Gardening and Horticulture - On hanging a porch swing from a tree

I have an old porch swing but no porch. What I do have is a stand of large, mature spruce trees with trunks over 2 feet in diameter. They're about 8-10 feet apart and appear healthy. I thought about suspending a bar or rod between two of them, and hanging the swing from this.

1. What is the best way to do this without injuring the trees? I'm thinking about drilling large eye-bolts into the trunks.

2. Can anybody recommend a website or book that gives information about this?

Thanks!

Here's 2 I saw:

http://www.ehow.com/how_17443_install-porch-swing.html

http://www.porchswings.com/porch-swings/helpfulinfo.cfm?page_id=6275

Good luck!

It seems to me that it is a contradiction to drill holes into a tree to avoid injuring it.

I've seen swings suspended from a branch of a single tree, but not from two trees.

A better idea is to build a structure to hang the swing. I built a pergola arbor for mine and it really adds to the landscape. A nicely shaped arbor will not detract from the beauty of the trees.

http://www.swingplans.com/tree_hangin.html

This will answer your question.