First try at casting

[kovalcik]

I did my first casting, clear over a painted sierra tube, (3/4 x 3/4 x sierra tube length, ~1oz poly resin, 5 drops of hardener/oz). I poured it 2 nights ago and let it sit outside for the night (~60 degrees). In the morning it was still pretty soupy. After a day outside (~75 degrees) it was solid but tacky to the touch. I moved it inside for the night. This morning it felt good, no longer tacky.

How long should I wait before turning it? Does it need to cure?

Thanks for the help.

 

[Ed McDonnell]

Here's what I think:

If it is hard and no longer tacky then it is ready to turn.

Temps below 70F really slow the cure. Living in NH, 60 is going to be a faint memory for you before much longer.:biggrin: and outdoor curing isn't going to be an option for you.

When my winter temps plunge into the 50s overnight in the depths of winter, I put my filled molds in a container with a lid (cheap glad containers are fine as long as you don't spill resin in them). That way I can let them cure indoors in the shop without stinking out the house. I also have one I painted black that I can put out in the sun in the breeze and it keeps things nice and warm.

Alternatively you can buy a cheap toaster oven (Goodwill?) and cure your blanks in there at a low temp (~90 - ~125 works for me).

Ed

 

[kovalcik]

Thanks, I like the glad container idea. Have to try that for the next one.

 

[Ed McDonnell]

One other thing to consider is the amount of MEKP you are adding. Check the recommended amounts for your resin.

I use Silmar 41 and the recommended amount is 10 drops in one ounce at 80F. The amount of MEKP can be adjusted by up to 50% to adjust for ambient temperature. Higher temps = less MEKP. Lower temps = more MEKP. During the summer (upper 80s) I use 5 or 6 drops per ounce. During my winter (usually 70s) I use 10 drops per ounce. That works for me. The main thing is you don't want to add so much that you overheat the resin.

With your temps, you might want to use more MEKP than the 5 drops you used in your ounce of resin.

As you get into more complicated casting with mixing of colors, you'll need to take into account the effect of various additives as well as the amount of MEKP (adjusted for temp and volume) to get the type of color blend / separation you want. But that's a problem for another day.

Ed

 

[Janster]

I use 3 drops of MEKP per one ounce of Simlar 41. I stir the Simlar for 2 minutes in a container placed in a bowl of hot water. The heated water thins the Simlar and I then add the MEKP and stir an additional 2 minutes and then pour it into my pre-heated mold. I check occassionaly ( the mold ) for air bubble and if there are none I place the mold into my pre heated Toaster oven at 125° for 30 minutes to cure. Works for me! Good luck.......Jan

 

[its_virgil]

I do much the same: heat the resin in a hot water bath (not necessary during the hot summers here in TX), stir in 3 drops per ounce, pour into mold and place mold in a toaster oven and de-mold in 1 hour.
Do a good turn daily!
Don

I use 3 drops of MEKP per one ounce of Simlar 41. I stir the Simlar for 2 minutes in a container placed in a bowl of hot water. The heated water thins the Simlar and I then add the MEKP and stir an additional 2 minutes and then pour it into my pre-heated mold. I check occassionaly ( the mold ) for air bubble and if there are none I place the mold into my pre heated Toaster oven at 125° for 30 minutes to cure. Works for me! Good luck.......Jan