Help! Excessive machine marks!

[Margaret TrelawnyParticipant @margarettrelawny34058]

My friends – HELP!
Not sure what is going on but I am getting excessive cutting marks – chatter!?

I love a good natter but not this chatter! It’s driving me mad! Everything seems to be tight: the cross slide and compound are tight but moving freely. The gib is tight(ish) on the compound. The tools are fairly new – carbide inserts and HSS are giving me the same results.

Any ideas please? The thinner brass stock is hopeless to turn – it’s bending when the tool is applied. Even facing is giving me rings!

The only tool which cuts without leaving marks is the parting blade. But that isn’t moving right to left.

I am so frustrated! (Using the original tool post from the lathe – as I can’t even begin to think about machining a new stud for the QCTP until I get this headache sorted.

Thanks

[Margaret TrelawnyParticipant @margarettrelawny34058]

[JasonBModerator @jasonb]

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

[Neil FranktonParticipant @neilfrankton16738]

Both types give similar results Jason. The tool looks centred – please see pics.

[Margaret TrelawnyParticipant @margarettrelawny34058]

Sorry, just had to reply off hubby’s phone as mine died and realised it was signed in on his account! 🫣

[Margaret TrelawnyParticipant @margarettrelawny34058]

The tools should be sharp Jason – they are both fairly new and not used much. Would being the wrong height give those results?
I can purchase another tool and try that perhaps? Any recommendations for best brass turning tool? Just straight reduction work at this point.

many thanks

[Stuart BridgerParticipant @stuartbridger82290]

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,

[Margaret TrelawnyParticipant @margarettrelawny34058]

Thanks Stuart. Could you recommend a tool I could purchase please? I am not experienced enough yet to grind things.

How can you tell when you buy brass whether it’s any good for machining? I just buy off ebay.

Could you enlighten me about the six inch ruler trick please?

many thanks

[Stuart BridgerParticipant @stuartbridger82290]

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

[Oily RagParticipant @oilyrag]

To set centre height accurately bring the tool up to contact the outside diameter of the work, back it off and slip a 6" rule (metric optional!) or a piece of old hacksaw blade (after the teeth have been ground off) between the tool tip and work. If the rule/blade is vertical you are 'on centre', if it is pointing away from you the tool is too high, if it points towards you then the tool is too low. This refers to the upper part of the rule/blade obviously.

This is a quick, easy and simple test for tool height taught to me when doing my apprenticeship – I always use this method. It can also be used for centreing work under a pedestal drill for cross drilling round bar. In this instance the rule/blade should be horizontal.

Whoops – Stuart beat me too it!

Edited By Oily Rag on 22/08/2023 18:14:58

[JasonBModerator @jasonb]

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

[Nigel Graham 2Participant @nigelgraham2]

The coarse groove on the end face is by too fast feed.

I've never had much luck with the rule technique as it seems to demand looking at the lathe from just the right angle. I point the tool at a centre, and use the facing behaviour to verify the (HSS or carbide) is on centre-height.

The work's projection is too much, especially on such a slender diameter. Best to support the outer end on a half-centre, though on some lathes (such as my Myford) that can lead to the tailstock and top-slide in each other's way without turning the latter partially round.

Try using a fine power feed, too, if that's not what you're doing anyway.

[Margaret TrelawnyParticipant @margarettrelawny34058]

Thanks guys. Appreciate your help.

Jason – this is the tool – which of those inserts for non-ferrous would fit? I’m not familiar with the coding and how you match up inserts.

thank you!

[Margaret TrelawnyParticipant @margarettrelawny34058]

Thanks Nigel

[JasonBModerator @jasonb]

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.

[Andrew TinsleyParticipant @andrewtinsley63637]

I had a similar experience with some brass from an Ebay seller. Machined more like soft, pure aluminium. i would get some brass from a respected seller like Macc Models, if the other suggestions fail to give results.

Andrew.

[SillyOldDufferModerator @sillyoldduffer]

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

[JasonBModerator @jasonb]

One other thing regarding the facing cut. Assuming you are hand feeding that then try to use two hands on the round outer edge of the handwheel to keep a constant even feed. If you are just using the handle that stickes out and cranking it round there is a tendancy to lift and then lower the cross slide

[Bill PhinnParticipant @billphinn90025]

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.

[Margaret TrelawnyParticipant @margarettrelawny34058]

Thanks everyone – super advice as always. Thank you for the pics and video – it really does help a learner. I have digested all the info (I think!) and it has given me new heart. I have purchased the silver inserts Jason linked (from APT) and some CZ121 bar to try. Will report back when I can.

Again, I cannot stress how valuable and helpful you all are. I very much appreciate your help.

M

[Margaret TrelawnyParticipant @margarettrelawny34058]

Chatter 2

Morning everyone, my machining marks continue.

To recap:

1: I have checked the centre height of the tool – it looks apot on.

2: purchased a piece of CZ121

3: purchased the tool tips recommended from APT.

4: feeding the cross slide with both hands (which has helped).

But, although an improvement – I would say I am far from happy with the results so far. The facing off is better after the second pass, but the turning isn’t.

Any suggestions where I am now going wrong please?

[Margaret TrelawnyParticipant @margarettrelawny34058]

More….

Edit: rotated photos.

Edited By SillyOldDuffer on 27/08/2023 14:13:56

Edited By SillyOldDuffer on 27/08/2023 14:14:41

[Andy_GParticipant @andy_g]

Posted by Margaret Trelawny on 27/08/2023 11:23:42:

Any suggestions where I am now going wrong please?

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.

[HollowpointParticipant @hollowpoint]

It might be your chuck!

I had a lathe with similar problems and it took me forever to pin down the problem! In old lathes you sometimes get a problem where the jaws are worn leading to the part not being held properly, this is commonly referred to as "bell mouthed jaws". Now your lathe doesn't appear to be old, and neither was mine. Unfortunately it seems some of the Chinese chucks suffer from poor quality control.

Remove the chuck from the lathe and clamp a piece of round bar in it. Hold the chuck up to the light and look through the back opening. If you can see any slivers of light between the jaws and the bar you have problems.

Another test is to clamp a piece of round bar stock in the chuck and run a dial indicator over it, then push on the bar stock to see if there is significant movement.

[Margaret TrelawnyParticipant @margarettrelawny34058]

A thought – I noticed that these bolts which hold the compound in place are very lose inside the channels – although when tightened the compound seems tight and rigid, I wondered if when under pressure from the tool contact it was moving?
Would it be worth trying to get better fitting bolts – they are nearly 2mm smaller than the channel.

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