3. What is SFM & Why it's overrated!

[@ChiralSymmetry]

I think I heard the following, but not sure, so take this with salt: Recommended SFM and IPT are designed to optimize two or three things simultaneously: (1) Surface Finish (2) Productivity (machine as many parts as possible per hour) (3) Cost of production (machine as many parts as possible per tool sharpening or tool replacement). For example, as mentioned in another comment, too fast or too slow will generate too much heat and/or wear out the tool prematurely. Some of the super high RPMs are recommended because, if they were possible, would help maximize productivity (while maintaining surface finish). Much of the time, these super high RPMs are simply not possible. That just means productivity is limited by the machine, not the cutting properties of the material. For a small shop, or a home shop, high-throughput productivity isn't important, let alone possible. Instead, surface finish probably matters the most. If you drop the requirement that productivity should be maximized, then you can use much slower RPMs and still get good surface finish. But I haven't seen any charts optimized this way, for small/home shops. So IPT may be a better way to think about it.

[@kchigley5309]

SFM is an under ideal conditions recommendation. Unless you get the numbers from the manufacturer of the specific tool you're using, you're not getting a good picture of what you can do. For instance, I just received a promotional insert from Seco for cutting low carbon steels. My general goto for turning steel with carbide is 400-800 SFM depending on the alloy. But on this insert, the recommendation was 1600 SFM...which is my baseline for aluminum. Since it was a free insert, I decided to go with their suggestion and it cut like a dream in 1018 hot roll with a beautiful surface finish. If I had only gone with my baseline (much like your spreadsheet), I would have been leaving a whole boatload of cutting power on the table and not using everything I paid for if I had bought the tool. That's what I use SFM for: the maximum capability of the tool in the material...NOT the absolute target number. Tools will work just fine, for the most part, if they're run at a lower SFM. There are some exceptions to this, but the people who use Tormach machines are not likely to ever see those scenarios.

[@kchigley5309]

Yup yup :)

[@VarkaTheDragon]

All I could think about, while John was going through how to calculate feed per tooth... was what the can of Silly String in the background was used for.

[@chiseled_face]

4 years later and still no answer. oh the mystery

[@LogicIndustries]

Two things: 1) SFM does matter and it varies by material. Why? Three letters (words) BUE. What is BUE? BUE stands for Built Up Edge, and is a process whereby the material being cut literally welds itself to the tool cutting edge as it is passing through the material, gradually building up a longer and longer ridge of material extending off the edge of the cutting tool until the length gets too long and the built up material breaks off. When it breaks off, it takes a bit of the cutting edge with it (remember, the BUE is WELDED to the cutting edge), and the process starts over (only with a slightly blunter cutting edge, which makes the next BUE build up faster). This condition is continuous and degenerative in certain bands of surface speed in certain materials. Mild steel and aluminum both have cutting speed bands where BUE is a big problem. So yes, you can ignore the MFG recommended cutting speed (SFM), but you always have to be aware of the SFM band on certain materials where BUE will be a problem. Slower is not always better. Coolant type and application style also influence where the BUE bands land on the speed chart. For instance, BUE is a BIG problem on 6061 alum at 600-700 SFM dry, but if you apply a flood coolant with even a little lubricity, the BUE problem drops off entirely. This is one area where misters and MQL setups are insufficient to the problem. Light mist and MQL air blasts are usually insufficient to ameliorate a BUE problem. 2) Travel speed and therefore IPT are dependent on may things beside just the tool geometry and the material hardness/tensile strength. Feed rate needs to vary according to your tool engagement. Side milling VS slotting, or one diameter DOC VS three diameters DOC, or both at the same time (side milling at one dia DOC VS slotting at three dia DOC) will drastically effect the chip load you want to use when programming that cut. The relationship is NOT linear. Feed rate also needs to vary according to chip evacuation and coolant supply. As an example, I routinely cut 6061 T651 alum bar stock with a 1/2" dia carbide two flute endmill (std 30° helix, nothing special, no coating) at 650 SFM (that's the top speed of my spindle, 5k rpm), 0.25" DOC (one half dia DOC), full 1/2" WOC (slotting), at a chip load of 0.004 IPT (40 IPM). At this speed, I can trust the machine to run all day with low pressure flood coolant. If I were to increase the DOC to one full dia, I would have to slow the travel speed down to about 0.0015 IPT (15 IMP) and either increase my coolant pressure or add an air blast nozzle adjacent to the coolant nozzles to prevent tool breakage from chip packing in the tool gullets and chip recutting in the slot. Twice the metal removal results in a travel speed that is less than one half the original, decreasing overall MRR. What I'm trying to say is that there are a LOT of variables to consider in this stuff, and a lot of them are interconnected such that ignoring one while varying another can lead to tears (or more probably curse words).

