Correct lathe speed

Yep, got the whole FPM concept. I just had no idea where a good starting point was. Thanks for the advice :thumbzup3:
 
gheumann said:
Turning and facing can generally be done much faster than parting.
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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.
 
-->Bamban, Not really no. Surface Feet per Minute 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
 
12bolts said:
-->Bamban, Not really no. Surface Feet per Minute 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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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?
 
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.
 
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.
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Many lathes have Constant Surface Speed where the spindle speed is slaved to the X position of the tool within
set limits.
 
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.
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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.
 
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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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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