Rebuilding Plastic RV Hatch

[bajajoaquin]

My Callen shell has a big (25" square) plastic vent/hatch on the roof above the cabover section. It sounds great: lots of ventilation, and an escape route if it's needed. But, in practice, it's been a problem. Sitting at the front of the camper, it's in a low-pressure zone, and keeps getting sucked open. I've replaced it twice, and f----d with it countless times. It finally blew off again in the last set of storms to come through here. And then it rained.

So, I need to fix it, and I'm tired of fixing it over and over again. My solution, confirmed by another post I saw here, was to fab a new hatch out of steel, so I never have to deal with it again. I have a bunch of the equipment, some random steel lying around, and a local steel supplier for the other stuff I need. The only problem is that my sheet metal brake only works up to 24" and, well, I'm not very good at metal fab!

But why let that stop me?

My original plan was to mimic the original shape, kind of a really flattened diamond. I'd put a crease in each triangle, and then spot weld them together, sealing the seam with some sort of silicon goo. But I had to stop that plan when I realized my brake was an inch and a half too small.



So my plan became to make some ribs with a nice curve in them, lay the sheet metal on top, and spot weld them in place.

My materials consist of some 10-ga sheet metal I picked up as scrap years ago, that was in 7"X8' strips, some 1/4" X 1" strap, and a sheet of 20-ga cold roll that I picked up.

First step: make the template for the ribs. In order to do this, I grabbed a thin sheet of arauco I had lying around, and used it as a bender board to draw out my curve.


After cutting, that gives me my rib template:

 

[bajajoaquin]

Next step was to cut out my ribs on my bandsaw. I bought a cheap used 4x6 saw a while back. And, although it doesn't cut exactly square, it serves my purposes.


And... repeat.



From there, I cut a couple sections of the 1" flat bar, and laid them out on a sheet of plywood (my metal welding table is.... you guessed it, 24" square). With my little brad nailer and some scrap wood, I set up a quick jig and tacked it into place.



Then, check for square...



And add the third rib, and weld it up all solid-like.

 

[bajajoaquin]

I'm going to have to cut away the center rib, in order to fit lip that the hatch will fit on, so I added some gussets to the center section.



Once the welds were all ground down, it was time to start on the sheet metal top. I got 20-ga, because I thought my hand shears would cut it, and I didn't want to go too thin, because I knew I had .035 flux core loaded in my welder. My shears said they would cut up to 18-ga, so I went at it. Unfortunately, "up to" doesn't mean "cuts well." I was having an issue with the metal not bending enough to clear the shears.


I didn't want to go and buy a set of offset shears (well, I kinda did), but then I remembered that I got a set of HF air shears a which also claimed to cut up to 20 ga.



After swapping an air line fitting from another air tool, they worked great. For about 3 seconds. The little 2.5 gal compressor I had was just not cutting it (no pun intended). So, off I go in the truck to my parents' place, where I reclaimed my 25-gal compressor. Now we're cooking with gas! It's a neat little tool, which cuts a 1/4" ribbon of steel real clean-like. When these wear out, I'm going to buy a real set.

 

[bajajoaquin]

I know this is pretty wordy, and lots of pictures for very little actual progress, but I have an ulterior motive: At the end of this post (which is where I have left the project for the day), I'm hoping that someone who is way better than me (that's a large population) will have some advice about my plan, and will offer unsolicited help!

So, with no sheet metal brake big enough, I decide to be a little creative. My first idea is to grab a section of 1" square tubing I had lying around, clamp it to a saw horse, and bash it with a 3-lb hammer.



No points for guessing it didn't work out well. I have a big vise (and an even bigger blacksmith's leg vise that I haven't set up yet), so I started looking around for something I could use that would keep me from marring the metal. I found some old bed frames. I love bed frames. You can get them for free, and it's medium-carbon steel, so it has some strength. I make random crap from bedframes all the time. I'm always threatening to make a gokart from bedframes. But that's another story.

I cut up 8" or so of frame to put in the vise as jaws.



Then put them in the vise.



Starting in the middle, I used a block of wood under the hammer this time, and got a pretty nice crease. I moved over to one side, repeated, then the other.



And that's where I am now. I'll fit one end over the hatch, then clamp it in place, mark my crease for the other end, and repeat. If I get lucky, the bend will be in the right place, and it will fit over my ribbed form. I cut the sheet metal a half-inch over on each side, so I'll cut out little triangles, bend them over on to the frame, and weld it all down.

Anyone have any bright ideas for makeshift brakes? I'm open to some suggestions on how to improve my process.

After this, I have to install the lip for the hatch to sit on, the little slider for the crank mechanism, and then fit the hinge (which is still attached to the camper side of the thing). I don't really know how I'll do this stuff, but I hope I can figure it out this week and weekend.

Otherwise, I'm not too proud to end this thread with a picture of a plywood plank bolted in place!

