Shape of insert on Sherline Lathe

[Chris TickTockParticipant @christicktock]

Hi, due to the consensus of advice on using indexable inserts for cutting Silver steel on the Sherline lathe I need some more help.

I get the point that a weak insert will be indicated by a sharp angle. I get the point aluminium inserts will cut most metals including Silver steel. I also get the point that for general work they are absoloutely fine and that other choices can be made for micro machining.

So for facing and turning on say 5mm silver steel what shape is appropriate. It seems the triangular shape is the usual choice but why would you chose a 80 degree rhombus over a 55 degree rhombus.

Regards

Chris

[Chris TickTockParticipant @christicktock]

[JasonBModerator @jasonb]

You have just answered that "I get the point that a weak insert will be indicated by a sharp angle"

More pointed = more prone to damage.

A 55deg will get into tighter spaces which is when I use mine otherwise 80deg does the job and I also have holders that let me use the two 100deg corners so more economic

[John ReeseParticipant @johnreese12848]

I got a set of insert tools from Glanze. They use CCMT inserts. The 89* included angle lets you face or turn without re-orienting the tool. It also included holders that let you use the 100* corner so you can use all the corners of the insert.

[John ReeseParticipant @johnreese12848]

That should say 80* included angle.

[Chris TickTockParticipant @christicktock]

Posted by John Reese on 29/08/2019 21:42:31:

I got a set of insert tools from Glanze. They use CCMT inserts. The 89* included angle lets you face or turn without re-orienting the tool. It also included holders that let you use the 100* corner so you can use all the corners of the insert.

Thanks John I'm still making sure I understand the uses of the different angles so the 100 degree angle is used for smoother turning than the 80 and the 80 would be for smoother than the 55. But sharper included ange lets you get in to tighter spaces but does it allow more metal to be removed during turning. If not you would if you did not have to get in tight always chose a wider included angle?

regards

Chris

[JasonBModerator @jasonb]

The 100degree angle is good for roughing cuts as the obtuse angle is more durable but is not good for turning to a shoulder so when roughing you end up with something like this where the resulting internal angle is over 90deg.

OK for facing cuts though but you do need two holders, one for facing the other for turning along the length.

The 80deg corner is a good all rounder as you can leave the tool holder in one position to both face and turn plus being less than 90deg it will work into internal corners.

a 55deg tool starts to get a bit delicate so is better kept for lighter cuts or where you need access into tight places such as when working with the tailstock ctr in place.

So for an all rounder the 80deg corner is the best option and what I would use most of the time, just changing to the other shapes as and when needed depending on the job in hand.

The 80/100 inserts can also be used in boring bars and as they are a smaller overall size than the 55deg ones will fit down smaller holes.

[Steve CrowParticipant @stevecrow46066]

This might interest you Chris.

For the first time, I had a go at turning blue pivot steel with an insert tool on my Sherline rather than with a hand graver on my watchmakers lathe.

I used a DCMT (55 degree) insert with a 0.4 radius. The pivot steel was around 2.6mm OD and I turned it with about 15mm hanging out of the collet.

The diameters are 0.45, 1.2, 2.0 and 2.4 mm. The 3 smaller sections are 2mm long.

I experimented with different depths of cuts. It comes off beautifully with a 0.25 cut (0.5 mm total). Also finishing cuts of 0.01 mm are fine. Nice finish too.

It might not be a suitable method for completing a balance staff but you might be able to use it for roughing one out before finishing between centres.

After this, I intend to use pivot steel a lot more rather than silver steel. Amazing things those inserts! I've got to say, I'm a total convert.

Cheers, Steve

Edited By Steve Crow on 30/08/2019 16:01:45

Edited By Steve Crow on 30/08/2019 16:02:28

[Michael GilliganParticipant @michaelgilligan61133]

Nice demonstration, Steve

… it could hardly be more convincing.

Looks like a marriage made in Heaven:

The traditional material, and modern inserts

MichaelG.

[Steve CrowParticipant @stevecrow46066]

Thank you Michael. This was primarily an experiment and demo for myself also.

But, the dimensions are not random. I have a potential use for each diameter starting from the smallest. As one is damaged, I face it off and use the next one for a different purpose. Waste not, want not.

Steve

[Chris TickTockParticipant @christicktock]

Great posts Guys and whilst I see what Steve has acheived I can only reply with what my 2 horological experts have told me. I am not in a position yet to know for sure but I am advised blue pivot steel if from certain countries can be unreliable to work with therefore silver steel is preferred. One of my expert advisors does think inserts are fine the other a definite no no. Soon I hope to attempt such work on a slightly larger scale to see for myself. One thing is for sure I will be getting some inserts to appraise.

Regards

Chris

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Chris TickTock on 30/08/2019 20:17:30:

… I am advised blue pivot steel if from certain countries can be unreliable to work with therefore silver steel is preferred. …

.

Try using the small sample that I sent you, Chris

This is top quality vintage material, purchase at auction from the estate of a watch & clockmaker in Prescot.

… You will then have your own benchmark for the [variable] quality of the modern stuff.

MichaelG.

[Chris TickTockParticipant @christicktock]

Posted by Michael Gilligan on 30/08/2019 21:26:55:

Posted by Chris TickTock on 30/08/2019 20:17:30:

… I am advised blue pivot steel if from certain countries can be unreliable to work with therefore silver steel is preferred. …

.

Try using the small sample that I sent you, Chris

This is top quality vintage material, purchase at auction from the estate of a watch & clockmaker in Prescot.

… You will then have your own benchmark for the [variable] quality of the modern stuff.

MichaelG.

Thanks Michael I promise to try the blue pivot steel you were kind enough to send me so I can ideed have a bench mark.

Regards

Chris

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