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Should I begin with mild steel on lathe?

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Chris TickTock15/08/2019 10:19:08
163 forum posts
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Hi Guys, Firstly I have a Sherline Lathe which I wish to improve my very basic skills. From various places including this forum people have kindly offered advice on cutters, cutting fluid and suitable metal for cutting for particular jobs. My question is as I only have limited experience machinig brass should I buy the cheaper and softer mild steel to practice various cutting techniques with before using the desired metal (Silver steel). If I do is mild steel machinable as is or will it need tempering etc?

Kind Regards

Chris

Emgee15/08/2019 10:23:10
1157 forum posts
206 photos

Chris

If you are in the UK get some EN1A steel, this is free cutting and a good place to start.
Some mild steels will be difficult to attain a good finish, they tear rather than clean cuts.

Emgee

Roger Woollett15/08/2019 10:27:00
106 forum posts
3 photos

If you are aiming to machine silver steel then mild steel would be fine to practice on.

Do buy free cutting mild steel from a reputable supplier (there are many who supply model engineers). With a small lathe like the Sherline it is important to use a sharp tool.

When you come to silver steel halve your speed.

Michael Gilligan15/08/2019 10:38:12
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13780 forum posts
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Chris,

I evidently mis-interpreted your question in this previous thread !! **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=143775

[quote]

I wish to learn how to machine parts for platform escapements namely the balance staff which is approx 20mm long

[/quote]

.

MichaelG.

Neil Wyatt15/08/2019 10:40:29
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EN1a Pb is the most free-cutting of all steels and is a good choice for practice.

Expect to be horrified when you move to silver steel as suddenly any the effects of shortcomings (e.g. blunt tools, wrong depth of cut, wrong speed, loose gibs) will be magnified.

Thats said it is definitely a good idea to get started on a more forgiving material. Using cutting oil, applied by brush, helps too, especially with silver steel.

Some people start out with aluminium and get very frustrated - it needs very sharp tools to avoid 'tearing up' the surface and metal can build up on the tool point very quickly leading to poor results.

Neil

Steve Crow15/08/2019 17:34:27
146 forum posts
32 photos

I get excellent results on my Sherline with silver steel using CCGT inserts with a 6mm JB Cutting Tools holder.

Also with Arc Euro 6mm HSS Co5 tools.

They also work great with brass and EN1A.

With small stuff, It's important to get the centre height bang on.

Edited By Steve Crow on 15/08/2019 17:37:05

Mike Poole15/08/2019 18:52:28
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As an apprentice we were started off on ordinary mild steel but we had the benefit of an instructor to oversee us so that advice could be given if we had not listened or were having trouble putting it in to practice. There is plenty of guidance in books and sources like YouTube. Being sure of what you are machining is important as steel looks much the same but the machineablity can vary widely depending on its specification. There are many variables in setting up a tool and all need to be correct to give yourself the best chance. Correctly identifying the material will give you the figures for speeds and feeds depending on your chosen tool material, if you are hand grinding HSS tools then the material you are working will define the angles needed for your sharpening. If you want to use carbide tipped tools then you need to select the correct tip, some are pretty general purpose and some are very specific purpose, fitting a random tip could be a problem if it is unsuitable for the task. If you follow a process to get the tool set up with minimum overhang, correct edge angles and tool height and the set the correct speeds and feeds then you have a starting point. The recommended figures are a good place to start and if things aren’t working out then adjust things methodically until you are satisfied. Treat recommended settings as a starting point and adjust to suit your machine.

Mike

Chris TickTock15/08/2019 19:18:04
163 forum posts
1 photos

Really useful advice guys will get back to you once I have reflected on all your points.

Regards

Chris

Jens Eirik Skogstad15/08/2019 20:04:16
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370 forum posts
22 photos

Hi, not just what material is easy to cut on lathe etc .. I read through the comments, nothing written a word about the cutting angles of lathe tools. The cutting angles are equally important when cutting a particular material with good results.

Read this link..

**LINK**

Chris TickTock16/08/2019 10:38:40
163 forum posts
1 photos
Posted by Steve Crow on 15/08/2019 17:34:27:

I get excellent results on my Sherline with silver steel using CCGT inserts with a 6mm JB Cutting Tools holder.

