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Interpreting Cutting Speed Tables

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Bob Gibson

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Please forgive me for what I suspect most of you will think is a very basic question.
I am a complete novice to machining and have purchased a Optimum TU-2004v. I'm having trouble interpreting the cutting table on page 39.
Here is a sample line

Material Non alloyed steel Steel casting C45, St37


Cutting materials

HSS P10 P20 P40

35-50 100-150 80-120 50-100

Am I correct in assuming
1/ Material = Work piece
2/ Cutting material = Cutting tool material
3/ 35-50 etc = SFPM (surface feet per minute)

To get chuck rpm i take the above number and divide that by the diameter of the work piece in ft.

Seasons Greetings to you all

just checked the post and the table did not layout correctly
hope you can understand it
 
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XD351

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Sfpm required / circumference of workpiece in feet = rpm.
You might be better off looking online for cutting speeds rather than use what is in th book that came with the lathe - baring in mind many of those cutting speed charts are based on the operator using an industrial grade machine and tooling, use them to get you in the ballpark but don't treat them as gospel . Things like depth of cut ,feed rate ,type of cutting tool and the material itself also play a factor as you can have two pices of steel that look the same but one will machine beautifully and the other will be a real pig !Experience is the best teacher here . Have a look on joe pyszynski youtube channel for a video called C's and 6's this will show you what you ideally want to achieve when machining on the lathe .
 
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XD351

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I have amended the formula as to get surface feet per minute the circumference must be in feet not inches .
Sfpm req / ( pi x d /12) = rpm
Where d is diameter in inches .
I hate the keyboard on ipad damned if i can find the pi symbol or work out how to show fractions with it !
 

Bob Gibson

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Thanks again XD351
I checked out the Cs & 6s Video on Youtube and found it most helpful.
Was I correct in assuming the numbers eg 35-50 represent suggested Sfpm range.
 

XD351

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If you have a smart phone or ipad look in the app store for an app called job shop lite - it is free and will do the sfpm calculationd for you plus much more .
I would say yes , i used the app to try a scenario , sfpm = 100, dia of work = 0.5 this gave 763 rpm which looks ok to me .
 

Bob Gibson

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Ok thanks
i should be ok to make some good looking chips now.
I will get the app and also look at more of joe pyszynski videos to fill in the knowledge gaps.
My next task is grinding some HSS cutting tools I'm sure joe pyszynski will have a video on that
 

XD351

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Another series of videos to watch are from " that lazy machinists " and cover everything from shop safety to advanced machinig techniques , the host Marc is a retired toolmaker and teacher and i think his videos are a must watch for those who are learning or want to improve their capabilities in the workshop . Mr pete 222 is also an excellent teacher and has hundreds of videos to watch - also a retired shop teacher .
 

Wizard69

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Sfpm required / circumference of workpiece in feet = rpm.
You might be better off looking online for cutting speeds rather than use what is in th book that came with the lathe - baring in mind many of those cutting speed charts are based on the operator using an industrial grade machine and tooling, use them to get you in the ballpark but don't treat them as gospel . Things like depth of cut ,feed rate ,type of cutting tool and the material itself also play a factor as you can have two pices of steel that look the same but one will machine beautifully and the other will be a real pig !Experience is the best teacher here . Have a look on joe pyszynski youtube channel for a video called C's and 6's this will show you what you ideally want to achieve when machining on the lathe .
Feedrate is a significant component in getting good results, I'm glad you pointed this out. Just yesterday at work I was trying to machine a bit of work hardening steel and had a feedrate that was too slow leading to work hardening and really ugly cutter behavior. A simple change in feedrate fixed this problem leaving the RPM as set.

In any event the point here is that feedrate can often be as important as having the right SFPM at the cutter.
 

lohring

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A good approximation for the circumference in feet is divide the diameter in inches by 4. That means that a 4" diameter cutter or workpiece has a circumference of about 1 foot. (Actual circumference is 1.05 feet.) That's close enough for cutting speed calculations.

Lohring Miller
 

goldstar31

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Of course, if the spindle speeds are controlled by pulleys----

Let's get real. Decisions have to be made to see which pulleys apply. Perhaps a bit of an educated guess

I saw this all and got a lathe with a speed controller and a fancy thing that lights up-- presumably with the speed of the spindle--- But old farts like me cannot see what it does.

Oh the joys of modern technology!

Norm
 

Entropy455

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The diameter of the part (in inches), times pi (3.14), equals the part's circumference (in inches).
The diameter of the part (in feet), times pi (3.14), equals the part's circumference (in feet).

Multiply either of the above circumferences by the spindle's rpm, to get the speed of the cutter (in the units of inches per minute, or feet per minute, respectively)
 

goldstar31

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The diameter of the part (in inches), times pi (3.14), equals the part's circumference (in inches).
The diameter of the part (in feet), times pi (3.14), equals the part's circumference (in feet).

Multiply either of the above circumferences by the spindle's rpm, to get the speed of the cutter (in the units of inches per minute, or feet per minute, respectively)
And then the diameter changes-- as one descends back into reality.

N
 

john_reese

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Job Shop Lite on the cell phone was a great suggestion. I tried it and decided to upgrade to Job Shop Pro for about $3.
 

Entropy455

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Goldstar31, a required topic in Mechanical Engineering school (Manufacturing Processes class to be specific) is learning how to calculate the temperature rise of metal chips as they exit the cutter-head of a lathe (a function of the material's yield strength, tensile strength, Young's modulus, Poisson's ratio, shear-angle of the cutter, and obviously the volumetric removal rate). It's calculus based equations, rooted in both Mechanics-of-Materials and Thermodynamics.

The purpose of the lesson was to show that it's mathematically possible to accurately predict the actual cutting-power requirements for any particular machining operation, and the expected temperature rise of the cutter (which will temper/anneal if it gets too hot), and also the expected temperature rise of waste chips - because some metals will make for very exciting shop-fires with inadequate cooling . . .

Welcome to reality. . . . .
 

abby

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In reality neither HSS or carbide tooling will temper or anneal even at red heat , or are we still using carbon steel cutting tools ? We are talking model engineering here using model engineering sized machines.
Don't make an enjoyable hobby more complicated than it needs to be.
Dan.
 

john_reese

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With the vast range of cutting tool geometries and materials and coatings available it seems best to follow manufacturer's recommendations as to surface speed, depth of cut and feed rate. What one can actually achieve is terms of speeds and feeds will depend a lot on the characteristics of his lathe. In the hobby and home shops we do not need to optimize the productivity of our machines to turn a profit. We usually do not have the horsepower needed to get the most an insert.

Just find an insert geometry and chipbreaker design that works for you.

For most hobby machines a "light finishing" chipbreaker and small nose radius will work best because they lack the power and rigidity to take the depth of cut and feedrate to break chips with other chipbreaker designs.
 
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Entropy455

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It's time to revisit the heat-treating tables for HSS & Carbide tool steels. If your cutter is visibly red (even dark red), then you are absolutely modifying the temper of the tooling.

Generally speaking, what works well within industry, works well for the hobbyist also. . . .
 

TonyM

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I was taught correct speeds and feeds when I was an apprentice. I quickly learnt the reality and how to get the max out of a machine or tool when I was put on piecework for a while.
Now I am a retired hobbyist and I have forgotten most of the theory but I can still judge practical speeds and feeds. I also have lightweight, low powered machines that I need to outlast me. I suspect many in our hobby have little or no experience when starting out and quickly learn what is too fast or too slow without a reference book, albeit at the expense of a few tool regrinds.
Much more important in my opinion is learning about well sharpened and positioned tooling.
 

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