I'm new here and hoping you can help me to locate a title for a friend who very much wants to re-read a book he purchased from the Sci-Fi book club in the 80s or early 90s (No word on the publication date of the story itself).
The plot, as he has described it to me, involves two children (he thinks they are a boy and a girl, maybe siblings), an adult who helps them, a college laboratory accident that has them teleported to a hollowed-out tree which has been hollowed out by the experiments of the college student (chunks of wood from this tree had been appearing in the lab while earlier experiments were conducted) and finding a hand held teleportation device ( looking something like a melon baller) to a parallel universe. Some of the tools from the lab went with them, allowing the college student/lab technician/whatever to build a communication device to talk to people "back home" from the parallel universe. And something about how they used the teleportation device to hoist up and remove the spines of enemies....
My friend is very vague on details, as he read it a long time ago, so that's all I can provide. He'd really like to find this book, so if this doesn't sound familiar if anyone can give me a good idea of a site or sites to search that might have the answer, I'd appreciate it. We've already checked Wikipedia's sci-fi novel stubs from the 70s-90s. My friend is also uncertain if the novel was a young adult novel or a regular novel.
Any help would be greatly appreciated.