While I would agree with the 1 thou (0.025mm) chip load for most cutters when you get down to the very small you have to take their strength into account and reduce the load on them hence the 0.003mm I suggested which is almost 1/10th the loading. Keep the 1 thou for 6mm and above dia cutters.

I forgot I had an ER 32  – R8 chuck! Another tool justified, Hurrah! 5000rpm, carbide stub mill, dry…. smooth like butter (I listen to Kpop in the workshop). And the mill seems to have ‘worn in’ a bit at the 5000rpm now.

How flat is ‘optically flat’? If you are looking for something that is better than a few fringes, then it is a bit of an art!

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What life should I expect from small cutters and what speeds/feeds would be best? To finish, I’ll be getting a carbide 2 flute and run it at 5000 unless advised otherwise.

Corner-radius end mills have slightly rounded corners that help distribute cutting forces evenly to prevent damage to the end mill and extend its life. They can create flat-bottomed grooves with slightly rounded inside corners.

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It comes with a trade-off, unfortunately. The end mill will be weaker and won't sustain heavy depths of cut with high feed rates. So lower helix angle cutters are stronger, but they give a less smooth surface finish.

14-15K rpm would be a reasonable speed for 2mm carbide in CI but as said will be limited to the 5000rpm top speed of the SX3.5. Three times HSS speed is a common rule of thumb when going up to carbide.

