How to learn speeds and feeds SFM vr IPM

[Learning_The_Hard_Way]

I Desperately need help to learn speeds and feeds I've talked to many people and watched just about every good YouTube video I can yet I still cant figure it out.
I dont understand SFM and IPM to me they both dictate how fast the machine will move relative to the rpm and cutting tool flutes?
can anyone clue me in to this??

 

[guythatbrews]

Sort of old fashioned but get a book. And read it.

SFM is Surface Feet per Minute. For we machinists it is used to talk about the velocity of a moving surface relative to a stationary tool.

IPM is Inches per Minute, the same type of unit distance/time, but it usually refers to the velocity of a moving cutter relative to a stationary workpiece.

BTW, it is RPM, not RPM'S. You don't say revolututions per minutes.

 

[mhajicek]

I Desperately need help to learn speeds and feeds I've talked to many people and watched just about every good YouTube video I can yet I still cant figure it out.
I dont understand SFM and IPM to me they both dictate how fast the machine will move relative to the rpm and cutting tool flutes?
can anyone clue me in to this??

SFM is used for the speed of the cutting flute relative to the material. As it moves faster, it generates more heat. IPM is the machine travel rate, how fast the center of the cutter is moving through the work. As it increases, the chipload (how big each chip is) increases, along with the cutting forces.

I use HSMAdvisor a lot, as it will make good recommendations for various cutting conditions. There's a free demo.

 

[DavidScott]

SFM and IPT are what matter, the rest is secondary. Don't think of RPM or IPM, they don't mean anything. The best way to learn what it means is to machine stuff and experiment. How does the cut sound, how do the tools wear, adjust to improve, repeat until you are no longer machining, the learning never ends. You will need a good loup, at least 10x, and a decent microscope can really help you see how the cutting edges are wearing. How good the machine, workholding, and toolholding are will affect your machining strategies.

Read what the tool mfrs suggest for SFM and IPT for their tools, all of them from different mfrs, then you will have an idea for starting points. DO NOT put any faith in them that they are right, they are STARTING POINTS, nothing else. They can be off by 70% or more, depending on the specific details of that cut.

To convert SFM to RPM 3.86 x SFM / cutter diameter.

 

[sinha]

The two are independent.
One relates to RPM: whether to use constant RPM or constant surface speed (CSS).
The other relates to feedrate: whether to use feed/min or feed/rev

SFM is the specified CSS in imperial units.
IPM is feed/min in imperial unit

This thread has some related information. It is a long thread. Reading the first page only is sufficient. https://www.practicalmachinist.com/forum/threads/css-formula.407831/

 

[guythatbrews]

Inches per minute is still relevant for asychronous feeds. You ought to know what it means and how to calculate it. It's not difficult. IPT x number if teeth x RPM = IPM

 

[tc227]

Machinist Calc Pro2 Calculator.
Best $100 I spent

 

[Ryan at Sparrow]

I know a lot of people who disagree with me on this, but you probably don't need to stress too much right now about exactly what it is if you're just starting out. Most tool manufacturers tell you what SFM and IPT to start a tool at, so you plug those into your CAM program and with a little experience and intuition you can make chips. After a while you get exposed enough understand what is happening and how SFM and IPT correlate to.. everything. I'm not saying you don't need to learn what specifically SFM and IPM are, but you don't really need to know much to start machining.

 

[EmGo]

I know a lot of people who disagree with me on this, but you probably don't need to stress too much right now

I'd agree no need to stress but ... wow. These are the basics of cutting. Should understand how it works and do it a few times manually to get the concept down even if you just use a calculator to get the numbers quick, no ?

SFM is speed. That's easy, you've driven a car. How fast are you going ? Miles per hour in a car, usually inches or feet per minute on a machine - unless you is one a them metric nazis, for that you can change units yourself

You have to measure it at the spot where the tool touches the part. This is where it counts. Same in a mill and a lathe. In a lathe, the part is turning. The speed is at the outside edge where the tool touches. In a mill the cutter is turning. Speed is at the edge where the cutter touches.

Both cases it's easy. Circumference is pi times diameter. So if the diameter is 1", the outside edge is 3.14159" and you can divide that into any speed you want to get your rpm.

