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SFM RPM Chart

whydontu said:
Feel free to ask for modifications.
Click to expand...

Mine are prolly a little different. Never heard your rule before. My own rule is "If I want to be happy, I have to keep the machine, the tool, and the part happy too." I can usually feel it in my hands or hear it in my ears when one of us isn't happy.

Did you make these in excel? If so, can you share those too?
 
YWIMC. Uploaded the original Excel spreadsheet into the DropBox folder.

My CAD program can't import text, so the spreadsheet isn't exactly the same as the finished CAD files. Feel free to tweak it as you see fit.

I restricted materials and sizes to only about a dozen values, I didn't want this to blossom into a zillion-page document. Just something to have at hand at the machines for quick-n-dirty work.
 
whydontu said:
YWIMC. Uploaded the original Excel spreadsheet into the DropBox folder.

My CAD program can't import text, so the spreadsheet isn't exactly the same as the finished CAD files. Feel free to tweak it as you see fit.

I restricted materials and sizes to only about a dozen values, I didn't want this to blossom into a zillion-page document. Just something to have at hand at the machines for quick-n-dirty work.
Click to expand...

Don't know about others, but that's really all I want anyway. Just a decent starting place. I let my shaky hands, one wonky eye, and tone deaf ears tell me how much to tweak it anyway.
 
DavidR8 said:
View attachment 53268
Click to expand...


Been off for a week sick, did you miss my crustiness? Betcha did...... I'll try to make up for lost time :D

I don't agree with these numbers , where did they come from? 215 SFM for steel? Twice what it should be imo. Am i missing something?

Why would the SFM be any different for turning or milling? Turning, milling, drilling..... shouldn't matter. What the cutting speed is, is the highest surface speed at which tool wear is still linear. There is no penalty except for time (most of the time) running below it. The more you go above it, you get more rapid tool wear, i.e. it's no longer linear and wear goes up more quickly than the removal rate does.

Determining a good cutting speed is simple, just something under the theoretical max. Memorize a few common fpm numbers and using the formulae RPM = CS * 4/dia, work out the rpm in your head as you're doing the set up. Lathe Mill or drill. Drop into the closest gear and make chips! e.g. 1.5" piece of steel with with hss cutter, 400/1.5, (slow brain says 1" would 400, 2" would 200 so rpm is 300, drop it into 280 on machine and proceed.
 
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Mcgyver said:
Been off for a week sick, did you miss my crustiness? Betcha did...... I'll try to make up for it :D
Click to expand...

Figures. None of us bothered with the numbers themselves. Just the idea. I guess we all assumed some Crusty Ornery Bugger would fix those for us.

Happy to see we were not wrong. Welcome back COB!
 
Mcgyver said:
Been off for a week sick, did you miss my crustiness? Betcha did...... I'll try to make up for lost time :D

I don't agree with these numbers , where did they come from? 215 SFM for steel? Twice what it should be imo. Am i missing something?

Why would the SFM be any different for turning or milling? Turning, milling, drilling..... shouldn't matter. What the cutting speed is, is the highest surface speed at which tool wear is still linear. There is no penalty except for time (most of the time) running below it. The more you go above it, you get more rapid tool wear, i.e. it's no longer linear and wear goes up more quickly than the removal rate does.

Determining a good cutting speed is simple, just something under the theoretical max. Memorize a few common fpm numbers and using the formulae RPM = CS * 4/dia, work out the rpm in your head as you're doing the set up. Lathe Mill or drill. Drop into the closest gear and make chips! e.g. 1.5" piece of steel with with hss cutter, 400/1.5, (slow brain says 1" would 400, 2" would 200 so rpm is 300, drop it into 280 on machine and proceed.
Click to expand...
Numbers are from Little Machine Shop. The LMS online speed & feed calculator uses roughly double milling SFM as turning SFM.

littlemachineshop.com

Speeds & Feeds

The premier source of tooling, parts, and accessories for bench top machinists.
littlemachineshop.com littlemachineshop.com

And from my 4Machining app on my iPad. Attached screen shot of generic SFM values in the app. 4Machining values on this screen are about half the SFM values given by LMS, but if you look up specific alloys on the app they are closer to the LMS values.

I’m working with a 3/4 HP 10x18 lathe, and a 2 HP RF30 round column mill. I used conservative values that empirically work with the machines I use. YMMV.



IMG_7557.jpeg
 
whydontu said:
Numbers are from Little Machine Shop. The LMS online speed & feed calculator uses roughly double milling SFM as turning SFM.
Click to expand...



Thanks for pointing out the source. I think the information they provide is incorrect. Maybe a programmer who didn't understand the theory and doesn't machine slipped a digit?

