# Spindle speeds for different metals



## Ryker Carruthers (Jun 8, 2012)

Since we got our lathe into the new machine shop I have been playing with feed rates and spindle speeds in our 12" atlas lathe, what spindle speeds do some of you use for different materials? like stressproof steel, brass and bronze and cast iron? the lathe should be running slower when parting, correct?
Thanks, Ryker Carruthers


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## rkepler (Jun 9, 2012)

You need to read up on the concept of "surface speed". As you surmise different metal and tool combinations like different speeds (and feeds and depth of cut, but we'll leave those for now) - IOW the cutting tool likes to have the material come by at a particular rate. I tend to use "surface feet/minute" and it's calculated by calculating the circumference of the work times the RPM divided by 12. So a 1" diameter bar has 3.14" circumference and if it's turning at 300 rpm you're seeing 78 sfm, a good starting point for a medium alloy steel on HSS tool.

If you poke around on the net you'll find plenty of references for SFM for different materials and tooling. One reference I like is the old Morse tools flip book, it has pages on RPM/diameter combos and the resulting SFM - so I look up a material, get the 'desired' sfm, the go to the chart and find the diameter and sfm and look up for the RPM. Use the given values as a starting point and maybe a high one, most model engineers are not happy changing tools as they do in industry.


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## kvom (Jun 9, 2012)

Once you get a starting speed as above, then the lathe and the chip color will tell you how to adjust. If the chips come off blue the speed is too fast, for example. A golden color chip (for streel) is usually ideal.


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## Tin Falcon (Jun 9, 2012)

this should get you started. 
http://www.littlemachineshop.com/Reference/CuttingSpeeds.php

i suggest you get a copy of the Army machine tool manual TC 9-524 and the navy repairman manuals both available fro free download. 

a caravat here many have said you can make small parts on a big lathe but can not make big parts on a small lathe while this is very true keep in mind small diamets of easily machined material can handdle some pretty high rpms. Large lathe chucks have a speed limit do not exceed it or bad things can happen. 
Also try to find a good condition used copy of the machieries handbook. basicly the bible for machinists and to some extent engineers. 
Tin


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## Ryker Carruthers (Jun 9, 2012)

thanks everybody, tin, where could i get the "Army machine tool manual TC 9-524" book? through the internet?
I will keep an eye out for the machieneries hand book, 
thanks, Ryker


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## mu38&Bg# (Jun 9, 2012)

If you're using insert tooling, follow the manufacturers spec for surface speed, depth of cut, and feed if at all possible. The trouble is that most inserts are made for very high production rates and it's all but impossible to run that fast on an old manual machine on small diameter parts. The difference in surface finish is dramatic in steel. For other metals running slower won't matter much.

Of course, experiment once you find the guidelines. For parting specifically, it takes a lot of experimentation. I found I could part steel very well and clean with HSS blade if I used a very thin lubricant like lamp oil(paraffin). I had all sorts of trouble before that and broke 3-4 blades. A carbide blade I had wouldn't cut anything, no matter how I set it up or sharpened it. Don't expect much from the Atlas 12" for parting. It is not nearly stout enough, I didn't bother parting steel in it when I had mine.

Greg


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## rkepler (Jun 9, 2012)

dieselpilot  said:
			
		

> Of course, experiment once you find the guidelines. For parting specifically, it takes a lot of experimentation. I found I could part steel very well and clean with HSS blade if I used a very thin lubricant like lamp oil(paraffin). I had all sorts of trouble before that and broke 3-4 blades. A carbide blade I had wouldn't cut anything, no matter how I set it up or sharpened it. Don't expect much from the Atlas 12" for parting. It is not nearly stout enough, I didn't bother parting steel in it when I had mine.



I didn't have trouble parting on my 12" Atlas but still did break the occasional blade, particularly at the small end of things (.040"). If nothing else tightening up the gibs and locking the saddle will add a lot of rigidity and save the parting blades.


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## Tin Falcon (Jun 9, 2012)

Read here:
http://www.homemodelenginemachinist.com/index.php?topic=9413.0
Army manual 
http://www.metalworking.com/tutorials/army-tc-9-524/9-524-index.html
Navy 
http://www.metalwebnews.org/ftp/machinery-repairman.pdf
Complete practical machinist Joshua Rose.
 http://archive.org/details/completepractic00rosegoog
probably close to a thousand pages total. should keep you busy 
Tin


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## Ryker Carruthers (Jun 9, 2012)

dieselpilot  said:
			
		

> Don't expect much from the Atlas 12" for parting. It is not nearly stout enough, I didn't bother parting steel in it when I had mine.


I havent had to part anything yet, just hacksaw and then face off, If i do have to part I will use the 16'' south bend


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## rake60 (Jun 9, 2012)

My hobby lathe is a 9 X 20. (OK, it's a Grizzly 9 X 19, SAME THING!)
The spindle speed is at 600 RPM. 
I use that speed for everything, on all materials except for parting.

At work the lathe is a 12 X 36. The spindle speed is set for 720 RPM.
I use that speed for everything, on all materials except for parting.

The manuals will drive you crazy if you allow them to.
Listen to the machine and watch the chip.
The same speed with adjusted feeds will work on most materials.

It doesn't need to be all that complicated.

Rick


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## abby (Jun 9, 2012)

You will find parting off much easier from a rear toolpost , less danger of "digging in" and so far less breakage even on very thin tools.


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