IPM is feed. That's how fast the tool moves along the surface. In a lathe it's usually IPR, "inches per revolution". You already got revs by figuring your surface speed. Lathe is done, that's all there is to it.

A mill is a tiny bit more arithmetic because an end mill has several flutes. So to get feed in inches per minute, take your speed in rpm which you got by using the circumference of the tool, multiply by the number of flutes in the end mill. This gives number of cuts per minute at the tool interface. Clear ? Then take the desired inches per tooth (same as inches per revolution in a lathe, it's a number you have to choose, depends on material and what you are doing) and multiply flutes per minute to get your ipm.

Number of flutes over minutes times number of inches over flute : flutes on top and bottom cancel out, leaving inches on top per minute on bottom, yes ? It's all just fractions.

After a while some basic numbers stick in your head, and you go up or down according to circumstances. Like, I remember 100 feet per minute for hss in steel, and 400 for carbide. That's not an ironclad rule, just a good startpoint. Harder steels slower, ledloy faster. It's just a beginning, but experience will give you the rest, or for something you've never used, a handbook. And grinders are even easier for a US person, it's 60 miles an hour.

It's easier than it seems at first. In a week you'll be moving on to trig

 

[guythatbrews]

I know a lot of people who disagree with me on this, but you probably don't need to stress too much right now about exactly what it is if you're just starting out. Most tool manufacturers tell you what SFM and IPT to start a tool at, so you plug those into your CAM program and with a little experience and intuition you can make chips. After a while you get exposed enough understand what is happening and how SFM and IPT correlate to.. everything. I'm not saying you don't need to learn what specifically SFM and IPM are, but you don't really need to know much to start machining.

You are right. I disagree. I'd even go as far to say don't start machining until you have this basic understanding. These are fundamental concepts, and not difficult fundamental concepts. If you can't grasp them maybe you should stay an operator until you have this minimum amount of understanding. If you try it won't take long.

The idea you don't need to know this stuff has been around since before CNC, since jacklegs have always been around. "I just eyeball it and usually I'm pretty close". But the reality has been not always pretty close and sometimes I wreck stuff. Why use this approach when a better approach is within your reach?

I've got to say you are not the only one who feels this stuff is not very important. Lots of evidence on this forum of running at so and so RPM with no mention of diameter and the question why is my shit not working?

Fundamentals are good to know. They are "fundamental" to being successful. Computers are great, but take some responsiblity to understand at least a little. It will pay dividends time and time again.

 

[BT Fabrication]

what id say, get on a manual machine, and try it out, break a few cutters and see what works. best is always find manufacturing recommendations to get you close +- 50% can happen depending on depth and width of cut per tool. sharper the corner, deeper you need per tooth to cut a chip and not rub. rub is wear, wear dulls things, dull tools don't cut well or at all and cause breakage and failure.

 

[Ryan at Sparrow]

I've got to say you are not the only one who feels this stuff is not very important. Lots of evidence on this forum of running at so and so RPM with no mention of diameter and the question why is my shit not working?

Fundamentals are good to know. They are "fundamental" to being successful. Computers are great, but take some responsiblity to understand at least a little. It will pay dividends time and time again.

I'm just a hands on learner, so while SFM and IPT were explained to me I didn't really get it at all until I started making chips for a while and saw how they factored into what I was doing. Of course I think they are important, but I think getting someone in front of a setup with mediocre feeds and speeds will help them learn faster than trying to explain fractions on a screen.

 

[michiganbuck]

Youtube and even much of the posting here may leave out the simple basic beginner stuff so a book is the good place to start. Feeds and speeds are varied as to the kind of cutters and materials that a simple answer is not easy to give.

 

[EmGo]

I think getting someone in front of a setup with mediocre feeds and speeds will help them learn faster than trying to explain fractions on a screen.

So you're a brandy newy guy never cut anything before, boss says "here, go make this ring" ... it's 4" o.d. with a 2" hole. Totally simple.

How fast do you turn on the lathe ? Just pick a speed and hope it's about right ?

If you have even the most basic understanding, 4" diameter x 3 (close enough for a first shot) is 12" around and if you've got a hss tool in there, and you can remember 100 fpm, then 100 rpm. If it's a modern shop, carbide, 400. At least no one will come running over screaming if you can handle that much.

