My parents have a 14yr old dog that has lost function from the lower spine down. Is it possible to make a wheelchair for him?

I wouldn't suggest this is a job for a 3D printer. Dog wheelchairs exist that you can just go out and buy, and even if they didn't, FDM plastic is no alternative to aluminum piping in terms of durability/weight. Plus you can't meaningfully print the wheels, tires, axels, bearings, or straps.

My suggestion to you as someone getting into the hobby: use your 3D printer to solve problems that are hard to solve any other way. Don't look for excuses to use your printer to solve problems that are already solved, unless you think it would be fun and you don't mind that it may be a waste of time and money that produces a worse result.

Especially don't try and make medical devices. Even for a dog. If you aren't an engineer and haven't done extensive research on the subject, you're going to make a shitty deathtrap that will not make the dog's life better.

/r/3Dprinting Thread