Cutting an exact diameter using a carbide tip.

Many thanks for the additional help on this.

Emgee, thanks for the pointer to Joe Pi's home page information, I will search through it.

As Buffer says, someone has missed the point which, as I understand it, is that though a rigid industrial lathe may take off 20 thou when you dial it in, a less rigid hobby lathe is more likely to take off 19 or 21 thou, and Joe's method of multiple cuts enables one to compensate for this so the final size is near enough.

Rod

.

’fraid not, Rod ... the point was that the calibration of the dials differs

[diameter vs radius]

MichaelG.

Crikey! This question encompasses almost all there is to know about turning!

Stefan Gotteswinter produced a video on 'balanced cuts'. I don't think he explained the idea very well, however the video is well worth watching - as are all his others. He often re-grinds carbide tip[s so they are sharp, and will take very shallow cuts. If you look at tip manufacturers' literature, you'll rapidly discover that those designed even for finishing cuts are not designed for 'our' idea of finishing cuts. There are ground tips available, like those intended for alloy, and, as others have said, carbide tips can (sometimes) take very fine cuts, but do they provide consistency?

The idea underpinning 'balanced cuts' is to discover how your machine cuts in practice. It will be different from what the dials say. Then you can take deep cuts, and finish to size, rather than creeping up to size and wearing out the tip by more passes than neccessary. So, get close to finished size, leaving, say, an amount oversize equivalent to three passes at a depth of cut that is known to produce good results. Measure, calculate oversize amount. Divide that by three (in this example). Take a cut at this one-third depth. Measure. Calculate the error (there will be one!), and build this error-compensation into the remaining two cuts.

This all assumes that your machine is consistent, if not accurate. If it's not consistent, all bets are off!