Smother finish when turning

[123hotchef]

How do I get a smoother finish when turning steel.
I am using tools with inserts.
I noticed it today when boring out some steel bar and reducing its diameter.

I have tried bigger cuts, smaller cuts, flood coolant, no coolant, brushed on oil, faster feed and slower feed rates

The only thing I have not changed is the lathe speed

 

[RobCox]

What sort of steel would be my first question. There's a world of difference between something like en24 which with the right speed and feed will give a smooth shiny finish with a standard insert, and something like en8 which tears a lot easier and responds well to the polished carbide inserts which are normally spec'd for aluminium.

 

[123hotchef]

Hum good question it was some bar ends off of here could well of been EN8

 

[123hotchef]

It certainly felt hard when drilling it.

 

[tom2207]

try a slower speed

 

[123hotchef]

try a slower speed

next time, is the speed not in relation to feed rate though?

 

[tom2207]

next time, is the speed not in relation to feed rate though?

slow everything down , far too much haste these days.

 

[123hotchef]

slow everything down , far too much haste these days.

I can only try

 

[Lewis_RX8]

As hood explained to me with the speed and feed rate , In theory the feedrate will always produce a threaded finish but the lower the feedrate the smaller the difference between ridges would be so would feel smoother so I would say try and do a real slow feed rate and see what that day , May not be mirror but should be smooth

Now I went and found it from the horses mouth

 

[Brad93]

It's to do with chip load, shear strength of the material, cutting angle of the tool and rigidity.

 

[Brad93]

The main issue. The material.

En8 loves to leave ragged sharp edges because the metal smears rather than shear off cleanly.

If you use soft steel, like en8 but free turning, I.e additions of lead, sulphur etc, you'll get beautiful finishes without too much effort.

Similarly if you use a tougher steel like EN24, the shear action of cutting process produces well formed chips, and the finish can be mirror.

You can use positive inserts like CCMT or CCGT with a small nose radius, that lowers the cutting pressure required to form a decent chip and therefore the finish improves.

Higher surface footage also aids finish quite often.

 

[tom2207]

Vibration may be the cause , that was my thinking , hence slower speeds less vibe and resonance .
No harm in trying as it wont cost anything , I like things that dont cost much to try.

 

[Kram]

All of the above is true however for boring, the type of insert and chip breaker makes a massive difference. In a bore and presented at a 15 degree angle, normal chip breakers dont work quite as well as OD turning. Theres also a compromise to have a chip breaker on either edge vs just the front edge.

I've been converted to these inserts, they have extremely low minimum depth/feed so its very easy to be in the sweet spot. While the radius is only 02, they seem to give me less feed lines and smoother than 04 radius inserts, just because they are cutting better.
As they have no more, 10 left, I got 30 of them. Plus they are 99p and last bloody ages

DCET 070202 L-E UM25 Carbide Inserts for Precision Turning and Small Parts Machining

Carbide Inserts for Precision Turning and Small Parts Machining type DCET 070202L-E UM25 by Uni-tip Carbide

www.shop-apt.co.uk

If they were not available I would be suggesting knux1604 type inserts as they are single edge, but have not tried.

Single edge are also better chip breakers for OD turning but with the DCET it means tool post behind chuck and running in reverse, chips fly away from you. The knux ones are available both handed.

 

[123hotchef]

All of the above is true however for boring, the type of insert and chip breaker makes a massive difference. In a bore and presented at a 15 degree angle, normal chip breakers dont work quite as well as OD turning. Theres also a compromise to have a chip breaker on either edge vs just the front edge.

I've been converted to these inserts, they have extremely low minimum depth/feed so its very easy to be in the sweet spot. While the radius is only 02, they seem to give me less feed lines and smoother than 04 radius inserts, just because they are cutting better.
As they have no more, 10 left, I got 30 of them. Plus they are 99p and last bloody ages

DCET 070202 L-E UM25 Carbide Inserts for Precision Turning and Small Parts Machining

Carbide Inserts for Precision Turning and Small Parts Machining type DCET 070202L-E UM25 by Uni-tip Carbide

www.shop-apt.co.uk

If they were not available I would be suggesting knux1604 type inserts as they are single edge, but have not tried.

Single edge are also better chip breakers for OD turning but with the DCET it means tool post behind chuck and running in reverse, chips fly away from you. The knux ones are available both handed.

whats that mean? you run the machine in reverse?

I just thought my boring bar cuts toward me when standing at the front of the lathe, I presume that is normal? never thought about it before
it does feel strange cutting winding back towards yourself

 

[Kram]

Picture will explain best. The "left handed" insert only has chip breakers on 2 of the four sides. Boring is as normal, and for OD the lathe is spinning in reverse but towards chuck. Its presented the same as boring, or with a left handed tool holder behind the chuck. Ignore the finish, I was just messing about on this.