turning spindle speed

I would recommend just chucking a piece of material up and trying different speeds and feeds. Getting the correct tool, either HSS or insert, makes a huge difference.

That's what I've been doing for the last 20 years. Thought I might actually try it"by the book"
 
Liljoebrshooter said:
Most of the time the suggested speeds on the inserts from the manufacturer are not realistic with the small lightweight machines we have.
The speeds they show are for machines that weigh 10,000 lbs and can spin 8k rpm or more.
Click to expand...

And probably another assumption for high suggested speeds like that is the use of coolant in large quantities.
 
If using coated negative rake inserts on on low carbon steel in a machine of questionable abilities or a weak set up a cutting speed of 200 SFM is a good place to start, at 1" this would be 750 RPM of the spindle.

If the set up is rigid, for instance a 1/2" length of cut from 1" stock down to 1/2" diameter held 1" out from the chuck then an aggressive cut will work fine, wick it up in every way.

As the spindle speed decreases the surface finish will also change, and not for the better.
 
200 SFM is a good place to start, at 1" this would be 750 RPM of the spindle

So what is the formula for this?
 
Surface feet equals the work perimeter times RPM, with conversions made for inches to feet.
So, SFM=(3.14)(1)(750)/12
That gives you about 200.
 
Mutt said:
200 SFM is a good place to start, at 1" this would be 750 RPM of the spindle

So what is the formula for this?
Click to expand...
The circumference of a 1" round is 1 X 3.141
3.141 / 12 = .261 FT
.261 is Feet Per Relution.
200 Feet per minute would therefore be .261 feet / 200 or 766 RPMs

It takes 766 Revolutions Per Minute for a 1" diameter round to pass the tool at 200 Feet Per Minute

A part that has a circumference of 12" (3.82" diameter) has a 1 to 1 relationship, the part is 12" around so every single Revolution Per Minute is 1 Foot Per Minute.
Easy as pie
 
sousing this formula and the littlemachineshop chart a piece of 12L14, 1.375" diameter spun at 750 rpm would be 270 SFM ?

I think what I am more interested in is what rpm various types of metals need to be turned at. So if I know the SFM and the diameter of the work piece, what is the formula?
 
Mutt said:
I think what I am more interested in is what rpm various types of metals need to be turned at.
Click to expand...
The speeds shown in charts and derived from formulae should be considered maximums, not targets. Unless you are in a production environment there is no need to aim for maximum. Why not continue to use your trial and error method based on chip formation, heat removal and finish?
 
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