Home › Forums › Beginners questions › Speeds/feeds for 2mm mill in cast iron This topic has 32 replies, 15 voices, and was last updated 3 March 2024 at 19:32 by Michael Gilligan. Viewing 25 posts - 1 through 25 (of 33 total) 1 2 → Author Posts 5 February 2024 at 09:29 #711850 jaCK HobsonParticipant @jackhobson50760 I wanted to cut some groves in 6″ dia cast iron plates like this: I had a couple of small HSS end mills so thought that milling would be easiest for me. Grooves are 1/16″ or 2mm, 0.5 mm deep. My mill goes up to 5000 rpm – this is the first time I used the high range, hurrah! It’s noisy at 5000rpm so I dropped speed down a bit.  I have power feed – I went about as slow as it will go. 1/16″ 2 flute lasted just over one plate maybe up to 4000 rpm. 2mm three flute maybe did one and two thirds of a plate maybe 2800 rpm. They snapped off when they got a bit dull. I used cutting fluid applied with brush. What life should I expect from small cutters and what speeds/feeds would be best? To finish, I’ll be getting a carbide 2 flute and run it at 5000 unless advised otherwise. Advert 5 February 2024 at 09:34 #711851 Bo’sunParticipant @bosun58570 Just a though, but would a slitting saw work, with the job mounted on an angle plate?  A little clamp shuffling might be needed. 5 February 2024 at 09:34 #711852 bernard towersParticipant @bernardtowers37738 Is it possible that using cutting fluid allowed swarf to get jammed under the cutter, shouldn’t you machine it dry and use a vacuum. 5 February 2024 at 09:44 #711853 Brian WoodParticipant @brianwood45127 A better approach if you can manage it is to use a suitable width of slitting saw on a horizontal mill. Saw speed should be about 50 rpm with a good steady feed, cut each run in one pass. Regards   Brian Sorry, I see that route has already been mentioned 5 February 2024 at 10:03 #711858 RobinParticipant @robin Quick, somebody sell this man a shaper. Some jobs simply cry out for one ? best Robin 5 February 2024 at 10:23 #711859 jaCK HobsonParticipant @jackhobson50760 Shaper – you need a bigger one than I have. Slitting saw – reach is the problem… I’d certainly have to come at it from both ends. It is 30mm thick so I could just clamp it vertical in the vice, but still, not sure reach gets me to the middle. Milling was the easy option for me – including workholding which is simples on a versatile vice. So what about feeds/speeds? 5 February 2024 at 10:27 #711860 BazyleParticipant @bazyle 1/ machine cast iron dry and use a gentle air blast to clear swarf. The graphite and chippy nature of CI makes lubrication unnecessary. 2/ calculate the cutting depth of each blade on each revolution – you need to avoid rubbing so your slow feed at high rpm was blunting the cutter. 1 thou min per bite per blade every revolution. 3/ yes a high feed rate will put a lot of sideways strain on the small cutter so you will have to reduce the vertical depth. 4/ a better bet is to make an engraving V cutter as the form is designed for doing lots of thin lines. 5/ without a shaper you can still improvise by mounting the work on the lathe saddle and making a non rotating between centres boring bar to hold the cutter. Or on the mill table and non rotating cutter. As you have proven by experiment that wasn’t the way to go. 5 February 2024 at 10:32 #711862 Thor ??Participant @thor Hi Jack, Your speeds seems to be OK. There is a nice calculator here. There is another calculator that gives both speeds and feeds here. I always machine Cast Iron dry, Bernard’s suggestion of using vacuum is good. Thor 5 February 2024 at 10:55 #711866 JasonBModerator @jasonb 2-flute HSS use all your 5000rpm but you need a small chipload on a 2mm cutter so around 0.004mm which equates to a feed of 40mm/min which is prossibly slower than the power feed will run at. Cut the full 0.5mm depth in one go and do it dry with air or vac to clear swarf. 3-flute HSS 5000rpm but as they are a bit weaker 0.003mm chip load which gives feed of 45mm/min. 2 & 3-flute Carbide you will be limited to your 5000rpm max but chip load can be increased due to stronger tool say 0.006 so 90mm/min feed 5 February 2024 at 11:36 #711874 RobinParticipant @robin On 5 February 2024 at 10:23 jaCK Hobson Said: Shaper – you need a bigger one than I have. Is this a case of large material or small shaper? We should be told ? best Robin 5 February 2024 at 11:44 #711879 jaCK HobsonParticipant @jackhobson50760 Thanks! I think I conclude, combining Jason’s 40mm/min and Bazyle ‘you need to avoid rubbing’ that a sensible compromise is to accept limited life of cutters in this scenario (if I want to get the job finished before I give up of boredom). I’ll try 2 flue carbide to finish off, dry. I really appreciate the ‘dry’ – cutting fluid everywhere is yuk. With this project I got to use some features that finally justified my tool purchase – 5000rpm, and wet-grinding six largish surfaces. 5 February 2024 at 12:28 #711882 SillyOldDufferModerator @sillyoldduffer Duffers patent rule of thumb for mild-steel: rpm = 10000 / dia in mm So 10000/2 = 5000 rpm. If cutter is carbide multiply by 1.5 = 7,500rpm In this case, material is cast-iron so a further correction may be needed.   A little complicated because cast-iron is a family of alloys with different cutting properties, not a single standard metal.   Generally, I halve RPM when cutting cast iron, so: 7500/2 = 3750 rpm   Then I experiment, because faster is often better: Jason’s 5000rpm is perfectly reasonable. Beware!  Cast-iron is frequently nasty, full of occlusions, and/or chilled super-hard by being hosed down in the foundry.  Machinability varies from wonderful to very poor depending on what you have.  Rule of thumb cutting calculations may not work out in practice because “cast-iron” is pretty random, especially if it was chilled, causing a hard skin of unknown depth.  A small diameter cutter could sail through it, or come quickly to grief. Using a small diameter cutter on an unpredictable metal is high-risk.   The cutter might happily plough through before suddenly hitting an occlusion or hard spot, blunting the edge or suddenly increasing the side load to breaking point.   Rapid swarf clearance is important, because it adds to side-loading and causes blunting.   Only the operator can judge, and I’d expect to break a few cutters before finding a safe optimum.  A steady hand is important too – bumping is likely to break a small cutter.  (You can guess how I know!) Jason recommends cutting full-depth in one go and he is a much more experienced and effective machinist than me.  However, another duffer rule of thumb is to cut no more than 20% of cutter diameter deep, which is 0.4mm.   Therefore I’d probably cut these grooves in two passes.   My 20% rule is conservative though, and not entirely sensible!  