Many first time lathe users have no feeling for what surface finish can
reasonably be expected from a 9x20 sized hobby lathe IN WELL ADJUSTED 
CONDITION. Passing this test does not mean everything is perfect. This is a 
quick surface finish check to detect MAJOR problems only. 

PREPARTION

Chuck up a 20-25mm (3/4 to 1") diameter free curring machining aluminium (I
used 2011), let it protrude some 120mm (5") from the chuck. No tailstock
support.

Set belt for maximum spindle speed, put a new RH carbide insert tool (like a 
CCMT with 0.4mm tip radius) at centre hight in the toolpost. Or use a PROPERLY! 
ground HSS toolbit (many beginners do not know what that means, therefore I 
recommend a factory shaped carbide insert with POSITIVE rake angle). Do not 
lock compound or cross slide for this test. If the gibs are properly adjusted, 
this should make no difference to the result of this "light duty" test.

TEST 1

Take one deep roughing cut (2mm dia reduction) over the whole length using 
manual feed via the carriage hand wheel (dry, use no cutting compound). Advance 
the carriage regularly and at such speed that the 100mm long rod is done in 40-
60 seconds:

RESULT 1

The surface will look dull and matte, much like an extruded surface. It should 
be regular in appearance over the whole length and have a very smooth, not 
rough feel. No distinct "record grooves" should be visible. No irregular 
patterns of any kind should be visible. 

TEST 2

Now take a 0.1mm finishing cut using the manual carriage feed (dry, use no 
cutting compound). Advance carriage so that the whole 100mm length is done in 
approx 60 seconds:

RESULT 2

The surface finish should look as good as the best commercial turned part you 
have ever seen. Free of any irregular pattern. It should look like the surface 
of a compact disc. Perfectly regular, despite NOT having used automatic feed. 
And it should definitely NOT be possible to improve roughness or looks or 
regularity of this finish by grade 1000 sand paper (any sandpaper should make 
finish WORSE). Short polishing (30 seconds) with cotton/polishing compound 
should produce a surface that looks like liquid mercury - free of any finest 
grooves. I did the test on an 8x18 with a vfd drive. The standard AC motor 
would leave a very fine, modulated vibration pattern, this is normal and 
unavoidable.

If your results do not match above description, you have one or more very 
serious problems that need attention. Very serious, because it is likely to 
become much worse as you cut harder or less free cutting materials. 2011 
aluminium is a a real beauty for surface finish.

Chris