[@xull1x123]

SFM does matter. It directly affects your tool life. A proper tool manufacturer does tool life studies as a function of SFM which clearly show the negative trend. You will see this info in their tech sheets. BUE is one reason like mentioned above. BUE is easy to easy to avoid though. Take a 5" diameter work piece. Face it at constant rpm. You will see two rings form where the surface finish is bad. You know RPM and the diameter where the surface finish goes bad. You can then use this info to find the upper and lower SFM to stay between to avoid BUE.

[@christophersmith2852]

Recommended SFM is not derived from a chemistry lab but from cumulative use data that includes a multitude of variables including tool material, part material, lubricant, and so on. While it is frustrating to try to find proper speeds and feeds for smaller tools while cutting softer materials I would never tell anybody that is not important. Aluminum has a very broad range of recommended speeds but that narrows considerably when the materials increase in hardness. Perhaps it would be better to say that chip load weighs more than sfm when machining soft, ductile materials and leave it at that. SFM is greatly appreciated on harder, more unforgiving materials.

[@christophersmith2852]

Absolutely, and as tooling technology increases we will see more and more variations from the norm....for the better!

[@christophersmith2852]

I read an article once about a shop who allowed their tooling supplier to implement every new tool that they introduced. As they began upgrading their tool technology they increased their production speeds and decreased tool breakage. They claimed to have saved so much money that they were able to quickly update and outfit their shop with the money they weren't expecting to save. We are reluctant to implement changes that cost us money.... sometimes the hardest thing to overcome is the belief that this new technology works as well as the reps say it does......but it does

[@ParallaxFPV]

Try U-drilling/turning 17-4, Saf 2205 or titanium. You'll find the manufacturers recommendations are essential for optimum tool life/productivity.

[@LogicIndustries]

Hey John, if you really want to understand chip theory and what is going on in the cut, I highly suggest finding and reading a copy of Sandvik Cormant's excellent book on the subject titled "Modern Metal Cutting, A Practical Handbook". It traces the development of cutting tools from the very beginning up through the cemented carbides of today. Very informative, and very in-depth vis-a-vis how a chip is made. Used copies come up on eBay and Amazon from time to time for $50-$75, or you can pop for a new copy off Amazon for ~$200. It's worth the $50, I assure you. If you don't like technical reading, it'll be a little dry, but I found it a fascinating read.

[@jbrownson]

Thanks for the book tip, just ordered a copy, I find this topic fascinating and would love to dig deeper

[@SuicideKang]

My professor just told us to never go over the recommended surface footage on our first year. The thing is materials that need low sfm react different at crazy sfm being cut with hard tool material like ceramic. You can even get away with higher than recommended sfm with chip thinning. I think chip load is where people are really coming short Example: I have studied suggested drill feeds and speed. I found out that every single drill company suggests the same proportional chip load for each tooth but just change the sfm How I calculate chip load for a 2 flute drill for ANY common material up to 440c is I multiply the tool diameter by .015 for conservative or hard steels (no jobbers go half) to .02 for fast cutting Just change the rpms

[@MineralGPK]

Where did you get that adjustable chart?

[@lineage13]

im running 9,000 rpm on my diy cnc router for milling hot rolled steel! Going 40 inches per minute, .039 inch width of cut & .39 inch depth of cut. I found that canola oil mist worked best (dont use water), I felt my tool & part afterwards, its cool to the touch & still super sharp!

[@cliffordernest7825]

Someone Else try diluting it with kerosene. 1:1

[@IndependantMind168]

Try lard

[@ChrisDePrisco]

Awesome John, that's a big help! Going by CPT makes a lot more sense; I've always wondered how we should reach the SFM for some of these smaller tools.

[@alonsorobots]

Could you make a video about advice for smaller less rigid and less HP machines like the Avis Benchtop Pro? I’m not sure if your advice on chipload and speeds and feeds applies to it

[@mikeatkurzzobelinc.7033]

I just wanted to kinda bring you back alittle bit. I understand what your saying about about the high end of aluminum tooling which helical does recommend 1600 to 2400 sfm. Now what I want to make clear is yes in aluminum you can basically go with your peak Machine RPM and then do you tooth load calculation. But where it becomes extremely important to know you SFM is when you work with materials including steel. Your machine may do 5100 rpm but if you try and run a half inch 4 flute end mill through a part to make a slot you will ruin it. If you say on the low end its 505 sfm for a slotting cut your speed should be (505*3.82)/.5 which is 3858. And that is just in say a piece of 1018. You start working with stainless 17-4 ph or titanium and you don't use sfm you will throw money right out the window. So I agree with you in the one aspect that yes in aluminum it does not matter but in harder metals it is an important part or programming.

