BS to the nay-sayers. Don't get me wrong; a purpose built self-feeding portable boring bar is great but they have limitations their users might not appreciate when compared to a general purpose machine tool of a size and suitability or the work. A turret (Bridgeport) mill was mentioned. First limitation in boring cylinders in a turret mill might be the 5" quill stroke but if you were extend the quill and bore with the vertical knee travel (need a knee feed unit, here) you can bore to maybe 10" deep - if the cylinder can swallow a 3 3/8" dia quill.
It was alleged that a cylinder bored in a mill would "egg out". This assertion needs to be supported by constraints under which this would happen. I submit if the tooling was suitable and the set-up was competent the limitation wold be dependent on the tracking of the quill or the knee.
Boring cylinders is not rocket science. They do have to be round, properly finished to seat the rings, straight (or properly tapered), and to size. I've bored lawnmover engines to cylinder liners for uniflow marine (22" bore, 40+" stroke) steam engines and trust me most any machine tool in reasonable shape can do the job. It's usually a gravy job once set up.
Where one-trick pony boring bars come into their own is they are portable and much less expensive than a full featured machine tool - and they have the expanding guide that follows the bore as the bar feeds out. In an auomotive machine shop dedicated cylinder boring apparatus is a shrewd purchase costing thousands less than a milling machine of sufficient capacity and probably quicker for a single bore than on a mill IF a plain bore is all that's required.
The cool thing about a machine tool is you can correct a bore geometry and adjust for bore spacing etc.
If you can fit a turret mill or an HBM in your budget you can do a hellova lot more than bore cylinders. And the cylinders you do bore can be made round and to size leaving just the right amount of honing stock.
Honing stock and how to hone is a whole other topic.
