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Discussion Starter · #1 ·
So about 12 months ago I decided that I wanted to chop my wagon into a dual cab. I live in Cairns so RWV is right around the corner but they are fairly expensive (10k no tray) and I enjoy a challenge so I decided to do it myself. I work in IT so my previous metal working experience is essentially zero.

First step was to work out the line. The neighbor is a draftsman and was able to loan me a fancy laser level. It shoots out 3 laser lines, one line is a 200 degree arc from front to back, one is left to right and one is 360 degrees around the unit. I jacked the car up on all 4 corners and then used a spirit level I got the car as level as possible. I then positioned the laser roughly where I wanted the cut and bingo, I had a line all the way around the car. Here is the line I came up with.






You can see in this closeup that I basically took the line as close as I could to the seat belt mounts without actually chopping them up. This was for my engineer, he said that while you could move the seat belt mounts it was more trouble that it was worth.



If you do decide to chop your patrol I highly reccomend buying a profile gauge, I got mine from ebay and it was a very handy gadget.



So once I had a line I stripped everything out of back of the car and chopped it off. I thought I would need a 9" angle grinder but I ended up only using a 5". I actually liked the 5" a bit better cause it gave me some more control



Once it was cut up the first thing I did was make up some supports for the seat belt mounts. As I quickly discovered the seat belt mounts are tissue thin (less than a millimeter) and without the added reinforcement of the rear plate they just flop around all over the place. One of these plates was made for each side and then welded up both sides.




Next job was to re-cut the outer skin (and only the outer skin) to allow the tube I was going to use to fit in. I suppose if you just wanted to have a flat back you could skip this but I wanted to have rounded edges so I needed to cut the outer skin further back toward the front of the car by a little bit more than 1/2 the diameter of the tube. I was using 2" exhaust tube and Im pretty sure I needed to cut it back by 34mm (dont quote me on that). You can see the extra cut below with the tube in place to show what I mean.

 

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Discussion Starter · #2 ·
Once I had made the extra cut in the outside skin I could fit the curves I had made in. These are the same 2" 1.6mm wall exhaust pipe. I made the curves by cutting and bending by hand and then test fitting (lobster back bends). Once I had them right I welded them up.






Next I had to cut some of the roof supports back by the diameter of the tube. This would allow the outside of the tube to sit on my line. I also cut the roof outer skin back by the same 1/2 diameter of the tube plus a bit.



Once that was done I was able to fit the sides and top to finish off the frame for the new rear wall.



Next I had a frame that went in the back. The frame serves to add structural rigidity and also acts as a point for the 3 required child restrain points. The top of the frame basically sits level with the bottom of the windows that were in the back. I actually made this frame before I cut the car and had it ready to go. The top bar is 40x40x2mm and the uprights are 20x20x1.6. In hindsight I should have made the uprights 20x40 so that the front face was all level. This caused more work for me later when I went to fit the new interior wall.



After that I checked all my lines about 50 times to make sure everything was sitting where I wanted it to and then I started welding all the edges and the inside frame in. Im not a master welder by a very long shot but I think I did a reasonable job.



 

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Discussion Starter · #3 ·
Im kinda proud of the way the my bottom corners worked out, I was able to blend the existing metal into the bottom of the pipe and get the curves all right so it looks pretty good.



Here is where I got a little bit lazy with the camera and I blame that on the fact that I ran into trouble with welding the back wall on and didnt really want anyone to see the mess I was making of it. Having never done a chop before I was convinced that the back wall had to be welded around the entire perimeter. As any actual welders will be able to understand instantly this is going to cause massive issues in a piece of sheet metal as big as this.

The first time I welded the back wall in the amount of distortion I got was truly amazing. I should have taken photos to show what not to do but I didnt think of that at the time, I was too busy swearing.

I cut off the first attempt and came up with a new plan. I marked the uprights of my frame on the new sheet. Then I drilled holes in the sheet every 100mm on the uprights. I plug welded the sheet onto the uprights and tacked it to the 40x40 section of the inside frame. I then welded around the perimeter with silicon bronze which is the gold colored welds. Silicon bronze does not actually weld the two pieces together its actually a brazing process. It is a much cooler process than mig welding steel and it does not have the same pull that steel does. End result was much less distortion. I found out much later that places like RWV dont actually bother to weld the perimeter, they just tack it all together and then bog over the top.





Ive got more but it will have to wait till later.
 

