G75

Introduction G75

I will start by introducing the G75 chamfer command by using the example from the main page and then I will go into some further details.

A simple external contour

Let me give you an example of a very basic contour that can be the outside of a simple part that will be made by turning.

G0 X20 Z5

G1 Z0 F0.1 G42

G1 X40

G1 Z-30

G0 X45

G40

The code above make a super simple corner but the problem with writing in this way is that the corner will become sharp and this will make it easy to get cuts in your fingers when handling the part, let me give you a basic way to remedy this, G75.

If I rewrite the code above using the G75 command instead of the G1 on the appropriate spots the code becomes:

G0 X20 Z5

G1 Z0 F0.1 G42

G75 X40 L0.5

G1 Z-30

G0 X45

G40

When using the G75 I will make a chamfer with size L0.5 in this case. If I want to make a radius instead of a chamfer I could use on of my favorite G-codes G76 instead, but on this page I will focus on G75

By changing the L-value I can give the chamfer a different size. I can for instance make the code like this:

...G1 Z0 F0.1 G42

G75 X40 L2

G1 Z-30...

And thus the chamfer will have a size of 2mm instead of a half as shown above. This can of course be generalised to almost any value on L, but there are some limitations.

Limitations of G75

The limitations of G75 works about the same as for those of G76 so the following discussion will apply to G76 as well. Let's bring back the example given above.

G0 X20 Z5

G1 Z0 F0.1 G42

G75 X40 L0.5

G1 Z-30

G0 X45

G40

There are some limitations to how to use the G75 command in this case. It can not be bigger than the radial difference between the minimum and maximum valus of X. Note also that X is diametric while L is radial.

Now to give an example, the following code is not good.

G0 X20 Z5

G1 Z0 F0.1 G42

G75 X40 L12

G1 Z-30

G0 X45

G40

The tool will first go to X20, Z0 and then try to make a chamfer with size 12 when going to X40. This will not turn out well as the radial difference between X20 and X40 is (40 - 20)/2 = 10 which is smaller than 12.

In the example I am using tool compensation on the contour and my tool will certainly have a radius which will complicate the situation with the limit of the L value further, but that is another discussion.