2" drill is an exercise for others

If you don't have even the vaguest idea, where are you ? Wandering around singing with pappy boyington's sheep ?

 

[Ryan at Sparrow]

So you're a brandy newy guy never cut anything before, boss says "here, go make this ring" ... it's 4" o.d. with a 2" hole. Totally simple.

How fast do you turn on the lathe ? Just pick a speed and hope it's about right ?

If you have even the most basic understanding, 4" diameter x 3 (close enough for a first shot) is 12" around and if you've got a hss tool in there, and you can remember 100 fpm, then 100 rpm. If it's a modern shop, carbide, 400. At least no one will come running over screaming if you can handle that much.

2" drill is an exercise for others

If you don't have even the vaguest idea, where are you ? Wandering around singing with pappy boyington's sheep ?

Yikes, no. You know thats not a realistic scenario either. You help a guy set up and program a few parts and see how things go and how you would adjust things from what you're seeing.

 

[guythatbrews]

Yikes, no. You know thats not a realistic scenario either. You help a guy set up and program a few parts and see how things go and how you would adjust things from what you're seeing.

Buy a guy a fish....

 

[michiganbuck]

Browse | New & Used Books from ThriftBooks

 

[CarbideCarGuy]

There are plenty of apps on your phone that will calculate everything for you. On android, I use CNC Machinist Calculator Pro. There is a free version but I use the paid "Pro" version and highly recommend it.

As far as Understanding the terms and how it all relates, I'll try to sum it up in terms that are simple and that have helped me understand when I was starting out.
SFM = Surface Feet per Minute = This determines the spindle speed based on the diameter of the work piece or tool. It is a constant number, so if you are on a lathe, the spindle speed will vary based on the work piece diameter. If you are on a mill, the spindle speed will remain the same because the diameter of your tool doesn't change. SFM can be determined by the manufacturer, so call your tool supplier if you want the SFM range for the tools you're using. You can adjust SFM and Feed rates in that range to get better performance out of the tool. SFM also changes for the tool geometry and material you're cutting. For example, a carbide insert in a lathe cutting 6061 aluminum might have a SFM of 900, but the same tool cutting 304 stainless might be closer to 300.

IPM - Inches Per Minute = The feed rate of the tool. This is usually determined by the chip load, or in other words, how much each flute will cut.
On a mill, you might have a cutter with 2 or more flutes so the chip load is multiplied by each flute. There are calculators to help with figuring this out but it's better to understand the formulas first so you know why it's happening. I'll put the formulas below.
On a lathe, the insert has one flute so the IPM is directly related to the chip load. We would then use IPR to relate it to the revolutions of the machine.
IPR = Inches Per Revolution = Chip load based on the RPM instead of time based like IPM. I prefer this since usually you have one flute on a lathe and you can tell it to go .010" per rev. and as you remember, the RPM can vary based on the diameter. So IPR keeps a constant chip load while the RPM Varies to accommodate the SFM.

Chip load and SFM can be determined by the tool manufacture. Different geometry, tool material, and work piece material will change the chip load and SFM. You can find this information from you tool supplier.

Basically, SFM and Chip load are given to you by the tool manufacture. The rest is calculated based on the material and number of flutes.
Here are some formulas to help you understand.
SFM= (Cutter Diameter * RPM) / 3.82
RPM= (3.82*SFM) / Cutter Diameter
Feed Rate= RPM * Chip Load * # of Flutes
Chip Load= Feed Rate / (RPM * Flutes)
3.82 is the constant. Converts tool circumference to diameter

 

[Ryan at Sparrow]

I Desperately need help to learn speeds and feeds I've talked to many people and watched just about every good YouTube video I can yet I still cant figure it out.
I dont understand SFM and IPM to me they both dictate how fast the machine will move relative to the rpm and cutting tool flutes?
can anyone clue me in to this??

So reading through this thread has any of this made sense or are you still at square 1. Also I'm curious what is your experience level. Do you only run mills or both mill and lathe?

 

[michiganbuck]

Buy a guy a fish....

and he will eat for a day, buy him a fishing pole...and then he will ask that you buy him a boat.

but let him go hungry and he will learn to work and take care of himself..

Give him numbers and he may use alluminnomum numbers for CPM and he will break your mill.