Another casting question

[jkeithrussell]

I made my first PR blanks last week using Silmar 41 and liquid coloring agent from US Composites. I did not use a pressure pot or a second cure with heat. The blanks came out great (well, the 3rd try came out great), drilled and turned well, then basically melted on the ends by the bushings when I was sanding them. Is this what happens when you don't do the second cure with heat? I just picked up a toaster oven and will try cooking the next batch.

 

[DozerMite]

No that isn't what will happen without putting in an oven. You just got the blank too hot while sanding. Try wetsanding and use a lighter touch.

 

[ngeb528]

Yes, definitely wet-sand PR and use a light touch. I never use a toaster oven. I take the blank out of the mold and let it sit for a few hours. That's all the 'cure' it needs.

 

[mtgrizzly52]

That is exactly what happened to me last week, and I wet sand at every grit level, with a light touch. 240, 320, 400, and then 1500 - 12,000 MM. Even when you are careful, "stuff" happens.

Rick (mtgrizzly52)

 

[its_virgil]

I never post cure my blanks, at least not in an oven. I do set them outside all day in the texas sun and heat. I do not wet sand and I've never had what you describe happen to me. But, I too think you created too much heat when sanding. Also, dull tools will create more heat than sharp tools. If your blank had tints or dyes then they may not have been fully cured. The only time I've had PR not fully cure was when I used tints and dyes.
Do a good turn daily!
Don