Weird blank texture

[Hippie3180]

So, I tried my first Alumilite blanks, they looked good on the outside, drilled fine but the texture is weird on the inside. Chalky weird like. I measured carefully only perhaps a 100th difference between A and B. I mixed well and had plenty of time to mix my individual three colors. Under pressure 55lbs for 4 hours. We're thinking too much mica to the divided parts of Alumilite, is this a possibility?

Also, after demolding how long should you hold off before turning?

Also, I should say that I'm using Alumilite Clear Slow. I should also say that I'm making a relatively small batch, 4/ @ 3/4 x 8/34 rods. In a silicone mold.

 

[SabertoothBunny]

I usually put all my casted blanks under pressure overnight and pull them the next day. I have had no issues with demolding alumilite blanks after pressure, it is probably 12+ hours and I don't think it even has to sit that long.

 

[Hippie3180]

I usually put all my casted blanks under pressure overnight and pull them the next day. I have had no issues with demolding alumilite blanks after pressure, it is probably 12+ hours and I don't think it even has to sit that long.

They demold okay, look fine on the outside, drill fine, but don't hold threads and are porous looking chalky like when turning. I'm leaving them in four hours the recommended time.

 

[SabertoothBunny]

They demold okay, look fine on the outside, drill fine, but don't hold threads and are porous looking chalky like when turning. I'm leaving them in four hours the recommended time.

You are turning them too soon I think. I would suggest waiting at least 24 hours before trying to turn alumilite in order to allow it to fully set. It is a resin so like epoxy it takes time to fully set to reach optimal hardness for turning. I don't think alumilite is ideal for threading, there are other materials far better for that. Lots of threads on the forum discussing that.

 

[Hippie3180]

You are turning them too soon I think. I would suggest waiting at least 24 hours before trying to turn alumilite in order to allow it to fully set. It is a resin so like epoxy it takes time to fully set to reach optimal hardness for turning. I don't think alumilite is ideal for threading, there are other materials far better for that. Lots of threads on the forum discussing that.

I will wait longer, but the Alumilite blanks I buy and make fountains out of hold threads very well. I think it's something on out end.

 

[egnald]

I think SabertoothBunny is spot on. According to the Alumilite Clear Slow instructions (copy attached), demold time is 2 to 4 hours, but Full Cure is 5 to 7 days at room temperature or 16 hours at 150F.

I always wait a full day after demolding to turn them and it seem that they have cured enough to take a pretty good shine; however, to insure full hardness (and the best shine) they really do need to be fully cured. You might try the 16 hours at 150F to speed things up if you have a toaster oven to put them in after you demold.

Good Luck - Dave

PS I suppose you could do some kind of experiment by cutting pieces off of a blank after demolding, +1 day, +2 days, etc. and drill and tap to see the difference longer curing makes.

 

[Hippie3180]

I think SabertoothBunny is spot on. According to the Alumilite Clear Slow instructions (copy attached), demold time is 2 to 4 hours, but Full Cure is 5 to 7 days at room temperature or 16 hours at 150F.

I always wait a full day after demolding to turn them and it seem that they have cured enough to take a pretty good shine; however, to insure full hardness (and the best shine) they really do need to be fully cured. You might try the 16 hours at 150F to speed things up if you have a toaster oven to put them in after you demold.

Good Luck - Dave

PS I suppose you could do some kind of experiment by cutting pieces off of a blank after demolding, +1 day, +2 days, etc. and drill and tap to see the difference longer curing makes.

I was kind of hoping to hear from you. I did think it was 5-7 days, but wasn't sure. Seems like a long time to wait for pen blanks. If I had an old toaster oven I would speed them up, but I think I'll just wait the few days they recommend. I really hope it's as simple as needing to cure.

Thank you guys!

 

[Kenny Durrant]

My 2 cents worth is 4 hours under pressure. As soon as I take them out of the pot I demold. If I remember correctly the cure time is 72 hours. I have gotten by with 24 hours before turning but I normally like to wait the 3 days. Depending on who you talk to at Alumilite the ratio is 1:1 by weight and if you're heavy on the A side or not mixing properly that's when the resin turns white. I was told by one person that if your going to error go light on the A side. I mix small batches so I usually short the A side a few 10ths of a gram.

 

[hooked]

When I first started casting, I experienced a similar texture. For me, it ended up being that I was waiting too long when combining colors and putting them under pressure trying to avoid difficult colors from bleeding into each other. It turned out that there wasn't enough time for the initial vacuum pressure to pull out all of the bubbles, and I would end up with a "bubbly" core and tiny bubble divots throughout when turning.

Maybe check what your resin temperature is when you put them under pressure, and make sure you leave enough time for the vacuum to work before the resin hardens too much to release the bubbles.

 

[Hippie3180]

When I first started casting, I experienced a similar texture. For me, it ended up being that I was waiting too long when combining colors and putting them under pressure trying to avoid difficult colors from bleeding into each other. It turned out that there wasn't enough time for the initial vacuum pressure to pull out all of the bubbles, and I would end up with a "bubbly" core and tiny bubble divots throughout when turning.

Maybe check what your resin temperature is when you put them under pressure, and make sure you leave enough time for the vacuum to work before the resin hardens too much to release the bubbles.

This could be it, with the first batch we let the temperature get up there before we started pouring into the mold. The rods do seem to have minuscule bubbles especially on the ends. The next couple of batches I started pouring in the mid 90's. I'm giving them a few days to cure and then we'll see if they are better.

 

[NGLJ]

I have had no trouble with Alumilite clear and slow polyurethane as long as I get the mixture into a pressure pot in plenty of time to do the job of compressing any bubbles. Although the clear and slow says that you have 12 minutes, that is at a specified temperature. You don't want to be anywhere near that limit because things can happen very fast after that. Raise the temperature and you have less time. It is a chemical reaction which is sensitive to temperature. If more time is needed to mix in colors, mica etc., you can chill the chemicals before mixing (see the technical sheet that comes with the product). Upon thorough mixing the reaction will start but more slowly. Needless to say you have to do some experiments, since every situation will be unique.

I did small experimental batches to get some idea how things change. You need to do it for yourself since the environment in which you work will be specific to you. The challenge with chilling is that more bubbles tend to be entrained, since it is more viscous. So, there is a trade off to be made, more time vs more bubbles! Yes, it is a bit of a pain, but you will be rewarded by consistently good casting once you understand the product use in your environment.

Like others, I leave the pours overnight in a pressure pot. After demolding I leave them for another 24 hours before attempting to use them. Even though they will not be fully cured I have found that the casting is usable after that. If that doesn't work for you then leave for another 24 hours. Patience is a virtue, and successful woodworking/casting requires lots of that!

 

[Hippie3180]

I so appreciate all of the input from all of you and am taking it all into consideration. I think that hooked gave the most feasible input as to my issue. We were trying to achieve good color separation and thus probably let things get too far along for the pressure pot to do its job effectively. We are really in the experimental stage of all of this for sure, I'm pouring at a bit cooler temperature and I'm hoping our colors don't bleed too much, we'll see. The room we cast in tends to be a bit cool so our Alumilite allows us enough time to stir well, so I think we're good there.

Thanks again, for all your helpful input.