Cutting Speeds

[Justin ThymeParticipant @justinthyme24678]

Some very basic questions here.

is the cutting speed the (m/min) the relation between the cutter and the workpiece ?would using a 10mm dia mill be the same speed as cutting a 10mm bar spinning in the lathe.

 

I am thinking 3 types of tools here.

Carbon Steel – this being the more traditional type of tool
HSS –   as in High Speed Steel,
Carbide – which I guess refers to Tungtan Carbide

 

I seem to find different recommendations for m/min – but how do you find the following speeds for cutting mild Steel

Carbon Steel 20 m/min
HSS  35 m/min
Carbide 80m/min

 

and for making the calculations, lets say 12mm HSS Mill cutting Mild Steel with a touch of Cutting Fluid

 

RPM = (35 x 1000) / ( 12 *pi) = 928 RPM

and if you had a machine with belts and pulleys where exaxt speed an not be set – do you go to next one up, next one down, or just the closest.

 

 

 

[JasonBModerator @jasonb]

I just uploaded the first part of my article that appears in MEW340 to the site here which may help.

Cutting speeds for various metals/tools can be found in books and on the web, play safe and start with the slower option if using a belt or geared machine and see how it goes. Other factors will come into it such as depth of cut and feed rate eg with a deep cut you may find you get a better finish runnng on the slow side but light cuts will allow a bit above.

[BazyleParticipant @bazyle]

For a hobby time is not money so no need to be in a tearing hurry, though going too slow can also be a problem as with pushing a wagon you want to keep up the momentum and stiction can be a problem leading to jerky movement and cause of chatter.

Strictly according to theory the optimum speed is when the cut is progressing at the speed of sound in that material. This is what some of the tables and formulas are aiming at, and some are just folk law from years of trying things out. Going too fast can also create so much heat that the sharp tool loses temper and fails which is probably one of the commonest problems for amateurs.

[SillyOldDufferModerator @sillyoldduffer]

Avoid Carbon Steel on any machine tool made after about 1900.   Although hard and easy to sharpen, it softens at remarkably low temperatures, about 200°C, and goes blunt in a blink when overheated.   OK for cheap tools,  especially DIY woodwork, but even for woodwork HSS tools are a better bet.

HSS is not only tougher than Carbon Steel, but – most important – it resists softening up to about 500°C, making it much better suited to cutting metal without having to stop and resharpen frequently.    When HSS was first introduced, the old boys weren’t keen to adopt such new-fangled rubbish, not least because HSS couldn’t perform on well on spindly Victorian lathes lacking in power and rigidity. They claimed Carbon Steel can be ground sharper than HSS, which might be true, but that didn’t stop a suitably heavy machine fitted with HSS being 5 or 6 times more productive than carbon-steel cutters.

Carbide was the next advance.  It has a similar 5 to 6x advantage over HSS, basically because it can take a lot more heat without softening.

So cutting speed depends on the material and on what the cutter is made of.  In a production setting, speed and efficiency very much favour carbide, run at high-speed, on a rigid powerful machine, and taking deep cuts with a high feed-rate.  Carbide isn’t suitable for everything though, so HSS remains popular.    HSS does a good job, but the cutting speed has to be reduced compared with carbide.  Likewise, using Carbon Steel rather than HSS means cutting speed has to be drastically reduced again.   A Carbon Steel cutter run at HSS speeds soon fails.

On a hobby machine, HSS keeps it simple.   Many of the older classic machines don’t have enough RPM to get the best out of carbide, and even though most far eastern machines are faster, they too are on the slow side for carbide.

Duffer method, which gets me in the right ball-park, is roughly thus.

A good approximation for cutting mild-steel with HSS is rpm = 10000 / diameter of job (or drill) in millimetres.   This speed is also suitable for Bronze, Soft Cast Iron, and Copper.

Aluminium Alloys cut 3x faster than mild-steel

Brass and Free-cutting steel cut 2x faster than mild-steel

Stainless, Cast and Silver steel cut ½ as fast as mild-steel

Hard Cast Iron cut ⅓ as fast as mild-steel.

