Floor hatches flexing

[BusyBuilder]

And how do you make the horizontal cut that forms the lip before the hatch bit is removed? And bear in mind both lips (floor and hatch) have to be made of plywood.

You make one opening at (say) 150mm dia for top and 130mm for bottom assuming two pieces of ply laid one on top of the other ?? this should give you a lip all around of 10mm. I've done this for openings in floors for bathrooms.

Thickest ply I've seen and used is 18mm, either structural or hardwood Birch etc. if Hymer floors are 30mm then why not 18mm and 12mm bonded together ?

 

[peterc10]

You make one opening at (say) 150mm dia for top and 130mm for bottom assuming two pieces of ply laid one on top of the other ?? this should give you a lip all around of 10mm. I've done this for openings in floors for bathrooms.

Thickest ply I've seen and used is 18mm, either structural or hardwood Birch etc. if Hymer floors are 30mm then why not 18mm and 12mm bonded together ?

Hymer floors are not solid ply. They are composite structure with thin structural skins bonded to rigid insulation. That is the same for all (or most) walls, floors and roofs in modern motorhomes. And in any event the problem is that the hatch piece will not come out will it? That is because they are still joined by the bit of floor (be it insulation or ply) between the 150mm and 130mm. And in any event none of Hymer's hatches are circular. All are either rectangular or square. And we are talking about dimensions well in excess of 150mm for most of the hatches

 

[BusyBuilder]

You have heard of CNC machines ? and cutters can be as little as 2-3mm

 

[peterc10]

You have heard of CNC machines ? and cutters can be as little as 2-3mm

Yes of course I have heard of them. But they still will not be able to cut the horizontal cut needed to make the "shelf", as opposed to the vertical ones. And by the way the gap on my hatches are only about 1mm. If you can work out how to do then I am sure there will be plenty of manufacturers interested.

 

[BusyBuilder]

https://www.tooled-up.com/artwork/ProdPDF/TRENpage_120.pdf

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[peterc10]

https://www.tooled-up.com/artwork/ProdPDF/TRENpage_120.pdf

Yep aware of that. But it needs a plastic insert for it to work. And it only works in solid board floors, usually of dense heavy chipboard, which motorhomes do not have, thank goodness. And it leaves an awful looking wide gap. That is not what I would want in a floor which is supposed to be the finished product, rather than being covered by a floor finish. And, as I said, none of the Hymer access hatches are round and most are bigger than that. In other words it simply won't work.

But if you think it will then by all means use it on your motorhome to see if it does. No more for me on this subject I am afraid.

 

[BusyBuilder]

That was just an example, if you are that bothered why don't you go visit Hymer and see how they make them.

I don't see how difficult it can be to cut 2 sheets of ply to different sizes and stick them back together, with a finish on top. I've done it in bathrooms/wet rooms.

 

[peterc10]

That was just an example, if you are that bothered why don't you go visit Hymer and see how they make them.

I don't see how difficult it can be to cut 2 sheets of ply to different sizes and stick them back together, with a finish on top. I've done it in bathrooms/wet rooms.

The bloody floor isn't made of plywood. It is made of a composite construction.

 

[funflair]

Our floor is made of plywood, but as a manufacturer is interested in productivity they would not mess around with two bits of ply and sticking them back together and then the problem of cutting the hatch out with very fine tools so that it would go back in, anything is possible but not always practical.

Martin

 

[BusyBuilder]

Our 2012 B544 has ply floor with PU inset, how do you think they put PU in there ? if not as a composite

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[Theonlysue]

Obvious really, magic!

 

[WonkyBass]

Picked up three of the five new Hymer hatches yesterday. The construction is, perhaps not suprisingly, unchanged from the 3 1/2 year old originals. Lightweight ply with visible voids in some layers and some splintering on the lip.

I handed back one hatch as a ply cracked a little when I flexed the edge. These hatches need to take a full adult body weight.

I studied an Exsis 588 floor hatch on the dealer forecourt and it may be made of a different grade of plywood, albeit the same depth (c. 15mm). It might be identical but with the the voids smoothed and coloured with filler that matched the decorative dark grey top.

