Usually in the pen turning world, "acrylic" frequently gets used synonymously for the word "Plastic" and not in reference to a specific material or polymer based on Acrylic acid. Generally speaking, the two materials you named, Alumilite and Ebonite can be less brittle than several of the other typical pen blank plastics.
Ebonite is a brand name for elastomeric polysulfide or styrene-butadiene rubber, materials made by vulcanizing natural rubber. It usually contains a relatively high percentage of sulfur and some linseed oil. It got its name because the early use was as a replacement for ebony wood.
Alumilite that is used to make pen blanks is a urethane rubber based resin. Urethanes sort of fall in between rubber and plastic materials. Alumilite typically falls in line with the hardness and brittleness of Ebonite, so I would expect them to have similar workability.
Other "acrylics" aka plastic pen blanks are made from a variety of plastic materials such as epoxies, polyesters, cellulose, acrylics, acetates, and combinations thereof.
Of the "acrylics" I have used, by far the most brittle has been Inlace Acrylester which I think is owned by WoodTurningz. They are gorgeous blanks and polish to a fantastic high gloss, but they can be quite difficult to work with because they are so hard and are prone to chipping. I have found that using a negative rake angle on my tool helps prevent chipping.
Right behind Inlace Acrylester I find Rhino Plastic blanks which are made from a polyester resin. Although they are still quite hard and they polish to a very nice gloss much like Inlace, I have found them to be less brittle and easier to turn without chipping.
Considering how brittle Inlace Acrylester can be, if that is one of the "acrylics" you are using, it would not surprise me that you would have problems with chipping.
Can you share the trade name of the "acrylic" you are using?
Regards,
Dave
