New member trying to machine silver steel

[nmw01223Participant @nmw01223]

Just to describe myself, as requested:

I’m a retired design engineer, but over the years have done a fair amount of hobbyist metal working – starting with a six month workshop training course over 50 years ago now. Got a very old small 8″ swing Myford lathe, arc welder, pedestal drill, small CNC router, 3D printer etc.

Introductory question: need to machine circlip grooves in some 1.5mm silver steel bar. The grooves need to be 0.5mm wide, and 1.2mm bottom diameter. First attempt, despite feeding very slowly, with an HSS tool (which from what I read should be OK) bent the bar and snapped the (very fragile) tool. Think I ground too much top rake on to the tool and it dug in. What should the top rake be for something like that?

[Andrew CrowParticipant @andrewcrow91475]

<p style=”text-align: center;”>Hello and welcome to the forum, I’m sure there will be a few more replies within lots of advice.However, my suggestion is that there probably isn’t anything wrong with the tool more likely with holding such a small diameter in a chuck on an old machine.
The chuck is probably a bit bell mouthed with lots  of use and is unable to grip such a small diameter right at the business end so that the bar has probably bent as you started to cut.
My suggestion would be to get an ER collet chuck that mounts on the  Myford spindle plus a suitable collet then you can cut the groove as close to  chuck as possible. Also don’t run the spindle too slow silver steel should be cut at about 15 metres per minute.</p>
I think that works out at about 30000 revs for 1.5mm diameter, I don’t think the Myford will run quite that fast but give it the best you can.

Andy.

[bernard towersParticipant @bernardtowers37738]

Any particular reason its got to be silver steel?. I find it very overrated for a lot of jobs, its difficult to tuirn with a good finish and yes parting off/grooving not for the faint hearted. collets do make it better and the small dia stuff i turn is travelling very fast when I have to use it.

[JasonBModerator @jasonb]

In the past I have run a Dremel cut off disk up against the rod to cut grooves. These days I use a Minithin parting tool with suitable width bit. As Has been said such a small diameter will want to climb over the tool so keep stick out to the minimum. If you chuck is worn or not closing down well then make a larger split bush of larger diameter.

 

These are 3mm Silver steel grooved 0.6mm wide for the E-clips The inserts have very little top rake.

[bernard towersParticipant @bernardtowers37738]

The split bush will still be in a bell mouthed chuck!

[SillyOldDufferModerator @sillyoldduffer]

Parting off on small lathes is notoriously difficult.  Lack of rigidity seems to be the main reason.   Parting off large diameters on a big lathe in good condition is much easier.

Andy mentions a bell-mouthed chuck, but anything that’s a bit off or can move will cause trouble:

• The job itself bending – very likely with thin rod, and especially Silver Steel, which isn’t easy to machine.  Minimise overhang, support the rod, cut as close as possible to the chuck, sharp cutter etc.
• Worn headstock bearings, bed, or cross-slide screw/nut.   (Fix lathe)
• Loose Gibs (Adjust)
• Bendy front tool-post (Substitute a Gibraltar-style rear tool-post, ideally cutting in reverse)
• Centring the tool on a small diameter rod is extra-fussy.  Slightly too high is bad, and so is much too low.   A ⌀1.5mm rod doesn’t allow much lee-way – a small error might be ‘much too low’!

And in addition to that lot,  a steady hand is vital.  As the slightest operator wobble is likely to be punished immediately, use power feed if the lathe has it.

I’d expect nmw01223 to suffer multiple failures getting this job done because it’s difficult.  Tempting to try Jason’s Dremel approach.  Grooving ⌀3mm rod, I cut a V with a sharp cutter first, and then opened it up with a parting tool.  The idea was to reduce the load on the parting tool, hence less bending forces on the lathe and job.  Although it worked for me, I’ve not seen the method mentioned elsewhere, so might be flawed.

Dave

[nmw01223Participant @nmw01223]

Thanks for all the comments, very helpful.

Play I had considered, but not a bell mouthed chuck. I’ll look into that. It is definitely a very old lathe and not in that good nick. I’ve had it 50 years and it was antique when I got it.

The reason for silver steel is I needed something pretty tough, ie not mild steel, and of an accurate diameter, silver steel seemed to fit the need – but it doesn’t specifically need to be silver steel.

The idea of a Dremel cut off wheel – well, actually, after the broken tool, that’s what I did with a 409 cutoff wheel, with the Flexi extension clamped to the tool post. Worked fine, except the grooves are U shaped, not square. Not sure if under any load the circlip might be able to be pushed off. The groove depth is also a bit of a guess as the wheel wears away so fast. I’ll look into other parting tools.

