Pin holes in Alumilite Aargh!

[Russknan]

I've gotten MUCH better at casting Alumilite without bubbles, but there are often one, two, or four tiny holes - like pin pricks - that need filling when I'm done turning. I've used mostly medium CA, but have also tried thin and thick. I've blown out the spots with compressed air, dug a bit with a dental tool, wiped the blank with DNA, have slowed down the lathe when turning after, etc., but I still get a fair incidence of the fill popping right out when I go to turn the excess off. Any suggestions on improving my hit rate? Russ

 

[ladycop322]

Are you using a pressure pot?

 

[Indiana_Parrothead]

I have had the same problems, it just seems like the CA will not stick in the hole, or in some cases not fill it properly. It takes more time but what I have started doing is take the smallest drill bit I have (the smallest wire gauge) and make the hole a litttle bigger, you can turn the bit in your fingers. Then mix up a little Alumilite and fill it, if there are several I may put the whole blank back in the mold and pressure pot.

I have tried it without making the hole bigger but it seems to work better if I do. In the epoxy blanks I do I just use epoxy.

 

[Russknan]

Ladycop322, yup. Pressure pot all the way. Swiss cheese without it. Indiana_Parrothead, thanks. I've been on the verge of enlarging and trying to undercut. Thought of using CA again, but hadn't considered a dab of Alumilite. It's a pain, because you can spend more time - especially including "down" time - fixing these tiny nuisances than turning and finishing the whole blank. But I do love making inclusion and "waste wood" blanks! Russ

 

[Dick Mahany]

Russ, I can't help with the fix for repairing the holes, but I have a question. Are the pinholes near the junction of the wood and the alumilite? I had some that were a result of a just a teeny bit of moisture in the wood. Now I dry all of my waste wood blanks in the toaster oven and monitor their residual weight until stable, and no more pinholes. The only time I get pinholes in Alumilite is if I wait just a tad too long before putting it in the pressure pot.
Just a thought.

Oh one other thing.......I have had Alumilite separate from already cured Alumilite (trying a multi layer pour). It took a while but the bond failed on two samples. Probably okay for pinhole repair though.

 

[Russknan]

Dick, you may have diagnosed my problem. It COULD be that, because I usually have wood underneath these spots. I'll do more with the toaster oven, as you suggest. Curtis has talked about that being important when stabilizing, even if the wood has been around for awhile, and you think your shop is dry. The biggest problem I've solved so far was my original failure to really vigorously stir the Alumilite in an attempt not to induce air bubbles. That got me inconsistent mixing and all kinds of problems. The pressure pot seems to do a good job of resolving most any, except for some voids along the edge where the mix didn't get down well enough into air spaces in the blank. Thanks for your help! Russ

 

[1080Wayne]

I suspect the reason some of the CA pinhole fillings pop out is air trapped underneath . Use only the thinnest CA for filling . Poking around in the hole with a needle to dislodge the air after filling with thin CA sometimes helps . If enlarging the hole , I suspect making it cone shaped would be best . Pre- heating the blank might help , but I have never tried it .

 

[Russknan]

One more thing. When you fill the hole with CA, do you use accelerant, or do you just let it do its thing? I've tried both and still am not sure. Of course, if there are holes around the blank, one (I) can get impatient. Russ

 

[1080Wayne]

One more thing. When you fill the hole with CA, do you use accelerant, or do you just let it do its thing? I've tried both and still am not sure. Of course, if there are holes around the blank, one (I) can get impatient. Russ

I have done both , and am not sure either . I use accelerant with medium CA to fill larger voids around knots , and frequently end up with pinhole ones afterwards . I try to keep the pool of CA over the hole as small as possible to minimize sanding , and I have sometimes felt that it reduces pinhole formation as well ., although I see no reason why it should .