is this a backlash problem?

[xspyke]

My gantry router is working great except one problem. When I route a square, the corners are not square. The straight sections are good but when I approach the corner there is a bump out.

I'm not sure if it is a backlash problem or flexing in the router bit. I don't think it is a backlash problem because when I mill a circle it is perfect.

I'm using a Bosch Colt router with a 1/4" spiral bit. I've tried slowing down my feed rate to 20ipm and depth of cut of 0.1". The problem still show up.

Here is a drawing what the corners look like. You do you guys think?

[Oldmanandhistoy]

Hi,

What CAM are you using?

Looks to me as if you have “over cut corners” or some thing similar set.

John

[ctate2000]

I think you have a a programming issue. Can you post the code for review?

[xspyke]

I'm using the wizard in mach3.

I've also drawn a square in autocad, used flashcut to generate g-code, and then use mach3 to control the machine.

[Claude Boudreau]

oups

[xspyke]

I did use the wizard in mach3. That is when I noticed the problem. Then I tried the autocad route.

[ARKADY]

Can you try the same program with a larger dia bit, or possibly a bit with more flutes?

I doubt it, but you may have a problem with the bit flexing. How heavy of a chip are you taking? For my 3 Onsrud routers I refuse to run a 2 flute 1/4" bit at anything faster than 18,000 rpm and 350ipm.

I tend to want to see your code to see if your post may be kicking out something weird, your cut is not deep enought to really cause you a problem like this unless your spindle speed is way too low.

[xspyke]

here is my code.


N10 G00 Z 0.10000
N20 G00 X 0.00000 Y 0.00000
N30 G01 Z-0.10000 F20.00
N40 G01 X 1.00000 Y 0.00000 F50.00
N50 G01 X 1.00000 Y 1.00000
N60 G01 X 0.00000 Y 1.00000
N70 G01 X 0.00000 Y 0.00000
N80 G01 Z-0.20000 F20.00
N90 G01 X 1.00000 Y 0.00000 F50.00
N100 G01 X 1.00000 Y 1.00000
N110 G01 X 0.00000 Y 1.00000
N120 G01 X 0.00000 Y 0.00000
N130 G01 Z-0.30000 F20.00
N140 G01 X 1.00000 Y 0.00000 F50.00
N150 G01 X 1.00000 Y 1.00000
N160 G01 X 0.00000 Y 1.00000
N170 G01 X 0.00000 Y 0.00000
N180 G01 Z-0.40000 F20.00
N190 G01 X 1.00000 Y 0.00000 F50.00
N200 G01 X 1.00000 Y 1.00000
N210 G01 X 0.00000 Y 1.00000
N220 G01 X 0.00000 Y 0.00000
N230 G01 Z-0.50000 F20.00
N240 G01 X 1.00000 Y 0.00000 F50.00
N250 G01 X 1.00000 Y 1.00000
N260 G01 X 0.00000 Y 1.00000
N270 G01 X 0.00000 Y 0.00000
N280 G01 Z-0.60000 F20.00
N290 G01 X 1.00000 Y 0.00000 F50.00
N300 G01 X 1.00000 Y 1.00000
N310 G01 X 0.00000 Y 1.00000
N320 G01 X 0.00000 Y 0.00000
N330 G01 Z-0.70000 F20.00
N340 G01 X 1.00000 Y 0.00000 F50.00
N350 G01 X 1.00000 Y 1.00000
N360 G01 X 0.00000 Y 1.00000
N370 G01 X 0.00000 Y 0.00000
N380 G01 Z-0.73000 F20.00
N390 G01 X 1.00000 Y 0.00000 F50.00
N400 G01 X 1.00000 Y 1.00000
N410 G01 X 0.00000 Y 1.00000
N420 G01 X 0.00000 Y 0.00000
N430 G00 Z 0.10000


I'm using 1/4", 2 flute, at 18000 rpm in MDF. I'll try running at a higher RPM later.

[vlmarshall]

Well, it's not a programming issue, you aren't cutting radiuses on your corners.

[Oldmanandhistoy]

Are you using “constant velocity” or “exact stop” in Mach? Not sure if this could be the problem but if you have CV set try switching to ES.

What are you using for anti backlash nuts, if there your own design do you have a picture?

John

[xspyke]

i'm using anti-backlash nut made by Zycon. Here is a picture. The mach is set to CV.

What is the difference between CV and ES?

thanks

[Oldmanandhistoy]

http://www.machsupport.com/docs/Mach3_CVSettings_v2.pdf