Problems machining brass – Bad finish !

[Chris machinParticipant @chrismachin]

Hi ,

I have today tried machining brass as below :

 

Clarke 300 mini lathe using machine mart supplied set of carbide tipped tools. I used the knife tool to machine 1 1/2″ round bar and the surface finish appeared rough and torn. Speed was around max i,e 2800rpm.

 

Cutting longitudnally towards the chuck seemed better than the facing cuts but both were poor finish !

 

I tried using both the very point of the tool and also the side of the tool but seemed to get some vibration and wasn’t cutting cleanly.

 

Can anyone give any specific advice about machining brass ?

Thanks

[Chris machinParticipant @chrismachin]

[David Clark 13Participant @davidclark13]

Don’t use carbide for brass.

Use a high Speed Steel tool with no toprake – top should be flat.

regards David

 

[nigel jones 5Participant @nigeljones5]

In addition to the tooling it Sounds like you dont have the tool at exact centre height…I use the same lathe for my small work and if its off height it leaves a rough, orange peel finish.

 

[Anonymous]

I have no problems turning brass using carbide tools. One, I’d be suspicious of the quality of the Machine Mart carbide inserts. Two, I’d drop the speed to 1400rpm, which is still 549fpm, pretty ambitious for a small lathe.

 

Regards,

 

Andrew

[Ian PParticipant @ianp]

Brass is one of the easiest of metals to get a good finish on so there must be something pretty basic wrong.

 

Carbide is not the best type of tool but even with blunt carbide you should not be getting vibration.

 

2800 is probably a higher speed than you need but if you take a facing cut over the material starting from the centre outwards you will see the effect of different cuttings speeds. Its very low (in fact its zero FPM) at the centre of the face but very high near the OD. Just experiment.

 

Check that the tool is not too high., also it sounds as if the tool is not rigid. Try another tool preferably HSS.

 

Ian P

[colin hawesParticipant @colinhawes85982]

The tool is not sharp enough or lacks clearance. Colin

[steve winchesterParticipant @stevewinchester]

tool needs a small radius on the front cutting edge an it will cut fine .

[Chris machinParticipant @chrismachin]

Tried again today but getting nowhere !

I have adjusted all the gib strips on the lathe as there was a tiny bit of play , now it is very smooth with no play at all.

I have tried different tools including some i ground from silver steel with zero top rake and also some other brand new tipped tools i have but the result is the same , lots of noise transmitted through the lathe and some vibration and resistance is felt on the crosslide handle as it fails to cut. The result on the material is just rough and torn.

I have tried a different brass but but its the same ! I tried all the cutting tools exactly on centre and in desperation below and above centre but no good.

I'm holding the work (which is about 1 1/2 " diameter tightly in the external jaws of a three jaw chuck.

Anyone any other ideas before i 'skip' this lathe ……!!!

[David Clark 13Participant @davidclark13]

Hi There

What happens if you try to part the brass off?

regards David

[Anonymous]

Definitely something odd here. If there's noise and vibration it would seem that the lathe/tool combination is not cutting correctly. Have you managed to successfully turn any other metals, ie, is it a generic problem, or just a problem with brass? Are you sure the material is brass? What does the swarf look like? For brass it should be a fine stream of very short chips; the damn stuff gets everywhere! What speeds, feeds and depth of cut are you using?

It must be possible to get to the bottom of this!

Regards,

Andrew

Edited By Andrew Johnston on 16/02/2012 16:32:02

[Ian PParticipant @ianp]

Chris

Definitely something odd about your problem. In my experience brass is one metal where it is hard NOT to get a good finish.

It might help if you could post a picture of your setup.

Your description of the finish you are getting make me wonder what sort of brass you have, could it be bronze or 'yellow' brass?

Vibration is not normal, noise could be. Its normal for brass to make a squealing noise especially when taking a decent size cut but I assume you are not doing that.

Ian P

[Chris machinParticipant @chrismachin]

Hi , Thanks for replys .

David , at the moment i have not got a parting tool so can't try that.

I am sure the material is brass , i have also tried another piece of brand new bar stock 10mm diameter and the effect is the same ! The swarf is small chips. I have machined brass on bigger lathes in the past and know what you mean by 'it gets everywhere'

I have tried all speeds on the high setting from around 1400 to 2800 the vibration is the same , i am only using small cuts of less than 0.5mm (even tried 0.1mm) and feeding by hand. With the smaller cut the vibration is less.

