I'm sorry if I raised doubts when I corrected my earlier posting – it simply occurred to me that my wording was unclear: if you maintain RPM constant, surface speed at the periphery would obviously increase with diameter; and it's surface speed you have to hold within limits, so to maintain that you must reduce RPM as diameter increases. I don't know how to make it any clearer.

Before delving into Rockwell hardness in particular, we must first understand what is meant by the term ‘hardness’. Hardness is one of many characteristics used to determine the overall durability and abrasive resistance of a material. It is a physical property defined as the ability to withstand surface indentation or localised plastic deformation. Generally speaking, it is a measure of a metal’s resistance to abrasion, scratching and indentation.

HRC Hardness chart

Maximum end mill size on the Sherline is realistically 1/4" and for that I would run at your maximum speed all the time except when fly cutting.

This article discusses what is meant by Rockwell hardness, the measuring process involved, how to understand the Rockwell scale and its application in determining suitable materials for their intended purpose.

This (A bigger end mill can cope with higher speeds removing metal.) sounds like feed speed as they are stronger and able to take the extra depth of cut..

HRC hardness full form

I just gave a generic speed for "steel" using HSS to show Chris how the numbers work in the formula, Speed could have been anything from 50 to 150 feet per min ( 15-50m/min) depending on what steel and type of cut, type of cutter, any coating, etc as per my previous comment. If you take a look at the likes of Tubal Cain in Model Engineers Handbook he gives us 2000rpm for a 1/2" cutter in free cutting steel in which case 800rpm is a bit tame

55 HRC meaning

Although the Rockwell method is the most widely used hardness testing method, it is not the only method for determining hardness.

It's cutter speed over the metal in metres per second that matters. Surface speed depends on RPM and tool diameter. To get the same surface speed a small diameter cutter has to be rotated faster than a big one.

Chris's first point is ambiguous: 'A bigger end mill can cope with higher speeds removing metal.' I'd restate it: 'A big cutter can remove metal faster than a small one.', which breaks the misleading link to 'speed' as used in No.2

Those last three can require quite good mathematical capability to resolve and may require data that isn't easy to obtain – so they are often only accurately resolved in volume production operations where the manufacturing cost saving would justify the resource cost in time and expertise.

Rockwell hardness is a series of indentation tests used to generate a standardised scale of hardness known as the Rockwell scale. The Rockwell testing method is widely used as it is highly versatile and relatively simple compared to other testing methods. It is often favoured commercially due to the speed and reliability of the tests, and it is also non-destructive. Materials can be tested numerous times without damage which is beneficial for heat-treated materials; for example, these will often require multiple tests before, during and after treatments. Other testing methods may result in damages caused to the test material.

Rockwell hardness scale

If you’re in the steel industry or simply looking to find the right type of steel for your tools, then you will have seen figures like RC60 or 45HRC. But what do these letters and numbers represent, and why is it important?

For more information about how we measure hardness and the range of steel products we have available, call (+44)114 233 5291 today.

The pair of inventors set about creating a testing method that was non-destructive, cost-effective and easy to implement – and that is precisely what they did. Over 100 years later, the Rockwell hardness test is arguably the most prominent testing method used today and will continue to be for years to come.

There’s fundamental problems with Tom’s tables in the past I have used them but i became exasperated with my copied tables until I realised the error why? His speed for a 1/4” 4 tooth endmill is 960 in steel with 1 -3/4” feed , yet for a slot drill it lists 1600 rpm and a feed of 3” min. He has the headings the wrong way round! If you follow this point then the tables are very low in cut per tooth

It's RPM that has to reduce in order to keep surface speed (unit length per unit time) at the periphery within working range.

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However, No. 1 can be correct in terms of volume per unit time of metal removal – providing the machine has the torque to achieve it, the mill and workholding have the strength to withstand it, and lubrication is adequate to prevent overheating.

How hard is steelcompared tosteel

I acknowledge carbon cutters can be run at higher speeds than HSS but as a generalisation is 1 or 2 my preferred mental guide as to RPM?

In 1914, Hugh M. Rockwell and Stanley P. Rockwell (surprisingly unrelated!) recognised the need for a quick and effective test used to measure the strength of materials. While working together at a ball-bearing factory in Connecticut, they realised they needed to find a standardised method for measuring the effects of heat treatment on their steel bearings.

Steam Model Days in the Industrie Museum in Lauf an der Pegnitz I am aghast at Mattel/Fisher Price Penny-Pinching New motor/esc for mill? Water tank Trapezoidal tap drill size ? Machining 1050 Grade Aluminium Spring material advice needed Tom Senior Vertical Mill Y axis stuck Verifying A Metal (Gilding Metal?)

All makes sense now. Nos 2 is correct. Nos 1 needs qualifying in terms of feed. If you were to feed a 1mm end mill too quickly it would not last long, especially if carbide (yes carbon was a typo). But that same 1mm carbide end mill needs higher speeds than say a 5mm.

