G40, G41, & G42 - cutter radius and tool nose radius compensation

Cutter radius compensation relates to machining centersTool nose radius compensation relates to turning centers

Commonly taught in basic CNC courses:

G41/G42 –cutter & tool nose radius compensation

Reasons for usingG41 is tool left, G42 is tool rightOffset specifies cutting tool radius

N055 G00 X5.6 Y-0.6N060 G43 H01 Z-0.25N065 G42 D31 X5.0N070 G01 Y4.2 F6.0

Example:

Instate cutter radius compensation




Not always taught in basic courses:The two ways to use offset with CRCHow cutter radius compensation worksProblems you can haveOther limitations of CRCIs control based TNR compensation required?Cutting on both sides of a button tool





Most basic courses only teach programming the work surface (offset is cutter radius)




Not always taught in basic courses:The two ways to use offset with CRCHow cutter radius compensation worksProblems you can haveIs control based TNR compensation required?Cutting on both sides of a button tool

G40, G41, & G42 – radius compensation

There are two ways to use cutter radius compensation

Program work surface path and offset is cutter radius

Program tool centerline path and offset is deviation from planed cutter size

This second method is rarely mentioned in basic courses

11 66






Programmed path

Method one

Again, this is the method taught in basic courses

Work surface path is programmed

66






Programmed path

Method one

11 66






Programmed path

Offset Method one

33 5959

11 66






Programmed path

Offset

3/4 end mill

Method one

33 5959

Offset is cutter radius

11 66






Programmed path

Offset

3/4 end mill

Offset value: 00.3750

Method one

33 5959

11 66






Programmed path


Method one

33 5959

11 66






Programmed path


Method one

33 5959

11 66






Programmed path


Method one

33 5959

11 66






Programmed path


Method one

33 5959

11 66






Programmed path


Method one

33 5959

11 66






Programmed path


Method one

33 5959

11 66






Programmed path


Method one

33 5959

11 66





G40, G41, & G42 – radius compensationMethod two

33 5959

This method is preferred by CAM system programmers…

11 66






Path based on 1” cutter

Method two

33 5959

Programmed path is cutter centerline path

11 66







0.5 typ

Method two

33 5959

It is based upon a planned cutter size

11 66







1.0 end mill

Method two

33 5959

If planned cutter size is used…

11 66








Method two

33 5959

…the cutter radius compensation offset will be zero

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66







3/4 end mill

Method two

33 5959

But if the cutter used is smaller than the planned size…

11 66







Offset value: -00.1250

Method two

33 5959

…the offset will be negative…

…and set to the radial difference from the planned cutter size

11 66








0.125

Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66







1.25 end mill

Method two

33 5959

If the cutter is larger than the planned cutter size…

11 66








Method two

33 5959

…the offset will be plus…

…and set to the radial difference from the planned cutter size

11 66








0.125

Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two

33 5959

11 66








Method two








Method two

11 66








Method two














Once CRC is instated, your series of motion commands

provide geometry for the control

The control will keep the tool on the left side or right side of this geometry for every movement

While this is a simple concept, it can be hard to visualize






Programmed path

Instating movement

Geometry of motions

Again, programmed path provides the geometry…






Programmed path

Instating movement

G42 - tool kept on right of motions

With G42, tool will be kept on the right side of this geometry

Most problems stem from the fact that you don’t truly understand this concept














Almost all cutter radius compensation problems are related to the size of the offset…

…the bigger the offset, the more likely you’ll have problems







Insufficient clearance for cutter at approachTool doesn’t fit into recessesAttempting to machine multiple contoursForgetting to cancelOffset bigger than smallest inside radius

Here are some specific problems















Prior Position

=> offset

4.5

3.0

Surface to mill

Prior position must be at least the offset value away from the first surface to mill








Prior Position

4.5

3.0

Surface to mill

1.0 endmill

=> 0.5







Insufficient clearance for cutter at approachTool doesn’t fit into recessesAttempting to machine multiple contoursForgetting to cancelOffset bigger than smallest inside radius4.5

3.0

Surface to mill

1.0 endmill

0.6 inch

X-0.6 Y-0.6

Prior position is far enough away for this cutter








3.0

Surface to mill

0.6 inch

X-0.6 Y-0.6

1.2 max

This is as large a cutter as can be used








3.0

Surface to mill

0.6 inch

X-0.6 Y-0.6

1.25 endmill

Violates here!