I cannot see it is anything other than the cutting tools as there is no play in the lathe that i can see and the spindle runs very sweet when unloaded , just can't see whats wrong with the tooling im using though , as mentioned i've tried silver steel , the machine mart tools and also now a brand new sumitomo indexable tool. I will try and cut a bit of steel later and report back.

Thanks again for taking your time to help.

Chris.

[Chris machinParticipant @chrismachin]

I will go back to the workshop and try to post up some pics of the set-up , tools i'm using e.t.c.

Thanks

[Russell EberhardtParticipant @russelleberhardt48058]

Chris,

It depends on the brass you are using. If it is leaded free cutting brass you should be OK but if it is common brass I would try a lower speed, say 400 rpm.

Did you harden your silver steel tools? Silver steel is supplied soft and needs to be hardened and tempered. You have to be careful not to overheat them when grinding.

I wouldn't try to cut steel until you have mastered cutting brass.

Good luck.

Russell.

[jason udallParticipant @jasonudall57142]

Finish relies on many things. one thing not mentioned is work holding….

Wahts yer chuck like?

[jason udallParticipant @jasonudall57142]

or spelling for that matter

[mickParticipant @mick65121]

Depends on the carbide tool your using, if its a small diamond profiling insert with small tip rad there should be no real problem, but if its a brazed tip then its most proberly blunt and rubbing, regrinding without some way of diamond lapping is a waste of time as you'll never get the cutting face smooth enough, any doubts stick to HSS.

[MichaelRParticipant @michaelr]

What overhang have you got on the tool, you may need to reduce the overhang which will help with the finish.

Mike.

[Chris machinParticipant @chrismachin]

I have been back in the workshop and decided to fit the internal jaws and try again on a smaller diameter piece of brass secured with just about 10mm hanging out the chuck. I set the machine mart tools dead on centre , locked the saddle and took very small cuts of around 0.1mm. This agve slightly better results and at least cuts the brass in both a facing direction and also when cutting towards the chuck. I tried again with the brand new insert tool and this gave the same result , although now cutting better the surface finish is still torn and rough. After fitting the external jaws back again i tried the larger diameter again after clocking the bar. There is now less vibration ,less 'digging in' but still poor finish !

Is it possible to buy a ready ground hss tool specially angled for brass ? At least if i did this and it gave good finish i would then know this is the problem.

Chris.

[Keith Wardill 1Participant @keithwardill1]

This is a 'long shot' – when I first got my minilathe (too long ago!), i had similar problems, with poor finishes on almost everything I tried. AFter many trials and tribulations (including all the suggestions here), I changed the bearings in the headstock for taper rollers (supplied by Arc Euro) – the differnece was unbelieveable – no chatter or odd noises, and the finish was vastly improved.

I know this sounds drastic, but may be worth considering – I nearly dumped the lathe until I did this.

[Ian PParticipant @ianp]

Chris

I'm not sure why you would want to use the internal jaws to grip a smaller diameter but regardless the last post does sound as if you are making some progress.

Do you have a grinder that you can use to make youur own cutters (or at least modify existing ones?

If you put some details on your 'profile' so that people here have an idea whereabouts you are located it may be that someone local will offer some practical help.

As others have mentioned you need a tool with no top rake for brass. with a oilstone or a diamond file you could quickly take the rake off just the very the tip of even a steeply raked tool.

Ian P

[DustyParticipant @dusty]

Chris

Have you tried adjusting the headstock bearings? if they are not properly adjusted it will not help your problem. Regarding a H.S.S. tool for brass If you get a suitable sized piece of H.S.S. for your lathe and the grind it with front rake and side rake of about 10 deg and angle the front of the tool to about 20deg stone a small rad on the tool at the junction of side and front rakes, then stone the top of the tool which should be dead flat (negative rake) and set it to cut on dead centre that should do the trick, and at the cost of less than a quarter of a ready ground tool.

[Sub MandrelParticipant @submandrel]

I second Dusty. For brass I use HSS just ground on the end and one side, left as is on top. I would use more like 600 rpm for 1 1/2" bar and expect a shower of chips but a decent finish.

Neil

[VCParticipant @vc44480]

Hi Chris

Long time ago I watched a pillar drill have one after the other of the drill bits be sharpened..

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