Also with Arc Euro 6mm HSS Co5 tools.

They also work great with brass and EN1A.

With small stuff, It's important to get the centre height bang on.

Edited By Steve Crow on 15/08/2019 17:37:05

Hi Steve what exactly is a 6mm JB Cuttings tool holder and where can i sorce one from. The main problem identified with inserts according to a poster here is fine cutting are the CCGT insets up to precision work?

Chris

Chris TickTock16/08/2019 10:44:04
163 forum posts
1 photos

Thanks Guys just a general question about a tangential tool holder. As a beginner my first thought is to try to lock onto the general concept. So am I right the main point / advantage of the tangential tool holder is to create a tool post that holds a HSS cutting bit at the angles necessary to acheive machining on a lathe but without having to grind all the angles on the tool bit that would be normal in a standard tool post. Thus one edge only to sharpen???

As always there are alternatives but what can be the disadvantages of the Tangential tool holder?

Chris

JasonB16/08/2019 10:48:10
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Chris, this is a typical holder that will do for both facing and turning along the length of the work. Most SCLCR holder swill do the same job not just those from JB.

Yes the CCGT wips will be precise, probably more so on the finer work you intend to do as they won't make it deflect away from the tip so much particularly if you select one with a 0.2mm tip radius which will have a code CCGT 060202

One disadvantage of the Tangental holder is that I don't think you will be able to buy one off the shef to fit your small Sherline lathe but happy to be proved wrong.

 

Edited By JasonB on 16/08/2019 10:54:39

Chris TickTock16/08/2019 10:56:48
163 forum posts
1 photos

thanks Jason sorry I thought initially we were referring to another post holder as the bits are 6mm and the Sherline holder is designed for 1/4 inch but all you need to do is shim to acheive alignment. As you have introduced the notion of insert radius and the effects upon cutting can you add something here. So what is the effect of no radius, little radius and large radius, where does a 0.2mm fit in here?

Chris

Martin Hamilton 116/08/2019 11:19:36
130 forum posts

On my Sherline i use inserts & hss, the ones i use of choice by a long way are the aluminium inserts. DCGT070204, CCGT060204 & TCGT1102040, these are fantastic inserts for Alu, brass & steel including silver steel. They give a finish like you would,t believe, i also use DCMT & CCMT inserts as well sometimes. I use a QR tool post on my sherline & 10mm insert holders mainly + a couple of 8 mm insert holders.Re taking fine cuts & precision with inserts, this is where the aluminium inserts really shine ( no pun intended on surface finish ), you can take cuts that fine that the metal comes of not as swarf they are to small to be called that really. You see more shinny particles glistening in the light rather than swarf falling, more of i dust coming off. Of course you can also take much deeper cuts also with the aluminium inserts, these are very sharp inserts indeed & care needs to be taken on catching your fingers & hands on the tool.

Edited By Martin Hamilton 1 on 16/08/2019 11:21:53

JasonB16/08/2019 11:20:48
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With no radius if you magnified the cut surface it would look like a very fine screw thread being made up of a Vee shaped helix and could feel quite rough but the pointed corner of the tool will easily cut into the material* . Another problem with a pure point is that it would wear very quickly and also be prone to damage particularly on brittle carbide tooling.

On the other hand a large radius will tend to flatten out the magnified form so you will get a smoother finish. however the larger contact area can increase the chance of the tool deflecting slender work and if deep cuts are taken you can also start to get chatter along the increased area being cut. A more rounded tip will have the advantage of being more durable.

Another thing to consider about a tool with a rounded end is that when working into a corner the face and edge will not meet at a crisp angle, this needs to be taken into account if something is going to be slid onto say a spigot turned on the end of a shaft usually by chamfering the mating holes edge. Where parts will be stressed it is an advantage to have a rounded internal corner as it helps to dissipate the stresses thus reducing the risk of a fracture starting in the corner.

