Birty Dastards Jeep Club
Tech Forum => Workshop => Topic started by: JamesH on July 20, 2014, 07:55:46 PM
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A thought has been building in my mind after chatting to a guy in France who had cut an access hatch in the floor of his Range Rover to give easy reach to the fuel pump.
This would be really helpful on the XJ but obviously is a unibody / monocoque design so cutting holes could be seen as reducing structural strength.
Anyone got any thoughts about the idea of cutting a hatch and how to go about doing it? I have matching sheet metal in the breaker that I could use for the cover but that's as far as my thinking has gone.
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Weld a frame to the floor before cutting the hole?
If the hole is only a foot square I am sure this would do.
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since the floor panels and structure flexes good, popping an access panel wont be too much of a problem. just make sure you not within the limits of structural points i.e suspension and such like, as the MOT man might take a dim view
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The area is braced well with all the reinforcing I've done underneath but a fairly small frame around the hole that connects to the rails either side underneath would be a good idea if it will fit with the tank.
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A circular hole lined up with the fuel pump or whatever you want to access is your best bet.
Weld a nice reinforcing ring to the underside of the bed about 0.6 to 0.8mm thick to match hole dia. and about 70mm dia. bigger than the hole with some M6 nuts welded to the bottom of that, but not spaced too far apart (say 30mm).
Bolts with washers to go through the cover plate from the top, same size as reinforcing ring with correct size spanner taped to the floor for convenience and you shouldnt have a problem.
No horrific stress risers because there are no sharp corners, just dont make it so strong the body cant flex as it should.
A cork or rubber gasket should keep any muck out.
Simples!
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Cut mine to access the pump qhen i had the lpg conversion done and no problems at all. Managed to change the pump in 10 mins when it went out from lifting the carpet to laying it down again:-)
(http://i1183.photobucket.com/albums/x463/Exdecuk/Jeep/20131231_124304_1.jpg) (http://s1183.photobucket.com/user/Exdecuk/media/Jeep/20131231_124304_1.jpg.html)
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Seeing that pic made me realise if I put a carpet or mat back in the boot then no one would even realise!
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Ok, a rectangular patch, but would be far kinder to the vehicle structure if it had 1" radii on the corners of the plate and cutout.
As a nation we made a great aircraft called the Comet, and then stuffed it up with tight corners on the cutouts.
Sorry, but fatigue will crack that cutout long before the steel worm does for it!
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Yep the good old comet proved that sharp corners are a stress point hence aircraft windows with rounded corners :icon_winkle:
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Rounded square will be easier with my tools than a proper circle
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Hippie techno...... Drill four holes with a 12mm cobalt and join the dots.......job done, round edges
:icon_super:
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Grinders don't like corners but I have some other tools gathering dust somewhere
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The patch is oblong but that doesnt mean the hole underneath is also :-) But regardless it wont ever crack during normal driving but flexing is another story.
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The rails on my unibody are reinforced with 3mm folded steel and the towbar and recovery bumper add structure so I'm happy that it will be ok with a bit of light reinforcing around the hole.
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I don't want to wind anybody up but this is what I do for a living, so maybe I am being paranoid, but if something is flexing then there are stresses being induced, end of story.
The easiest way to produce an aperture with radiused corners is with a 50mm hole saw and a jig saw but an artist with an angle grinder can still get damn close.
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How about two circles of 1/4" steel big hole of 8" in the Middle.
One piece above and one below the floor drill and bolt at 12, 3,6,9 o'clock.
Or just weld together for a nice Fat 1/2" sandwich type thing. Can't see that splitting the floor???
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The trouble with boiler plating the floor like that is that you change the load path.
Then when the body is forced into a flexed condition the stress loads are forced to take an alternate and possibly less desireable route to the stiffer sections of the structure.
This is why it is always best to keep the reinforcing and patch as close to the original strength of the structure as possible. Also use continuous welds around the reinforcing ring, close spot welds or flush rivets with a 2.5 to 3 D pitch.
Using a section of floor from a donor vehicle and similar thickness reinforcing would be the best route if possible.
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I have a donor vehicle and was planning to use that for the access panel. I was also thinking of 48mm hole saw for the corners of the opening based on what you said.
All of the in-built strengthening runs front to back and consists of the two main frame rails, two sub rails inside these and the pressed sections in the floor panel. I'm not going to get onto this for a while but plan to cut only the minimum out and then try and use a larger access panel that fixes into the sub rails.
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you cant turn a unibody into a ladder chassis.
no matter what sort of hole you put in the floor, the jeep floor from an xj will still twist and flex.
a reasonable radius on each corner is all you need and then cut the straights with a grinder. no need to go over the top but keep flipping the carpet to see how much of an effect the froading does in regards to the new hole. I would paint a 10mm edge all around the hole in white as this will show any crack quicker than a dark colour.
If a crack does appear then drill a 2mm hole at the end and that should be enough for a stress relief, this obviously will be dependant upon the type of of froading and flex is being seen
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you cant turn a unibody into a ladder chassis.
no matter what sort of hole you put in the floor, the jeep floor from an xj will still twist and flex.
a reasonable radius on each corner is all you need and then cut the straights with a grinder. no need to go over the top but keep flipping the carpet to see how much of an effect the froading does in regards to the new hole. I would paint a 10mm edge all around the hole in white as this will show any crack quicker than a dark colour.
If a crack does appear then drill a 2mm hole at the end and that should be enough for a stress relief, this obviously will be dependant upon the type of of froading and flex is being seen
I concur.
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Cut mine to access the pump qhen i had the lpg conversion done and no problems at all. Managed to change the pump in 10 mins when it went out from lifting the carpet to laying it down again:-)
(http://i1183.photobucket.com/albums/x463/Exdecuk/Jeep/20131231_124304_1.jpg) (http://s1183.photobucket.com/user/Exdecuk/media/Jeep/20131231_124304_1.jpg.html)
Is that a pic of one of the repair plates on the titanic?
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I you replace the structure and maintain your load path then you are not substantially affecting the unibody design.
If you did all this and then went driving without the cover plate fitted you wouldnt be surprised if it cracked and you'd deserve it too, but you wont.
This is no different to repairing a rusted floor on any car, except you have chosen where to put the hole as opposed to fate.
So now you just need some doublers at the front and rear that follow the shape of the opening.
Seam weld in place with some nuts on the underside and Fannys your aunt!
Just dont forget to take all reasonable steps to prevent rust on the heat affected zones because they will rot faster than the parent metal.
I'd use more of the donor floor again if possible for the doublers.
When it's finished it'll look like it was meant to be there!
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No carpet so always visible, I'll keep an eye on it.
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How about two circles of 1/4" steel big hole of 8" in the Middle.
One piece above and one below the floor drill and bolt at 12, 3,6,9 o'clock.
Or just weld together for a nice Fat 1/2" sandwich type thing. Can't see that splitting the floor???
Strangely enough, I am also an engineer who is heavily involved with stress calculations and applications within the automotive industry and to be honest this idea, given that the hole/hatch is relatively small, is not likely to have fatigue issues. With or without a tightly bolted down lid.
If the vehicle is uses constantly off road with serious suspension flex taking place, distortion could possibly be a factor, but I very much doubt it.
When pre release prototypes or very early production vehicles are road tested on public roads, they have numerous holes in numerous places to allow the many data collecting cables and devices, to run from the drivetrain, suspension and many other bits and pieces back into the various different storage and live data devices inside the cabin.
I haven't seen a stress crack yet, or even stressed paintwork!