Endmill RPM

Hi all,

im new to machining, i have recently purchased a small metal lathe and a mill. so far im going ok with the lathe but im having trouble working out cutting speeds for the mill. i have looked at a few RPM/cutting speed calculators on the net but they all confuse me. the mill i have is a SIEG U2. it came with an end mill/slot drill set ranging from 4 - 12mm. i want to machine some slots through mild steel plate. any assistance with speed and feed rate would be appreciated.

thanks in advance

stevo

I can help in inches.. rpm = cutting speed x 4 divided by cutter dia. cutting speeds roughly alloy steel = 50 feet per minute, cast iron, 70 mild steel 80 to 100 and brass and aluminum, 200 these are for hss tools. If you talk limey its aluminium. In the lathe dia is the diameter of the work you are turning. Of course if you are drilling a 1//4" hole in 2" dia stock then 1/4" is your cutting dia.not the 2" Hope this helps. The speeds are ballpark numbers. Remember if you are dividing by a fraction you are multiplying be its reciprecal(sp) Peter

When manual machining, I've never relied on any formulas. I've always just listened to the machine, cutter & feel to tell me if things were right.

Of course, that takes some practice. Good luck.

Tom

67Cuda said:

When manual machining, I've never relied on any formulas. I've always just listened to the machine, cutter & feel to tell me if things were right.

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I had hired some guys that went by "feel". I was either dodging flying cutters or watching somebody take 3 hours to do a 2 minute job. I hate retraining people.

Contrary to popular belief, the material and the endmill don't know if they are in a home shop or a pro shop, or weather a servo or a monkey are the turning the handle.

The properties don't change.

Surface speed and feed rates are the simplest most basic calculations you'll come across in machining. Simple monkey math, there is no excuse to not do it, and even if you aren't doing it, you're doing it in your head or already did it and know the answer.

SteveO, there are a bunch of calculators out there. Bob Warfield (not me, but his parents had good taste in names) and MRainey both have some good calculators. Regular folks on this site.

Machinery's Handbook, as much I think its a giant outdated POS that hasn't been updated except for cover color in 40 years, has some very good info, formula's the whole deal. Just buy the cheapest one you can find on e-bay, if its old, the price will be a bit higher (old machining books are cool). If its new it will go higher because it has a pretty cover.

Be a bit wary of calcs at manufacturing sites, remember they are in the business of selling tools. Back the feed and speed down 20-30% and you will usually be in the range of long tool life.

Here is a bit of wisdom, and I'm sure most will agree, backing off of feed and speed will not always make your tools last longer. At a slow speed, you may not get proper chip flow over the cutter (even in a home shop), you might not get the proper sheer. As for feed, a too low feed can cause rubbing (chip thinning comes to mind, look that up once you completely grasp basic feeds and speeds). Rubbing can destroy a cutter very very very very very fast.

I'm not a metric guy (not because I don't like it, I just don't see it much), but 12mm cutter in a mild steel. Off the top of my head, 550-650 rpms, and feed 40-80 mm per minute, count it out on the dial. 1-Mississippi 2-,Mississippi, 3-Mississippi etc.... That would land you 60-80 sfm and .001 to .0015 per tooth, conservative #'s, but they should work well for you.

Double check my head math, I've got 5 calculators here... somewhere...

Bobw said:

Double check my head math, I've got 5 calculators here... somewhere...

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If you need a calculator to tell you how fast to run a cutter or turn a spindle on a manual machine, then you my friend are not a machinist.

You are somebody in search of a clue.

Do those calculators you use tell you how to compensate for tool wear? Machine condition or rigidity of a set-up?

That's what I though? NO.

Good luck in your endeavors.

Tom

Well im pretty sure bobw runs a business and needs to crank out parts ON TIME. If u have a shop full of guys running what they think "feels" right on the manual mill you may have some people running a 1/2" em at 200 rpms and someone else at 3000....... burnt up endmills and Rubbed to death endmills cost time and $$. I see BOTH sides of the fence (manual and cnc) I can make tools work just fine on the manual mill But its a good possibility that im usually wasting time by running the tools way too conservative.

