Speeds And Feeds Question

[Joe Pitz]

I have been looking at a lot of charts of the proper lathe speeds and feeds.
It appears that many of the charts show feeds for different material cutter material, either HSS or carbide.

The charts show feed per revolution, usually either in metric or fractions of an inch per revolution.

My lathe is a Clausing 6316 and has a feed chart, but it does not have a unit of measure, I am assuming it is based on SFM (surface feet per minute).

See included chart.

My question is is there a way to convert the recommended FPR to SFM or IPM (inches per minute)

I see some feeds in thousands of an inch, but what about the other feeds not given in thousands of an inch.

So when I turn a given material I can use the appropriate feed rates?

Thanks

Joe

 

[kd4gij]

Don't know about your chart but. A manuel lathe is usley FPR (feed per rev ) A mill is SFM or IPM

 

[JimDawson]

I have been looking at a lot of charts of the proper lathe speeds and feeds.
It appears that many of the charts show feeds for different material cutter material, either HSS or carbide.

The charts show feed per revolution, usually either in metric or fractions of an inch per revolution.

My lathe is a Clausing 6316 and has a feed chart, but it does not have a unit of measure, I am assuming it is based on SFM (surface feet per minute).

See included chart.

My question is is there a way to convert the recommended FPR to SFM or IPM (inches per minute)

I see some feeds in thousands of an inch, but what about the other feeds not given in thousands of an inch.

So when I turn a given material I can use the appropriate feed rates?

Thanks

Joe

View attachment 106738

The large font numbers are threads per inch, used when threading.
The small font numbers is feed in thousandths of an inch per revolution of the spindle.
You could use any of the settings to turn with, I don't know why they didn't print all of the possible feeds.

Appropriate feed rate is what works for what you are doing, and the desired finish. The slower the feed rate, generally means a finer finish, but more time spent on a cut. If I feel that my feed is too high, I slow it down, and vise versa. I almost never look at the numbers when feeding, they really don't matter unless you are doing production work where time is money.

 

[British Steel]

As Jim says, the chart is for threads and feeds (only some feeds are marked because - well, how much difference would you see going from 8 thou" to 9 per turn?).
To work out your CUTTING speed in SFM, multiply together the spindle RPM, the work diameter in inches and divide by four - eg 200rpm x 2" / 4 gives 100sfm.
Going the other way (SFM to rpm) divide 4 times the SFM by the diameter to get the rpm, eg 4 times 100 SFM divided by 2" gives 200rpm.
This points out that for the same SFM, the bigger the work the slower the spindle, and that small lathes may not go slow enough for big work, big lathes may not go fast enough for small stuff!

 

[brino]

Hi Joe,

I think there's a little confusion of terms.
SFPM is used for speeds; "inch per revolution" is used for feeds.

Speeds:
The surface feet per minute(SFPM) is controlled by two things: the lathe spindle RPM and the diameter of the work.
Most speed charts show desired cutting speeds in SFPM(or just called FPM) based on tool type (HSS or carbide) and work material (steel, aluminum, brass, etc.).
Given the tool type, work piece material and work piece diameter, you can calculate what RPM to use.

You cannot just think about RPM.
If a cylinder "A" turns at a particular RPM, then you see every point on its' circumference once per revolution.
If cylinder "B" has a diameter twice that of cylinder "A", you still see every point on its' circumference once per revolution.
However, cylinder "B" has a circumference that is twice that of cylinder "A"; therefore its' surface moves twice as fast for the same RPM!

Feeds:
-the rate that the tool moves
-for threading, feeds are expressed in threads per inch
-for surface cutting, feeds are expressed in thousandths of an inch per revolution of the spindle
-for roughing a coarse (larger) feed rate may be used; roughing is about faster stock removal the surface may have rings, etc.
-for finish cuts a finer (smaller) feed is used to give a smoother finish

That little chart contains a lot of info; Jim covers it above.

Your longitudinal feed (left-right) is shown directly in the table.
Your cross feed (used for facing) is 1/4 the rate of the longitudinal feed.

Use back gears for threading; it's the only way to get the RPMs low enough to actually disengage the feed manually before the carriage hits the headstock.

-brino

 

[Joe Pitz]

Thanks everyone for the great info. Jim as always, your information is always well explained and concise.

British Steel, (love that name), thanks for the formula, I have seen the calculators online, it is always good to be able to work the formulas to understand what is going on.

brino, thanks for the clarification on RPM, diameter and a good definition for feeds.

With all of this good help I will make it to junior machinist in no time

Joe

 

[Wreck™Wreck]

Feed Per Revolution is often not well understood by lathe users.
Picture turning a 1" diameter round at .001 IPR, ignoring the tool nose radius and depth of cut for simplicity of the math would produce a chip .001" wide X 3.14" long per revolution.

Turning a 2" diameter round at .001 IPR will produce a chip .001" wide X 6.28" long per revolution, exactly twice the Metal Removal Rate per revolution.

This is of course unrelated to SFM because the feedrate remains constant, the metal removal rate changes considerably however, I suspect that many lathe users have experienced the "I put a 4" diameter piece in the lathe, slowed the spindle speed way down and got a great finish" moment.

 

[Rex Walters]

I saw someone somewhere (probably Tom Lipton) make the "obvious" point that doubling the feed and halving the depth of cut removes the same amount of material in the same amount of time (or vice-versa of course).

For some reason that simple little comment was a bit of a light-bulb moment for me. This "obvious" little tidbit can be incredibly helpful in reducing chatter or preventing long-stringy chips. I've been playing with feed rates much more since realizing this fact.

 

[Tozguy]

This video source has been a great help to me. The videos on chips, feeds and feeds might echo some of what has been said here but it has more explanation on choosing speeds, feeds and depth of cut.
http://www.thatlazymachinist.com/my-shop-videos.html

 

[Joe Pitz]

Thanks Wreck Wreck, for the clarification on speeds and feeds.
Thanks Rex Walters for saying, it will be a good reminder.
Thanks Tozguy for the video link, I will watch it.

Joe