Having trouble turning grooves

So I made my first cuts today on my first lathe (Cowells ME90)

All went reasonably well and I managed to produce some fairly satisfactory results turning and facing some 20mm brass round.

I wanted to cut a recessed groove into the brass. say 5mm deep by 5mm wide, so thought I would use a parting tool see photo below

I started getting a lot of chatter and unsatisfactory results so reduced the speed and gave a slight hone, which didn't help a great deal...

I also tried this cutter, since it was thicker...

not entirely sure the actual purpose of this cutter but since it had a flat top and right angle sides, I assumed it might be up to the job, alas I was wrong.

Any ideas where I could be going wrong?

Edited By Frances IoM on 04/08/2018 17:37:52

Edited By Frances IoM on 04/08/2018 17:38:45

For what it,s worth [not much,perhaps ] but I have managed to cut good grooves in steel,using my rear mounted tool post,tool mounted upside down,even using form tools,which are never kind to lathes.

No doubt others more experienced will be along to help put you right,just hang in there.

By the way,I found a slow speed worked a bit better.

You could try making the tool a little narrower than the groove that you require, and move it from side to side as the groove deepens. Also, I had a similar problem a while ago on some rather "odd" brass, and found that a little negative rake helped a lot.

It's not the best photo but the 1.5mm blade does look a bit blunt to me. You should have no problem with one of those even on the smaller lathes an an easy material like brass. Slide the blade back into the holder a bit more to reduce the distance from the tool post as much as possible.

The wider tool will put quite a load on the Cowells so I would expect some chatter from that.

On enlarging the pic it looks as though the 1.5 mm blade is dull / has a radius on the cutting edge which is where I assume you mean ...​'

...'gave a slight hone, which didn't help a great deal'...

​It needs to be really sharp on the tip otherwise you are 'rubbing' rather than cutting. I assume that you have the tip dead on centre height ( no insult intended ) otherwise you will be 'rubbing' just under the tip if the tool height is high, conversely if the tool height is 'low' then the tool will be 'dragged under' as the work tries to climb over the tool tip... broken tool / work / both.

​Once you start to 'cut' continue to feed the tool in at a steady feed, iirc your machine is too small to have a power x feed so you will be feeding in by hand, keep it steady & constant & you'll be ok. As with all of us at some time or other we have been frightened by parting off, gingerly feeding in then immediately withdrawing the tool as soon as it chatters, don't! keep the in feed going, with practice you'll soon get to 'feel' the cutting action & know when to increase / decrease the in feed.

As for lubrication...
Brass / Cast iron ... dry.
​MS & other ferrous material... Neat cutting oil or similar applied with brush works fine, ( for me )
​Aluminium... WD40 does fine for me, other members use a variety of mixes so...

Enjoy

George.

I have the same parting off tool and a small Proxxon PD230 lathe which I use for making clock bits.

It´s a matter of feel for speed and how fast to feed. Sometimes it will scream a bit but the finish is OK.

- one more vote for sharpening the blade and reducing the over hang,

- also make sure the tool is set a little below centre.

-

I think you've got too much protrusion on your parting tool in pic 1.

The game is usually to set it accurately to centre height, minimum tool protrusion to reach depth or cut the piece off, as close to the chuck as you can get away with, about half nominal surface speed for starting, a sharp tool kept well into the job and maybe a spot of oil.

Like I said,loads of expert help out there. Give it a bash !

Thanks guys, some really great advice to get me going there, I actually have a 1/8" cutter blank that came with the lathe so I will grind that at some point. I think you are correct about too much protrusion as there was a lot of flex.

Thanks for the explanation of WHY tools need or rather recommended to be set centre height as well mechman. Every learning material I have read states to set it centre and as daft as it may seem I never knew why as no one explained it, but now it makes sense.

That smaller parting tool actually has a side rake angle, Does it need that? or can I grind it off? I only ask because when I tried to make the groove I could get a square edge on one side (left) then the other (right side) was obviously tapered because of that rake ground in the tool.

Steve, best not to have any angle on the front when grooving, even if parting if excessive it can cause the blade to cut towards the point giving a concave/convex cut.

Emgee

I would blame the parting tool holder, with that overhang there looks nothing much to stop the cutting edge pivoting on the front and lifting the back edge as the clamp looks very flimsy.

Side rake is to give clearance

I agree with Jason, the tool looks blunt, in fact the cutting edge looks rounded. You are no stoning the cutting edge by mistake by any chance?

I was trying to just hone the front face, but there is definitely a good chance I did a bad job it was slightly tricky for me trying to maintain the compound bevel angle that was ground on it with such a narrow edge.

Don't think there is much to blame with the tool holder, probably mor rigid than the little Cowells.

As the others have said grind the end straight across which will also help prevent it wandering sideways, make your groove with a plunge cut at each end to define the width almost to depth, plunge out the waste in teh middle also almost to depth then move the tool from side to side feeding in a thou or two at a time.

Same tool but a bit of 40mm EN1A did all thos efin grooves and the recess in one go no sharpening between cuts.

It looks like you need to touch it on the bench grinder, not a hone stone. Edge should be about sharp enough to cut your finger.

It helps a lot, too, to lock the carriage and top slide while parting or grooving.

.

... or, to avoid getting blood on a nice little machine;

sharp enough to 'noticeably drag' when sliding it across your thumbnail [with no additional weight or pressure applied] ... if it skids, it's blunt.

MichaelG.

Edited By Michael Gilligan on 05/08/2018 07:45:20

Test honed edges by seeing if they will slice a sheet of copier paper. If you obtain a clean cut then they are sharp enough.

When turning fins on model aircraft engine cylinders a re-cycled piece of hacksaw blade makes a useful cutting tool.

Biggest PITA is making the tool holder.

* Danny M *

Thanks Guys, so with me not owning a grinder at the moment and confined to a kitchen table... I had to resort to a mini proxxon belt sander to grind the bevel off the parting tool. Which seemed to do a much better job than I expected to be fair.

installed the new ground tool in the holder and readjusted to shorten the protrusion as suggested nipped up the small clamp on the parting holder only slightly and the chuffing allen head broke off. Only spare bolts I have don't fit can't quite work out the size and pitch.. appears to be 3mm x 1mm pitch but the head itself was an imperial size, so either way I'm out of action until I can figure out the size and source a spare bolt or a better parting tool holder, since someone mentioned that model doesn't look too great.

That sounds Great Danny. How does the hacksaw blade stay tentioned? 

Edited By Steve Sherlock on 05/08/2018 15:14:08