I conclude that our van was not fitted with poorly manufactured examples of floor hatches that gradually collapsed after 3 1/2 years. It is rather a faulty design and material specification issue. The narrow hatch 2 in my early picture would have collapsed completely soon.

 

[BusyBuilder]

As my vans out of warranty, I think I would remove the top vinyl layer and make my own hatches re applying the vinyl layer to match originals. I would probably use Birch ply. Though it is quite expensive, it is good quality furniture grade ply.

 

[WonkyBass]

The most damaged hatch is 17 mm deep 7 ply. This consists of the top 3 plies forming a 7mm deep layer and the bottom 4 plies forming a 10 mm layer that been routed to provide a 10 mm rebate on all 4 sides of the rectangular hatch measuring 120 mm x 330 mm.

The weight of a person is applied to the hatch and is bourne by the edges that rest on a similarly routed ledge in the surrounding floor.

"The principal function of the core layers is to increase the separation between the outer layers where the bending stresses are highest, thus increasing the panel's resistance to bending. As a result, thicker panels can span greater distances under the same loads. In bending, the maximum stress occurs in the outermost layers, one in tension, the other in compression. Bending stress decreases from the maximum at the face layers to nearly zero at the central layer."

(Softwood plywood for)" Subfloors are at least 3/4" (18 mm) thick, the thickness depending on the distance between floor joists. "
Source: Wikipedia

I think the maximum bending stresses within this hatch are in the upper ply 1 (compression) and the middle ply 3 (tension), not between the outer plies 1 and 7 as should be the case in good material design/usage. This allows excessive bending in the top, inadequately supported layer generating a sideways shearing force in the lower 4 plies at the glue boundaries and this further leads to progressive weakening of the hatch as more glue boundaries are torn apart laterally. As can be seen in the picture of the failed part.

Would a different plywood such a birch overcome a) the excessive flexing and b) the shearing forces in the centre of the composite whilst still retaining the dimensions of the piece? Is it too much to demand of any 17mm plywood or is it just the wrong plywood?

 

[BusyBuilder]

That looks to me like cheap structural ply generally used for shuttering and none load bearing situations, such as sarking on the roof of a house.

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[Steve and Denise]

yes it is a cheap ply with the center filled with a polystyrene slab the rest of the floor seems to be a PU filling with wood edges.

 

[WonkyBass]

yes it is a cheap ply with the center filled with a polystyrene slab the rest of the floor seems to be a PU filling with wood edges.

I do have one hatch in the kitchen over the grey waste tank with some type of foam filling the centre. This is a much deeper hatch and is not collapsing.

None of the collapsing floor hatches in our Hymer contain polystyrene or similar.

 

[CazPaul]

Why can't they use solid pieces of wood, I would be tempted to get some proper ones made by the local joiner, belt and braces, especially as they don't match the floor pattern. All you would need then is a bit of top lino the same as the existing floor. I have a couple of pieces of solid hardwood in the garage which would be ideal for 2 or 3 hatches. It would only take a joinery workshop a few minutes per hatch with the machines they have.
Messing about driving over 1000 miles to Bad Walsee, OK if you fancy a break, but they are just going to shove a bit more ply on, get it done properly.

 

[funflair]

Why can't they use solid pieces of wood, I would be tempted to get some proper ones made by the local joiner, belt and braces, especially as they don't match the floor pattern. All you would need then is a bit of top lino the same as the existing floor. I have a couple of pieces of solid hardwood in the garage which would be ideal for 2 or 3 hatches. It would only take a joinery workshop a few minutes per hatch with the machines they have.
Messing about driving over 1000 miles to Bad Walsee, OK if you fancy a break, but they are just going to shove a bit more ply on, get it done properly.

The trouble with solid wood is that it tends to bend and warp if you are not careful with it, just decent ply is all that is required, our van has big hatches in the walkway and after 12 years of use guess what? Yes they are fine.
If they were rubbish ply I would be tempted to drill some holes part through from underneath and squirt some epoxy resin into them, thereby increasing the interlaminar strength.