[@mikeatkurzzobelinc.7033]

Oh and I just figured I would add this, the majority of manufacturers give you the low end of the spectrum with there SFM for the longest tool life possible. So you can also have the opposite problem that you are running on the low end. But if you use it as a guide to start from and then increase from there that is the best choice. I have run titanium that has a recommended SFM of I believe it was around 200 or so at closer to 400 with no problems. But for the home machinery and people doing this as a hobby you don't want to break a $150 end mill on the first cut. So do your research and start at the recommended sfm when possible they are a great starting point. I recommend getting ahold of the tooling company's catalog or going online where some company's have tooling apps and wizards to help you out.

[@gsimplecregk]

Dog: "there is a human, in a room, alone, sitting on a chair, talking, articulating... and theres nobody there... hmm... ok, whatever, I'm out a here".

[@tomdchi12]

In looking at the specs of systems like the Tormach PCNC systems, I've wondered about that RPM range with smaller end mills/parts in materials like aluminum. Good to know that going with a slower SFM than the standard charts is very doable. In my case, I'm currently using a Shapeoko 3 with a DeWalt router with an RPM range of 16k to 27k - the opposite problem. It's hard to get the SFM *down* to recommended ranges, even with small diameter (1/8" or 3/32") end mills. Maintaining a reasonable chip thickness without blasting ahead at 100ipm (and deflecting the not-so-rigid gantry) is the problem that goes with that, so I just got a single O flute end mill to try out in aluminum. My take away is "go ahead and give it a try - SFM recommendations aren't absolutes." Thanks!

[@occamssawzall3486]

I can't help myself. SFM is actually very significant, especially regarding carbide tooling. Carbide tooling isn't sharp per say. It's actually rather blunt. Compare a carbide endmill to a HSS endmill's cutting edge. Under a 20x loupe. A carbide tools looks like a ballpeen hammer compare to a HSS. Carbide cuts with heat and pressure it physically fractures the grain of the metal AHEAD of the cutting edge, where HSS shears it. Think of in terms of wood. If you have a really sharp knife you can shave off a thin piece of wood no problem. This is shearing. Where the absolute edge maintains contact with the material through the whole cut. This is how HSS cuts. It shears. Now carbide, that's more like a splitting maul. You focus a heavy force to a rather blunt edge. That force gets transferred into the material and caused it to fracture along the grain. But you don't need the maul to go all the way through. And the edge only contacts the material at the first moment of impact.

[@occamssawzall3486]

Now back to SFM. SFM is that initial impact force. And you need a bare minimum of force to drive the carbide edge into the material and cause it to fracture. Too low an SFM and there's not enough force. Which means no material fracture and leads to falling and edge wear.

[@occamssawzall3486]

And if your machine doesn't have the required rip'ems to meet the minimum SFM (lowest mfg suggested number) switch to HSS tooling whose SFM requirements are much lower.

[@slome815]

Solid carbide endmills can be very sharp as well. There are carbide tools that are much much tougher then they used to be 20 years ago.

[@lineage13]

Occams Sawzall ya.. I love john, but sfm is very important.. it reduces heat on both the work material and endmill once sfm reaches past 1,000 sfm.

[@salvadorebertolone]

Its huge in carbide. Most carbides tools are made to fracture grains. Too low and they cant fracture the grain structure and more or less wind up smooshing and rubbing instead. Just look at what type of wear you are getting. I think johns problem is he doesnt do much production, like hundreds or thousands of parts so he doesnt see the tool wear that these charts are intended for. Hes right on being maxed out on a machines spindle speed though, if you cant get to the required sfm, max the spindle speed and then adjust the feed to get the right chip load to ease rubbing as much as possible. Im not sure how this applies to sintered/cemented cobalt hss tools though, im not sure how sharp those are, ive really used them as thread formers, and they seemed really sharp like hss.

[@flikflak24]

The about center of the drill is actually not turning at all ( since it's a point and points can rotate)

[@Tom-cs3zf]

Your whole video pertained to machining soft metal. The surface feet per minute is very important for harder metals and metals that produce a lot of heat when machining. You don't need a sliding chart to calculate the RPM, all you need to know is the suggested SFPM and the cutter circumference. And a little algebra. Some metals cant exceed certain SFPM because the speed of the chip removed would cause excessive heat for the cutting surfaces.

