What's new
What's new

feed rate quesiton

rich_machine

Plastic
Joined
Apr 11, 2013
Location
Louisiana
For single point turning on a metal lathe, I understand that various work material/cutting tool material have a recommended SFM cutting speed. With the SFM the correct spindle RPM can be determined using your works diameter. That is straightforward to me.

However, for a given part diameter and rpm is there a specific formula to calculate the ideal feed rate (IPR)? Or is IPR simply determined by trial and error while seeking the best surface finish?

I researched and read many articles regarding lathe speeds however none specifically state the best way to determine IPR.


Thanks
 
Insert manufacturer lists feeds for a given flavor of insert, it doesn't matter what size the insert is, if it can fit where you want.

I've used a CNMG 432 to bore out a 300" diameter hole before as an example.

Of course generally the larger the work, the larger the style.of insert you can use because machine HP and size scales up proportionally to the work.
 
Thank you myrmidon.

However, let my simplify my question. Is there any formula or method to calculate ideal feed rate (inches per revolution) when turning with a single point tool on the metal lathe?

Thanks
 
There is no ideal feed rate for the simple reason sometimes you want the metal off NOW and sometimes you would like a nice finish

Example from 103 years ago - they wanted to show what the lathe could do as to metal removal. The extra heavy chips that form the border around the lathe picture are the result
 

Attachments

  • 1915 Ad.jpg
    1915 Ad.jpg
    95 KB · Views: 129
Inch per rev and surface finish are linked to tool geometry and most importantly tool radius in most cases.
All lathe cutting is a threading operation, depends on how small of threads (cusp) you want.
Big rad more feed with low cusp, small rad smaller cusp, lower feed.
Catalog feedrates have nothing to do with this world.
Want to move metal? IPR up until you run out of horsepower or the tool breaks.
High feedrates, like threading tools need more clearance on the front side and this side rake can be a limiting factor as you are cutting into a helix.
Bob
 
Thank you myrmidon.

However, let my simplify my question. Is there any formula or method to calculate ideal feed rate (inches per revolution) when turning with a single point tool on the metal lathe?

Thanks

The answer is simply NO

Is there a formula or method to make the best cookie??

Or more importantly is there a formula or method to make the best Margarita???



Too many variable... Someday... Maybe... Stephen Hawking will get bored with the
piss ant question of the formation of the universe and turn his attention to turning
on a lathe, but until then, the answer is NO... Too many variables...

Experience is key... Knowing what your tool/insert is "supposed" to do helps also.
Beyond the manufacturers recommended #'s, it doesn't take much "experience" to figure out
what those #'s actually mean in the real world. And what those #'s mean on your lathe,
may be totally different than what they mean on my lathe... Experience...

Its fun learning.. Enjoy the ride... As a machinist it never stops, it does slow down some,
but it never stops.. If the learning ever stops, you need to quit and go work at Subway.
 
As said above, the limit on feed rate is usually based on the machine or the tool. If the cutter has a nearly vertical face to the side that is feeding into the cut, too high a feed rate will cause it to bear on the face of the work and just push, which will push the toolpost, break the cutter, or bind up the feed on the lathe. Adding clearance to that leading face allows a higher feed rate, but also takes support from under the edge of the cutter, so there is a give and take where you gain feed, but lose strength to where the huge bite you are taking finally breaks the edge of the cutter off. This is more applicable to a hand ground HSS tool where you can put as much clearance on it as you desire.

On low strength materials like aluminum and cast iron, you can run pretty insane feed rates for roughing, just to put chips on the ground and get on with the job. On high strength alloys, tough materials and interrupted cuts, that lack of support is going to result in a broken tool.

Within reason, set your speed to the proper sfm for the cutter and material and start a cut at whatever depth of cut you desire. If the chip is stringy, up the feed rate until it breaks clean into tight 9s or the tool starts pushing the post or you fear breaking the cutter or feed on the lathe. If you are concerned about the load, drop the feed while hand feeding and see how hard it is to feed the tool by hand at that rate. If it is REALLY hard to feed, back up and punt. If you just can't get it to break, drop the speed a little and see if the chips curl more. Some materials just WILL NOT break (some stainless alloys like 304), other material like cast, ductile iron or bronze can't help but break. In those cases, just jack the feed up until it gets scary.

Lastly, some machines do better with HSS than carbide... lighter lathes, especially. The little Jet at the hydraulic shop couldn't run a carbide cutter to save its life. You could get these little scratch cuts at 300rpm, .030 depth and .005 feed and just pray it didn't start chattering. I got a stick of HSS, ground a high rake hook tool with pretty generous front clearance and set it to about 100rpm in backgear, but went to .100 on the depth of cut and jacked the feed rate to .015/rev. The foreman walked by and did a double take. It wasn't running very fast, but it was flat laying metal in the pan. Tripling depth of cut and tripling the feed rate resulted in a faster metal removal rate than the carbide could provide because carbide couldn't take that kind of shearing grind on the edge without chipping. I had dropped the speed by a factor of three, but upped the depth of cut my three, so that was a wash. Upping the feed rate made it work three times faster.
 
For single point turning on a metal lathe, I understand that various work material/cutting tool material have a recommended SFM cutting speed. With the SFM the correct spindle RPM can be determined using your works diameter. That is straightforward to me.

However, for a given part diameter and rpm is there a specific formula to calculate the ideal feed rate (IPR)? Or is IPR simply determined by trial and error while seeking the best surface finish?

I researched and read many articles regarding lathe speeds however none specifically state the best way to determine IPR.


Thanks
.
1000 rpm x .010 ipr = 10 ipm
.
each insert manufacturer has a recommended feed rate for different materials like
.003 to 0.010 ipr
.
many manual lathes the feed levers are directly labeled like .003 ipr so no math needed
 
Thank you all for the replies. I plan to continue testing various feed rates and spindle speeds as well as grinding my own HSS tools. There's definitely no replacement for experience when it comes to lathe work.
 








 
Back
Top