Need help with Silmar 41

[navycop]

I bought a can of silmar 41 a couple weeks ago. I poured some blanks in Fred's molds. I let it dry 48 hrs. When I went to turn them they shattered like glass. Before I was using castin craft (with no problems) and adding 5 drops per oz. Is it different for this? I am using the catalyst that came with the can.

 

[IPD_Mr]

Mike many people recommend 3 drops per oz. This will typically leave the blank, just slightly tacky. We then put ours in a toaster oven at 125 for 30 minutes and it is good to go.

 

[corian king]

Hello Mike!
I have been using the silmar41 for about three years and have never had a problem.
I use between 5 and 7 drops to a blank.Good Luck!!

 

[its_virgil]

I use three drops per ounce but I really don't think five would make much difference. Explain what you mean by "shatter like glass." Were they a total loss? We're you clear casting? Using colors? Powders or liquid? Do a good turn daily!
Don

I bought a can of silmar 41 a couple weeks ago. I poured some blanks in Fred's molds. I let it dry 48 hrs. When I went to turn them they shattered like glass. Before I was using castin craft (with no problems) and adding 5 drops per oz. Is it different for this? I am using the catalyst that came with the can.

 

[navycop]

I use three drops per ounce but I really don't think five would make much difference. Explain what you mean by "shatter like glass." Were they a total loss? We're you clear casting? Using colors? Powders or liquid? Do a good turn daily!
Don

I guess it didn't "shatter like glass" I just had a blow out on the lathe. Was clear casting over a decal. I was using an old blank that I had color coated in castin' craft. Maybe the two were not compatable?

 

[Ed McDonnell]

Were you getting nice ribbons of shavings with almost no sound coming from the cut? Or were you getting dust / little chunks coming off with a scraping noise as you cut?

If you weren't getting ribbons with almost no sound then you might try some or all of:

-sharpen tools
-take light cuts. don't try and hog off the material. especially at the start if you have square edges.
-slow down your speed of cut (not the lathe, the speed you are moving the tool as you cut. Don't force the cut.)
-use a shearing cut (try a pull cut if you are using a spindle / bowl gouge)
-increase the lathe speed to the highest level you feel is safe (don't forget safety gear)

If you were getting nice ribbons with almost no sound and you still had a blow out, then I would suspect that the core blank you were casting may have had wax or something else on it that interfered with the Silmar 41 bond.

Silmar41 calls for 10 drops of catalyst per oz. But you can go plus or minus 50% (5 to 15 drops) to adjust for temperature (more on cold days less on hot days). At least that's what the instruction sheet packaged with my catalyst said. Read yours to be sure.

Good luck.

Ed

 

[Brooks803]

I've used anywhere from 3 to 7 drops per oz without that much of a radical difference. Was it very cold when you were turning? Cold PR can be more brittle than normal.

 

[jaeger]

I use three drops per ounce but I really don't think five would make much difference. Explain what you mean by "shatter like glass." Were they a total loss? We're you clear casting? Using colors? Powders or liquid? Do a good turn daily!
Don

I guess it didn't "shatter like glass" I just had a blow out on the lathe. Was clear casting over a decal. I was using an old blank that I had color coated in castin' craft. Maybe the two were not compatable?

I'll bet that your top coat with the simlar 41 was just to thin. If you had a tube with a blank using c/c and than added a decal and than more acrylic, simlar, it wouldn't matter what acrylic you were using, I think you just had to thin of a layer.

 

[Sylvanite]

I was using an old blank hat I had color coated in castin' craft. Maybe the two were not compatable?

Polyester Resin will form a chemical bond with already hardened PR, but only if the surface is still tacky. Once the surface has cured, the newly poured resin can only form a mechanical bond. PR won't adhere well to a smooth surface -- it needs some "tooth" to grip onto. So, if you are casting over already set PR, it would be best to scuff the surface a little with 400g sandpaper first.

If your blowout was a separation between layers of polyester resin, poor adhesion may have been a contributing factor.

I hope that helps,
Eric

 

[PenMan1]

Mike:
You didn't tell us the other ingredients in the blank. The reason I ask is because the over use of mica pearl will do more to make the blank brittle than 3 extra drops of MEKP.

I have found that more than 1/8 teaspoon of mica per ounce causes issues. Additionally I have found that "staged pours" (where one part is poured, then another when the previous pour has gelled) will also have very brittle properties if catalysed or cured at different rates.

For example, it is difficult for me to achieve excellent results by pouring half of a mold catalysed at 3 drops per ource, the pouring the second half an hour or so later with a different amount of catalyst. These blanks tend to crack or break at the "seam"