Basically most machinists can make anything work, but is it the best?

Rstewart said:

Basically most machinists can make anything work, but is it the best?

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Ya, I can see working for Bob. "Tom, I don't think I saw you using that fancy calculator I gave you. You better use it or I am going to get mad!!"

I have never seen anybody use those calculators, why? Because they are a joke. Only people who have no confidence in their ability uses them.

Here's an example of how useless they are. I need to engrave a part number in aluminum using a .020 end mill. I use this program that's on the work computer, "Machinist Toolbox" is the name I believe. What does it tell me to run the speed and feed at? Way more than the TRAK 2 mill that I'm using can handle. Now what am I to do, start dividing the speed and feed until it gets into the range the machine can handle?

Even if you can run the speed on a manual machine, what are you going to do for the feed? The feed is dependent on your input.

To each his own.

Tom

So what did you rely on before you had accumulated enough practice. I guess you must have destroyed a lot of cutters practicing, or possibly you were born with the ability.

The OP says he's new to machining and you brag about how good you are, way to go.

Phil

67Cuda said:

When manual machining, I've never relied on any formulas. I've always just listened to the machine, cutter & feel to tell me if things were right.

Of course, that takes some practice. Good luck.

Tom

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I agree that "feel" on manual machining plays a role, and that it's part of the equation. You can feel when your overloading an endmill on a manual mill just like you can feel small bumps in the road in the steering wheel when your driving.
On a small mill as the op describes, i would use go under what a calculator suggests. On a "Full" size mill/cnc the calculator will help you get in the ballpark(Sometimes dead on), and i use this method to calculate my feeds/speeds. But even then, as said rigidity/set up, the mill being used, rpm limits of the mill all come into play. Sometimes there needs to adjustments from what the calc spits out to run at a slower feeds/speeds, and sometimes you will need to increase.
Basically, you want proper chipload. Rubbing destroys a cutter as said. One feed/speed calculator isn't the perfect solution for every machine. Use it as a base to get a "feel" for what your machine can handle, then adjust accordingly. You'll know when your machine is being pushed.

I'll throw in my $0.02. As a manual only guy, (conversational CNC mill) I have to say that the truth is somewhere in between science and feel. I rarely turn the spindle speed above 3000 on my mill because I want to preserve the spindle bearings on the mill. Even when using a Ø.020" end mill. Manuals don't have the rigidity, flood coolant, or mechanical integrity of a VMC. If I push the numbers, I generally run at about 75% of the recommended SFM and a little less than the recommended chip load. I often see the broken, chipped, destroyed end mills on the other knee mills used by the predominantly CNC machinists. Their exuberance and training leads them to ruin costly carbide because they go for broke as they learned in school. Not to mention the horrific chatter. There is a lot of "feel" involved, whether those here care to believe it or not.

Manuals are not production machines. Anything routed through to be run on manuals needs to be bid accordingly.

67Cuda said:

If you need a calculator to tell you how fast to run a cutter or turn a spindle on a manual machine, then you my friend are not a machinist.

You are somebody in search of a clue.

Do those calculators you use tell you how to compensate for tool wear? Machine condition or rigidity of a set-up?

That's what I though? NO.

Good luck in your endeavors.

Tom

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Apparently PM is not a place for a green horn noob to come and learn from the best, even if they just think they're the best? Hardly an atmosphere to learn by maybe asking a stupid question for fear of getting slam dunked by a know it all asshole like you...

Phil Burman said:

The OP says he's new to machining and you brag about how good you are, way to go.

Phil

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caracadon said:

Hardly an atmosphere to learn by maybe asking a stupid question for fear of getting slam dunked by a know it all asshole like you...

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The OP was asking thoughts on speeds and feeds, I gave my response. Good or bad, I wasn't slamming him in any way, just a different prospective.

