Resin shrinkage!

[wm460]

I had a couple of goes at turning Resin and Timber Off cuts Bowls like Brendan Stemp video.

https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwj98o3op47OAhVIj5QKHVs2CHMQtwIIHTAA&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D9-81Cwk9lPg&usg=AFQjCNHx64iY1yB1-08ZDsNREtugAl35TA&sig2=IvL94Caw5sYN-ey5IjPuSQ

For some reason the resin shrunk away from the timber, why did it do this?
How can I stop this happening?

The first two photos are eucalyptus and last photo is mulga, the timber has been dead 10 years or so


http://i393.photobucket.com/albums/pp17/wm460-1/Casting/P7251474_zpsw8ct28ar.jpg (http://s393.photobucket.com/user/wm460-1/media/Casting/P7251474_zpsw8ct28ar.jpg.html)


http://i393.photobucket.com/albums/pp17/wm460-1/Casting/P7251473_zps8nt3felq.jpg (http://s393.photobucket.com/user/wm460-1/media/Casting/P7251473_zps8nt3felq.jpg.html)


http://i393.photobucket.com/albums/pp17/wm460-1/Casting/P7251471_zpse9pk7dem.jpg (http://s393.photobucket.com/user/wm460-1/media/Casting/P7251471_zpse9pk7dem.jpg.html)






This is the resin I used.


Clear Casting Resin - 4kg [C200036-M] - $68.05 : Adelaide Moulding & Casting Supplies (http://www.amcsupplies.com.au/index.php?main_page=product_info&cPath=2015_2016_2017&products_id=5216)

[GlennD]

Polyester resin has a shrinkage factor of about 7%. Epoxy, although more expensive has 0% shrinkage.

[Rod Gilbert]

Epoxy resin is the way to go far more stable, polyester moves way to much for this type of application.
Regards Rod.

[dai sensei]

Shrinkage of the polyester resin (PR) is a problem, but also pressure and how dry the timber is. For PR to stick well you should dry your timber to 0%MC (ie only achieved in oven, open air gets only 10-14%, dehydrator gets 4-6%), and cast under pressure until completely cured.

You can fix your casts however by flooding with thin CA (good stuff, not that $2 shop crap), clamping where required, then leave overnight.

[brendan stemp]

Yep, I can only agree with the others. Polyester resin is attractive because of its price compared to epoxy but there are several reasons why I don't use it. You now know one of the reasons; shrinkage. Time to switch to epoxy a leave the polyester for pan blanks.

I have also found, even epoxy doesn't stick well to some timbers. Extremely hard timbers can be problematic because the resin can't (for whatever reason) penetrate well enough into the timber to provide a good bond.

[wm460]

Thanks for your replies.

My shed is a toasting oven, after I cut it, it spent a couple of months sitting in my shed.
I live in the middle of a desert, It is extremely dry here.
The average rainfall is 12".
The average evaporation is 12'


Heating wood in the oven How long and at what temp?

This any good?

Clear Epoxy Resin 2 1 Ratio 6LTR UV Stabilised Free Freight | eBay (http://www.ebay.com.au/itm/Clear-Epoxy-Resin-2-1-ratio-6Ltr-UV-Stabilised-FREE-FREIGHT-/142065805651?hash=item2113c82953)

They have 2:1 also 5:1 which is better?

[dai sensei]

Heating wood in the oven How long and at what temp?

At 120C for as long as it takes to get no reduction in weight. ie weight it, dry for 1 hr, weigh again, dry it, weigh it again etc etc until you get at least 2 in a row the same - it will take some time, depends on size and type of wood.


This any good?

Clear Epoxy Resin 2 1 Ratio 6LTR UV Stabilised Free Freight | eBay (http://www.ebay.com.au/itm/Clear-Epoxy-Resin-2-1-ratio-6Ltr-UV-Stabilised-FREE-FREIGHT-/142065805651?hash=item2113c82953)

They have 2:1 also 5:1 which is better?

Sounds Ok but you do need to be careful when casting, too much in one pour with normal epoxies like this for surfboards etc can have issues with heat, but for pen blanks it's fine. I use Megapoxy HX, a low exothermic water thin clear casting epoxy, to ensure Ok with larger pours like pepper grinders and bowls with large % volumetric resin

[wm460]

Where do you get your Megapoxy HX from Neil, and what is the price.