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Glasshouse Bogan #1
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Nice work. RWV do a really nice chassis brace behind the cab over the rear diff would be worth copying if you want to brace your's. I tried to buy it them but they wouldn't sell to me.
 

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Discussion Starter · #10 ·
Alright so Ive welded in the rear wall. For anyone who wants to do this make sure you think about welding distortion before you strike a single arc. As i mentioned previously I could only generously be considered a hobby welder and distortion was one thing that bit me in the ass big time. And it wasnt just in the sheet for the rear wall, I tacked that sheet to the internal brace every 50mm along the top and the internal frame (40x40x2) bent like a banana. From side to side it was like 25mm out from where it should have been. I underestimated weld related distortion big time, learn from my mistake.

Next up I started working on my chassis brace. The RWV brace that I have seen is basically the same shape as the chassis rail and welded onto the outside. What I wanted was an integrated chassis brace and tray mounts. First step was to take measurements of both the top and bottom of the chassis at 10mm intervals from a fixed height. I took both sets of measurements (I did both rails at the same time) added each measurement together and divided by 2 to average it out. In practice both rails came out basically the same. I ended up with a bit of MDF board with a drawing of the rear chassis rails on it. I didnt take great photos but you can see it below.




I took all those measurements and fed them into autocad to get the same curve. I mucked around with a few ideas but eventually I got a design laser cut out of 3mm plate. The first two photos show the plate installed with 2 of the 3 support sections, there is another vertical support that sits at the very end. As you can see in the last two photos the leg of the chassis brace goes right down past the pivot point that the tray will cause in the chassis. Im not an engineer but I hope it will end up being strong enough.






Somewhere around this point my engineer came for a visit and told me that I would need both a vent in the back wall and also body mounts at the back of the cut. First one was easy, went down to the wreckers and grabbed a vent from some ute, came home and cut a hole.



Putting the body mounts in can be tomorrows installment. Turns out I didnt take as many photos of that as I thought.
 

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Discussion Starter · #11 ·
For anyone who is interested here is the CAD drawing that I used to get my chassis plates cut. The file fishplates1.dwg has 3 layers, supports which is the upright c chaped supports, constructed2 which is the constructed frame shape and "Full Pass Side 2". If you want to just use my curve data to make your own plates then use the data in "Full Pass Side 2" this is the top and bottom of the rail with as much accuracy as I could manage. The shape that I actually got laser cut, which is the shape on the contructed2 layer, is smaller by about 5mm than the actual chassis rail to give me somewhere to weld.
 

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Try and use the smallest, most flexible body mount you can to keep the engineer happy.

You really don't want one there is what I know. A friend of mine used to do conversions when he had his own shop, and tried both methods. He turned out the best conversions I have ever seen, so was no mug. He tells me that he saw a number of issues arise form extra body mounts at the end of the cab not allowing enough flex. The bloke who did my chop agreed.

My 2c anyway.
 

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Discussion Starter · #14 ·
Try and use the smallest, most flexible body mount you can to keep the engineer happy.

Interesting that you say that. My engineer claimed that the front and back body mounts on a patrol wagon were the stiffest and the middle were all soft.

His reasoning for putting them in at all was that there is about 500mm of horizontal distance between the new rear wall and the last set of factory body mounts. He was of the opinion that if you did a lot of corrugations that the whole rear section would be inclined to flex up and down and would eventually break something.

I ended up using a set of front body mounts because of their shape. I managed to fit the mounts on top of the chassis rail on either side of the cab. I'll get some photos of the setup when I get a chance.

At the end of the day I have to do what he wants to get it passed.
 

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What are you going to do about child restraint mounts now that you have cut yours off most people cut just behind them

Sent from my SM-G920I using Tapatalk
 

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Discussion Starter · #17 ·
What are you going to do about child restraint mounts now that you have cut yours off most people cut just behind them

Sent from my SM-G920I using Tapatalk

That internal frame has 3 child restraint points incorporated into the 40x40 bar along the top. The top bar sits about 30-40mm below the top of the seats.
 

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Discussion Starter · #20 ·
Try and use the smallest, most flexible body mount you can to keep the engineer happy.
This is what I have come up with, there is one of these on each side. The body mount is a front body mount style (an old one is shown). If you look at the bottom of the body you can see I have fabricated a 3mm plate that sits underneath where the mount pushes against the body. The body is only 0.9mm thick in this area so I wanted to spread the load out.
Obviously there are other parts of the body mount that go underneath that are not shown.


 
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