[@pooriashams]

SFPM is the maximum recommended. Not the exact value. So as long as you are below that, you are fine. It’s just that in a large manufacturing firm, they want to go with the maximum to get the minimum time per part. So as you said, as long as you are not rubbing, you are fine.

[@MrDaniell1234]

yep the speed you used that cutter I said about what you used on the toolstoday vid I run it 3 time the speed what you did and it was fine. in the end if the chip load is correct it all works out in the end using the SFM loaded to what you can run to, be it a mill or a router it scales.

[@tubbytimmy8287]

John, is it true that a coat of Silly String makes your machine run faster?

[@daveb1870]

And then you have the harmonic tap test which opens up another parameter which is closely related to chip per tooth and not sfm. The the tool life, manufacturing percentage and how much money it will make or loose. We have a cincinnatic 850 and 2500 with 18k spindles but you can stall them out with your tounge. Little to no hp, I take .060 cut depths, full width tool (most dia are between .5 and 1 inch) 3 flute data flutes and 400 ipm and faster. If the hp was capable of handling more and it does on linear cuts its when it gets into corners where you have at or more than 90 degrees of arc contact it boggs down or stalls out. We use catia too which is very powerful but id like to see some intuitive feed and speeds coding instead of manually selecting slow down in corner and slow down in rpm and trying to match it with the tap test harmonics you can spend 3 hours on one tool path for perfect paths and speeds and feeds and then the machine controller defaults to some magical number all by itself and youve just encountered an exercise in futility lol. Great explanation on sfm and why it plays a part when needed and why chip load/thickness whatever you want to call it is still a better limiting factor when it refers back to rpm and hp. I always look at whats the max rpm and then torque, then cross ref cutter manufacture recommended chip per tooth and whatever sfm is, is what it is, unless the machine cant actually handle the feed which almost always happens when you have extremely high rpm spindles and small dia cutters. We have a mag with a 30k spindle its feeds doesnt come close to utilizing that feed rate when you have smaller cutters.

[@TheOnlyWretch]

Thank you for doing this series, really learning a lot.

[@Southardknives]

Great series, Thanks Carl and John!

[@bbarker5766]

I used a chart that was given to me years ago that got me in the ballpark for manual or cnc machines. We had 6 manual lathes and vertical mills that always used different speeds and feeds for each one even if cutting the same metals. An old machinist told me that no matter what machine you have or how old it is you have to learn what it does or doesn't like and it'll treat you how you treat it.

[@mattruth7109]

3:30 lol I've never seen a dog stretch like that before, but my cat does it all the time

[@contrakt0r]

This is a great series for me to watch, as I've been thrown in the deep end with our new CNC. But please, give that poor dog a pat! ;)

[@tugaminhoto4969]

Really useful this tools video series, thanks a lot. Help alot

[@robertkutz]

your videos are always very interesting. bob

[@damianderungs6210]

no cutting speed definitly matters, example face turn and your finish will be better at outside with the right speed, than in the center of the piece, because of the to low cutting speed.

[@hiquality_distraction4084]

Great video, great info.

[@codenstar]

Metric Excel file please!

[@slome815]

Something tells me you machine a lot more aluminium or brass then steel. You can get away with a lot when machining aluminium. In steel, and certainly tool steels, the cutting speed is extremely important. A cutting speed that is too high will ruin a tool in a short time, a speed too low will mean a feed that is very slow as well.

[@SuicideKang]

Exactly! I think too many machinists think the exact opposite. Lighter chip load and faster feed. No!! Bigger chip load and slower feed will get a job done. You can always increase sfm. But if your tool is not getting big chips out then it's number of hits per tooth increases. Remember. Once a chip is formed, the point is not doing the cutting

[@CNCGuy]

Tell that to Guhring. They ramp 45 degrees in to 4140 tool steel like it was plastic... just tested one of their endmills with ridiculous numbers and HSM toolpaths.. 600 sfm or 4954rpm on 304ss .05 doc and .....180ipm, on a worn out endmill. RF Diver series. I only did a few pieces just to test. Was looking for built up edge. There was some but if I add air oil mist, should better I think than coolant.

