What type of tool are you using HSS, Carbide, shape.

Is it on ctr height. The pip left in the middle suggests not

Is it sharp?

Edited By JasonB on 22/08/2023 17:15:38

There could be a number of things here

1) Tool needs to be very sharp for brass
2) Best practice says zero top rake (top edge of the tool should be ground flat, not tilted back like your knife and insert tooling is. That said I have never had any problems with using "standard" tooling for brass.
3) Your work is a long way out of the chuck unsupported, this is defintely not going to help. Either get it much closer to the chuck of use a centre to support it.
4) It could just be "bad" brass, some just don't machine well
5) Centre height is critical as this does affect rake if it is above or below centre. I still use the old trick of pressing a 6 inch rule between the tool and the work (not under power). It should be vertical if the height is correct,

I have never seen HSS tooling sold suitable for brass, As mentioned I have never bothered with grinding specifically.

For the six inch ruler trick, just bring the tool up to the workpiece (not the end face) with the rule held in between and apply enough pressure to just pinch it. It should be completely vertical,. It if the top of the rule is towards you it is too low and if away from you it is too high.

As for purchase you should be looking for grade CZ121 brass which is free machining. I usually get mine from Chronos and haven't had any issues

I would use the insert holder that you have but get one of the inserts intended for Aluminium and other non ferrous metals Yours looks like a CCGT 060202 or 060204 would suit. The CCMT that you have can be a bit blunt even when new due to how they are made

The HSs one just wants the end rubbing on a Diamond slip to sharpen it up a bit but I'm not keen on those preground ones with the chip breaker groove

The pip (but sticking out) in the middle of the faced part is a good indicator that you are not on ctr height

Either of the two will fit your holder, the ones from APT have a smaller corner radius of 0.2mm and are what I tend to use, the ARC ones 0.4mm as they don't do 0.2mm.

This shows the ruler method, don't press a carbide tool too hard against the ruler as they are a bit more brittle than HSS.

Then facing a bit of brass, no pip and a reasonably good finish. Too much stick out really on the piece of 6mm dia brass that follows but still gives a good finish once I get it into focus. That's an 8mm Glanze holder I'm using so the same as yours with the APT inserts, the link is to a pack of two which will be enough to give you an idea of how well they work and can be use don all metals.

Both tools Margaret is using should be OK on Brass, though the sharp silver inserts are much better.

Rule of thumb, an unsupported rod shouldn't protrude more than 5 times it's own diameter. Beyond that the cutter pushes the work away, and chatters. Note that a blunt insert has to be pushed harder into the job before it will start cutting.

The Brass is a suspect. Though most Brasses machine well I have a rod that doesn't!

Centre height is important, especially on small diameters. Too low and the cutter tends to dig in and chatter.

Here's a photo of tool height being checked with a steel rule. The cutter is wound gently to nip the rule in place. When the cutter is too high the top of the rule tilts away from the operator. If too low, the top of the rule tips towards the operator. When the rule is vertical the cutter is exactly right.

I suspect all these factors have come together to spoil Margaret's day. In order, I'd:

1. Set Centre height
2. Reduce how far the rod protrudes from the chuck to much less than 5x diameter
3. Try a sharper insert (or sharpen the HSS)
4. Try a different Brass – though it's probably OK

There are other possibilities, such as bell-mouthed chuck jaws, but deal with the most likely first. It's possible that steps one and two will fix it.

Dave

Edited By SillyOldDuffer on 22/08/2023 18:46:14

Like Jason, I'm not that keen on the pre-ground deeply grooved HSS tools for facing or turning, though they do the job well enough when kept nicely honed.

Try having a look at Tom's Techniques.

He has some print-offs [under "reference"] on grinding HSS lathe tools, as well as videos. The first tool I ever made was his facing tool, which gives nice results in brass.

Just one: When you finish the cut, back the tool out slightly before returning to your start position. A lot of the marks look like you're winding the tool back over the work without doing this, giving the coarse spiral marks.