Eliminating base warp....a guide.

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vinman
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Eliminating base warp....a guide.

Post by vinman »

Short story is I’ve been building skis for a decade now. Over the years I’ve had issues with base warp. Much of which was solved early on. However intermittently this creeps back in. Below you’ll see what I’ve done to solve this issue in my process. This info is scattered about in the text of this site so I decided to put my thoughts in one spot.

1. Warm you base material. UHMWPE base has a “grain” and a thermal memory to how it was rolled from the extruder. Use your heat blanket to warm the base to at least 120 deg F on a flat surface. Placing some flat weight on top like a piece of mdf also helps. Heat it for at least 15 min and allow it to cool to room temp before cutting. This will remove any thermal memory or curl from being on the roll and give you a better result. Allowing it to cool to room temp is also important so there can be no movement of the material after cutting.

2. Edge tension is a huge cause of base warp. It is absolutely imperative that your edges match your base. You should be able to hold your edges to your base with only a single clamp. If you are forcing your edge to match your base with anything more than fingertip pressure it is likely going to cause your base to warp some. If you have to force your edge into place you should be working on cleaning up your edge bending skills.

3. When using edge material that comes in a roll, you
Must take the memory out of the edge material. Straiten it manually until it sits flat on your work table and doesn’t flip on its side. You essentially have to take any bow out of the material. You can use a modified edge bender with a roller to do this. Pull it thru the rollers until the bend is taken out. Failing to take the stress out of the edge material will almost definitely cause your base to warp.

4 apply both edges at the same time to make sure any tension applied us balanced by having both edges in place.

This is my approach to base symmetry. If you have other tips please feel free to add them.
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mammuth
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Re: Eliminating base warp....a guide.

Post by mammuth »

Nice!

If you have edges from the roll you can build yourself a true machine, its simply a set of rolls (5 pair or more) where you feed the edge trough and it comes out straight.

You find this things for wires on the internet, to see how it works
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vinman
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Re: Eliminating base warp....a guide.

Post by vinman »

As an update to this. I have learned what I’m sure others may already have figured out. I can control the base shape with edge tension. If I use the finished core with sidewalls as a template I can clamp the base to this to help it main Shape or as I apply an edge. As long as I can see sidewall on either side of the base I know it is straight.

I can straighten any base out using this method. Pre-heating the base is not necessary if this method is used.

I now understand why I see builders like ON3P continue to use templates.

This only took me like 10 years to figure out…..🤣
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Jonrezz
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Re: Eliminating base warp....a guide.

Post by Jonrezz »

Nice guide! this was one of the more frustrating things to get right for me - turned out that I wasn't bending my edges evenly enough when I was doing it straight to the base - which resulted in a warped base even though it looked fine when I was bending.

what I like to do now is cut out the core and pour the sidewalls, then place the edges on top of the core with the edge tabs flush on the core/sidewall (edges are upside down essentially), then I bend the edges to match the sidewalls before even cutting the base. I find that the edges are much easier to bend when the part of the edge you grab with the nippers is face up not face down. then I'll cut out the base, flip the edges onto it, and its just fine adjustments to get the edges just right after that.
gozaimaas
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Re: Eliminating base warp....a guide.

Post by gozaimaas »

Base material grows and shrinks with temp changes and edge does not to the same degree, so don't glue your edges on until the very last minute before you start the lay up and make sure the lay up surfaces are all at the same temp. Placing your base on a cold aluminium cassette will shrink the base which can lead to edges popping off.
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