Martin

 

[CazPaul]

The trouble with solid wood is that it tends to bend and warp if you are not careful with it, just decent ply is all that is required, our van has big hatches in the walkway and after 12 years of use guess what? Yes they are fine.
If they were rubbish ply I would be tempted to drill some holes part through from underneath and squirt some epoxy resin into them, thereby increasing the interlaminar strength.

Martin

Yes it could but this hardwood is an inch thick, that wont warp or bend, a lick of oil top, bottom and sides every year, its a cheaper fix which I would be doing see how it goes, we also have a load of spare reclaimed floor board, its an inch and half thick, 120 year old quality, same thickness as a scaffold board, sure that could be utilised, can't see that warping ever, tongue and groove and glued with a strengthening piece underneath.

Cheap solid timber from the builders merchant will warp, its all crap quality, you need some decent solid seasoned wood.

How do they know decent ply is going to be used by Hymer, I would definitely do my own.

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[funflair]

Yes it could but this hardwood is an inch thick, that wont warp or bend, a lick of oil top, bottom and sides every year, its a cheaper fix which I would be doing see how it goes, we also have a load of spare reclaimed floor board, its an inch and half thick, 120 year old quality, same thickness as a scaffold board, sure that could be utilised, can't see that warping ever, tongue and groove and glued with a strengthening piece underneath.

How do they know decent ply is going to be used by Hymer, I would definitely do my own.

For your own fix it's fine for sure, I meant just not for the factory.

Martin

 

[Lenny HB]

yes it is a cheap ply with the center filled with a polystyrene slab the rest of the floor seems to be a PU filling with wood edges.

Just lifted the hatch over the tank and noticed I could see the filling via the slot where the handle is fitted, it's PU foam in mine.

 

[Steve and Denise]

Well the van is in getting some warranty work done including all the hatches I did take a look at the others as you say they are pu but the one that failed lots of white crumbs fell out of the split it looked very much like polystyrene on the floor but I may be wrong I can not see them using a different filling for one hatch as the van had been on display at some shows maybe that particular one has had a repair before ? That may explain why the small white bits when I prized it open to get the glue in.

The funniest thing the said was they will need to send them back to Hymer look out for a new van with secondhand hatch tops

 

[bellabee]

Just lifted the hatch over the tank and noticed I could see the filling via the slot where the handle is fitted, it's PU foam in mine.

Yes, I've had a look at ours, too. The ones in the main part of the van are all thick and sturdy. PU foam, I think. The ones in the bedroom area i.e. the steps leading up to the beds, are thinner and may be the same construction as those in the photo.
I took out the box thing in the bottom of the wardrobe under the bed, and the 'floor' there seems to have polystyrene in it. That's not a load-bearing floor, of course. It's just the base of the wardrobe, dividing it from the garage. I'm guessing that they've put that in to save weight, while using the sturdy stuff in the parts which come under the most stress.
Maybe we'll have to start launching ourselves at the beds, so as to avoid falling through the floor into the laundry basket at bedtime .

 

[WonkyBass]

Maybe we'll have to start launching ourselves at the beds, so as to avoid falling through the floor into the laundry basket at bedtime .

I've become very aware of what's underfoot moving around the van bedroom. As I got out of bed this morning to bump the Truma up to 3+ "breakfast temperature" I gingerly placed my foot on the edge of the platform, away from one of the hatches I had glued and clamped awaying replacements. No movement today.

In our layout these ply-only bedtoom floor hatches do not last more than 3 to 4 years of 80 to 100 nights a year usage by average weight people. As they say on the internet, your mileage may vary.

A couple of hatches are for plumping and electrical services access and are therefore above another continuous floor layer, rather than a tank, for example. The upper floor is elsewhere supported by cylindrical supports fastened by screws to the upper and lower floor. I am thinking about trying to fit similar supports under the hatches where practical. I think Hymer should be doing the same.

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