Surface Finish

High, slow, and shallow as a very simple answer. But really you've got to talk about the metal you're turning, the toll material and shape you're using. There is no "one size fits all" answer. Do you have access to the Machnist's Handbook?

Hi,

spindle speed is not critical if spindle and lathe is really good.

We are turning and flycutting ultra-precision surfaces with speeds between 0.1cm/s and 20m/s.

Feed is dictated by tool nose: if circular then to be calculated by adding many small parts of this circle to generate the final surface.

Depth of cut depends on quality (sharpness) of tool.

Very good surfaces can be cut only with mono-crystalline diamond tools. These have a cutting edge sharpness of below 10nm if good. Then you can have a depth of cut (for the final cut) of near 1µm.

If you have a coarser tool you shall select a depth of cut of 2 to 5times the cutting edge sharpness.

You shall use the best possible machine (look for LT Ultra, Moore and Precitech and Hembrug) or build yourself one according to your needs and budget.

Don't forget a fine 2-plane balancing system, an elastic base in a non-vibrating building and a moderate temperature control.

RHABE

remember it is the speed at the tool not the rpm that is important. the greater the diameter of the piece, the faster the speed of cut.

a machinist handbook is essential as it gives speed of cut, finish required, material to cut, cooling fluid required and also angle and height of tool tip with respect to the object. i've probably missed out on a few but maybe others might add them?

experience is the best way, but that you will have to acquire the hard way.

There are quite a number of factors which affect this, including the material you are cutting (Mild steel? brass? cast iron? -sometimes the manufacturer will recommend metal removal rates), the type of cutting tool you are using (carbide? diamond? High Speed steel?), whether or not you are using coolant while cutting, continuous or intermittent cutting, available lathe spindle speeds and feeds, the actual required surface finish ("good" can mean almost anything, so you should decide what you actually need and aim for that), and so on. A very GENERAL rule would be to go to high spindle speed, fine (shallow) cut, and a low feed rate, and check lathe performance and what finish you get, then adjust speeds and feeds as necessary.

Machinerys Handbook provides lots of detailed information on this topic, and would be well worth reading, there are also plenty of other sources of data for specific applications out there; check out www.metalillness for a good machinist's forum.

Good luck!

On board destroyers we only had a lathe and bench drill...............I can recall many times when components had to be machined with small tolerances and good surface finish....................to obtain good surface finish, round off the tip of the tool with a stone (this is important), use slow speed, very low feed AND plenty of coolant............this will give an excellent shiny finish.(looks like a ground surface).

The only draw back is............the time it takes..........this method can also be used for facing, grooving, fillets and radii.

What material are you machining? 1018? 304? 316L? 12L14? Titanium? Monel?

How big is the piece? If you are turning your speed (rpm) will depend on the diameter of the work piece. Some NC lathes have a setting that will give constant cutting speed. It will use a constant feed and variable speed (rpm) which will yield a constant surface speed.

What cutting tools are you using? HSS? Cobalt Steel? Carbide? Carbide inserts? PCD?

If you are using inserts look at the package - usually they will have a table of suggested feeds and speeds.

What is the nose radius of the tool? Often you will get a very good finish with a larger tool radius but there are trade off's as well.

One of the best ways to know your feeds and speeds is to just get some scrap and experiment. Run it at one speed and then see what happens if you increase the speed while keeping everything else the same. Try changing the depth of cut and feed rate.

Also, get a copy of Machinery's Hand Book and also Machine Shop Practices is a good pair of books to have around.

You could have asked a simpler question like, "How high is up?"

Travis

(Who sold his commercial machine shop about 15 years ago.)