Although shallow cutting reduces the side-load, taking two passes blunts the cutter extra fast, which increases the side load.  The pros and cons aren’t black and white. How long will the cutter last?   Roughly speaking, a lightly loaded HSS cutter machining mild-steel will last a couple of hours before it gets too blunt.   Driven hard, fast and deep, perhaps only 15 minutes.   Jason’s 40mm per minute feed-rate is about right, so the number of cutters needed can be estimated from the groove lengths, and assuming mid-range life of an hour.  Except 2mm diameter cutters are easily broken… In short, a highish RPM with a slow steady feed-rate, in either one or two passes, varied as necessary by the operator depending on the nature of the cast-iron.  Could be straightforward, or tricky, or somewhere in the middle – I’d expect to break a few cutters finding out, because so much depends on the cast-iron’s properties, which might be lovely, horrible, or mixed. Dave   5 February 2024 at 13:04 #711901 JasonBModerator @jasonb 14-15K rpm would be a reasonable speed for 2mm carbide in CI but as said will be limited to the 5000rpm top speed of the SX3.5. Three times HSS speed is a common rule of thumb when going up to carbide. While I would agree with the 1 thou (0.025mm) chip load for most cutters when you get down to the very small you have to take their strength into account and reduce the load on them hence the 0.003mm I suggested which is almost 1/10th the loading. Keep the 1 thou for 6mm and above dia cutters. 5 February 2024 at 13:16 #711908 Michael GilliganParticipant @michaelgilligan61133 On 5 February 2024 at 11:36 Robin Said: … Is this a case of large material or small shaper? We should be told ? Shaper with less than 6” stroke might be a reasonable guess … although 3” stroke and a lot of faffing-about may suffice. MichaelG. 5 February 2024 at 14:54 #711929 ChrisLHParticipant @chrislh For anyone who doesn’t have a compressor or a suitabe vacuum cleeaner I have found blowing down a large diameter drinking straw to be surprisingly effective in clearing swarf if ultimately rather tiring. 5 February 2024 at 15:09 #711934 jaCK HobsonParticipant @jackhobson50760 On 5 February 2024 at 11:36 Robin Said: On 5 February 2024 at 10:23 jaCK Hobson Said: Shaper – you need a bigger one than I have. Is this a case of large material or small shaper? We should be told ? best Robin I have one of those Adept hand cranked shapers. Nice tool to cuddle but I don’t use it much… not at all anymore. 5 February 2024 at 15:28 #711937 RobinParticipant @robin On 5 February 2024 at 15:09 jaCK Hobson Said: I have one of those Adept hand cranked shapers. Nice tool to cuddle but I don’t use it much… not at all anymore. This is perhaps not a good time to have money, this is a time to have things that will hold their value. Things like shapers ? best Robin   5 February 2024 at 16:00 #711943 Anonymous A decent grade carbide cutter should be able to do all three plates without replacement. I use K2 cutters from YG. These are South Korean professional, albeit bottom of the range, cutters. For this job I would use a 2mm, 3 flute, stub cutter; 0.5mm DOC, 9500rpm and a chip load of 0.01mm/tooth, giving a feedrate of ~285mm/min. Running at 5000rpm would give a feedrate of 150mm/min. Andrew 6 February 2024 at 07:01 #712147 David George 1Participant @davidgeorge1 I have made similar plates which were used to lap the face of levers for aircraft controls. This was before CNC was around. To find hard spots they were surface ground and then laped on a granite surface plate with fine wet and dry paper and hard spots would usualy show up as shiny  spots or area’s and discarded. They were eventually cut on a horizontal mill with a slotting saw cutter. David 9 February 2024 at 12:15 #713187 jaCK HobsonParticipant @jackhobson50760 I was excited to open my package from ArcEuro containing new carbide 2mm stub 2 flute….. aaargh! The stub cutters have 3mm shank and I got a 6mm collet. Frustrating! 9 February 2024 at 18:01 #713299 Neil WyattModerator @neilwyatt As has been said above, speed isn’t critical although ‘as fast as possible’ probably isn’t bad advice for 2mm on a standard mill. What is important is tooth load as too little will wear cutters rapidly leading and too much will snap cutters. People have already suggested feed rates. Neil 9 February 2024 at 18:18 #713302 jaCK HobsonParticipant @jackhobson50760 I forgot I had an ER 32  – R8 chuck! Another tool justified, Hurrah! 5000rpm, carbide stub mill, dry…. smooth like butter (I listen to Kpop in the workshop). And the mill seems to have ‘worn in’ a bit at the 5000rpm now. Now I just have hours of hand polishing to do. 11 February 2024 at 19:45 #713811 jaCK HobsonParticipant @jackhobson50760 To (almost) finish off the story, I now have three lapping plates and surface plates. Now with a whole days experience, I’m not so keen on the grooved side – it can easily cause scratches, either because the grooves are difficult to clean and retain largest grit sizes, or because the edges can cause scratches. The flat side is used to flatten a pitch lap. I can then get shiny glass with cerium oxide, but it is still a bit milky so I’ve got some learning to do still. And I don’t think the glass is coming out ‘optically flat’. So the whole project – a fail so far… unless you count the learning… 12 February 2024 at 09:52 #713856 Andy_GParticipant @andy_g On 11 February 2024 at 19:45 jaCK Hobson Said: I can then get shiny glass with cerium oxide, but it is still a bit milky so I’ve got some learning to do still. And I don’t think the glass is coming out ‘optically flat’. Has the surface you’re polishing previously been ground flat? Do you know what type of glass it is? You may well be seeing ‘short finish’ where the glass between the grinding pits is shiny, but the pits remain – you should be able to see this with a loupe, etc. There are two answers: 1) Polish some more, at the risk of losing the accuracy of the ground blank and rolling off the edges; 2) Re-grind to a finer grit. Ideally the blank should be ground finely enough that it has a waxy sheen before you start polishing. How flat is ‘optically flat’? If you are looking for something that is better than a few fringes, then it is a bit of an art!   Good luck! 12 February 2024 at 11:32 #713868 jaCK HobsonParticipant @jackhobson50760 I bought it as an optical flat off ebay. A bad purchase is at is scratched/worn beyond use. Throwing good money after bad, I thought I’d have a go a repolishing and then seeing how flat it still is ? I’ll try a lot more polishing. I don’t expect it will be very flat. Author Posts Viewing 25 posts - 1 through 25 (of 33 total) 1 2 → Please log in to reply to this topic. Registering is free and easy using the links on the menu at the top of this page.