May be a typo in Chris's Point 2 where he refers to Carbon Cutters running faster than HSS. Carbide Cutters can be run 5 to 20 times faster than HSS, not Carbon. Carbon Steel Cutters are run considerably slower than HSS and require careful attention to cooling because they can't take heat. These days most cutters are made of HSS, the obvious exceptions being Silver Steel, inexpensive taps and dies, and woodworking tools. (Which don't get hot!)

Steelhardness scale

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The Rockwell hardness test involves a mechanical operation where an indentation tool made of diamond is placed against the test subject. Then, a preliminary force is applied, and the indentation depth is measured. Next, the total force load is added, with the indentation depth measured again. The total force load is then removed, so only the preliminary force remains in action. The difference between penetration depth before and after the total force is applied is then used to calculate the Rockwell hardness number. The Rockwell Hardness number is calculated by the equation:

Steelhardness HRC

So from that you can see that to keep the materials cutting speed the same the RPM of a smaller cutter will be more than that of a larger cutter

Identifying the correct scale for the material you are testing can be difficult, but generally, the softer the material, the lighter you want the load to be. The same goes for thickness; if you have a thin material to test, you don’t want to choose a scale with a large indenter and heavy load as it will damage the test piece. Typically, if you are measuring hardened steel, you would apply the Rockwell C scale. Ideally, you would use the E or F Rockwell scale for softer materials as these have much lighter loads.

Overall, hardness is a significant factor you need to consider when selecting the most suitable materials for a particular purpose. To determine a hardness value, you can perform several tests, including the Rockwell Hardness Test, the Brinnel Hardness Test, Microhardness, Knoop, Vickers, and the Superficial Rockwell. In this article, however, we are focusing purely on the Rockwell Hardness Test.

The Vickers hardness test was developed in 1921 by Robert L. Smith and George E. Sandland. They set out to create a simpler version of the Rockwell test while still following the same overall indentation method. Differing from the Rockwell method, the Vickers test uses universal indentors and applies pressure for longer. Although the Vickers test can be applied to a broader range of materials than the Rockwell method, it is not the most common hardness-testing method. This is because it takes a long time to generate data, the indentation process damages the test material, and the equipment needed for the test is costly.

There are multiple scales to use when following the Rockwell method of hardness testing. Which scale to use depends on which type of indentor you use and the load you apply. For example, the Rockwell C scale uses the diamond cone shape indentor, and the B scale uses a ball-shaped indentor with a lighter load. The scales are abbreviated to HRB, standing for Hardness Rockwell B, and the same for the C scale (HRC). This is sometimes further abbreviated to just the letter R, followed by the scale letter (RC).

So from that you can see that to keep the materials cutting speed the same the RPM of a smaller cutter will be more than that of a larger cutter

= 1600*4* 0.001= 6.4 Inches per min. Tom’s numbers are at the bottom of this range, and he states the tables came from Clarksons Autolock Chuck data. with more modern spiral endmills with various coatings and the increasing use of carbide cutters in the home workshop, his tables aRe becoming outdated

It's RPM that has to reduce in order to keep surface speed (unit length per unit time) at the periphery within working range.

That would depend on what cutting speed they chose to use for steel, it's quite a wide range, coatings or lack of would also determine speed . Type of cut would also comes into it as a full width cut is usually run slower than a side cut.

This thread is a good starting point for this topic it is reachable through the home page under workshop processes but here is the link for it. Thread 95687 cutting speed tables

How hard is steelMohs

We are tool steel suppliers for the UK and worldwide. Our tool steels are manufactured under carefully controlled conditions to guarantee the highest quality results. The table below shows the tool steel grades we supply, with their Rockwell hardness values and uses.

Hardness is an important property to measure as it is an indicator of durability; the higher a material’s hardness value, the more resistant it is to wear and tear. Applying hardness testing to steel, or any material, allows you to determine whether or not it is the most suitable medium for the intended application. For example, if you need a malleable metal to make utensils, you wouldn’t choose one with the highest hardness value as it would be brittle and challenging to work with.