Having set the rpm by formula and above, I take an experimental cut.  It’s only the first step because a great deal depends on the exact material, and on the cutter, how rigid / powerful the machine is, how solid the work-holding, and whether coolant / lube is used.  In practice, I rarely change the RPM, instead tuning for best finish and progress by altering the depth of cut and feed-rate for best results on my machine.    If the machine has fixed speeds set to the nearest, and again tune by altering the depth of cut and feed-rate for best results.

I mostly use carbide, in which case I do the sum above as if for HSS, then multiply the RPM by 2 or 3.

The cutting advice in books and on the web is aimed at production engineers who must maximise efficiency.   Production speeds are  usually too fast and brutal for hobby and jobbing workshops.

The optimum cutting rate for a particular alloy depends on it’s internal structure, and massive amounts of information about that are available if need be.  But, bearing in mind the limitations of my hobby equipment, I’ve not found it necessary to do more than apply the rule of thumb approach described above.   The answer it produces is mostly ‘good enough’, and if it’s not, tweaking DOC and Feed-rate generally fix it.  Occasionally, I fail to get a good finish from carbide,  usually fixed by switching to HSS and slowing down, but some alloys are pigs!

Dave

 

[Clive FosterParticipant @clivefoster55965]

When it comes to multi-variate queries like Justins it’s annoying that the art of making nomograms seems to have been largely lost.

The great thing about a nomogram is that simply laying a ruler across the various scales and pivoting it about a chosen point on one scale clearly shows how things mutually change and interact. After trying this sort of thing on a few points you rapidly get a feel for whats going on and, possibly more important, whats important in particular case you are dealing with.

General advice and following rules of thumb just doesn’t easily generate this overview. Which can be limiting when it comes to how you work. Especially should you need to go “off-piste”.

Personal example here. I use one of the once common cardboard milling cutter speed-n-feed slide rules for my basic milling machine set-ups. Then tweak from experience. Which works adequately ‘cos I’ve been playing about with such things for “not admitting how many years” and run a Bridgeport which is large enough and heavy enough that I don’t have to worry about working around machine limitations in the manner that folk with more typical ME equipment do. The proper way to do things is to work things out from tooth load. Which I just don’t do, despite being easily capable of running the calculations in my head, because I’ve never bothered to learn how to visualise how tooth load actually fits int other great scheme of things. If I’d had a nomogram I’d have started out with tooth load and, probably, after the tenth cutter or so my visualisation would have been solid and I’d have been calculating things in my head pretty much automatically. Mr Osborns slide rule would have been a curiosity and the nomogram an almost never looked at wall poster in the same way as my lathe data. But I found a nomogram for later work very early on.

It would seem trivial to generate a nomogram from a spreadsheet file but I’ve never found a suitable computer program.

Clive

[JAParticipant @ja]

It should be remembered that quite a few things influence cutting speed such as time to do the job and lathe vibration. Really it is what you are happy with. This comes with experience and if you don’t like what is happening, first lower the cutting speed. There are some materials out there that no one will quote a cutting speed. The speed is found by doing trials.

I very rarely work out turning or milling speeds. There are far more difficult things to consider such as how are you going to hold the work.

JA

 

[SillyOldDuffer]

On SillyOldDuffer Said:

Avoid Carbon Steel on any machine tool made after about 1900.   Although hard and easy to sharpen, it softens at remarkably low temperatures, about 200°C, and goes blunt in a blink when overheated.   OK for cheap tools,  especially DIY woodwork, but even for woodwork HSS tools are a better bet.

 

I would not say avoid carbon steel. If you want to make a form tool, “D” bit, etc then you don’t really have much choice as HSS and carbide will be a lot more difficult to shape.

 

[SillyOldDuffer]

On SillyOldDuffer Said:

Avoid Carbon Steel on any machine tool made after about 1900.

Clang; that’s my jaw hitting the floor!

Here are some cutting tools made from gauge plate and silver steel, aka carbon steel, and running on 20th century industrial machine tools. Here’s a home made cutter, mostly using a hacksaw and files, cutting slots in steel:

A cutter made from gauge plate for cutting splines (actually the spaces) on a SG cast iron crankshaft:

And a hob made from silver steel free hobbing a cast iron worm wheel:

I use carbon steel, HSS and carbide as appropriate.

