White spots with segmented blank

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M

musicman

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Jun 24, 2019
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15
Location
Texas
Hey Penturners,
I have recently started to make segmented blanks out of acrylic (alumilite) and I noticed white spots where I join the two pieces together. I'm using Mercury EPOXY 15 minute to glue them together. The epoxy is about nine months old. I was wondering if anybody can share their opinion on the cause of these white spots.
20200602_083701.jpg
 
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Which Alumilite resin? Alumilite is a brand and not a product. Alumilite makes both urethane (clear and clear slow) and epoxy (amazing clear cast) resins. And, as an aside "Acrylic" is a type of resin and not a generic term for all resins or plastics. Yes, I have used the word acrylic incorrectly to describe most any resin. Just offering a little information and not being critical.

To answer your question, my opinion is the white is sanding dust in the join between the two pieces but I can't tell if the picture is of a turned and sanded blank or a blank just out of the mold. Alumilite urethane resins will react with CA glue with similar results but you mentioned you used an epoxy glue. Maybe someone will have a better answer.
Do a good turn daily!
Don
 
I think Pete's suggestion is worth looking into.

Looks like the segmentation was done by gluing the pieces end-to-end. . Were the mating pieces cut on a saw ?

If so, the mating ends ... were their faces "trued-up" on the lathe before gluing ? . They really should be, because surfaces left from sawing are never exactly flat/smooth. . So there can be small gaps/irregularities that fill with glue.
 
Thank you for giving me your opinions. To give you all more information, I used Alumilite clear slow set. The picture is after I turned and sanded. Before I glued them together, I drilled the holes in each blank separately using the lathe. I cut them on a benchtop bandsaw. Then I sanded the ends by hand and used denatured alcohol to clean it and let it dry. I then epoxy the pieces together around the tube. I clamped it together and let it sat for a few days.
 
To add one more thing. I used this same epoxy on a wooden blank and as I was finishing turning it to size, I noticed some white speckles or small white dots. I believe the wood blank was blood wood. I was able to correct it by scraping it out with a tac.
 
After cutting, I would recommend that you true up the two ends that will be glued together.

You can do that in the same way that you square up any blank ends ... turn on the lathe and use your usual lathe tool on the end.
A barrel trimmer might also work.

Cutting on the band saw will leave you with ends that are not smooth enough for gluing together.

Some people actually insert a very thin metal or plastic layer between the two pieces. . Sometimes this can "hide" irregularities.

Those thin layers are often called "accent pieces".
 
My opinion is the epoxy itself. Is that clear epoxy or does it dry white?? I suggest you mix some up and place on a clear plastic something or even a piece of glass. Yes when cutting with a bandsaw the cut lines are not always the smoothest unless you have a finely tuned saw. You get away with more when using woods but with a hard surface such as acrylics or metals, not so much. What I do many times is add some color to the epoxy by either using epoxy dyes or just plain model paints close to one of the main colors of the blank where I am gluing.
 
I use System3 T88 epoxy glue for just about all my epoxy glue jobs and that includes segmenting and gluing tubes in blanks. If I must use a clear epoxy for some reason and there have been some such as doing watch part pen blanks or some other blank I use JB Weld Clear. Both are excellent epoxy glues in my opinion and have never had a failure. These glues require at least 24 hour cure time.
 
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