Single Block CNC Beginners Guide

Single Block CNC Beginners Guide

Category : Beginners

CNC beginners guide (using Single Block)

CNC beginners guide

This article CNC beginners guide is about Single Block and how it is used.

When you write a CNC programme it will consist of blocks of programme.

What is meant by a block?

Well it’s everything until the control sees a semicolon ;

The semicolon is called an end of block or EOB

CNC beginners guide

Try not to confuse this with a line of code.

Depending on how your screen is set out a block could be more than one line. The control reads everything until it sees the semicolon or EOB (End of block).

In most cases and on most controls it does not matter what order the code is in. The main reason to follow a set pattern for your code is to make it easy to read.

Try to always put things in the same order.

In one block of code you can have loads of stuff.

You could write:

G0 X50. Y50. S1500 M3;

But if you wanted you could put the S1500 M3 on a different line.

When doing this think about why you might want to do it. For example you may want to get the tool ready to use before switching on the spindle or the coolant. This saves the excitement of the spindle wizzing round when proving the programme.

Oh yes and you could get soaked.


Most of this applies when you first test your programme. This is when we use single block.

The Switch

To run a programme in Single Block we have to throw a switch.

CNC beginners guide

This can be a normal Single Block switch or a button or a soft key. Read the article below to learn how to prove out your CNC programme in Single block.


Read this if you don’t know how to prove out a CNC programme.

Once single block is enable the machine will do exactly what it says on the tin.

It will run that block and wait for its next command like a good doggy.

The beauty of this is you only need to think about one block.

If you turn single block off the machine will still stop at the end of it’s current block and wait for another press of CYCLE START button to carry on.

Also when you first turn single block on it will stop at the end of the block it is executing.

CNC beginners guide

Those of you who read my articles will know that I love these old Matsuura machines (they make me feel young again).

Anyway these machines have a one line display so you have to step through to read each line. I once input a whole programme into one of these controls not realising I had no end of blocks .

(Now I would never say fuck in one of my articles so I will refer to it as the F word.)

On this occasion I said the F word after taking about an hour trying to realise why the programme wouldn’t work.

The whole program was in one block!!!


Don’t mix your G Codes

(here is a nice way to make a John Collins if your bored with this CNC Shit)

Let’s continue with this CNC beginners guide to CNC programming.

In one block of CNC code you can only have G codes that belong to the same group. I’ll tell you about this in another article when I can be bothered to do it. Anyway it’s easy, they can’t argue with one another. You can’t put G1 and G0 on the same line for example because they are in the same group.

You can’t say feed and rapid in the same line. That would be stupid.

Obviously you can’t repeat things like having two speeds in the same block.

G0 S1200 X50. Y50. S2000;

I don’t think anyone who reads my articles is that stupid….. Except for that bloke in Bolton, but I think he took up plumbing in the end.


If you have a Heidenhain control the single block works the same. You select Full Run or Single Block

CNC beginners guide

You don’t hear me criticise Heidenhain very often cos I love em. Brace yourselves cos I’m about to.

Those bloody icons.

They all look the same. Everytime I come back to working on Heidenhain I can never remember which is which.

I sometimes suggest making little sticky labels to go underneath to identify them.


This one will do wonders for your relationship with the guy on nights.

Oh and Before You Go A Few Other Things

  1. What about a tool change?
  2. What about a canned cycle?
  3. What is the meaning of life?

Ok the last one is easy. Question 3 ….. the meaning of life is 42 

Right, now the difficult ones.

Your tool change M06 is probably aliased to a macro. This means that a programme is running in the background that you can’t see. Single block may well be inhibited. This means one press of the CYCLE START button will do the tool change. Sometimes however single block works. In this case it will take loads of presses to get through the tool change.

This is the sort of thing that’s running in the background.

CNC beginners guide

I won’t go too much into this, afterall it is a CNC beginners guide.

Canned cycles depend on parameter settings. It will normally be one press to rapid to the R Point. Then one press to drill the hole. It may or may not need another press to bring the drill out of the hole.

The exception is G84 Tapping Cycle. You definitely wouldn’t want single block to work on this. Imagine the tap gets to the bottom of the hole and sits there waiting for a push of the button.

Sometimes feedhold is inhibited too in a canned cycle.

Hope you enjoyed this CNC beginners guide

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