Problem with Banksia pod hybrid blank

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Cactus Jack

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Sep 22, 2019
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Hi
I have just had a go at turning a stabilised banksia pod cast in resin (opticast 2000 - polyurethane resin). While the colour combination is awful i decided to put a CA boiled linseed oil finish on it. While the finish was fine after the micromesh, i notice a day later that the pod appeared to have swollen and there are fine ridges (unevenness) around the resin pod interface areas - hard to see in the attached image. On occasions i have noticed a similar effect with cast pincones. Any insight into why this is happening would be greatly appreciated.
 

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Cactus Jack

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Hi Thanks for this,
love your pen. I will certainly strip it back and refinish. There is definitely a "crease" mark at the pod/resin interface. I was wondering if the resin shrunk a little as the blank was turned 3 days after casting?
 

Bats

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I can't offer any solutions, but I've run into similar belatedly-appearing ridges on segmented blanks - both with PVC/gift card layers (which I initially thought was a failure of the CA to bond with the plastic) and with veneer layers. Not enough to see, but enough to feel. It doesn't always happen, but it's frustrating when it does, and I have yet to figure out what's going on.
 

KenB259

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Hi Thanks for this,
love your pen. I will certainly strip it back and refinish. There is definitely a "crease" mark at the pod/resin interface. I was wondering if the resin shrunk a little as the blank was turned 3 days after casting?
Definitely not an expert on this subject, but I don’t think resin is fully cured in 3 days. I believe you shouldn’t turn a cast pen for at least 7 days after casting.
 

Cactus Jack

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Hi Ken B
Thanks for getting back to me. This would make sense as the resin may shrink slightly when fully cured. I have another half of the blank which i will let cure for another another week and see if that sorts the problem.
 

Dalecamino

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Hi Thanks for this,
love your pen. I will certainly strip it back and refinish. There is definitely a "crease" mark at the pod/resin interface. I was wondering if the resin shrunk a little as the blank was turned 3 days after casting?
Sand down the blank with 320 grit until you don't see any shiny spots, and reapply your CA. Are you wet sanding? Do so. I believe I'm seeing ridges in the resin areas as well as the pod areas. I have never heard of anything shrinking. I may be missing something.
 

Cactus Jack

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Hi Chuck
I will sand it down and refinish as suggested. Yes it was wet sanded. I have just looked up some technical sheets and alumilite can shrink by 0.005" and opticast 2000 can shrink by <0.2%. Maybe this is what causing the slight ridging at the interfaces - not withstanding any sanding issue i may have.:)
 

Dalecamino

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Hi Chuck
I will sand it down and refinish as suggested. Yes it was wet sanded. I have just looked up some technical sheets and alumilite can shrink by 0.005" and opticast 2000 can shrink by <0.2%. Maybe this is what causing the slight ridging at the interfaces - not withstanding any sanding issue i may have.:)
Hope you work it out Paul.
 

leehljp

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I want to go along with what Ken said as a possibility, and add another possibility here. 1. the polyurethane was not fully cured and 2, it may not have been fully stabilized. That is often what I have seen with green wood that was not 100% dried. Not being completely dried and/or not being fully stabilized will result in wood movement, which occurs overnight, particularly with humidity swings from day to day or from night to day.

For people not fully aware of what humidity can do - they can be in for a surprise what humidity swings do to wood. And what you experienced can be a direct result of humidity causing the edges, or center parts - of a banksia pod to swell in comparison to other parts.
 

Cactus Jack

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Sep 22, 2019
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Hi Hank
thanks for the info. In addition to sanding the one above down are retrying the finish. I will stabilise another one in new cactus juice (in case the old one was off - it may be older tha n1 yr) and use alumilite as the resin. Hopefully this will sort the issue.
Paul
 

Cactus Jack

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Update,
3 extra days to cure, returned using a skew, sanded and refinished in CA with micromesh. No sign of the crinkles after 2 day. Hard to say what sorted the problem, but i think it is primarily down to the extra cure time. Thanks for all the suggestions. Still doesnt help the colour combination - apple and watermelon!
Paul
 

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KenB259

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Glad it worked out. When I was a kid I had a Huffy bike that the color scheme graduated from green on one end to red on the other, I loved it and you pen reminds me of that bike. So I'm a fan of the colors in this blank.
 
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