The real problem I see with the toggle bolts you show is they appear to
spread the load out onto the two edges of the plate that ends up under
the deck. This is not a flat bearing surface, and concentrates the load
on two relatively thin edges. This is not a good idea on a laminate
surface, as it will easily crush the laminate, even if you've
reinforced it with thickened, high-density filler, epoxy.

The load really needs to be spread out over a large surface area when
working with laminates. The toggle bolts can't do thisÑthe concentrate
the loading stresses onto an area smaller than that of a proper backing
washer...

Oh boy, just when I thought I can safely use the toggle bolt to secure
the bench on my boat...

Seem like I will have to somehow mount a metal plate underneath the
deck with a pre-drilled hole for each toggle bolt in order to spread
the load. This will mean that I need to cut open the inner skin of the
cored deck in order to insert that metal plate.

The other alternative was to weld the nuts on the metal plate before I
put the metal plate under the deck. But this would be very tricky to
line up the welded nuts if the metal plate with the mounting holes of
the bench seat. I guess I am better off using the toggle bolts but
with metal-plate and epoxy re-inforcement.

Oh well... This is getting more tricky than I thought.

Jay Chan


dog wrote:
The real problem I see with the toggle bolts you show is they appear to
spread the load out onto the two edges of the plate that ends up under
the deck. This is not a flat bearing surface, and concentrates the load
on two relatively thin edges. This is not a good idea on a laminate
surface, as it will easily crush the laminate, even if you've
reinforced it with thickened, high-density filler, epoxy.

The load really needs to be spread out over a large surface area when
working with laminates. The toggle bolts can't do thisÑthe concentrate
the loading stresses onto an area smaller than that of a proper backing
washer...

I find an easy way out. I can simply place the metal plate above the
inner skin of the cored deck, add two layers of fiberglass cloth over
the metal plate, and then place the thickened epoxy and the outer skin
over it -- kind of encapsulating the metal plate inside the deck. Then
I don't need to cut open the inner skin.

Jay Chan

wrote:
Oh boy, just when I thought I can safely use the toggle bolt to secure
the bench on my boat...

Seem like I will have to somehow mount a metal plate underneath the
deck with a pre-drilled hole for each toggle bolt in order to spread
the load. This will mean that I need to cut open the inner skin of the
cored deck in order to insert that metal plate.

The other alternative was to weld the nuts on the metal plate before I
put the metal plate under the deck. But this would be very tricky to
line up the welded nuts if the metal plate with the mounting holes of
the bench seat. I guess I am better off using the toggle bolts but
with metal-plate and epoxy re-inforcement.

Oh well... This is getting more tricky than I thought.

Jay Chan


dog wrote:
The real problem I see with the toggle bolts you show is they appear to
spread the load out onto the two edges of the plate that ends up under
the deck. This is not a flat bearing surface, and concentrates the load
on two relatively thin edges. This is not a good idea on a laminate
surface, as it will easily crush the laminate, even if you've
reinforced it with thickened, high-density filler, epoxy.

The load really needs to be spread out over a large surface area when
working with laminates. The toggle bolts can't do thisÑthe concentrate
the loading stresses onto an area smaller than that of a proper backing
washer...

This is probably a really bad idea for several reasons.

1) The thermal expansion coefficient of metal is far greater than that
of foam, wood or fiberglass. The heating and cooling cycles will cause
stress cracks and delamination.
2) The metal plate will cause hard edges along the laminate, which
will be natural stress points and probably fracture the laminate along
them.
3) Prepping the metal to accept the epoxy can be a pain, and it may
not bond well enough to prevent a void.
4) installing the plate, and having the holes in the proper position
is difficult to do without introducing additional voids into the area
of laminate directly under the high load area.
5) If it fails, it will likely tear a section of deck away that is the
size of the metal plate or slightly larger. Fun Fun Fun.

But it is your choice.

On 2006-06-26 12:32:42 -0400, said:

I find an easy way out. I can simply place the metal plate above the
inner skin of the cored deck, add two layers of fiberglass cloth over
the metal plate, and then place the thickened epoxy and the outer skin
over it -- kind of encapsulating the metal plate inside the deck. Then
I don't need to cut open the inner skin.

Jay Chan\

Good point about the metal will expand/contract more than the epoxy
will. I didn't think of that. But I can easily avoid this problem by
leaving the metal plate kind of free floating by only sticking the
middle section of the metal plate with epoxy, and leaving the rest of
the metal plate free floating -- similarly to the way woodworker takes
care of wood expansion not to crack the joint.

As of epoxy doesn't bond well to the metal plate, this may not be a
problem if I intend the metal plate to be free floating anyway. Please
note that metal plate will be pressed against a new layer of fiberglass
not directly against the foam core. Basically, I use the metal plate
as somekind of a washer to distribute the load; therefore, it being
free floating should not be a problem.

