This is the insert mike is using.

Yamaloy insert

Steve.

Edited By Steviegtr on 18/03/2020 14:12:59

[This posting has been removed]

Carbide inserts are designed to operate at speeds and feeds so that the metal/tip interface becomes so hot that the metal softens. Given the lower co efficient of friction than steel, this may be more difficult with copper based alloys.

My suggestion would be to grind up a HSS tool and use that for the finish cut.

Before going for the finishing cut, it might be worth checking that any drive belts are in good condition, and not sending any vibrations through the drive train. Single phase motors are also known to give similar problems if the conditions: speed / load/rigidity/tooling are not correct

As ever, the devil is in the detail!

Howard.

Inserts

Well just tried again & got the exact same number as mike posted.

Normally one would invoke the following equation:

Ebay insert = crap shoot

However the linked to Yamaloy insert (even if they're not the ones being used) are sold by Cromwell, albeit at a slightly lower price. But they're on 2 days which makes me slightly suspicious as Cromwell customers are most likely to be commercial machine shops, not used to waiting.

From the picture the ridges seem quite obvious, but they're stated to be a bit over 2 tenths of the thou deep. At that sort of depth I don't think they'd be so obvious? Not sure it has a bearing on the finish, but 3 thou is a pretty shallow finishing cut.

I've not really had a problem turning bronze or gunmetal with inserts so difficult to make suggestions. But the wide spacing makes one think of a machine related problem rather than the basic cutting process or, possibly, the casting itself?

Andrew

Edited By Mick B1 on 18/03/2020 17:00:22

Yes, that’s what I thought. Less than £3 per tip in a packet of ten. Might even have been less, if bought from bang good!

Could be anything – like a loose insert for instance. Let’s await some decent feedback.

I've seen that effect caused by drive belt thrash !

The pattern seems to repeat evenly, as the op said at ) 0.125 spacing. How does the insert know it has cut that much over and over again? If it were a random pattern maybe somehow but not a neat repeat.
I'd say 3 prime suspects.
1/ cross slide screw, bent, or bearing problem or even unevenly made but would expect that to be related to the pitch ie 1/10 in.
2/ drive to the cross slide with a changewheel or other gear that is off centre or even dirty or damaged on one tooth.
3/ Spindle drive due to belt or back gear or pulley or bearings though all of these would probably be making a more frequent pattern repeat. The bearing cage may precess with a much slower rate than the spindle itself. There are reasons why top end lathes avoid back gear and use incredibly expensive bearings.

edit – just re-read the fist post and see he did manual feed in the end so 2 & 3 discounted. I'm impressed he has managed such a good finish manually as slight changes to hand pressure and feed rate show up. When I hand feed I use two hands and can get marks where I change grip, not necessarily at exactly one turn.

Edited By Bazyle on 18/03/2020 17:34:38

I would rough with carbide as the skin of the casting wil be abrasive ,then finish the last ten thou with two cuts with HSS tooling ,the rings look like the product of a tool with insufficient clearance,or the side clearance has been worn away. Brass and bronze cut far better if the tool is ground on a fine grit wheel and then stoned to give a clean cutting edge, the biggest mistake made is to stone the tool too hard and to let the stone roll in your fingers so that the cutting clearance is lost. Back lash in screws rarely affects finish as the tool is being pushed,too much is made of baclklash,belts and single phase motors causing finish defects,the problem is lack of experience in grinding tool and too high a speed wearing the tool.

I stand corrected.

Steve.