Straight flutesend mills have a zero degrees helix.  They work well for materials where the lifting effect of a spiral flute might cause unwanted results, such as wood, plastics and composites. For those materials, the straight flute minimizes the fraying of the edges and provides better surface finishes than helical general purpose end mills.

Secondly, having more flutes on a tool creates smoother cuts, but it also leaves less space for chips to evacuate. This can be somehow overlooked if you are cutting soft materials, but not at all if you are cutting aluminium for instance. The reason is that aluminium produces very large chips compared to other materials. So when the end mill is cutting down in a hole or a slot, its flutes provide a crucial path for chips to escape. That explains why it is recommended to use 2 or 3 flutes end mills with aluminium since they have more chip clearance than with a 4-flutes one, where the chips will jam progressively, overlapping the cutting edges of your tool and making it break eventually.

As has been said above, speed isn’t critical although ‘as fast as possible’ probably isn’t bad advice for 2mm on a standard mill.

Each of these features has a direct influence on how the end mill will behave during a machining operation and on the cutting possibilities in terms of performance and shapes.

A decent grade carbide cutter should be able to do all three plates without replacement. I use K2 cutters from YG. These are South Korean professional, albeit bottom of the range, cutters.

The diameter of your tool will have a direct incidence on the profiles you can cut. Let’s say you want to make a box and assemble it using 90° interlocking joints.

What is an end mill actually, is it like a drill bit? It is a usual question that comes up since terminologies are often mixed up, but the answer is no. A drill bit is designed to plunge directly into the material and create holes only, while an end mill can cut laterally into the material and create slots or profiles. Besides, most end mills are designed to be centre-cutting, meaning they can plunge into the material as well and making them far more versatile than drill bits.

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This article aims at explaining the basics of end mill science while answering the simple question you might have: which end mill should I use on my CNC machine?

Imagine you want to mill a very deep pocket inside a high part. You will need a long tool to be able to machine the bottom without colliding your spindle mandrel with the stock of the material. Hence, the length of your end mill will be determined by how deep it must penetrate into the material. The associated concept with this observation is called “stickout”. It is defined by the distance from the end of the tool holder to the tip of the end mill.

A better approach if you can manage it is to use a suitable width of slitting saw on a horizontal mill. Saw speed should be about 50 rpm with a good steady feed, cut each run in one pass.

