canned threading cycle cuts fresh air for first 3 or 4 cuts.

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TimPower
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canned threading cycle cuts fresh air for first 3 or 4 cuts.

Post by TimPower » Fri 27 Oct , 2006 10:35 am

Hi folks,
this should be an easy one for you. After I put in a canned cycle to cut an M10 thread, it makes a couple of passes without cutting anything.
N150 G00 X10 Z-12
N160 G76 P050060 Q035 R.05
N170 G76 X8.16 Z-25 P920 Q070 F1.5
N180 G28 UO WO
N190 M30

Can soneone tell me which variable controls this. Also I'm curious about the P920 variable. What does this do? I can't see why you need to put in a thread height if you are putting in a min diameter. If you cut a thread but the nut is loose on it should you increase the min diameter or increase the thread height. I don't know how increasing the thread height can change anrything though as I'm already starting with a 10mm bar.
Thanks again,
Tim. :)

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Post by Denford Admin » Fri 27 Oct , 2006 14:09 pm

P920 is 920 microns thread depth (according to the help in VR Turning)

TIP - In the editor, highlight the gcode you want to know about, and press CTRL + F1 at the same time and hey presto - you'll get.....
The G76 command contains, within two blocks, all the information required to generate a standard thread form and pitch.

A G76 uses one edge cutting to reduce the load on the tool tip.

Click here to show G76 Canned Cycle General Diagram.

A G76 command is written in the following format:

G76 P (A) / (B) / (C) Q (Min) R ;

G76 X(U) Z(W) P (DEP) Q (1st) F ;

where,

P (A) is the number of thread finishing passes (1 to 99).

P (B) is the chamfer amount. This is the angle at which the tool leaves the billet, at the end of the thread cutting cycle.

P (C) is the angle of the tool tip (8Ø°, 6Ø°, 55°, 3Ø°, 29° and Ø°). Note - (A), (B) and (C) are all specified at the same time by the address P, eg, PØ36Ø6Ø = number of cuts is Ø3, chamfer amount of 6Ø and tool angle of 6Ø°.

Q (Min) is the minimum cutting depth (in microns). When the depth of the cut calculated by the CNC control becomes less than this limit, the cutting depth is clamped at this minimum value.

R is the finishing allowance. This is the final, or finishing, cuts applied to the thread. The number of stages to complete this finishing allowance is determined by the value of P(A), ie, the value of R divided by the P(A) number of finishing passes equals the value of each finishing allowance stage.

X(U) is the end position of the thread in the X axis (the core diameter).

Z(W) is the end position of the thread in the Z axis.

P (DEP) is the depth of the thread as a radius value (in microns).

Q (1st) is the depth of the first pass as a radius value (in microns).

F is the size of the thread pitch.

Click here to show the G76 General Notes Page.

Click here to show a G76 Multiple Thread Cutting Cycle Example.

Click here to show a G76 Internal Thread Cutting Cycle Example.
(for example) :D

TimPower
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Joined: Thu 27 Apr , 2006 17:19 pm

Post by TimPower » Fri 27 Oct , 2006 14:24 pm

That's great thanks a lot for the tip.

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