Cutter is too big!

10M

MESSAGE SETTING SERVICE +

ALARM

PS-041: OVERCUTTING WILL OCCUR DURINGCUTTER RADIUS COMPENSATION

With most controls, an alarm will be sounded






















Note recess






















Cutter fits into recess




































Cutter doesn’t fit into recess!

10M


ALARM


Again, an alarm will be sounded






















Note three workpieces to mill















Rapid movement

When finished with first, the tool rapids to the next workpiece – still under the influence of cutter radius compensation








Mill second workpiece








Rap

id m

ovem

ent

Rapid movement to third workpiece, still under the influence of cutter radius compensation








Rap

id m

ovem

ent

But remember, we never cancelled cutter radius compensation…

…the control sees this as one series of motions…

…and will keep the tool on the left side of all motions


Not always taught in basic courses:


Rap

id m

ovem

ent

Motions will not be as you expect…

…and in many cases, you’ll get an alarm…








10M


ALARM


If you must rapid the tool to another surface…

…cancel cutter radius compensation first

Treat each contour separately - Instate, Machine the surfaces, and then cancel






















Cutter compensation is instated








Surface is machined, but we forget to cancel…








Offset from previous tool!

Drill

The next tool will be off by the amount of the offset!

Once instated, you must remember to cancel cutter radius compensation (with G40)




































Cutter fits in radius

But if it does not…

…an alarm will sound





















You must be prepared for other CRC limitations based upon control models…

Two moves in the same directionNon-motion commandsAngles less than 90 degreesReversal in motion direction















Most versions of CRC do not allow consecutive moves in the same direction

Weld area









Weld area

Normal feed & speed









Weld area

Slower feed & speed









Weld area

Normal feed & speed

Most controls do not allow this series of motions with cutter radius compensation instated






















CNC controls can only look a few commands into your program

You must ensure that the control can “see” the required geometry

.N050 G42 X5.0N055 G01 Y4.0N060 M08N065 S400N070 Z0.2 N075 X0.

Too many non-motion commands!

Once you instate cutter radius compensation, minimize the number of non-motion commands you give






















Some (older) controls cannot handle CRC motions under 90 degrees

























Motion not allowed with some controls!






























Most controls don’t allow you to reverse motion direction when using CRC









Programmed path









Programmed path

Cutter same diameter as slot width









Programmed path

Now what?









Programmed path

If you simply reverse motion direction…









Programmed path

…the tool will stay on the right side!









Programmed path

…the tool will stay on the right side!









Programmed path

Instead…









Programmed path

…you must program the entire contour
















Turning center discussion






The major reasons why you need machining center CRC do not apply to turning center

tool nose radius compensation

Range of cutter sizesSizing and trial machining

Turning center operators use inserts having the size nose radius specified






The major reasons why you need machining center CRC do not apply to turning center

tool nose radius compensation

Range of cutter sizesSizing and trial machining

Wear or geometry offsets are used for sizing and trial machining






If you have a CAM system, you can have it generate motions based upon

the required tool nose radiusThis eliminates the entries a setup person must input to TNR offsets

The CAM system is performing the tool nose radius compensation!

If you must use G41&G42, use G10 to automatically specify TNR offsets!

See lesson nine to find out how to use G10 to automatically set tool nose radius compensation offsets














There is one time when you do use the tool nose radius for sizing













Tool nose radius size in offset will determine radius of workpiece





Documents

G40, G41, & G42 - cutter radius and tool nose radius compensation