In general cutting speeds are not that critical. A caveat is that carbide inserts are more sensitive to cutting speeds and feedrates, especially with the more esoteric materials. Depth of cut and feedrate are as important, if not more so, that cutting speed. If the cutting tool is fed too slowly, so it rubs rather than cuts, then it doesn’t really matter what the speed is. The result will be the same; a fudged cutting tool.

As mentioned above the type of machine also plays an important part. Bigger, industrial, machines tend to be more rigid and can take heavier cuts, but experimentation is still needed.

Andrew

[Andrew Johnston]

On Andrew Johnston Said:

On SillyOldDuffer Said:

Avoid Carbon Steel on any machine tool made after about 1900.

Clang; that’s my jaw hitting the floor!

Here are some cutting tools made from gauge plate and silver steel, aka carbon steel,

…

 

 

 

Hurrah, after all these years I’ve finally caught Andrew out!   I’m not guilty because Gauge Plate and Silver Steel aren’t Carbon Steels!

By Carbon Steel I mean the medium and high carbon steels used since the dawn of time to make chisels, knives, axes, springs, and files etc.  In contrast Gauge Plate and Silver Steel are both modern alloys, the result of much metallurgical and scientific research in the last century.

From Wikipedia,  The definition of carbon steel from the American Iron and Steel Institute (AISI) states:  no minimum content is specified or required for chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium, zirconium, or any other element to be added to obtain a desired alloying effect; the specified minimum for copper does not exceed 0.40%;
or the specified maximum for any of the following elements does not exceed the percentages noted: manganese 1.65%; silicon 0.60%; copper 0.60%.

O1 Gauge Plate emphatically fails the AISI definition:  it’s an Alloy Steel, containing specific proportions of Silicon, Manganese, Chromium, Tungsten, and Vanadium.   Silver Steel is of similar composition, except no Vanadium, and perhaps some Sulphur and Phosphorous.   Neither is a Carbon Steel.

Victorian tool-steels were all Carbon Steels, the best available at the time because HSS, stainless and other alloy steels weren’t perfected until the 20th Century.   Carbon tool-steels are still useful, but avoid for cutting metal.  Their chief virtue is cheapness.

Dave

 

 

 

 

[Anonymous]

Silver steel and gauge plate are high carbon steels and are described as such by commercial steel stockists. Silver steel in particular is stated to be a carbon steel.

The way I read the quoted specification is that most elements (apart from iron and carbon) have no minimum requirement specified or required. That doesn’t mean the those elements must not be present. A maximum percentage is specfied for manganese, silicon and copper. Both silver steel and gauge plate do not list silicon and copper as present and the manganese percentage is well below the maximum figure listed. So in my book and, I think, the AISI they are carbon steels.

I suspect that an alloy of only iron and carbon is unobtainable so it’s a moot point as to whether it should be avoided.

Thwack; ball is now in SoD’s court!

Andrew

From the same Wikipedia page:

Carbon steel is often divided into two main categories: low-carbon steel and high-carbon steel. It may also contain other elements, such as manganese, phosphorus, sulfur, and silicon, which can affect its properties.

[Justin Thyme]

On 10 June 2024 at 14:36 Justin Thyme Said:

Some very basic questions here.

is the cutting speed the (m/min) the relation between the cutter and the workpiece ?would using a 10mm dia mill be the same speed as cutting a 10mm bar spinning in the lathe.

 

Yes and yes.

And re belt changes, yes go for the closest. Going a bit slower will reduce chatter and increase tool life. Going a bit faster may exacerbate these problems.

With carbide insert tooling, you can go twice as fast as with HSS. If chips are coming off blue but not sparking, you are doing well. But running that hot with with HSS will reduce tool cutting edge life.

Sometimes, if you just cannot get the tool to cut right, going one speed slower, or even faster, can cure the problem. A matter of harmonics on your particular machine – and the alignment of the planets.