* the angle of the tool also plays a big part in what the surface may look like. Taking the thread example if you had a tool with a large clearance angle behind the cutting edge it would form more of a Vee than one with a shallow angle that tends to flatten things out in much the same way that a rounded corner will do. Luckily the C*** inserts being discussed give a shallow 5degree angle behind the tool so you get the best of all the available shapes. The down side is that in some situations this can prevent you getting to the work and a more pointed shape will be the best bet such as when working close to a tailstock centre where a DCMT tip and matching holder are ideal.

So it's a case of weighing up finish, durability, work in hand, access, etc and picking the best combination for the job.

Martin Hamilton 116/08/2019 11:32:39
130 forum posts

I use the GT inserts with an 04 radius tip because this seems the cheapest & more popular size from places like Banggood where i get my inserts. I looked at the 02 radius tips which are quite a lot more expensive than the 04 tips & not so available from the cheaper shall we say suppliers in my experience. If anyone knows where you can get DCGT070202 inserts for £7-£8 for 10 inserts like i do with the DCGT070204 i would deff buy some.

Lainchy16/08/2019 11:44:42
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93 forum posts
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I don't want to change the direction of the thread here, but quick question... I have one of the 5 piece sets they sell at RDG, it came with my lathe. Fitted with TCMT inserts. Is it possible to change to other inserts. The naming standards are very confusing as a noob. I ordered some new inserts from Banggood for it anyway.

Looks like they are VP15TF inserts TCMT110204

Edited By Lainchy on 16/08/2019 11:50:50

JasonB16/08/2019 11:48:24
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Few quick sketches to illustrate the effect of tip radius on a CC** tip on finish for the same given feed rate.

Zero radius

r0.jpg

0.2 radius

r2.jpg

0.4 radius

r4.jpg

0.8 radius

r8.jpg

JasonB16/08/2019 11:51:00
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Posted by Lainchy on 16/08/2019 11:44:42:

Fitted with TCMT inserts. Is it possible to change to other inserts. The naming standards are very confusing as a noob. I ordered some new inserts from Banggood for it anyway.

You will have to stay with triangular inserts of the same size and fixing method anf relief so the first, second & fourth letter and first two numbers will have to stay the same in the code otherwise you can use other tollerances, , tip radius and any one of the many coatings and material specific geometries.

 

 

 

Edited By JasonB on 16/08/2019 15:42:14

Chris TickTock16/08/2019 11:58:52
163 forum posts
1 photos
Posted by JasonB on 16/08/2019 11:20:48:

With no radius if you magnified the cut surface it would look like a very fine screw thread being made up of a Vee shaped helix and could feel quite rough but the pointed corner of the tool will easily cut into the material* . Another problem with a pure point is that it would wear very quickly and also be prone to damage particularly on brittle carbide tooling.

On the other hand a large radius will tend to flatten out the magnified form so you will get a smoother finish. however the larger contact area can increase the chance of the tool deflecting slender work and if deep cuts are taken you can also start to get chatter along the increased area being cut. A more rounded tip will have the advantage of being more durable.

Another thing to consider about a tool with a rounded end is that when working into a corner the face and edge will not meet at a crisp angle, this needs to be taken into account if something is going to be slid onto say a spigot turned on the end of a shaft usually by chamfering the mating holes edge. Where parts will be stressed it is an advantage to have a rounded internal corner as it helps to dissipate the stresses thus reducing the risk of a fracture starting in the corner.

* the angle of the tool also plays a big part in what the surface may look like. Taking the thread example if you had a tool with a large clearance angle behind the cutting edge it would form more of a Vee than one with a shallow angle that tends to flatten things out in much the same way that a rounded corner will do. Luckily the C*** inserts being discussed give a shallow 5degree angle behind the tool so you get the best of all the available shapes. The down side is that in some situations this can prevent you getting to the work and a more pointed shape will be the best bet such as when working close to a tailstock centre where a DCMT tip and matching holder are ideal.

So it's a case of weighing up finish, durability, work in hand, access, etc and picking the best combination for the job.

Great explanation Jason, very helpful.. Would any cutter even when maching precision very small items have a radius on its cutting point/ I ask this as on another forum a renowned craftsman and horologist only uses braxrd carbide for this type of work as he cannot get the precision required with inserts. This must mean almost no radius surely/ At my stage of the game it matters little but being aware of pitfalls in precion maching cannot be a bad jhing?

Regards

Chris

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