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Paul A. Franz, P.E.
Joined: 02 Dec 2008
Posts: 280
Location: Bellevue WA
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 Posted: Wed Dec 24, 2008 10:38 am Post subject: use of HDPE as ski base material |
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On Wed, December 24, 2008 9:23 am, Lynn Matteson wrote:
| Quote: |
Jim-
I just bought 3/16" HDPE for my temporary ski bottoms. When I've
proved the design, I may or may not go with the laminated ply bottoms.
The HDPE is half the cost of UHMW, but a little more friction, I'm
told. Have you heard of it?
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I'm very familiar with HDPE. I have used it for dredge pipelines. The stuff is very
tough and you can easily drag thousand foot sections across the frozen tundra. It is
even resilient to damage. When the eskimo kids shot holes in the 12" pipeline at Pt
Hope, they heal enough so that no repairs were needed.
It has a rather serious downfall though. You cannot glue anything to it. It can only
be welded. Even compression fittings are difficult because the stuff creeps and
relaxes.
The only way you're going to be able to use it on skis is with some kind of mechanical
attachment like screws. No glue will stick to it. Pipe sections are joined via a
welding process. The ends are first machined square then the two sections are squeezed
against a hot plate until they just start to melt, the hot plate is removed and the
two sections are jammed together.
I don't think you're going to like it much since you can't bond anything to it except
more HDPE and that has to be done quickly and the temperature varies for fusion
depending on the molecular length of the HDPE batch you've got. If you bend it, then
leave it alone, it'll just return to its original shape unless you get it hot in the
bend.
Since you're only planning it temporarily to get your design shape right, maybe screws
through it won't be much of a problem. Forming it is not too difficult, but it just
returns to it's original shape when the load is removed.
--
Paul A. Franz
Registration/Aircraft - N14UW/Merlin GT
Engine/Prop - Rotax 914/NSI CAP
Bellevue WA
425.241.1618 Cell
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_________________
Paul A. Franz, P.E.
Registration/Aircraft - N14UW/Merlin GT
Engine/Prop - Rotax 914/NSI CAP
Bellevue WA
425.241.1618 Cell
425.440.9505 Office |
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Lynn Matteson
Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan
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| Posted: Wed Dec 24, 2008 12:06 pm Post subject: use of HDPE as ski base material |
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Thanks for the heads up regarding bending it...I was going to try for
a slight bend up on the sides, but I'll forget about that. My method
of attachment...like my present skis...is with rivets, but this time
I'm going to go with flat head screws through rosette-welded tubes in
the 6 corner locations. I've had a few of the rivets pop (no pun
intended) loose before. Like now, the fronts will have as a cable
attachment, at least one AN-42 eye bolt to insure a through-the-
bottom attachment, which will also serve to bolt the bottom at that
location.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062, 596+ hrs
Sensenich 62x46
flying again after rebuild, and new Electroair direct-fire ignition
system;
also building a new pair of snow skis
On Dec 24, 2008, at 1:36 PM, Paul Franz - Merlin GT wrote:
| Quote: |
<paul(at)eucleides.com>
On Wed, December 24, 2008 9:23 am, Lynn Matteson wrote:
>
>
> Jim-
> I just bought 3/16" HDPE for my temporary ski bottoms. When I've
> proved the design, I may or may not go with the laminated ply
> bottoms.
> The HDPE is half the cost of UHMW, but a little more friction, I'm
> told. Have you heard of it?
I'm very familiar with HDPE. I have used it for dredge pipelines.
The stuff is very
tough and you can easily drag thousand foot sections across the
frozen tundra. It is
even resilient to damage. When the eskimo kids shot holes in the
12" pipeline at Pt
Hope, they heal enough so that no repairs were needed.
It has a rather serious downfall though. You cannot glue anything
to it. It can only
be welded. Even compression fittings are difficult because the
stuff creeps and
relaxes.
The only way you're going to be able to use it on skis is with some
kind of mechanical
attachment like screws. No glue will stick to it. Pipe sections are
joined via a
welding process. The ends are first machined square then the two
sections are squeezed
against a hot plate until they just start to melt, the hot plate is
removed and the
two sections are jammed together.
I don't think you're going to like it much since you can't bond
anything to it except
more HDPE and that has to be done quickly and the temperature
varies for fusion
depending on the molecular length of the HDPE batch you've got. If
you bend it, then
leave it alone, it'll just return to its original shape unless you
get it hot in the
bend.
Since you're only planning it temporarily to get your design shape
right, maybe screws
through it won't be much of a problem. Forming it is not too
difficult, but it just
returns to it's original shape when the load is removed.
--
Paul A. Franz
Registration/Aircraft - N14UW/Merlin GT
Engine/Prop - Rotax 914/NSI CAP
Bellevue WA
425.241.1618 Cell
|
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_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM |
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Wed Dec 24, 2008 1:44 pm Post subject: use of HDPE as ski base material |
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You should use something with an anvil lock like cherry max for that.
Noel
--
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_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
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Lynn Matteson
Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan
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| Posted: Wed Dec 24, 2008 2:44 pm Post subject: use of HDPE as ski base material |
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|
I think the ones that popped on my skis was due to the head being
pulled...like an umbrella in a windstorm. I used aluminum rivets
because I didn't want to use the much stronger steel, which would
have crushed the UHMW, I thought. But I used enough rivets to
compensate for loosing a few. I may try a few steel rivets in a test
to see how much the countersunk HDPE will crush.
I think that with the through-bolts, (machine screws actually), the
rivets will be merely holding the material flush, and not so much
subjected to side loads, etc.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062, 596+ hrs
Sensenich 62x46
flying again after rebuild, and new Electroair direct-fire ignition
system;
also building a new pair of snow skis
On Dec 24, 2008, at 4:43 PM, Noel Loveys wrote:
| Quote: |
You should use something with an anvil lock like cherry max for that.
Noel
|
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_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM |
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