 

[Michael GilliganParticipant @michaelgilligan61133]

I’m in a disruptive mood this morning … so please have a look at the video linked from this page:

https://www.eternaltools.com/carbide-gravers

It’s only a couple of minutes

Unfortunately there is no audio, and the spindle speed is not declared [so we’re guessing] but it seems to ride rough-shod over the dogma regarding Tungsten Carbide tools.

Andrew can probably explain it nicely in terms of chip-load or somesuch.

MichaelG.

.

Edit:and to add to the mystery, they state ‘Tungsten Carbide’ … but might they actually be ‘Carbide Steel’ [whatever that is] ?

Ref. https://contenti.com/engraving-tools/gravers-n-handles/carbide-steel-gravers

[Andrew Johnston]

On Andrew Johnston Said:

Silver steel and gauge plate are high carbon steels and are described as such by commercial steel stockists. Silver steel in particular is stated to be a carbon steel.

The way I read the quoted specification is that most elements (apart from iron and carbon) have no minimum requirement specified or required. That doesn’t mean the those elements must not be present. A maximum percentage is specfied for manganese, silicon and copper. Both silver steel and gauge plate do not list silicon and copper as present and the manganese percentage is well below the maximum figure listed. So in my book and, I think, the AISI they are carbon steels.

I suspect that an alloy of only iron and carbon is unobtainable so it’s a moot point as to whether it should be avoided.

Thwack; ball is now in SoD’s court!

Andrew

From the same Wikipedia page:

Carbon steel is often divided into two main categories: low-carbon steel and high-carbon steel. It may also contain other elements, such as manganese, phosphorus, sulfur, and silicon, which can affect its properties.

Well, what I mean by Carbon Steel is sometimes called ‘Plain Carbon Steel’.  They are allowed to contain Iron, Carbon, Silicon, Manganese, Phosphorous and Sulphur.   Adding anything else, notably Vanadium, Chromium, Tungsten, Molybdenum, & Nickel means we are no longer dealing with a Carbon Steel, because these elements are added for a specific alloying effect.  To add to the confusion, some of these alloys are called ‘Carbon Tool Steels’.

By my definition EN8 is a Carbon Steel, but EN24 definitely isn’t because the latter is alloyed.  Silver Steel is an alloy, not a plain carbon steel, because it contains Chromium.  And the Chromium was specifically added with malice aforethought by a metallurgist in order to achieve a desirable property not available from a plain Carbon Steel.

Next table indicates the properties of plain Carbon Steels: note they don’t contain any elements other that Iron, Carbon, Silicon, Manganese, Phosphorous and Sulphur.

These pages may be of further interest, in that they highlight Carbon Steels of the same mix can have different properties.

 

For example Rimming Steel and Mild Steel both have the same range of Carbon content, so one might expect their performance to be identical, and they’re not!   The difference is due to when the metal is extracted from the furnace.    Rimming Steel, also called Effervescent Steel, is taken whilst still gassing.   Too much gas would cause blow-holes and other problems, but just the right amount of fizz in the mix improves rolling properties, highly desirable in the right circumstances, but otherwise bad.     Mild-steel is ‘Killed’, that is not taken from the furnace until gassing has stopped, producing a general-purpose steel, better in every way except for rolling.  This sort of difference explains why machining random scrap in a home workshop can be a confusing disappointment.   All smiles if by good luck the scrap is a free-cutting mild-steel, but tears before bedtime if it’s a lump of rimming steel, or work-hardening stainless, or any of the many other alloys used by industry that don’t machine well.

An unlucky collection of scrap metal nearly derailed by career as a Model Engineer.   Try as I might, I couldn’t get my mini-lathe to turn any of it satisfactorily, chief symptoms being poor finish and tools struggling to cut,   Finally suspecting the metal, I coughed up for some known free-cutting Aluminium, Brass and Mild-steel, after which all was sweetness and light.   Now I’m more experienced, I can machine awkward metals if I have to, but results require much more experimentation with cutting speed and all the other contributory factors.  It’s not a matter of simply dialling in an RPM formula, though RPM is a good place to start!   Much easier to machine metals that are machinable, rather than to waste time hacking inappropriate scrap.    Appropriate scrap is fine.

