Mach offseting my work

[kak]

Hello.

Could someone tell me why Mach is offsetting my work with 1mm on X and Y axis in the positive direction?
 
Here is what I do. I mill the X edge og material, my router bit is 3mm in diameter, so I type X -1.5 in the X DRO. I do the same on Y axis. I didnt use the touch off plate, to minimize...my mistakes/settings.
The milled part ( a square) has the right dimensions,  but its milled 1mm from where I expect it to be, in the North - East direction from Zero.
I have been reading the last 2 weeks and cant find the answer.

[Hood]

Would really need to see the code.
Hood

[kak]

Ok, thanks.  Here I was trying to mill a pocket. Pocket start/corner is located  X20  Y20 from Zero and pocket dimension is also 20x20mm.
But after milling, the left and buttom side of my square pocket is about X21 Y21  from Zero when I messure it with a ruller. I didnt messure exactly, because its very clear that its not where it shoul be.
The pocket has the right dimensions.
Im sure its my fault, but I dont know where to find it.

The code is generated with Vcarvepro. I dont know if its changing when loaded to Mach with Machs offsets and fixtures.
I mean I have never changed any offsets and fixtures, because Im not sure how to use them - maybe here something is wrong.
I was milling like this for 2 years, but first now, when I had a piece of material with exact dimensions I realized that something is wrong. I was always cutting things out, so I didnt see it.

( Pocket 2 )
( File created: Saturday, May 07, 2011 - 12:38 AM)
( for Mach2/3 from Vectric )
( Material Size)
( X= 100.000, Y= 100.000, Z= 5.000)
()
(Toolpaths used in this file:)
(Pocket 2)
(Tools used in this file: )
(2 = End Mill {3 mm})
N100G00G21G17G90G40G49G80
N110G71G91.1
N120T2M06
N130 (End Mill {3 mm})
N140G00G43Z20.000H2
N150S5000M03
N160(Toolpath:- Pocket 2)
N170()
N180G94
N190X0.000Y0.000F1200.0
N200G00X28.025Y31.975Z2.000
N210G00Z1.000
N220G1Z-2.000F600.0
N230G1X29.000Y31.000F1200.0
N240G1X31.000
N250G1X31.975Y31.975
N260G1X31.000Y31.000
N270G1Y29.000
N280G1X31.975Y28.025
N290G1X31.000Y29.000
N300G1X29.000
N310G1X28.025Y28.025
N320G1X29.000Y29.000
N330G1Y31.000
N340G1X28.025Y31.975
N350G1X26.500Y33.500
N360G1X25.525Y34.475
N370G1X26.500Y33.500
N380G1X33.500
N390G1X34.475Y34.475
N400G1X33.500Y33.500
N410G1Y26.500
N420G1X34.475Y25.525
N430G1X33.500Y26.500
N440G1X26.500
N450G1X25.525Y25.525
N460G1X26.500Y26.500
N470G1Y33.500
N480G1X24.000Y36.000
N490G1X23.025Y36.975
N500G1X24.000Y36.000
N510G1X36.000
N520G1X36.975Y36.975
N530G1X36.000Y36.000
N540G1Y24.000
N550G1X36.975Y23.025
N560G1X36.000Y24.000
N570G1X24.000
N580G1X23.025Y23.025
N590G1X24.000Y24.000
N600G1Y36.000
N610G1X21.500Y38.500
N620G1X38.500
N630G1Y21.500
N640G1X21.500
N650G1Y38.500
N660G00Z2.000
N670G00Z20.000
N680G00X0.000Y0.000
N690M09
N700M30
%

[ger21]

Sounds like you're part is not placed at 0,0.

[kak]

Gerry, I discribed how I Zero the material in my first post. I think I do it right. Thats what I did a few times to be sure its Zeroed, but there is still some offset.

I dont know much about Gcodes and I wasnt even trying to understand them, but now in the buttom of the posted code I can see X21.500 and Y21.500. Its milling the pocket from the inside and out.
Shouldnt the last moves be X 20 and Y20 ?

[ger21]

No, At X21.5, the edge of the bit is at X20. And at 38.5, the edge is at 40mm.

You could be seeing bit or machine deflection. Try cutting the same pocket in the opposite direction, and see if the pocket moves. Also try cutting at half the speed.

[kak]

Ofcourse 21.5 and 38.5 - Im learning:-)
Do you understand all the gcode and numbers, before it starts to cut? I think I can see where it is, N190.  No offset signs before cutting?

Is there some offset, fixtures, tool database, something else in Mach that can affect this offsetting?
I mean, if there was a backlash or deflection, my pocket would not be 20x20, but it is. I will try to cut in the oposite direction and slow.

[ger21]

Is there some offset, fixtures, tool database, something else in Mach that can affect this offsetting?

No, but even if there was, then it would affect your zeroing as well.

[BR549]

Coding looks good.

Just a thought, (;-) TP

[derekbpcnc]

Hi,

What does the work offsets table show?

ATB
Derek