As of the metal plate will have a hard edge against the laminate, I
think we can round the edge to minimize the problem. Thanks for
pointing this out. But this should not be a major issue considering
the fact that the metal plate is there to distribute the load;
therefore, the load gets to the edge of the metal plate should be
minimum (at least that is what I think).

As of this will tear a large part of the deck out, I really don't think
there is any mounting method can get around this if the force is so
great that it can tear out the deck. I don't worry about this.

Thanks for your reply though.

Jay Chan

dog wrote:
This is probably a really bad idea for several reasons.

1) The thermal expansion coefficient of metal is far greater than that
of foam, wood or fiberglass. The heating and cooling cycles will cause
stress cracks and delamination.
2) The metal plate will cause hard edges along the laminate, which
will be natural stress points and probably fracture the laminate along
them.
3) Prepping the metal to accept the epoxy can be a pain, and it may
not bond well enough to prevent a void.
4) installing the plate, and having the holes in the proper position
is difficult to do without introducing additional voids into the area
of laminate directly under the high load area.
5) If it fails, it will likely tear a section of deck away that is the
size of the metal plate or slightly larger. Fun Fun Fun.

But it is your choice.

On 2006-06-26 12:32:42 -0400, said:

I find an easy way out. I can simply place the metal plate above the
inner skin of the cored deck, add two layers of fiberglass cloth over
the metal plate, and then place the thickened epoxy and the outer skin
over it -- kind of encapsulating the metal plate inside the deck. Then
I don't need to cut open the inner skin.

Jay Chan\

On Fri, 07 Jul 2006 04:41:35 GMT, dog wrote:

This is probably a really bad idea for several reasons.

1) The thermal expansion coefficient of metal is far greater than that
of foam, wood or fiberglass. The heating and cooling cycles will cause
stress cracks and delamination.

My data book gives linear thermal expansivities as follow:
glass 8 to 9 X 10-6 /degC
epoxy resin 39 X 10-6/degC
18/8 stainless 16 X 10-6 /degC
Aluminum 23 X 10-6/degC
Bronze 17 X 10-6/degC

Hardwood 10 X 10-6/degC on up....

Plastics 80 to 240 X 10-6/degC

Seems like they are all in the same ball park except the plastics in
general?

Brian Whatcott Altus OK

Interesting numbers. We typically use a glass reinforced epoxy which would
seem to put the composite's coefficient somewhere between 8e-6 and 39e-6.
The average is squarely on top of aluminum's 23e-6.

Roger (I'd put the reinforcement under the deck, myself)

http://home.insightbb.com/~derbyrm

"Brian Whatcott" wrote in message
...
On Fri, 07 Jul 2006 04:41:35 GMT, dog wrote:

This is probably a really bad idea for several reasons.

1) The thermal expansion coefficient of metal is far greater than that
of foam, wood or fiberglass. The heating and cooling cycles will cause
stress cracks and delamination.

My data book gives linear thermal expansivities as follow:
glass 8 to 9 X 10-6 /degC
epoxy resin 39 X 10-6/degC
18/8 stainless 16 X 10-6 /degC
Aluminum 23 X 10-6/degC
Bronze 17 X 10-6/degC

Hardwood 10 X 10-6/degC on up....

Plastics 80 to 240 X 10-6/degC

Seems like they are all in the same ball park except the plastics in
general?

Brian Whatcott Altus OK

Brian Whatcott wrote:
On Fri, 07 Jul 2006 04:41:35 GMT, dog wrote:

This is probably a really bad idea for several reasons.

1) The thermal expansion coefficient of metal is far greater than that
of foam, wood or fiberglass. The heating and cooling cycles will cause
stress cracks and delamination.

My data book gives linear thermal expansivities as follow:
glass 8 to 9 X 10-6 /degC
epoxy resin 39 X 10-6/degC
18/8 stainless 16 X 10-6 /degC
Aluminum 23 X 10-6/degC
Bronze 17 X 10-6/degC

Hardwood 10 X 10-6/degC on up....

Plastics 80 to 240 X 10-6/degC

Seems like they are all in the same ball park except the plastics in
general?

Brian Whatcott Altus OK

Honestly, I don't know how to read that thermal expansion coefficient
table. I assume you mean that the expansion rate of a 18/8 stainless
steel metal is close to epoxy resin, and we should not need to worry
about the difference in their expansion rate. I guess this may explain
the reason why people use epoxy as a bedding to secure metal fitting
onto the boat in addition to metal fasteners. Great! This means I can
embed the whole metal plate in epoxy instead of free-floating it, and I
will have one less thing to worry about. Thanks for the info.

Jay Chan