 

[Treenail]

Rather than bashing on cold steel, get out your torch and lay a little heat on it. I don't know if propane is hot enough but 'most anyone has a soldering torch.

Or, when I have a question I generally ask Google first:

http://tinyurl.com/7rcv3xz

have fun, so far so good!

Tom

 

[bajajoaquin]

Good idea. I think that the large sheet may be too much of a heat sink, though.

I've seen some of the home-made brakes, before, but I'm trying to avoid building a whole bunch of things before I build something. I did, however, come up with an idea last night: I'll clamp two 1X1 tubes to either side of the panel, then put that in the vise, then bend. That way, I can get a clean bend the entire length of the panel.

 

[86cj]

I don't have a break and have used the vice and wood block method, oak works well. To control size you could beat the metal over a big wood block the size of the hatch.
.
I have had one of those same hatches for over 20 years and am on my second plastic lid, mine has not had any issues with the mechanism. You are fixing the only downside to the hatch though, Security. A nice welded bracket to lock it from the inside would be good, if the racoon that tried to get in my hatch would have been a black bear he would have been in, my new plastic lid won.
.
I have really enjoyed the veiw over the years, waking up with dew on your bed is possible and not such a bad thing.

 

[Treenail]

Can you spot/tack the flat stock to the ribs to the frame pieces then use the heat from the spot welds to soften the flatstock and beat it into form?

Or..tack and heat with a torch?


Tom

 

[bajajoaquin]

Good ideas. I thought about tacking it in place and then bending, but I was worried that I wouldn't get a good edge. I have a MIG, but no real torch, other than a propane plumber's torch, so I was thinking that I might not get enough heat.

So I went with the 1" tubing idea. I clamped on the side that was bent, and marked where the next bend should be. From there, I clamped on the tube, and then put it in my vise. Hammered on it with a 3lb sledge through a block of wood, and came up with this, pretty nice, bend (also hammered my thumb once; that freaking hurt).



From there, I clamped it on, and found that I hadn't allowed sufficient room for the length of the bend. Oh, well, live and learn. But I was able to get it clamped into place to see that it fits well enough.



I marked the space where the sheet metal overlaps the frame on each end, and then trimmed. That little air shear works really well. At one point, the curls wrapped around in front of the shear while I was cutting, and it cut through both layers of 20 ga. Impressive for $20 air tools.



I put it on the frame again with clamps, and it seems to stretch over just fine. My wife had dinner ready, so I just left it clamped like that. I'll go and try to measure and make sure it's square tomorrow. I don't know what I'll do if it got warped out of square, but I'll figure something out.



After that, the next step is to put it up on the truck, and make sure it fits! It should, since I took the measurements of the old hatch, and then went oversize by a half inch. In order to check the fit, I think I'm going to have to tack it in a few places. After the test fit, I'll cut notches in the sides to get the edges to bend down flush on the frame, welding the whole way around. To avoid warping, I'll skip around and do opposite sides.

Then I'll weld in tabs for the rubber strips to mount on, then I'll install the crank runner. The old hatch broke away at the hinge mount, so I can grab it and use it for a template for holes. I have aluminum rivets, but I'm thinking that I want to go steel, or perhaps some stainless bolts with nylock nuts. I mean, at this point, why go underkill?

 

[bajajoaquin]

So not much progress over the weekend, since I had some family stuff to attend to.

After it sat clamped together for a while, I checked for square again, in case my bashing had warped it. Finding that it was square, I put on a few tack welds to hold it in place:



Once that was done, I used my had shears to cut little notches out of the sides so I could bend them around the arc of the frame. Turned out that my cross-peen forging hammer was perfect for getting the sheet metal to bend right around the frame in a tight radius. I still needed to clamp the metal in place so that it was in tight contact with the frame, but then it was a matter of doing some more tack welds.



Unfortunately, my 0.035" flux-core wire was still a little to big for the 20-ga material, and it was tough to get it on without burning it through. Kinda sucks, since I had bought heavier material than I would have if I was going to use 0.025 and gas, but that's what I get for not checking the chart before buying the steel. I made it work, though. I was able to focus most of the heat on the frame, which is about 10-ga, and just blip the torch up onto the 20-ga to get some fusion.

I'll switch out the wire tonight and hook up the tank, and finish welding the seam. I want it sealed before I paint.

 

[bajajoaquin]

Not much progress, but I did get the flux-core swapped out for solid wire, and got most of the panel stitched up. It was a bit of a challenge, since I had three different thicknesses of metal to run together, and my bending left a number of air gaps to try and fill.



I suspect that there will be a bit of grinding and hole-filling in my future. It is, however, on to the point where I will add the flanges for the rubber seals, and get it on, at least to cover the gaping hole in my roof. Then, mount the lift-mechanism track, seal, paint, and mount the hinge bracket, and Robert's your mother's brother.

Easy, right?