# Correct lathe speed



## Southtowns27 (Dec 5, 2014)

Hi guys, this is my first post here.  I'm wondering how to pick the correct lathe spindle rpm and feed rates for cutting various materials.  I've faked my way through several projects, but just curious if there's a chart out there someplace or a good "rule of thumb".  
Kinda OT, but does anyone know how I can determine the build date of my South Bend 9A?
Thanks in advance!


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## Bill Gruby (Dec 5, 2014)

This is one of many on the net. Just Google search Machine speed and feed rates. There are even calculators on the net to figure them out for you. Don't forget the Machinerys' Handbook either.

 "Billy G" 


http://littlemachineshop.com/reference/cuttingspeeds.php


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## chuckorlando (Dec 5, 2014)

Get acquainted with the math process IMO. Using a calculators fine, just know whats what. Then get a cutting speed chart and it's easy enough. What ever number you reach, I would cut in half and work up till it's happy. 

If your gonna play with it on a project, practice before your finish cut


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## sk1nner (Dec 5, 2014)

What I'very used is 4 x cutting speed (inches per minute)  /part diameter


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## Karl_T (Dec 5, 2014)

Nothing wrong with calculators for a start point. But that's all it is. The optimum speed "depends" on a great many variables with the exact machine and its condition being one of the biggest factors.

You can't beat experience when cutting metal. Don't be afraid to try things.

Karl


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## Hamstn (Dec 5, 2014)

Karl_T said:


> Nothing wrong with calculators for a start point. But that's all it is. The optimum speed "depends" on a great many variables with the exact machine and its condition being one of the biggest factors.
> 
> You can't beat experience when cutting metal. Don't be afraid to try things.
> 
> Karl


Yep...I don't have a clue what speeds my lathe turns. I just know about where to set it and then let the machine and part tell me if I need to make changes. 90% of the time it's the same speed for 90% of the jobs. Not including drilling a larger hole, threading, or parting in which it is slowed way down.


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## Andre (Dec 5, 2014)

FWIW, I don't pay any attention to feed/speeds. I run my lathe at any speed that looks right and cuts well. Only when using reamers I am careful about going too fast.


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## chuckorlando (Dec 5, 2014)

Oh by all means use a calculator. Just know what your doing. I dont calculate much any more as you get to know kinda were to be. And I like to find that limit. Where any more and something aint happy. 





Karl_T said:


> Nothing wrong with calculators for a start point. But that's all it is. The optimum speed "depends" on a great many variables with the exact machine and its condition being one of the biggest factors.
> 
> You can't beat experience when cutting metal. Don't be afraid to try things.
> 
> Karl


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## Southtowns27 (Dec 6, 2014)

Thanks guys, helps a lot! 
I did check out one of those speed charts. I didn't realize that carbide is supposed to be run *that* much faster.  My tooling is HSS right now, but I think down the road I'd like to pick up some stuff with the replaceable carbide inserts so I don't have to keep grinding tools.


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## gheumann (Dec 7, 2014)

I hope it is obvious but because it hasn't been said, I will say it. The cutting speed is related to how fast the surface being cut is moving past the tool - referred to as FPM (feet per minute) or IPS (inches per second) or something like that. In one revolution of the lathe, a piece of 1" round bar travels 3.14" (pi) past the tool. Diameter matters! A 6" round at the same lathe RPM is moving 18.9" of material past the cutter in the same amount of time.

Like others I use "what works" and when I'm hogging out aluminum (which I do a lot of) I use speeds much faster than recommended. The most important implication of your choice is productivity vs. heat. To a lesser degree, speed will affect surface finish as well. With steel you can watch the chip color for a heat guideline.

Turning and facing can generally be done much faster than parting. Parting too fast is the root of most people's trouble with parting.


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## Southtowns27 (Dec 8, 2014)

Yep, got the whole FPM concept.  I just had no idea where a good starting point was.  Thanks for the advice :thumbzup3:


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## Bamban (Dec 8, 2014)

gheumann said:


> Turning and facing can generally be done much faster than parting.



Sorry to hijack the thread, not entirely off topic though, but I often wonder how the machinists do it. Is it a standard practice to turn and face at the same set up, speed and feed rate for a given material?


Thank you.


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## 12bolts (Dec 8, 2014)

-->Bamban, Not really no.* S*urface* F*eet per *M*inute changes with material diameter. A 1" rod turning at 150 RPM has a speed of (approx) 39 SFM. A 6" rod turning at 150 RPM has a speed of (approx) 235 SFM. Big difference even though the only thing that changed was the workpiece diameter.
When facing a large diameter the SFM will change dramatically during the cut. This is obvious when you are making the cut as the finish changes progressively. It can even be noticeable on small dia stuff. You may have seen it yourself and not realized what was happening.

Cheers Phil


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## Bamban (Dec 8, 2014)

12bolts said:


> -->Bamban, Not really no.* S*urface* F*eet per *M*inute changes with material diameter. A 1" rod turning at 150 RPM has a speed of (approx) 39 SFM. A 6" rod turning at 150 RPM has a speed of (approx) 235 SFM. Big difference even though the only thing that changed was the workpiece diameter.
> When facing a large diameter the SFM will change dramatically during the cut. This is obvious when you are making the cut as the finish changes progressively. It can even be noticeable on small dia stuff. You may have seen it yourself and not realized what was happening.
> 
> Cheers Phil




Phil,

Thank you.

