Tuesday, July 31, 2012

How To (and not to) Make a Belly Pan

Meet Pete.
 Pete, Repete, and Threepete have been hanging around the shop the last few weeks and providing entertainment for hot and tired minds.  Pete came wandering in the shop today to check on our progress.

The underside is completely insulated, and most of the insulation for the body of the trailer has been measured and cut. 
 Three layers will go on the inside to keep it cool/warm as needed and because we had plenty of Prodex so we might as well use it.

All of the outside panels for the belly pan have been cut.  Once I figured out what I was doing, it was quite easy.  Keep in mind that my trailer is an early 60's model and does not have the dreaded banana wraps:
These are (I believe) formed pieces and can't be made out of flat sheet metal without some special tools.

All of pieces I needed started out as flat metal. If you need to make a new pan, here are the steps I took to get it made. 

1. decided to have the perimeter pieces separate from the pieces between the main rails instead of having two long sheets riveted in the middle (so if the tanks ever developed problems, it would be easy to get to them without doing another shell-off or having to cut the pan up.)
2. purchased 9 4'x8' sheets of .032 aluminum (at $37 each, which is probably on the low side) with white coating on one side and mill finish on the other (because it was much cheaper that way and the white coating adds another barrier between the steel frame and aluminum (steel + aluminum = RUST)).
3.  cut the old pan up into sections to use as templates for the new
4. traced the old pan onto the sheet metal, then used shears and snips to get the cuts needed
5. used a heavy duty cardboard tube to bend the metal where it needed to curve with the outriggers, putting my weight on the tube and pulling the edge of the metal up and over it in a rocking motion

1. Heavy-duty cardboard roll
2. Electric Metal Shears
3. Tin Snips

When attaching the curved corner pieces, I had a rather ugly go at it the first time:
(after removing it)
 I had even been warned that this could happen beforehand, but didn't know what caused it.  I had to stand back and have a good hard laugh at myself and what a disgusting mess I had just made.
The way to avoid this is to cut the tabs and bend them BEFORE attaching it to the channel, not trying to cut and bend, rivet, cut and bed, rivet etc...
Make sure the curve of your corner is the same as the plywood, drawing a nice, smooth line on the hidden side of the metal, in my case about 2.25" in from the edge.  Then make your cuts about every 4 inches or so being sure the end of the cut ends exactly at the line you drew.  Bend the metal tabs (I just used my hands) at a 90 degree angle, making the crease start and end exactly where the cuts end, thus making a smooth curve and not the snaggle-toothed look previously seen.

 
That's more like it!

The best advice I can give is to do it in small sections rather than two large metal sheets.  Even one sheet that went from the wheel to the back end (8 ft) was too long.  The curved part fit, but then the edge would be well below the channel near the wheel.  It is so much easier to do it one piece at a time.  Here are the approximate sections we divided the pan into if laid out:

If you are debating whether to make a new pan or not, and afraid that you don't have the necessary skills, don't let it scare you off.  I am a wussy girl with noodle arms who had never used metal shears before last week and I was able to pull it off.  So can you!

Getting it attached, however, is the pain-in-the-rear part...

Clecos (or Plinkos, as my hubby calls them) are great.  They are like being able to pin before sewing.  You will need one of these to use them. 


UPDATE:  Even after very carefully measuring and trying to make an exact replica of the original pan, things were still wonky with the curved corners.  I wound up cutting the tabs to make them just a little longer so the 90 degree angle in the pan would match up with the floor.  I then used a rubber mallet to pound the tabs against the plywood(instead of having two bends in them).  Now that I have entirely confused you, here is an equally murky diagram:

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