[@Kyle_Roberts]

As being a Lathe Machinist in the past and seeing the subject as I felt like I was mislead after watching a little bit of this video. At a diameter of 7.643 a SFM of 500 equals 250 rpm while a SFM of 500 at the diameter of .318 equals 6000 rpm. SFM is not overrated ignoring the actual contents of this video I’m offended

[@SuicideKang]

For all materials I multiply the drill diameter by .015-.02 Just change the sfm. With a fast and strong enough spindle, I noticed my feed rate doesn't change, only my rpms. It's interesting. I have never had drills last so long

[@andrewclarke86]

All well and good to use aluminium as an example with a 6mm E-mill, but wait till you start machining more up the hardness scale and then tell me it's overrated. maybe if you called this video chip thickness or chip load is more important than cutting speed id be ok with it but sorry this is rubbish. throw an 80mm dia insert cutter at some 4340 and tell me running it at 1/4 its recommended cutting speed is still fine and economical for yourself or the company you work for

[@shammient]

Really informative so far. Also, silly string.

[@alklosterman9464]

Big boys know that SFM matters. Just because your machines are limited by max rpm doesn't make it BS.

[@alklosterman9464]

Fair enough. As your company grows SFM may become more important to you, so you can get the most out of your machines... like the HAAS. Good luck on a great 2017.

[@ivanvazquez7465]

Wow, is that sliding chart how feeds and speeds calculators apps look like back in the day 🤔

[@miguelmuniz8742]

Not overraated when working on stainless 😂

[@willysnowman]

Ever machine shiney 304SS? Definitely not over rated.

[@EnderElectrics]

-SFM is actually an animation software-

[@kenshiromilesvt.7037]

I knew I’d find this comment

[@Southardknives]

I also keep silly string in my office

[@jrazzarelli]

My human is talking to no one. Can't he see by the look on my face that I have to poop? I will do it in the corner.

[@JamesHall1980]

Better tooling gives you higher SFM. How can this benefit you. Faster productivity. If your buying tooling that has a higher SFM than your machines can handle, your simply wasting money. If you need faster productivity, buy tooling that meets the maximum your machines can handle. If that's lower SFM. Buy high speed or lower grade carbide. If your machine can haul. Spend the exter cost on high feed mills and drills. Good luck. Awesome Video though.

[@lineage13]

with an 8mm cutter im going at 730.98 SFM!

[@lineage13]

& My End Mill Stays sharp! Great tool life!

[@jaysilverheals4445]

I know and do what you do and always have however there is a misperception of the so called reccomended surface feet per minute. Actually what they are based upon traces back to on HSS that the interface temperature cannot exceed 1100 F. that is the point that the steel will begin the break down rapidly not just from friction but chemically because of extreme heat. I never have thought nor was told anything else but they were maximum speeds. I have always known that with aluminum especially you go far beyond rpm and also issues of chatter and things in relation to the length. Where the failing is is that the writers of the charts--such as the slide rule your using are "inept"--smart in some ways but dry personalities that left the info off because the engineers are so "narrow" and cant speak english to regular people. They grew up as only childs--got bullied and ended up in a lab and are penny wise pound foolish and drew up charts and graphs to confuse people. The more confusion they create "makes them look all the smarter".

[@heinzhaupthaar5590]

This is probably one of the dumbest comments I've read in a while. You failing to apply quite simple concepts to your work isn't the fault of anyone but you. And especially not the fault of a very simple chart. If anyone's inept here it seems to be you. Try working with an application engineer from a major cutting tool company to optimize your process and you wouldn't talk such utter nonsense insulting a whole occupation as inept idiots because of your incompetence. Or maybe you still would, because his simple advice might fly right over your head, who knows.

[@Houcnc]

gold nuggets thrown here

[@johnalexander2349]

9:00 Bottom left corner. New channel sponsor?

[@johnalexander2349]

LOL, yeah. Featured quite prominently. As always, thanks for the videos. I'm going through your older stuff, and particularly like the firearms projects, like the biathlon target. Pity shipping one here would cost an arm and a leg. I'll probably take inspiration from your design (sorry) and get one laser cut locally. So much to watch, and it's all great.

[@chrisscar005]

Oh.. i thought this Was for the Program SFM

[@johnnovotny2877]

I that this was about how source film maker or [sfm] is overrated

[@nicholassoobramoney1259]

It's mathematical....not some sliding chart. It's a ratio given your machine. It's science.....not a slide ruler. Learn the formula and different cutting strategies. It will help

[@mikechambers1875]

You never explained what silly string has to do with SFM...

[@arnljotseem8794]

+Mike Chambers Agree, that's what I want to know as well. Maybe as a lubricant?

[@isabellmizizzy214]

Judd=😃😀

[@cayenne7792]

Judd wants to know who the hell ya talkin to... : )

[@mattruth7109]

Yeah I've found its really IPT that matters most

[@israelcisneros1476]

This kind of information is dangerous.

[@jeffreyschmiedeck4254]

You have no idea what you are talking about! Go back to going to other machine shops for Tours.