Thanks for the useful comments.

[DiogenesParticipant @diogenes]

You might be able to reduce the internal radius with a small tool now the bulk has been ‘roughed out’  – to go back to your original query, you probably won’t need any top rake – but do make the cutting edge as sharp as you can, ideally finishing by hand with a slip, not forgetting to give the corners a lick just to knock the points off.

I wouldn’t eat into the root of the blade trying to make ‘proper’ relief ‘going back’, but just stone a tiny bit off – you can always stop & dress it a bit more if rubbing is evident.

 

 

[bernard towers]

On bernard towers Said:

The split bush will still be in a bell mouthed chuck!

But the thin flexible wire will be supported right at the end of the bush, Decent length and diameter bush will be held rigidly enough, if you are really fussy turn a taper on the OD of the bush to match jaw wear.

Could even use a solid bush with grubscrew to lock the work and hold in a 4-jaw if the 3-jaw is knackered.

Other thing to mention is tool height becomes more critical as the diameter of the work get smaller.

[Brian WoodParticipant @brianwood45127]

If I may add a few pennyworth.

Try silver steel as the rod material, it is not stainless but a good deal tougher than mild steel and easier to work with. Brass is another alternative but be careful, that can grab and do unexpected things.

Another possibility is to follow up the Dremel cutter with tooling to scoop out the round bottom.

Are you able to add tailstock support to provide as much stiffness as possible?

Finally, put the job out to a volunteer!

Regards   Brian

Ooops, sorry. Elderly brain translated the material into stainless, Terry Wogan beware.

 

[JasonB]

On JasonB Said:
Other thing to mention is tool height becomes more critical as the diameter of the work get smaller.

I think that’s probably the real “killer”

… the truth is that the finesse of adjustment needs to suit the scale of the work.

MichaelG.

[DellParticipant @dell]

I use silver steel to make very small parts in restoring torsion clocks , IE small screws 12BA & 1.1mm but I find turning them down using a HSS graver much more reliable than using the crosslide even when cutting very fine , I don’t know if it’s the shape of the tool bit but definitely less chance of bending the steel, I also turn blue steel down with graver when re pivoting and that’s harder than silver steel but the most important thing is minimal stick out from chuck/ collet and if you need to have quite a bit stuck out put a sleeve in tailstock to slide stick out into for support.

[JasonBModerator @jasonb]

Looks like you have it sorted but while waiting for a soldered fabrication to cool down I had a go.

First as I did not have any 1.5mm Silversteel I turned down some 1/8″

My 3-jaw does not close down to 1.5mm so as the 5C was on the lathe I used that to start with. Left it in low range so about 1000rpm for all.

0.7mm with carbide insert 0.012″ off dia = 0.3mm, You can see the top rake of the insert. If not filming I would have used a bit of cutting fluid for all the grooving cuts

Then I had a dig about to see what HSS I had, can’t remember what this one was ground for but measured 0.4mm wide, just eyeballed ctr height, cut OK in the collet. Shot of top rake at the end

But what is that about worn chucks. So dug out my Unimat 3 chuck that is 49yrs old and as you can see not that true when on an arbor held in the 5C but agian cut OK even if the result was a bit eccentric

Photo of the two insert cut grooves and then the three HSS, one at the end was in the collet

[Michael GilliganParticipant @michaelgilligan61133]

2:36 of inspirational video, Jason

MichaelG.

[Chris CrewParticipant @chriscrew66644]

Any parting-off, IMO, needs to be done from a rear tool-post and lubricant/coolant – and lots of it. If I were to be cutting circlip grooves in any material I would use an old hacksaw blade suitably ground and mounted in an old fashioned J&S tool holder in the rear tool-post.

[JasonBModerator @jasonb]

Bit more Front mounted inspiration for those that may need it, First image cut dry.

 

 

[nmw01223Participant @nmw01223]

That is a very interesting video, thanks. Makes me think I ought to be able to do it (doesn’t mean I can). I had way too much top rake, I think, looking at yours it seems to be in the 0-10 degrees range? Mine was a lot more, based on an existing tool. Well, since I’ve broken that one, I’ll have to grind it again anyway.

Hacksaw blade idea is interesting, as is the HSS graver (never heard of it, just looked it up).

[JasonBModerator @jasonb]

5deg at the most on the inserts and about 1-2 deg on the HSS.

If using a hacksaw blade make sure you cut with the HSS part a smany are Bi-metal and the main backing is not really upto cutting.

[nmw01223Participant @nmw01223]

Yes, mine was 10x that at least.

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