2 & 3-flute Carbide you will be limited to your 5000rpm max but chip load can be increased due to stronger tool say 0.006 so 90mm/min feed

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As your CNC router spins the cutter clockwise, the helical direction of the flutes determines if chips are ejected towards the top or bottom of the workpiece. Upcut end mills are the most conventional ones, pullingthe chips away from the material, which is a very important feature for most milling operations on many different materials. It has a downside if you want to cut laminated materials since it leaves a poorer surface finish on the top of the workpiece. A downcut end mill has the advantage to push chips down, leaving a cleaner cut on top, but then it will also fray the bottom edge.

At this point, it might seem smart to buy end mills that are as long as possible to have the flexibility to use them in more situations, right? It’s actually not the case, because the more stickout, the less rigid a tool is. If it sticks out too far and you work it too demanding, the cutting forces will make it bend, which is what is called “tool deflection.”

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The flat side is used to flatten a pitch lap. I can then get shiny glass with cerium oxide, but it is still a bit milky so I’ve got some learning to do still. And I don’t think the glass is coming out ‘optically flat’.

Standard End Millsizeschart

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First, it makes your tool more rigid, which will allow you to make deeper cuts while minimizing tool deflection. A lot more rigid actually, since increasing diameter by 2x will increase its rigidity by a factor of 16x.

In short, shorter end mills are more rigid and less expensive. So save the extra-long ones for operations where they are really needed

With this project I got to use some features that finally justified my tool purchase – 5000rpm, and wet-grinding six largish surfaces.

2-flute HSS use all your 5000rpm but you need a small chipload on a 2mm cutter so around 0.004mm which equates to a feed of 40mm/min which is prossibly slower than the power feed will run at. Cut the full 0.5mm depth in one go and do it dry with air or vac to clear swarf.

You may well be seeing ‘short finish’ where the glass between the grinding pits is shiny, but the pits remain – you should be able to see this with a loupe, etc.

Another easy way to increase the performances of your end mills is to add a good coating. The most common one, TiAlN (Titanium aluminium nitride), will allow you to cut 25% faster on average without spending too much money.

Jason recommends cutting full-depth in one go and he is a much more experienced and effective machinist than me.  However, another duffer rule of thumb is to cut no more than 20% of cutter diameter deep, which is 0.4mm.   Therefore I’d probably cut these grooves in two passes.   My 20% rule is conservative though, and not entirely sensible!  Although shallow cutting reduces the side-load, taking two passes blunts the cutter extra fast, which increases the side load.  The pros and cons aren’t black and white.

Tapered end mills are centre-cutting tools that can be used for plunging, and are designed to machine angled slots. They are generally used in die-casts and moulds.

End mill Corner Radius chart

Based on those observations, I know that I need a flat-end mill type to get a nice flat surface inside the pocket. I will go for a diameter of 8mm, quite large because I don't want to waste too much time while removing all that material and because the inside corners are already designed to be rounded. I'll use a short carbide end mill as well, like 30mm long, because oak is a hardwood and I will need the rigidity to keep a high feed rate. Since the pocket is pretty shallow and chips will evacuate easily, I will choose a 3-flutes end mill with a 45° helix angle to get the best surface finish possible and spend little time hand-finishing.

Milling was the easy option for me – including workholding which is simples on a versatile vice. So what about feeds/speeds?

Is it possible that using cutting fluid allowed swarf to get jammed under the cutter, shouldn’t you machine it dry and use a vacuum.

Secondly, it improves your MMR (Material Removal Rate) since the end mill can remove more material per unit of time when it is moving inside the material, allowing you to optimise certain operations and do the same job faster.

If you don’t care too much about performance, then choose carbide end mills that are 8mm or less in diameter. Consider HSS for larger cutters to save some money, when the tool rigidity can be compensated by its larger diameter. Besides, if you are beginning with CNC milling, don’t forget that you might make mistakes and break a few end mills before getting it right, better HSS ones as well then.

End mill size chart pdf

To (almost) finish off the story, I now have three lapping plates and surface plates. Now with a whole days experience, I’m not so keen on the grooved side – it can easily cause scratches, either because the grooves are difficult to clean and retain largest grit sizes, or because the edges can cause scratches.

Since they can run way faster than HSS, they will increase your machine productivity a lot. They are also more durable and have a longer tool life, making them worth the investment.

