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Old 06-16-2019, 06:54 PM
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How to cut a cowl?

Iím nearly done with my 3DHS 106 Edge V2. One of the last things to do is cut the cowlings. Iíve cut dozens of cowls over the last 30 years and Iím not sure Iíve ever had one Iím happy with. My cuts never end up straight and then the holes get too big as I try to fix the uneven cut. Any tips and advice for not making a mess of my new cowling?
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Old 06-16-2019, 07:57 PM
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Quote:
Originally Posted by dshriver View Post
Iím nearly done with my 3DHS 106 Edge V2. One of the last things to do is cut the cowlings. Iíve cut dozens of cowls over the last 30 years and Iím not sure Iíve ever had one Iím happy with. My cuts never end up straight and then the holes get too big as I try to fix the uneven cut. Any tips and advice for not making a mess of my new cowling?
Laser......Google....R/C Cowl and Laser
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Old 06-16-2019, 08:20 PM
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I use the laser pointer trick to know where to cut. My issue is that my cuts are always terrible!
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Old 06-16-2019, 08:36 PM
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I lay down painters tape all over it, then draw my cut outs. I use the dremel to cut just short of my lines, then finish off sanding by hand till i hit the lines. The dremel can easily get away from you and it is hard to keep perfectly straight. Do your final sanding by hand.
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Old 06-16-2019, 08:40 PM
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What exactly are you cutting the cowl for?
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Old 06-16-2019, 08:42 PM
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Cooling and muffler exits.
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Old 06-16-2019, 09:07 PM
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I use the Dremel 562 tile cutting bit (https://www.dremel.com/en_US/product...le-cutting-bit). It cuts fiberglass well but as gapple12 said it can get away from you.
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Old 06-16-2019, 09:21 PM
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You can always use thick construction paper taped to the firewall, locate where you want to cut out and transfer it to the cowl.Just put the paper where the cowl will be when bolted up, the put the paper on the cowl. Pretty easy really.---Smitty
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Old 06-16-2019, 10:13 PM
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Quote:
Originally Posted by Harold Smith View Post
You can always use thick construction paper taped to the firewall, locate where you want to cut out and transfer it to the cowl.Just put the paper where the cowl will be when bolted up, the put the paper on the cowl. Pretty easy really.---Smitty
+1
Without the cowl installed......Tape manilla paper to your fuselage at the bottom F-1/Firewall then mark and cut (with exhaust installed) also your cooling air vent until satisfied with the holes, then install the cowl (exhaust removed) with the manilla still taped to the fuse....pull it over the bottom of the cowl and then use a felt pen to transfer the cuts to the cowl....remove paper. I use the dremel with 1/2" sanding drum for good control.
as Harold said it works very well.
RSnow
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Old 06-16-2019, 10:17 PM
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Tip,,, never cut the lines. Cut next to them and finish with sanding to the lines or in the direction you need to go.


I recently did something similar but in my case I needed to cut my cowl for my USRA Unlimited Ashley race plane intake scoop. Engine is a BBC 200 on nitro and a solid CF customized race 21x27 prop


I used regular packing tape over the area wanted the scoop hole to be. Applied a generous coat of plain ol mothers car wax and let it dry.


Applied a single layer of cloth and some west systems epoxy. When that cured I peeled it off the cowl.


With the scoop bolted up to the intake I used the 2 bottom cowl screws to hold my sheet of glass in place and laid that over the scoop and traced it out.


Cut the hole and then transferred that over to the cowl. Cut the hole in the cowl, Finished off by sanding the scoop to fit and glassed in the scoop,,, done.
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Old 06-16-2019, 11:02 PM
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SWEET!! Love to watch these monsters in the air!!!
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Old 06-17-2019, 10:49 AM
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Patience, and a steady hand. I don't use anything but a dremel and a sanding drum to cut my cowls. Mark your lines, cut close to them, but try not to overshoot. Also, move your dremel in the opposite direction that it wants to pull so that you can have more even pressure when you move it.
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Old 06-17-2019, 11:35 AM
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I do a rough cut inside the lines with a dremel cut off disk then finish the cutout with a fine sanding drum. I always direct all cutting dust into a nearby vacuum hose so it doesn't get into the surrounding air. Nobody needs to breath fiberglass dust! I finish the cutouts by dressing the edges with 320 - 400 sandpaper to radius and smooth the cut edges.
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Old 06-17-2019, 02:27 PM
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Yep. I do much of the above. I make a template with the holes of the area want cut with everything installed(except the cowling) , with the template big enough to tack/tape to the fuselage. I tack/tape the template to the fuselage, then fold it back on the fuselage(don't remove it, as that's your target), and remove everything that interfered with the cowl seating where it should be.

Then I tape the cowling to the fuselage, in the position I want it(being mindful of spinner and other important relationships.. if your cowl has a spinner ring, put the spinner backplate on the engine so you know where to place the cowl... tape the cowl on, then lay the templates back in place(they should have only been folded back remember, so the overall template should lay back in the same place it was when you made it). Then I'll trace inside the template on the cowl for a reasonably close cut(maybe 1/4"... or a bit more).... then like most everyone else, I'll use a cut-off wheel and make a rough cut out well inside my marks... and finish it off with a fine Dremel drum sander. After a few final fittings it's usually very decent.. but bottom line the overall census says use a Dremel.

It's a bit easier with an unpainted cowling, but with a bit of practice, you can have a perfect cut out. Good luck with it.
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