Dave

 

 

 

 

[Michael Gilligan]

On Michael Gilligan Said:

I’m in a disruptive mood this morning … so please have a look at the video linked from this page:

https://www.eternaltools.com/carbide-gravers here It’s only a couple of minutes

Unfortunately there is no audio, and the spindle speed is not declared [so we’re guessing] but it seems to ride rough-shod over the dogma regarding Tungsten Carbide tools.

Andrew can probably explain it nicely in terms of chip-load or somesuch.

MichaelG.

.

Edit:and to add to the mystery, they state ‘Tungsten Carbide’ … but might they actually be ‘Carbide Steel’ [whatever that is] ?

Ref. https://contenti.com/engraving-tools/gravers-n-handles/carbide-steel-gravers

Interesting video! Really strange that there is no information on spindle speed. I wonder what is actually used – tungsten carbide or carbide steel?

[Anonymous]

SoD: So is there a plain carbon steel readily available, with a high enough carbon content, for making cutting tools that are hardened and tempered in a similar fashion to silver steel and gauge plate?

Andrew

[duncan webster 1Participant @duncanwebster1]

Sorry SOD, your definition disagrees with that used by that used by legions of engineers. Referring to Silver Steel, Tubal Cain (page 25 of Hardening, Tempering & Heat Treatment) says ‘these steels are carbon steels with additives to improve performance’. Tubal Cain real name was Tom Walshaw, here’s a link

https://en.wikipedia.org/wiki/Tom_Walshaw

He clearly knew what he was about.

 

https://www.westyorkssteel.com/tool-steel/silver-steel-bar/ describe silver steel as  precision ground carbon steel.

Don’t expect absolute logic in engineering, it’s been going on for too long.

[Michael GilliganParticipant @michaelgilligan61133]

There is a useful catalogue/catalog from Starrett available via this page:

https://watchmaking.weebly.com/toolmaking.html

Given the way that Starrett seems to be dumbing-down its product range, I suggest it’s worth grabbing.

MichaelG.

 

[Michael Gilligan]

On Michael Gilligan Said:

Edit:and to add to the mystery, they state ‘Tungsten Carbide’ … but might they actually be ‘Carbide Steel’ [whatever that is] ?

Ref. https://contenti.com/engraving-tools/gravers-n-handles/carbide-steel-gravers

Although the metal is being sheared the process shown is more akin to skiving. The shape of the tool is less important, provided that a sharp edge with zero rake is present. I am pretty sure the tool material is tungsten carbide; the point of the video is that being harder the tungsten carbide will last longer.

The dogma regarding tungsten carbide tooling refers mainly to inserts for the lathe I think. These are a different kettle of fish to the tool in the video as the cutting edge is generally not sharp; except for those inserts that are ground and polished for non-ferrous metals, before someone points it out. The insert shape is also carefully designed to roll and break chips. Inserts tend to work best with specified DOC, feedrate and cutting speed, most of which are applicable to industrial machines. Hence the disparaging comments in the modelling world. But the reality is more complicated. How an insert behaves depends upon the quality of the insert and is also strongly dependent upon the material as well as cutting parameters. Some materials will cut nicely over a wide range of parameters and with small DOC. Others need to be run at specific (high) speeds and DOC to get an acceptable finish.

Ages ago I offered to write some articles for MEW on turning different metals with insert tooling and quantative surface roughness measurements. Maybe the idea should be resurrected.

Andrew

[Michael GilliganParticipant @michaelgilligan61133]

It would certainly interest me, Andrew

Thanks for your observations.

MichaelG.

[JAParticipant @ja]

Ages ago I offered to write some articles for MEW on turning different metals with insert tooling and quantative surface roughness measurements. Maybe the idea should be resurrected.

Andrew

Andrew

Yes please. Although I do not use Tungsten Carbide tooling any good information on machining is useful.

One caveat. In the ME, please. I have just not renewed my subscription to MEW.

 

As for silver steel, it is a carbon steel since it has the properties of carbon steel and not high speed steel (as far as I am concerned).