Since your tool is a cylinder with a certain radius, it won’t be possible to do it as such. Indeed, the tool will leave a circular profile in every internal corner, with a radius equal to half its diameter. The larger your end mill diameter, the bigger the radius of this circular profile. In order to overcome this problem, CNC operators use what is called “dogbones”. Dog bone corners describe the shape of a corner that is extended outside the cut area to create a perfect 90º corner.

Feed rate is indeed directly linked to the number of flutes of your end mill: if you add flutes, you will have to increase the feed rate, or decrease the rotational speed of your spindle, to keep a constant chip load. So depending on the speed capabilities of your CNC machine and of your spindle, you might have to choose an end mill with less/more flutes.

Milling cutter size chart

This is perhaps not a good time to have money, this is a time to have things that will hold their value. Things like shapers ?

Combine an upcut and a downcut and you have a compression cutter, where the flutes are carved one way for the bottom half of the flute length and the other way at the top.  That feature makes them a very good candidate to cut plywood, composites, and laminates. Try to use one to cut a sheet of plywood in one pass, and you should obtain cleaner edges on both sides.

In short, a highish RPM with a slow steady feed-rate, in either one or two passes, varied as necessary by the operator depending on the nature of the cast-iron.  Could be straightforward, or tricky, or somewhere in the middle – I’d expect to break a few cutters finding out, because so much depends on the cast-iron’s properties, which might be lovely, horrible, or mixed.

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Using a small diameter cutter on an unpredictable metal is high-risk.   The cutter might happily plough through before suddenly hitting an occlusion or hard spot, blunting the edge or suddenly increasing the side load to breaking point.   Rapid swarf clearance is important, because it adds to side-loading and causes blunting.   Only the operator can judge, and I’d expect to break a few cutters before finding a safe optimum.  A steady hand is important too – bumping is likely to break a small cutter.  (You can guess how I know!)

Coated Carbide end mills are more expensive than HSS ones, but they provide better rigidity and can be run 2 to 3 times faster than HSS. They’re also extremely heat resistant, making them suitable to mill tougher materials as well.

High-Speed Steel (HSS) is the least expensive of the two, it provides good wear resistance and can be used to mill many materials, such as wood, metals,...

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Square end mills are the most common ones and can be used for many milling applications, including slotting, profiling and plunge cutting.

On top of these geometric features, end mills are characterised by their type, number of flutes, material (and coating). Thus, in a classical catalogue, the end mill above would be described as:

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Grooves are 1/16″ or 2mm, 0.5 mm deep. My mill goes up to 5000 rpm – this is the first time I used the high range, hurrah! It’s noisy at 5000rpm so I dropped speed down a bit.  I have power feed – I went about as slow as it will go. 1/16″ 2 flute lasted just over one plate maybe up to 4000 rpm. 2mm three flute maybe did one and two thirds of a plate maybe 2800 rpm. They snapped off when they got a bit dull. I used cutting fluid applied with brush.

This section could deserve an entire article, so let’s keep it concise and talk about the two main materials used to make cutting tools: HSS and carbide.

End mill specification

Flutes are the deep spiral grooves that allow chip formation and evacuation. They are the part of the end mill anatomy that create those sharp cutting edges (sometimes referred to as “teeth”).

Just a though, but would a slitting saw work, with the job mounted on an angle plate?  A little clamp shuffling might be needed.

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For this job I would use a 2mm, 3 flute, stub cutter; 0.5mm DOC, 9500rpm and a chip load of 0.01mm/tooth, giving a feedrate of ~285mm/min. Running at 5000rpm would give a feedrate of 150mm/min.

For anyone who doesn’t have a compressor or a suitabe vacuum cleeaner I have found blowing down a large diameter drinking straw to be surprisingly effective in clearing swarf if ultimately rather tiring.

Answering these questions will help you determine the desired tool geometry, based on your project type, the material being cut and on the desired surface finish. So let’s dive into the theory and answer those questions later with some concrete examples.

I was excited to open my package from ArcEuro containing new carbide 2mm stub 2 flute….. aaargh! The stub cutters have 3mm shank and I got a 6mm collet. Frustrating!

General-purpose end mills typically have helix angles around 30°. Increasing the helix angle will reduce the cutting forces and the amount of heat and vibration generated during the milling process. Hence, end mills with a higher helix angle tend to produce a better surface finish on the workpiece.

