This posting concerns the fuel tank I installed for the Webasto diesel heater. The tank is made from spun aluminum and is so light you can pick it up with your pinky. With it installed under the van I'm worried about a possible puncture from road debris. Because of this I'm going to make a shield to protect the underside of the tank. I have no prior experience with spun aluminum fuel tanks so this might be overkill
but better safe than cold at night in the van while camping.
When I climbed under the van to get take some measurements I find that there is already a good scratch along the underside of the tank and I haven't taken it off-pavement yet.
The radius is about 4.5" to the outside of the tank brackets that the shield must fit over.
The length to fit over the tank is 31".
I'm a little chagrined to admit I had forgotten the formula for a circumference of the circle and had to look it up in my Pocket Ref. It's 2(pi)r. So 4.5 times a rounded down (pi) of 3 will give a half circle circumference of 13.5". Cut out a section of posterboard 31" long by 13.5" wide and do a test wrap around the tank.
Using a divider to lay out a circle with radius of 4.5" then cut out a bit more than a half circle from posterboard.
Tape the circle to the first posterboard section and use it to do a test fit on the tank.
I found that the posterboard mock up fit better with the tank brackets if the width was cut down to 12.5". Making easy changes is the beauty of posterboard.
Now to transfer the design onto sheet metal.
Start with two sheets of 4' x 5' 16 gauge steel.
Actually it started as one 4' x 10' sheet but I had it cut at the local steel supplier so it would fit inside Hal.
This is more than I need but it's cheaper to buy more than needed from the steel supplier than exactly what is needed from Lowe's. I'll be using the metal on several other projects.
Cut out a 12.5" x 31" rectangle. I've previously been cutting pieces off this 4' x 5' sheet.
Here's where it gets interesting. I've been thinking about this shield project for sometime and knew the next step would be difficult. I need to to bend the sheet metal into a semi-circle that will fit around the bottom of the tank. A machine shop would have a device that does bends like this but I don't. In my planning I came up with four different ways I could do the bending. Unfortunately planning to bend 16 gauge sheet metal and actually bending it are two different things. The 16 gauge is a lot tougher that the 22 gauge I bent just the other day. I could bend the 16 gauge but not into a semi-circle
I'm hiding my shame but not showing any pictures of various bending rigs I came up with since none of them worked. After at least a couple hours of fruitless effort I was reduced to literally just standing in the garage and looking around for something to try next. Here's what I came up with.
Draw parallel lines spaced one inch apart down the length of the shield metal. Number the lines and write the numbers on each end of the line.
Take a length of 1-1/2" x 1-1/2" x 1/8" steel angle that is longer than the shield. Place the angle so it's pointed downward. Balance the shield on the upright ends of the angle. Use the lines and numbers on the shield metal as a guide to keep the shield parallel to the angle steel underneath.
Since the distance between the two upturned steel angle edges is close to 2" it's easy, in this example, to look to the left of the shield and place line #1 above the closest upturned angle edge then look to the right and make sure line #1 is above the same edge. This will also place line #3 above the farther angle edge. Line #2 is now suspended halfway between the two angle edges.
Now get a ball-peen hammer and use the ball end to strike along the length of line #2.
After doing this the length of line #2 shift the shield one inch so that lines #2 and #4 are supported by the angle edges and #3 is suspended in the middle. Hammer along line #3. Repeat. Nothing is clamped into place. You have to keep adjusting the shield to keep it aligned after every couple hits.
Believe it or not it actually works.
Use the posterboard cutout to check that I'm getting the curvature correct.
Hammer away until I have a semi-circle
Do a test fit.
Needed to do some more hammering in the center to tighten up the fit.
Ready for the end pieces. I'm going to cheat a little. Set the shield on end and trace out the shape onto a piece of sheet metal.
Each end is different so be sure to label. I've added about 1.5" to the top of the semi-circle tracing.
Cut out the end pieces. I'm not worried about being extremely accurate with the cutting.
Here's the cheating part. If I was cutting the end pieces so that they would fit inside the semi-circle I'd have to been really careful with the tracing and cutting. This is much easier. Place the shield on the end piece then slide it upward, to the right in this picture, so that the end piece extends below the shield. This give a margin of error to the previous cuts.
I added the 1.5" to the top of the end piece so there is room to move the shield upward.
Tack weld into place then do the same to the other end.
Test fit on the van.
Weigh it for curiosities sake. 9 lbs.
Complete the end welds.
Use an angle grinder to remove the excess overhang from the end pieces.
Drill a 1" hole in each end for drainage.
Clean up the end holes with a round file.
Apply a couple coats of Rust Bullet rustproofing.
Here's what I'm going to use to hold the shield into place. They are industrial strength cable ties. I had these laying around.
The ties aren't long enough so I'll have to double them up.
Use electrical tape to hold down the loose end.
Place the cable ties over the tank being very careful to route them so they don't cross over the fuel or electrical line.
Place the shield into place and snug up the cable ties.
Cut off the excess from the ties.
Almost all done. One more step.
Put a Tiger in your tank!