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  1. #201
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    Quote Originally Posted by noamw View Post
    I took some 35mm brass that I tested before. I made several cuts but this time the surface finish was much better then before.
    Noam,
    Brass or particularly bronze can be a little difficult to machine as it does not like positive tooling and can grab. So your tool can 'jump ahead' occasionally. Result = bad finish. Try zero top rake on lathe turning tools.

    Drills are bad for this. So you grind or stone a tiny flat on the drill cutting edges.

    IMO, the usual cause of a poor finish is with the tooling.

  2. #202
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    Sep 2012
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    Quote Originally Posted by noamw View Post
    Hi Evan,

    Well I decided to make a new part and replace the original warn one. I am talking about the holder of the
    cross slide half nut. I made it from 1020 steel (this is what I had) and I fucked up the most important
    measure, the 45mm (minus 0.02-0.03mm) diameter hole that holds the half nut .

    I was planing to start from scratch but after talking with a friend, he convinced me to salvage it. I enlarged
    the hole to about 48mm and made a 2mm cutoff shoulder.

    I then took some bronze and turned it to make a bushing with a shoulder. I honed and polished the internal until
    I had a tight fit over the half nut. Then I used Loctite 648 and glued it inside the steel part.

    Today I finished it and installed it on the lathe. To my surprise I still have some play. I figured out that this
    is the half nut itself. everything else has minimal play. Maybe it is warn out (makes sens ... its old).

    Any way, I tightened the half nut and after also tightening the Gib I checked again.

    I took some 35mm brass that I tested before. I made several cuts but this time the surface finish was much better
    then before. Maybe at some time in the future I will also replace the half nut but for now I am happy with this result.

    Thanks for reading and commenting.

    My apologies for not taking any images this time...

    Take care,
    Noam.
    Noam,
    There are a lot of contributors to surface finish. Hard to say whether the half-nut is at fault, or your cutting edge/tool, or some other chatter source.

    I'm actually pretty surprised how good (er, not bad) the finish is on my lathe given the rather bizarre motion I measure with a DTI.

    You might try some leaded steel to see the best you can get, or try a shear tool on the brass.

    Skip to about 5:00 in this video...
    The other metal lathe finishing tool - the shear tool - YouTube

  3. #203
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    Hi All,

    In my case it is definitely rigidity. I see the difference in surface.

    I am not saying that a tool does not have a weight on surface finish, sure it has
    but in my case its first and most the play and vibration.

    Thanks,
    Noam.


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