Interpreting G41/G42 and sign value of TNR comp.

[gibsoni]

Hi Guys,

I thought I understood TNR comp in G41 and G42 and then I read a lot on the forum and realised I didn't. I was more confused but concluded that I had it wrong in the least.

Tell me if this analogy works: I'm a little guy (lego man) and I stand on the top of the insert (exposed to the air not the seat/anvil) which cover the tool being upside down scenario as it is for me. I face in the direction of tool travel.

If the surface being machined is on my right - G42, if its on my left, G41. Does this work?




Secondly, I looked at some drawings to determine the sign of the TNR comp as entered in an okuma TNR comp columns on the tool offset page.

It seems it would be simply put: Where is the centre of the tool nose radius compared with the theroetcial imaginary sharp point of insert.

Is this a fair and true statement?


Lastly- I want to be able to program a parting/grooving tool to come in and make a radial groove before parting off, retract out, put a radius on the tailstock (part) side of the corner it has just made and then continue back into the groove and part off.

What will I use ? G41/G42 and what will be the signs for the TNR comp values?

I am assuming it is G41 and assuming 0.4mm TNR, X= +0.4, Z= -0.4


Thankyou so much for your help everyone.

Regards, Iain.

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[deadlykitten]

hi / a nice analogy would be if a lego man would drive an ufo* tangent to a real road ( ready to kidnap someone, etc )

if the ufo is on the left side of the road : G41




radius is always positive; lathes don't work if r<0 is used, but if you wish to use a negative radius i can help

about the center of the radius, or P values, right now i have no analogy to make it simple to understand, but pls find attached images : maybe they bring a bit of light to you

now i don't have time to explain those images, & i did not had time for that chamfer / kindly




* : i am reffering to a standard ufo ( round, hat type, with clean windows all arround 360 degrees ) not to a trans-dimensional material shape shifting phase stuffs

[deadlykitten]

i know that you try to understand comp; now i wish to share a thing about r<0

is 4 your future self when a code between G41/2 and G40, contains a trajectory that does not represent a part geometry, then we talk about virtual toolpaths or virtual trajectories ( also called ' center toolpaths ' )

such toolpaths are designed to work at comp=0; obviously, a small corection of only 0.1 may mean a comp=+0.1 or comp=-0.1 ( negative )

they are used more for milling operations, and less for turning; still, the classical comp method is when a code is designed to work at comp=tool_radius



sometimes i combine both " classical " and " virtual " : for example, for a turning operation, i create a center toolpath, on which i apply translation factors, accordingly to the P quadrant; the final code is not intended to be used with G42/1, because it allready has comp inside it; when the tool is declared, i no longer input a value for the TNR and also i don't input a value for the P

less input values means less operator errors

[gibsoni]

Thanks for the help.

I am really stuck trying to use TNR COMP AND G41/42 in programming a grooving tool.

I was to use a turn/groove tool to profile some parallel surfaces and chamfers on the OD of the part between 2 shoulders.

I know I need to use different tool offset for each side of the grooving tool but its not working perfectly.

I have the following: (I call G41 as I am using the back side of the tool for TNR comp as it comes down the 45 deg, and then part way along I switch to other tool offset and change to G42 so the control uses the other side of the tool (offset and TNR comp value) for climbing up the other 45 deg etc.)

I haven't used the P values but rather I have assigned the correct value for the TNR offsets using +or - as per the manual. What P value would a turn/groove turn have for working off both sides?


(EXT ROUGH CYC- GROOVE TOOL)
G00 X400 Z200
T130313
G00 X53 Z50
N0102 G96 S100 M03
N0103 G85 NAT02 D2 F0.2

(EXT CONTOUR)
NAT02 G81
T130313 G41
N0000 G01 X50.8 Z50
N0001 G01 X47.3 Z50
N0002 G01 X47.3 Z46
N0003 G01 X45.3 Z45
N0004 G01 X45.3 Z30
N0005 T030303 G42
N0006 G01 X45.3 Z6
N0005 G01 X47.3 Z5
N0006 G01 X47.3 Z0
G40
G80