Need a perfect 8mm hole - to ream or bore?

[ptjw7uk]

Hank,
Cutting on the retract stroke will make the bar cut better as it is in tension. Your bar looks quite fat for the size of hole and could be rubbing near its bottom, it is quite important to get the clearances right but its ultimately a trade of against size and rigidity as the larger the hole the larger the cutter.
This is why I think most small holes are finished with a reamer.
Also somethings wrong if the drill is flexing all over the place, I've had it happen when the drill was sharpened off axis(ive a lot to learn about sharpening)
Peter

[Robin Hewitt]

Cutting on the retract stroke will make the bar cut better as it is in tension.

The 'joys' of boring bars on small lathes

If there's any twist on the saddle the return stroke will cut deeper, I usually switch off before I pull it back. (Myford ML10)

Tempting to use the reverse pass if you want a flat bottom hole because you can run the saddle up to a stop for the next cut, but I don't find boring bars like being pulled sideways in to a deeper cut. They like a bit of X motion to stop them chattering.

If the bar doesn't cut sweet as a nut all the way through on the first pass you have to stop and figure out what's wrong. If the tool height/angle is wrong you can cut a taper.

The bar will flex. If I want an exact size I make several, same depth passes at close to final diameter until it stops cutting, measure, wind the tool out to size then do repeat passes until I get the desired fit. If the material is likely to work harden and I don't have an appropriate reamer, I like to keep the cut depth fairly constant and just hope the flex stays consistant :heehee: