turning aluminum - surface is "wavy", why?

[Florin Andrei]

Just started to use my 7x12 mini-lathe. I put a chunk of 1/2" aluminum in it, and just tried to reduce it to 10 mm diameter. I used pretty slow speed. Then I parted it with a parting blade. The result is a cylinder about 60 mm long, 10 mm thick.

It went well, but there's something puzzling me: if I look very, very closely at the surface of the resulting 10 mm rod, the part that was close to the chuck is very smooth, very even. The other end looks a bit "wavy", for lack of a better term.

Make no mistake, this is a very small difference, most people would not notice, but it's clearly there if you look at it carefully for a few moments, you turn it around with your fingers, and the light is falling at just a certain angle. The "waves" don't show a regular pattern - they look kind of like sea waves, or like the bumps on an orange peel - just bigger.

The end that was close to the chuck is very smooth, almost lacking any features whatsoever.

Is this because the rod was flexing a little, as I was removing material from it? If so, this would not happen with a thicker rod?

The cutting tool was driven at constant speed along the whole piece, so that can't be the cause.

(I could take a picture, but I think not much would be visible.)

 

[Holescreek]

Measure the OD of the rod at the smooth end and the rough end. If the rough end is larger it's due to the material flexing away. Centerdrill the end of the rod and pt your tailstock center in it and make the cut again. 10mm OD is really small for aluminum (with regard to rigidity on a 3" part).

 

[chuckorlando]

It's chatter from something. Part flex, tool flex, saddle flex, something is moving or ringing

 

[higgite]

If you're describing what I think you're describing, I had the same problem with a 7x14 mini lathe. A very light ripple effect that looked sort of like zebra stripes. The pitch of the stripes was 16 per inch, which coincided with the leadscrew pitch of 16 tpi. I readjusted the carriage, cross slide and compound gibs and the stripes went away. HTH.

Tom

 

[Bill Gruby]

I agree with Tom on this. Readjust all the gibs and the lead screw and all should be fine again.

"Billy G"


NOTE -- Make the adjustments with the apron at the tail stock end of the bed.