They present the standard way to to calculate RPM. More descriptively, you could call it the maximum rpm before you get accelerated tool wear (speed vs removal rate). The idea is the machinist should be running a fast as possible up to just before accelerating tool wear. Its an economic thing really, max throughput without squandering tooling.

There are lots of reasons to run more slowly than the theoretical max; set up, finish, rigidity, DOC, feed, chip size etc, however the calculation of that theoretical max speed is the same regardless of operation; i.e. you don't generally use different cutting speeds for milling/turning/drilling.

Coming at it another way, look up in Machinery's Handbook the cutting speed for turning HSS in low carbon steel and free machining steel. LMS is 150 and 250. MH for ow carbon is 70-120, leaded is 110 - 140 (some variation on exact alloy and hardness). The LMS numbers will have you runing too fast for turning.
 
@whydontu - I generally agree with what @Mcgyver says but I get there via a different path.

First off, as I said before, I like your charts. I never did look at the numbers in it because I noted your comment about them being what works for you and might not work for me. So I just assumed I would develop my own numbers. That's also why I asked for the excel spreadsheet.

That said, I like to let my machine, my tooling, and my metal tell me what they like. Since most of my metal is farm yard mystery metal, that's prolly best anyway. What I liked about your chart is the diameter / rpm / surface speed info. Not the material and tooling factors. I can usually interpolate in my head plenty well enough.

Generally speaking, I like to run as slow as I can. Productivity is for businesses not me. They would fire my ass clean to Antarctica for workin at my normal snails pace for makin stuff. I like slow for obvious reasons - I'm slow, mistakes are easier to deal with, safety is improved, easier to recover when things go bad. My numbers are generally MUCH lower than yours.

One thing is certain - your data is high....... Certainly higher than I generally run. In fact, I very often wish my lathe could run below 70rpm - hence my interest in a VFD for my lathe and this winters big project.

Since many people will prolly end up using your chart, maybe it would be worth figuring out what the recommended minimums might be too.... I'd volunteer, but as I said earlier, I'm more of a touchy feely kinda fellow and I don't really have hard numbers.
 
I'm happy with the charts and apologies if I'm seeming critical, whatever people find makes it easier. My pushback is what I believe is bad info from LMS - e.g. if the max speed for HSS in 1018 is 100SFM, its 100 SFM. It's The relative surface speed between work and tool....... regardless of whether it is work or cutter or both that is turning
 
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OK, revised chart using values from 2000 edition Machinery's Handbook. I've added alloy designations, these are the ones i typically work on and are relatively generic. Feel free to change for your specific needs. And M/H does show slightly different values for milling and turning, but the ones I checked are maybe 10% variance so not worth worrying about.

Some of my confusion is how M/H shows SFM with a factor for feed rate in the fifth and sixth column from the right. So for my new values I'm only using the SFM numbers in the 3rd column, and using the mid-range Brinell values.

New Excel file is in the DropBox folder, dated 10-28-2024.
 
Sounds like you are well on the way.

whydontu said:
And M/H does show slightly different values for milling and turning, but the ones I checked are maybe 10% variance so not worth worrying about.
Click to expand...

I'd love to hear the person who came with those explain it. My guess is it involves tool costs, downtime etc. Maybe of value to a production engineer somewhere, just unnecessary confusion for the rest of us. Nevertheless, when a molecule of HSS meeting the molecule of steel hasn't a foggy clue which one is rotating, hence you can use the same CS and RPM = 4*CS/Dia formula for a max speed for all ops.


To quote the American Society of Metals Handbook vol 16

"The cutting speed is the most important
factor in economical machining. Too slow a
cutting speed results in poor throughput and
an increase in overall production costs. Too
fast a cutting speed can result in lower tool
life with higher tool costs and more downtime.
Somewhere between these extremes lies the optimal"

Figure 11 shows production costs plotted
against cutting speed. The optimal cutting
range lies between the point of minimal cost
and maximum production"


1730162677894.png



They do also note that the wear of a milling cutter compares favourable with single point tools for a given cutting speed, but that the mill does in some ways have a tougher life, changing chip loads, entry and exist shocks, possibly vibration etc. This is all or partially offset by the benefit of less than 100% duty cycle letting it cool and pick up some lubrication.

Just ponding why MH would have any variance, which I agree is immaterial for what we do
 
So I did what I normally do, and waffled around without making a decision, so I ended up making both the Arduino electronic version, and also trying out an engraved version.

Arduino nano, 20x4 lcd display, two 12-position rotary switches, couple of dozen resistors, and a cheap plastic enclosure.

6”x6” dollarama plywood blanks, 5w laser engraver. Still needs to be cut to size and lacquered.

I’ll probably still make an engraved aluminum plate version, wanted to see what it would look like before I commit to cutting metal.

IMG_4267.jpeg
IMG_4268.jpeg
 
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