JA

[Andrew Johnston]

On Andrew Johnston Said:

SoD: So is there a plain carbon steel readily available, with a high enough carbon content, for making cutting tools that are hardened and tempered in a similar fashion to silver steel and gauge plate?

Andrew

1095 Knife Steel for one.   But I admit many of the old favourites have gone, replaced by Alloy Steels because of their superior performance.

Dave

[duncan webster 1]

On duncan webster 1 Said:

Sorry SOD, your definition disagrees with that used by that used by legions of engineers. Referring to Silver Steel, Tubal Cain (page 25 of Hardening, Tempering & Heat Treatment) says ‘these steels are carbon steels with additives to improve performance’. …

I’m surprised this is controversial, because, with all due respect to Tom Walshaw, the definition I quoted is that of the American Iron and Steel Institute.   This is the crowd who:

… in the ’30s, it became apparent that the industry’s technical terminology had become chaotic. The Institute came to grips with the problem, and out of its efforts came the AISI steel products manuals. They provided makers and users of steel with generally recognized definitions, descriptions and practices pertaining to the manufacture, chemistry, metallurgy and adaptability of steel products.

The AISI definition isn’t unique to them.   This is from the Chambers Dictionary of Science and Technology:

By that definition, Silver Steel is not a Carbon Steel, because it contains Chromium.  Ditto Drill Steel and Gauge Plate.

Perhaps the confusion arises because two different approaches are used to classify steels.  Hence what British buyers call EN1B-Leaded, will actually be 9SMnPb28, 9SMnPb36, 11SMnPb30 or 11SMnPb37.   One approach categorizes steel by Usage & Mechanical Properties, the other by Chemical Composition.  Not making it up, I am quoting the official chemical definition of Carbon Steel.

Dave

 

[Martin ConnellyParticipant @martinconnelly55370]

I know the internet is not a 100% reliable source of information but I just thought I would copy this from Wikipedia since it matches all other sources of information:

Steel is an alloy of iron and carbon with improved strength and fracture resistance compared to other forms of iron.

Since steel is already an alloy I suggest that all this talk of plain carbon steel, alloy steel and non-alloy steel is the sort of talk that ends up muddying the waters of what people are talking about. We need better descriptions than those that are being used in this thread.

Martin C

[JasonBModerator @jasonb]

I think for all of us except Dave who has been trying to dig himself out of a hole the term Carbon Steel has always been taken to include Silver Steel and Gauge plate.

BTW Dave the US term is “Drill Rod” not Drill steel.

Maybe Dave should have looked at our good Editors Recently published A-Z of metals😎

[SillyOldDuffer]

On SillyOldDuffer Said:

On duncan webster 1 Said:

Sorry SOD, your definition disagrees with that used by that used by legions of engineers. Referring to Silver Steel, Tubal Cain (page 25 of Hardening, Tempering & Heat Treatment) says ‘these steels are carbon steels with additives to improve performance’. …

I’m surprised this is controversial, because, with all due respect to Tom Walshaw, the definition I quoted is that of the American Iron and Steel Institute.   This is the crowd who:

… in the ’30s, it became apparent that the industry’s technical terminology had become chaotic. The Institute came to grips with the problem, and out of its efforts came the AISI steel products manuals. They provided makers and users of steel with generally recognized definitions, descriptions and practices pertaining to the manufacture, chemistry, metallurgy and adaptability of steel products.

The AISI definition isn’t unique to them.   This is from the Chambers Dictionary of Science and Technology:

By that definition, Silver Steel is not a Carbon Steel, because it contains Chromium.  Ditto Drill Steel and Gauge Plate.

Perhaps the confusion arises because two different approaches are used to classify steels.  Hence what British buyers call EN1B-Leaded, will actually be 9SMnPb28, 9SMnPb36, 11SMnPb30 or 11SMnPb37.   One approach categorizes steel by Usage & Mechanical Properties, the other by Chemical Composition.  Not making it up, I am quoting the official chemical definition of Carbon Steel.

Dave

 

But I’m not an American. They can call it what they like. In the UK silver steel is a carbon tool steel.

[Author]

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