007, 05:34 PM

Today I set the rivets that hold the hinges to the sides of my cowl and something unexpected happened. The two halves now fit too tightly together. I guess the clecos allowed things to move a bit so that the gap between halves was acceptable before rivetting, but once things were rivetted together, the gap all but closed up completely, and in some places was too tight to even get the hinge pin in. So how does one trim a few thousandths off of such an edge? If the hinge weren't there, a sanding block would make quick, straight work of it, but with the hinge there you really can't use a block. I tried, but all that happens is that skinny sharp edge removes the grit from the paper. What I really needed was something akin to a cabinet scraper. What finally worked very well was to attach some scrap hinge and pin to the area that needed timming. This would create a solid edge for me to run my mini scraper along. For a scraper, I used the side (not the edge) of a razor blade, with the actual blade running along the hinge. It worked just like a cabinet scraper and you could see the material coming off. Very quick and controllable.

DanH · #2 12-09-2007, 08:23 PM

And that folks, is craftsmanship.

Nice work Steve.

AllanC · #3 12-10-2007, 11:38 AM

My 2 cowl halves actually fit together pretty well, but I did have an issue (still have) in that I didn't check the thickness of the 2 adjoining halves. My upper cowl half is thicker at the hinge line than the lower with the consequence that there is a distinct shadow line on the lower cowl. I recommned that you check this before you rivet the hinges and shim to ensure that both are in the same plane. I'm upgrading to camlocks on the horizontals at this time, and will make sure I get it right at my second opportunity.

Allan

szicree · #4 12-10-2007, 11:44 AM

I'm not too worried about small differences in thickness since I will probably put a skim coat of micro over the whole thing and block sand it back.

terrykohler · #5 12-10-2007, 05:30 PM

If you can still get the pin into the hinges, assemble the upper and lower cowl. Take a fine hacksaw blade (without holder) and work this up and down the seam, keeping the blade parallel. Make your "cut" deep enough to feel the hinge with the blade. You'll end up with square edges, no waviness, and a uniform seam from the back end of the cowl to the front end.
Terry

Norman CYYJ · #6 12-28-2007, 02:20 PM

One of the ways that I sanded down the cowl edges along the hinge line before and after the hinge has been installed is to take a piece of hard wood about 11/2inches by 3/4 inch by 18inches. To this piece of wood hot glue a piece of #120 grit sand paper. This makes a long sanding block and you can get a very straight and even edge with no wavyness.

sf3543 · #7 12-28-2007, 09:51 PM

I have found that if you epoxy the hinges in place first, using clecos to hold everything together, and letting it set up with the entire cowl installed, you can countersink and rivet later and still maintain a perfect fit. The pins will work in the hinges better this way, too, since there will not be any hinge deformation during rivet squeezing.
Probably too late for you, but may help someone else.

sportpilot · #8 12-28-2007, 10:50 PM

Mark where it is hard thght, Use a file, careful not to cut into the hinge and work the edge down till you have the gap you want.

Nuisance · #9 12-30-2007, 05:53 AM

If you offset the hinge like this...

Then it is easy to sand the edge (of the other side), and the hinge keeps the light from leaking through between the halves.

az_gila · #10 12-30-2007, 07:51 AM

Quote:

Originally Posted by Nuisance

If you offset the hinge like this...
....
Then it is easy to sand the edge (of the other side), and the hinge keeps the light from leaking through between the halves.

Great idea John...

Is there a preferred cowl half for the extended hinge side that would make regular cowl installation easier?

gil A