I guess I did not phrase the question properly, assuming the same diameter, say you have 1 inch diameter work piece, would you face and turn at the same machine set up?


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## chuckorlando (Dec 8, 2014)

The simple answer is no. Though I do it all the time. But lets say the part is 4 in. As you get closer to center, you should tech give more rpm. Though the feed is the same and cutting speed is the same. The rpm is not. Every material has a cutting speed. That and the dia determine the rpm.

When you do this math, thats perfect everything. Big HP, stiff machines, proper coolant, optimal DOC. This is why I say cut it in half. If your math says 1000 start at 500.


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## Wreck™Wreck (Dec 9, 2014)

Bamban said:


> Sorry to hijack the thread, not entirely off topic though, but I often wonder how the machinists do it. Is it a standard practice to turn and face at the same set up, speed and feed rate for a given material?
> 
> 
> Thank you.



Many lathes have Constant Surface Speed where the spindle speed is slaved to the X position of the tool within
set limits.


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## xalky (Dec 9, 2014)

Wreck™Wreck said:


> Many lathes have Constant Surface Speed where the spindle speed is slaved to the X position of the tool within
> set limits.


I've only ever seen that in a cnc machine. I'm no cnc expert but I believe the changing speed has to be programmed into the code, for it to happen. I've never seen a manual lathe with that capability.

Ideal spindle speeds, are just that, an ideal. In most cases, we have to find a happy compromise range on a manual machine. The more experience you gain on your machine, the more natural it becomes too select the right speed and feed. Use a chart ie a formula, in the beginning, to help you find a good starting point. There are also a lot of variables that play into finding the right speed and feed, such as Cutter geometry, machine rigidity/capability, material being machined etc... It's not as complicated as it seems at first, machine time, eventually, will make it a no brainer.


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## Wreck™Wreck (Dec 9, 2014)

xalky said:


> I've only ever seen that in a cnc machine. I'm no cnc expert but I believe the changing speed has to be programmed



They are out there, LeBlond for example.
http://leblondusa.com/blog/2014/08/16/leblond-rkl-series-manual-lathes-constant-surface-speed/

Not inexpensive however. The shop where I work now used to have one, not a LeBlond but another manufacturer whose name I cannot recall at the moment and it was old.


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## Smithdoor (Dec 9, 2014)

Look here in the download section speed and feeds 
The best way make simple chart to hang on wall close to your lathe
If you the SN off the lathe look here I just post the chart at 
http://www.hobby-machinist.com/showthread.php/29036-9A-build-date

Dave




Southtowns27 said:


> Hi guys, this is my first post here.  I'm wondering how to pick the correct lathe spindle rpm and feed rates for cutting various materials.  I've faked my way through several projects, but just curious if there's a chart out there someplace or a good "rule of thumb".
> Kinda OT, but does anyone know how I can determine the build date of my South Bend 9A?
> Thanks in advance!


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## British Steel (Dec 13, 2014)

12bolts
When facing a large diameter the SFM will change dramatically during the cut. This is obvious when you are making the cut as the finish changes progressively. It can even be noticeable on small dia stuff. You may have seen it yourself and not realized what was happening.

Cheers Phil[/QUOTE said:
			
		

> Of course, if you have a VFD on the lathe you can fit a slider potentiometer to the cross-slide to control spindle speed and get an even finish facing and parting plus diameter dependant turning speeds, just like.the CNC boys do....


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## British Steel (Dec 13, 2014)

British Steel said:


> Of course, if you have a VFD on the lathe you can fit a slider potentiometer to the cross-slide to control spindle speed and get an even finish facing and parting plus diameter dependant turning speeds, just like.the CNC boys do....



Hmm, a couple if likes, I'd better fill in some details!

A pair of 10k linear taper rotary pots set max and min speeds, max has a 10k fixed resistor from its 'cold' end to 0v, so can swing its wiper from 5v to 10v, min has the 10k from +10v to its 'hot" end so it can swing from 0 to 5v, the wipers then go to the ends of the slider pot, sliders wiper then swings between max and min set on the rotaries. A.centre-off switch connecting either end of the slider to its wiper gives a quick 'set max - run -set min' facility.

Slider pots are NOT rugged, encase in a piece of aluminium channel and fit a rod to operate the pot with travel stops and some sort of sprung coupler so it can't be forced past the stops. Get the longest-travel pot for your lathes envelope, I. Use 60mm travel (on radius) so get a little under 5" diameter ranger -I'm looking for 150mm travel as I have a 13" swing! Expensive!

A 2-pole 2-way switch let's you select between 'constant surface speed(ish)' and normal operation....

Hope this elucidates, my lathe's in storage for a few more weeks (just.moved house) so I can't add pics, sorry


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## Shadowdog500 (Dec 13, 2014)

When I had my mini lathe which had infinitely variable speed, I would just adjust the speed knob until I got a good cut.  After a while I just knew where to set the knob for whatever I was cutting, which was usually aluminum, mild steel, brass, or stainless.

My bigger lathe only has 6 speeds in high gear and 6 speeds in back gear.    For now I just set it faster for aluminum, and slower for mild steel. I use HSS or cobolt tooling  for almost everything since it gives a better finish than Carbite for me.(my lathe Capps out at 1,200 RPM)   I haven't done stainless or brass on it yet.  

Since i I only have a handful of speeds available I was thinking of making a simple table for the materials I commonly cut that just gives one of the available lathe Rams for th diamater of the handful of metals I commonly cut.

chris


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