This is a rocket I designed to use Estes engine sizes A8-3 through C6-7. I added a test tube that has the engine, body and launch lug so you can print and test sizes. If it is too small you can scale up to fit. On my Anet A8, the tubes fit the engine and launch lug as they should. I have not flown this rocket as of yet. I will post pictures once flown.

UPDATE: Changed the nosecone as I found it fit too snug and I don't want to do a ton of sanding (Because I'm lazy)
UPDATE 1/31/19: I decided to add a Booster stage. I'm printing the Booster as I type, so It hasn't been tested yet. I have added the file in. The booster is for B6-0 or C6-0.
UPDATE 1/31/19: Booster length measurements were short. That has been fixed.

Assembly:

After Printing, sand all edges to remove the flash from the brim. Before gluing anything, tie your shock cord through the tube to the crossbar attachment point. Tie the other end of the shock cord to the bar inside the nose cone. Tie your parache or streamer to the nose cone cross bar. I use CA (superglue) to attach the tubes. Make sure the nose cone can detach smoothly. I find it is better to be a bit too loose than too tight. I plan to hold the booster engine with a small ring of masking tape around the top of the engine casing to make it fit extra snug. I don't think I will need clips to hold in place as I've done it this way before.

Enjoy!!
Jimmy