Rob Gray :: ontheroad :: wothahellizat :: wot1 :: diaries :: issue-023


10 Jan 2000

Something of a milestone was passed today, the first sheet of cladding was installed. For those who don't believe we are cladding the motor home with checker plate here's a photo of the first sheet.

The first panel of checker plate is attached.

That's 2mm aluminium checker plate, it is fairly heavy and will look weird but it will take a hammering and that's what I want.

So how is this sheeting attached? Pop rivets?, tech screws?, Sikaflex? None of the above. It relies entirely on double-sided tape.

That's right, double-sided tape. But this is not your average hardware store mirror tape. It's 3M VHB (Very High Bond) and believe me, this stuff sticks. When I asked the 3M rep what I do if I make a mistake placing the sheet he simply said "You don't make mistakes".

Apparently the minute you press the sheet a 20% bond is created. At this point you need an air chisel to remove the sheet (destroying it in the process).

So the first thing we needed was a method of placing the sheet in exactly the right place. Bob and I came up with a solution, as follows...

Step 1. Shape the sheet as required then clamp it in position.

Step 2. Drill two or three pilot holes large enough to allow a pop rivet mandrel to be inserted.

Step 3. Remove the sheet and enlarge the holes in the body to a size appropriate for the pop rivet body.

Step 4. Insert pop rivets and hand pull so the rivet is firm, but don't pop. This will leave the mandrels sticking out from the body, thus creating some locating pins.

Step 5. Prepare the body for your VHB (I'll describe this later).

Step 6. Press the tape to the body and peel back the non-stick backing slightly from each strip of tape. Stick the backing to one side with masking tape.

Step 7. Hang the sheet on the mandrels ten or so mm off the tape.

Step 8. Starting at one end/side or the middle as appropriate for the situation, remove the backing entirely and press the sheet home.

Step 9. Now pop the rivets leaving them behind the sheet.

Step 10. Fill the small locating holes if you feel it's necessary.

There, that was simple wasn't it. Now what about preparing the body for the VHB tape.

If possible remove any paint, loose material etc then clean the areas to be taped with the appropriate 3M cleaner (I think you can use hydrocarbon thinners but I decided to use the official cleaner).

You should have a large supply of clean, lint-free rags for this job. The cleaning should take the form of a single stroke on each section of rag. Once you've wiped with an area of the rag it is dirty and should not be re-used. Also do not rub backwards and forwards as this simply moves the dirt from one place to another.

This should leave you a nice clean steel frame, something like this...

Now add the VHB tape...

Note that I haven't taped the cross member, I don't think it's necessary to tape everywhere and besides, VHB is very expensive (about $1.25 a foot). However this depends on the sheet size, larger sheets may need to be taped through the middle.

I plan to paint the entire interior with the Barrier 2000 insulating paint but if I'm not careful there will be some Achilles heals. The small areas behind the sheet that are not covered with tape, if these are not painted now I will never have another chance.

Now I add a bead of sealant to the cross member so there is no metal-to-metal contact to cause noise and possibly electrolysis.

Once the sheet is applied I run sealant around all the joints at the back and, eventually, paint the entire inside with Barrier 2000.

Note: Diary #24 has more info about using the VHB tape.

16 Jan 2000

Move over Eiffel tower, stand aside Sydney Harbour bridge, the Golden Gate?, child's play. Of the many steel marvels in this world the rear steps of my motor home must surely be the most astounding.

The steps took on a life of their own, taking a couple of weeks to complete (not full time though). Still, as the entry point to the lounge room is two metres from the ground the stairs have to be a fairly serious affair.

Here is the computer drawing of the stairs.

The hardest part was determining the locations of the pivot points for the top step and the link from there to the body. Here is some detail of that area.

The top step is fixed to the body. The second step is controlled by the top link (both shown in raised and lowered positions). Various other constraints caused the pitch between the top and first steps to be different to that of the rest of the steps, therefore the position of the top pivot point was not a no-brainer as it would have been if all steps where equal.

Once I got the top step working it was a fairly simple matter to hang the other seven parallel to the first.

There are eight steps in all, they collapse to a height of about 60mm when raised and stay parallel as they lower. This is so we have horizontal steps regardless of the distance the stairs get lowered due to different ground levels (Ok that's my excuse, really I just wanted the challenge, and besides they look great).

This is a semi-animated JPEG, place the mouse on a number to load the sequence images showing the steps in action. The first time may take a few seconds, after that it will be instant.

Originally I was going to used hydraulics to raise/lower the stairs but decided that a winch was easier and more appropriate.

The winch in its original location.

Above we see the original location of the winch, in the lounge room. The trouble was this particular winch (a Superwinch T1500) is unbelievably noisy and this location does not lend itself to much soundproofing as this would encroach even more on our lounge area. I moved it under the floor.

The winch after being moved to an under-floor location.

After re-installing the winch it worked well but due to a slight miscalculation in angles the cable bunched at one end of the spool.

The uneven winding of the cable causes the steps to drop unexpectantly.

At first I thought this wouldn't matter but I soon realised that it did.

As the cable wound onto the spool it built up about four layers of itself then the top layer or two "fell off" causing the steps to jerk downwards a few inches. Not a catastrophe but disconcerting and the resultant shock load may have caused problems in future.

Originally I figured to add another pulley to redirect the cable, then I reasoned that if the new pulley was spring loaded it would remove any sudden shocks from the system and help keep some tension on the cable when the steps were lowered.

The winch with its new spring and pulley (or "sheave" as they are more correctly called).

I installed the pulley and spring then realised that there was another benefit to this spring loading.

As the stairs raise and the geometry changes they effectively get heavier, this in turn causes the spring to extend and the cable to "walk" up the spool thus producing a very even winding.

The cable winds evenly onto the winch's spool.

Once raised a pinchweld seal is engaged and the load is taken off the winch by a cam lock.

As mentioned, the winch is incredibly noisy and will need to be boxed in and soundproofed but, all-in-all, the system seems to work well.