G code help

[drchilvers]

Hello

I’ve just started creating g codes with fusion 360 to cut part in my router, the parts are cutting out fine but I’m having problems cutting holes on dimension.

The perimeter dimensions are always perfect so I think this issue is due to the part flexing under cutting loads since the generated G code tends to cut the perimeter out first or very early in the process and then cuts the holes.

I’ve tried adding more tabs to stop deflection and this did help but it then takes longer to finish the part after machining 

Is there a way to change the order of operations when generating the g code so the holes are cut first ?

Thanks for your help

[leo.castellon]

You might be running into this problem if your outside contours are cutting fine, but internal dimensions are off, see attached video: YOUR FEEDRATE IS WRONG! – Haas Automation Tip of the Day - YouTube . It could also be a flexing issue with your machine.

LeoC

[m.vangrouw]

Assuming you are using 2d contour, if you go to the passes tab and check "preserve order", your geometry will be cut in whatever order you select it. From there, all you need to do is select your geometry from the inside of your part out, with the perimeter last.  

Hope this helps!

[drchilvers]

Thanks for your suggestion, I’m not sure if this is the issue as my feed rate is already low but I’ll definitely look into it as the parts I’m cutting have a lot of curves and radii

[drchilvers]

Thanks for your reply. Yes I’m using a 2d contour operation. I had a feeling there’s was an option somewhere but was unable to find it. I’ll try this and let you know how it goes

[programming2C78B]

Duplicate your path, then delete all the contour things from the first path. Then, delete all the holes from your 2nd copy. 

[drchilvers]

I stand corrected. I've tried both solutions and yours has almost solved the issue. The holes are coming out almost on dimension but the reduced feedrate only kicks in after 180 degrees of the cut regardless of what I input into maximum directional change box.

I've attached a screen shot of the options I'm adjusting, is this is correct?

Hopefully if I can get reduced feedrate to apply to the whole of the hole path, the hole dimension will be correct

Feel free to correct any mistakes I've made as I'm still learning

[Warmingup1953]

Tell us about your machine, Tooling and workholding.

[programming2C78B]

Without knowing anything about your part (since you attached 0 data) I'd say the numbers just need to be raised to the proper amount.

[leo.castellon]

Ignore that section, use the main control box for speeds and feeds to control the actual cutting feed rate, use the circled control box 

For more specific help, attach your file, we will help you better then.

LeoC

[drchilvers]

I’m using a IT-Tech 3040-MGN, cutting 3mm carbon fibre using a 1.5mm carbide endmill

[drchilvers]

Sorry but like I’ve said I’m new to this, so have no idea what info I need to post. Let me know what data you need and I’ll attach it

[drchilvers]

I think I’ve got those options set correctly, well at least it cuts the external and internal dimensions correctly. The problem is the holes are always undersized. I can’t post all that data at the moment but I know my feed rate is 250mm/min. I can post it later if you want to check it over

I’ve played with the setting like the video you posted earlier recommended and that’s helped, as the holes are almost on dimension. The problem I’ve got is the reduced feed rate only kicks in halfway though cutting the hole no matter how I adjust the option in the box I’ve screenshot

[programming2C78B]

we need your entire file, not a screenshot. The numbers are all related to the toolsize and part dimensions. 

[drchilvers]

Here you go, I've attached the file for the part and the G code

[leo.castellon]

Looking at your program, in my opinion, I still say you are going too fast in the holes. Try breaking your program into two parts. First tool path is just do the internal hole work but add a finishing pass. Second tool path is just what you have now, but just cut the outside perimeter and see if that works better. What kind of material are you cutting?

LeoC

[programming2C78B]

"The problem I’ve got is the reduced feed rate only kicks in halfway"
That's not whats happening. Everything in yellow is at 83, blue is at 250.


The bottom hole is acting differently because for some reason you added a Tab inside of it! With that gone, it works as it should.