67Cuda said:

When manual machining, I've never relied on any formulas. I've always just listened to the machine, cutter & feel to tell me if things were right.

Of course, that takes some practice. Good luck.

Tom

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The Mr. Asshole part was directed at Bobw, because apparently he feels "Everybody" needs a calculator to be able to machine parts.

Tom

Well not to incite flames in any way

The OP might do well to "google" a few Speed and Feed equations and metal types, cut and paste them on Note pad and then print out a little generic Speed and Feed chart he can paste onto the wall in his shop like I did a good while back. Doesn't hurt to punch out a few numbers on a calculator now and again until you get the feel for it

As for Cuda describing "Seat of the Pants" feel for machining - even with automated Speed and Feed calculations running in most Cam software for the CNC I still have that handy 0-150% Feed Override selector on my CNC which I use quite a bit running a new part.

Of course the "Feel for It" came from reading "The Practical Machinist" as I was instructed to do when I first started haunting these boards. Perhaps there are better examples for the English description of chip load and color, but I have yet to find it

67Cuda said:

Ya, I can see working for Bob. "Tom, I don't think I saw you using that fancy calculator I gave you. You better use it or I am going to get mad!!"

I have never seen anybody use those calculators, why? Because they are a joke. Only people who have no confidence in their ability uses them.

Here's an example of how useless they are. I need to engrave a part number in aluminum using a .020 end mill. I use this program that's on the work computer, "Machinist Toolbox" is the name I believe. What does it tell me to run the speed and feed at? Way more than the TRAK 2 mill that I'm using can handle. Now what am I to do, start dividing the speed and feed until it gets into the range the machine can handle?

Even if you can run the speed on a manual machine, what are you going to do for the feed? The feed is dependent on your input.

To each his own.

Tom

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Bullshit, you'd get destroyed by someone running proper speeds and feeds over your "feel" technique. Bob is right and I trust a guy like him any day over a joker like you. "feel" is what they used before they figured it with science.

When you talk about milling, it's just not speed but chip load. Chip load is the combination of speed and feed rate, and depth of cut. It's not that important with a light machine, but in higher HP machines you want the machine working to its capacity. That is where experience and "feel" enters into it, with experience you can tell by the color of the chips, the sound of the machine etc. No chart or manual can teach you that. The charts are a good starting point if you don't have much experience.

grandtools said:

When you talk about milling, it's just not speed but chip load. Chip load is the combination of speed and feed rate, and depth of cut. It's not that important with a light machine, but in higher HP machines you want the machine working to its capacity. That is where experience and "feel" enters into it, with experience you can tell by the color of the chips, the sound of the machine etc. No chart or manual can teach you that. The charts are a good starting point if you don't have much experience.

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Try micro machining, there are no chips or sound to tell you shit. Your feel technique will get you nowhere.

John Welden. ......

Tom

Tom , Science is dumb, just wing it like I do. Real machinists eyeball everything.

The OP was in regard to milling slots in steel plate, so no one (except you) was talking about micro machining. We were talking real machining., and most everyone who posted here machines real stuff, on real machines, not micro toys.

John Welden said:

Try micro machining, there are no chips or sound to tell you shit. Your feel technique will get you nowhere.

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Micro machining is no joke and the machines to do it properly are no joke either.

Cutting tool manufacturers spend countless hours testing to provide feed and speed parameters for you to use. This is one great reason not to buy "cheap" tools with no posted information.

When I write a program for a CNC machine or head out to use the manual machines, I would much rather know where to set the spindle, a starting feed rate, and most important, depth and width of cut. It is no trivial task to re-write a 100 line pocket program because my feeling was wrong. It would be a lot faster to pull out the tool catalog and spend 2 minutes to determine the proper cutting parameters.

I can't count the number of times I have seen guys running carbide tools at HSS speeds because they never bothered to look up the right speeds and feeds. They just went with their feeling.