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Chris, it sounds to me like your lathe headstock may be angled just a bit. If that is the case then even taking multiple passes at the same setting can still result in a taper. Not sure how long your cylinder is but it wouldn't take much to misalignment to give you a tapered bore though .010" sounds like a lot if the cylinder is pretty short.Put a good piece of truly round stock in the lathe and use a dial test indicator. As you move along the round bar, check to see if you are getting any indicator movement. My suspicion is that you will get some, meaning the headstock is out of alignment even if by only a fraction of a degree.Bill
I mounted a Dial indicator perpendicular to the chuck. Spinned the chuck around and saw that it varies from 0 to 3 thou. I moved the saddle to about how much my work piece was and noted that it varied about 1.5 thou.
Sometimes it would take a little and produce some swarf, other times it would take nothing at all. I dont get what gives here
Am I reading Nerdz post right? .0005 over 6 inches? I also have a mini-lathe...wouldn't I feel ecstatic? I really don't know.
It may be counter-intuitive but bigger depths of cut when boring often lead to a more stable cutting operation. Make the hole first and don't sweat about the size. Then make the piston to suit.Andrew
Nerdz, was the bore of the brass bit parallel, and was the out side of the CI liner parallel before you assembled them? If so my next thought is that as you pressed them together some of the metal (probably the brass) got scraped as they slid together so that one end of the bore in the brass piece was larger than the other.I would make up a lap (you can go quite fancy), I make them from wood, with a slit down it's length, and a wood screw in the slit to adjust it, I use grinding paste, mine's quite fine, so it just gets that. If you have a coarse and fine valve paste, make another lap for the fine, coarse grit will be embedded in the first lap. If you are really over enthusiastic, you can then try Brasso, or even tooth paste.Ian S C
Quote from: jadge on January 27, 2016, 12:27:21 PMIt may be counter-intuitive but bigger depths of cut when boring often lead to a more stable cutting operation. Make the hole first and don't sweat about the size. Then make the piston to suit.I noticed this with my "real" boring bar. Cuts around 10 thou would cut beautifully, but then if I try to take a finishing cut of say 1 thou it would chatter like crazy and leave all kinds of marks. I would be happy taking cuts of 10 thou if I knew it didnt spring.
It may be counter-intuitive but bigger depths of cut when boring often lead to a more stable cutting operation. Make the hole first and don't sweat about the size. Then make the piston to suit.
Took the whole chuck apart, cleaned it and oiled it. Tested a bar, and I get 4 tho worth of run out. Time for a new chuck! The good news is the runout is consistent all the way down my test piece, so thats good. Looks like I'll be using a 4 jaw for accurate work.