How (not) to machine a cylinder

Interesting day in the shop. I was machining the bore of a cylinder (iron casting) for a model stationary steam engine. I took a fair bit of time setting it up the way I wanted so that I could machine some other surfaces too at the same setting. Then I grabbed a boring bar out of my tool drawer, decided that it would be a bit flimsy over this length and took a larger diameter one instead (these are the types with replaceable carbide inserts). Had to extend it from the toolholder a bit to get the length (then had to extend it again when I realised that, although the bar was long enough, part of the casting would impact the topslide before I got there).

So, all ready to go I start boring, break through the cast-iron skin and bore the diameter out from the as-cast 0.85" to about 0.960" of the 1.000" that I want to end up with. Everything is going really nicely - finish is good and no problems, no funny noises. Decide on a diameter check ( about the third I'd done) before I start creeping up on the final diameter. So I move the carriage back a way to get in with a mic and notice ....... that the blxxdy boring bar doesn't have a carbide-insert installed.

Huh? It's been cutting on the corner of the holder itself - which actually looks in pretty good shape!

I blame the glasses.

Ooops!

Are the glasses filled with beer or vodka?

Shuda gone to Specsavers.

Regards Ian.

Oh well, at least you know your boring bar is made of some darned good steel.

Perhaps the boring bar is also carbide! Carbide bars are very stiff which can be useful.

Well, it wasn't a selling point when I bought it (CTC) but who knows? *** At least I know what to do when I'm out of inserts on a Sunday.

I've actually decided to re-state the whole thing as ' roughing ' cuts followed by finishing cuts (with an insert).

I think it probably says a lot for the quality of the PMR casting actually .... highly machinable with a thin skin.

*** it's actually described thus:

• Tool Holder made of High Density Forged Alloy Steel
• Hardened to HRC40, Ground and Black Oxidated (sic) or Silver Coated depending on Size

Maybe an insert was there but loose screw and both new the bar could handle the job well enough. Bit like leaving a 1st year apprentice to do a tradesman job.