Standard End Millsizesmetric

Also, keep in mind that the cutting depth should never exceed the flute length of your end mill. If cutting deeper than the length of the flutes, chips won’t clear properly, heat will build up and you risk to damage your tool.

The number of flutes on your end mill is a crucial parameter that depends mostly on the material you want to cut and on the capabilities of your machine. Indeed, the number of flutes on your end mill will impact:

Shaper – you need a bigger one than I have. Slitting saw – reach is the problem… I’d certainly have to come at it from both ends. It is 30mm thick so I could just clamp it vertical in the vice, but still, not sure reach gets me to the middle.

I can then get shiny glass with cerium oxide, but it is still a bit milky so I’ve got some learning to do still. And I don’t think the glass is coming out ‘optically flat’.

Ball End Mill Size chart

1/ machine cast iron dry and use a gentle air blast to clear swarf. The graphite and chippy nature of CI makes lubrication unnecessary. 2/ calculate the cutting depth of each blade on each revolution – you need to avoid rubbing so your slow feed at high rpm was blunting the cutter. 1 thou min per bite per blade every revolution. 3/ yes a high feed rate will put a lot of sideways strain on the small cutter so you will have to reduce the vertical depth. 4/ a better bet is to make an engraving V cutter as the form is designed for doing lots of thin lines. 5/ without a shaper you can still improvise by mounting the work on the lathe saddle and making a non rotating between centres boring bar to hold the cutter. Or on the mill table and non rotating cutter.

How long will the cutter last?   Roughly speaking, a lightly loaded HSS cutter machining mild-steel will last a couple of hours before it gets too blunt.   Driven hard, fast and deep, perhaps only 15 minutes.   Jason’s 40mm per minute feed-rate is about right, so the number of cutters needed can be estimated from the groove lengths, and assuming mid-range life of an hour.  Except 2mm diameter cutters are easily broken…

Inside Corner Using a Coped Joint · On the first wall, cut crown moulding for a butt joint in the corner. · Make a 45-degree inside miter cut on the piece to be ...

2) Re-grind to a finer grit. Ideally the blank should be ground finely enough that it has a waxy sheen before you start polishing.

There are as many different end mill types as there are possible cutting operations: profiling, contouring, slotting, counterboring, drilling,... Here is a short overview of the main ones.

Beware!  Cast-iron is frequently nasty, full of occlusions, and/or chilled super-hard by being hosed down in the foundry.  Machinability varies from wonderful to very poor depending on what you have.  Rule of thumb cutting calculations may not work out in practice because “cast-iron” is pretty random, especially if it was chilled, causing a hard skin of unknown depth.  A small diameter cutter could sail through it, or come quickly to grief.

Choosing the right end mill before turning on your CNC machine can be a pretty complex task. Many variables come into play, such as end mill length, geometry, profile type, material, while several trade-offs have to be considered: performance, cost, surface finish, tool life,...

Your speeds seems to be OK. There is a nice calculator here. There is another calculator that gives both speeds and feeds here. I always machine Cast Iron dry, Bernard’s suggestion of using vacuum is good.

High-Feed Milling · m_546_t_01. DoFeedTri. High feed milling cutters featuring strong double-sided inserts with six cutting edges. ø16 – ø50 mm – (APMX): 1 mm.

End mill Cuttersizesin mm

In this case, material is cast-iron so a further correction may be needed.   A little complicated because cast-iron is a family of alloys with different cutting properties, not a single standard metal.   Generally, I halve RPM when cutting cast iron, so:

I have made similar plates which were used to lap the face of levers for aircraft controls. This was before CNC was around. To find hard spots they were surface ground and then laped on a granite surface plate with fine wet and dry paper and hard spots would usualy show up as shiny  spots or area’s and discarded. They were eventually cut on a horizontal mill with a slotting saw cutter.

Roughing end mills are used to quickly remove large amounts of material during heavy operations. Their design allows for little to no vibration but leaves a rougher finish.

Thanks! I think I conclude, combining Jason’s 40mm/min and Bazyle ‘you need to avoid rubbing’ that a sensible compromise is to accept limited life of cutters in this scenario (if I want to get the job finished before I give up of boredom). I’ll try 2 flue carbide to finish off, dry. I really appreciate the ‘dry’ – cutting fluid everywhere is yuk.