How to use G50 on a CNC lathe

How to use G50 on a CNC lathe

CNC Turning Basics G50 Speed Clamp

How to use G50 on a CNC lathe

How to use G50 on a CNC lathe

How to use G50 on a CNC lathe.

G50 in a turning program is a speed clamp. The machine accelerates up to the speed you set (G50 S2000) and will not go any faster.

Now before I get arrested by the “Correct Word and Grammar Police” I know it’s not actually a clamp. The truth is it’s just what everybody calls it, so get off my fuckin case.

Black dog his name is Boris

Anyway if I start to call it something else all my CNC mates (and I do have some) will be confused.

Just check me out on LinkedIn. Anyway as I was saying my mates wouldn’t know what the fuck I was on about.

You must program a G50 before each tool and at the beginning of the program for safety reasons which I will explain later.

It’s Modal

G50 is a modal G code (it stays active). If you have a program where you do not want to clamp the speed you must still put the G50 at the beginning of the program (set the clamp to the machines maximum RPM).

Otherwise it may pick up the G50 from the last program and you may not get the RPM you want. It can have the effect of slowing down production because the speed is being restricted and you didn’t realize.

Don’t use someone else’s G50 get your own.

You wouldn’t wear someone else’s dirty pants. (Americans call underpants underwear I think)


These are mine (sorry I din’t get time to wash them).

Modal G code explanation here.

Now Here Is Something You May Not Know

Historically G50 was used to set the machine datum. This still works so do not put any X or Z figures on this line. You will get some weird shit happening if you do. Oh and you will probably trash your 100 grand machine.

Anyway how to use G50 on a CNC lathe

G50 S2000 (SPEED CLAMP 2000 RPM)

Some G code systems, or depending on parameters, may use G92 instead of G50. This is not very common but it works exactly the same way.

On a Fanuc control they are called A type and B type G codes and depends on machine tool builder. Most of the G codes remain the same but proceed with caution.

It is particularly useful when you are facing a part using G96 (constant surface speed). When the tool reaches the centre of the part the machine will be running at maximum RPM. This could be very dangerous on large or out of balance components. When you set a G50 speed clamp, once the machine reaches the clamped speed it will go no further.

Here is a tutorial video about G96 and G97


  1. Use a G50 at every tool-change
  2. Use a G50 at the beginning of a program (even if you think it’s not needed)
  3. G50 S2000 (Only G50 and speed on one line, nothing else)
  4. There is no rule 4
  5. Never eat yellow snow.

Toshiba VTL CNC

This is a Toshiba VTL (Vertical Turning Lathe).

If you want to buy one or fix one go to Leader CNC

Now imagine this revolving too fast you would soon need their services oh and a good trauma team.

More CNC Turning Help (G70 and G71)

Please contact me if you require:

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Services offered at CNC Training Centre

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Don’t forget we offer training on all types of Mazak Machines and all Fanuc Controls 6m to 31i Oi old to young.


Ravi Ashok Yadav

September 1, 2020 at 6:36 am

Thank you gentlemen for sharing such a valuable informations. from india

Ricardo Reyes

September 3, 2021 at 10:26 pm

HAAAAHHAHAHAAH this G50 explanation made my day . “never eat yeloos snow” noted


    September 4, 2021 at 9:19 am

    glad it’s of use Ricardo

Patrick Brennan

September 16, 2021 at 2:33 pm

Informative and entertaining as ever!


    September 16, 2021 at 4:00 pm

    Thanks Patrick

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