Home › Forums › Beginners questions › Milling Speeds for end mills This topic has 32 replies, 16 voices, and was last updated 8 November 2020 at 01:13 by duncan webster 1. Viewing 25 posts - 1 through 25 (of 33 total) 1 2 → Author Posts 23 October 2020 at 10:33 #10507 Chris TickTockParticipant @christicktock Advert 23 October 2020 at 10:33 #502885 Chris TickTockParticipant @christicktock Hi Guys, Have read contradictory advice over milling speeds for end mills. I should state I have a Sherline Mill Namely I have read: A bigger end mill can cope with higher speeds removing metal. RPM is approx the recommended 4 X CS (per metal) divided by size of cutter in inches.   Nos. 2 then means increasing speed as cutter size is reduced, Nos. ! implies the opposite. Which is right here? I acknowledge carbon cutters can be run at higher speeds than HSS but as a generalisation is 1 or 2 my preferred mental guide as to RPM?   Regards Chris Edited to fix formatting only. Edited By SillyOldDuffer on 23/10/2020 11:23:25 23 October 2020 at 10:53 #502895 Mick B1Participant @mickb1 No. 2 is correct in that surface speed at the periphery has to reduce as diameter increases. However, No. 1 can be correct in terms of volume per unit time of metal removal – providing the machine has the torque to achieve it, the mill and workholding have the strength to withstand it, and lubrication is adequate to prevent overheating. Those last three can require quite good mathematical capability to resolve and may require data that isn't easy to obtain – so they are often only accurately resolved in volume production operations where the manufacturing cost saving would justify the resource cost in time and expertise. 23 October 2020 at 11:02 #502898 EmgeeParticipant @emgee Chris In 1, are you confusing "volume of material removed" by a larger endmill with cutting speed ? A larger cutter will always win on volume of material removed provided adequate machine specs are suitable. Emgee 23 October 2020 at 11:07 #502901 Martin ConnellyParticipant @martinconnelly55370 This thread is a good starting point for this topic it is reachable through the home page under workshop processes but here is the link for it. Thread 95687 cutting speed tables Martin C 23 October 2020 at 11:21 #502903 SillyOldDufferModerator @sillyoldduffer Agree with Mick. Chris's first point is ambiguous: 'A bigger end mill can cope with higher speeds removing metal.' I'd restate it: 'A big cutter can remove metal faster than a small one.', which breaks the misleading link to 'speed' as used in No.2 It's cutter speed over the metal in metres per second that matters. Surface speed depends on RPM and tool diameter. To get the same surface speed a small diameter cutter has to be rotated faster than a big one. May be a typo in Chris's Point 2 where he refers to Carbon Cutters running faster than HSS. Carbide Cutters can be run 5 to 20 times faster than HSS, not Carbon. Carbon Steel Cutters are run considerably slower than HSS and require careful attention to cooling because they can't take heat. These days most cutters are made of HSS, the obvious exceptions being Silver Steel, inexpensive taps and dies, and woodworking tools. (Which don't get hot!) Dave 23 October 2020 at 12:00 #502910 Dave HalfordParticipant @davehalford22513 This (A bigger end mill can cope with higher speeds removing metal.) sounds like feed speed as they are stronger and able to take the extra depth of cut.. 23 October 2020 at 13:25 #502922 Chris TickTockParticipant @christicktock Thanks Guys, All makes sense now. Nos 2 is correct. Nos 1 needs qualifying in terms of feed. If you were to feed a 1mm end mill too quickly it would not last long, especially if carbide (yes carbon was a typo). But that same 1mm carbide end mill needs higher speeds than say a 5mm. Chris 23 October 2020 at 15:29 #502951 Mick B1Participant @mickb1 Posted by SillyOldDuffer on 23/10/2020 11:21:25:

Treat published speeds as a starting point and adjust to suit machine and job in hand and as I tend to find with teh smaller machines they are best run towards the fast side but with reduced DOC and possibly feed to keep the motor in the sweet spot and to compensate for their lower rigidity.

A general rule is that the higher the number, the harder the material – however, it is essential to remember that the hardness figures are relative to the scale used when testing them. To demonstrate, a soft steel may have a hardness of 70 HRB, while a hard steel may have a hardness value of 64 HRC.

View our helpful guide on how to choose the correct tool steel, or if you’re still unsure, contact our friendly team of experts who will gladly answer your questions and help you find the right tool steel grade for your intended use.

I agree with Martin C – whether milling or turning I'm very often using speeds very much lower than maximum with HSS tooling, and you can, of course, still obtain very satisfactory finishes. Carbide demands much higher speeds in some situations – I'm less inclined to use it because I'm uncertain of its flexibility in that regard.

I understood Mick to say in his 1st post rpm would have to be reduced to bring down the surface speed if using a larger cutter, although he didn't state rpm in his post, reducing the rpm reduces the surface speed at the cutter tip.

These recommended speeds are generally maximums for industrial use where time is money. For a tool material such as HSS they are the speeds at which you can expect overheating to occur which will reduce the working life of the cutting edge. It will not hurt the tool to be running below the recommended speed but there may be other issues such as the finish of the cut surface being poorer. For small cutters the biggest risk is that running them slowly requires a very slow feed rate to keep the chip load acceptable to avoid broken bits. Not too hard to achieve with well controlled motor drives or CNC but jerky hand wheel movements can snap a small cutter with ease.

The Brinnel method was devised in 1900 by Swedish engineer Johan August Brinnel. Brinnel’s approach also involves indenting a material and using this figure to determine the overall hardness value. However, instead of a small diamond, the indentor used is a steel ball; the resulting larger indentation causes a damaged test piece that is no longer fit for purpose. It may have been the first standardised example of hardness testing, but the invention of the Rockwell method meant that Brinnel’s test was no longer the most effective way to measure a material’s hardness.

The ground flat stock we manufacture goes through the same quality-controlled procedures as the rest of our products to ensure high hardness levels and durability. At Sheffield Gauge Plate, we have been manufacturing the highest quality ground flat stock for over 40 years. We stock a wide range of standard sizes to suit all needs. However, if you’re after non-standard dimensions, we can produce these on request; enquire via telephone on (+44)114 233 5291, or email our service team at sales@sgpltd.co.uk.

using the 4*cs/ dia yields 1600 rpm ( cs= 100 fpm) Using a feed per tooth as recommended between 0.0005” and 0.002” this yields a feed rate of