Manufacturing circle - Incorrect dimensions

[VGBenjamin]

Hello,

I am trying to just manufacture a very simple circle but the result is not correct. So before selling or unmounting my machine, I would like to check if I have done everything correctly.

Here is what I am trying to do:

To be as clean as possible I have done that in two time:

1) a first pocket with 4 mm on each step with a multiple depths and a stock to leave set to 0.5mm

2) a second pocket without multiple depth or stock to leave

I am not sure that I need to do it in two time... Both pockets are done with a 5 mm end mill

When I visualize my toolpath I have the following result:

First thing I see is the fact that it isn't a perfect circle => why (see the little hole pointed by my the arrow)? (it is reflected in the real manufacturing)

When I inspect the nc code. I am at G1 X25.000 Y2.132 Z-13.500 F1440 in this  little hole (bottom left) and then G3 X22.814 Y16.150 Z-13.500 I-2.186 J6.650 F1440 on the other side of the circle.

so if my calculation are correct I have a diameter of 14.138mm of course I need to add the radius of my mill on both side => 2.5mm * 2 so the manufactured radius should be 19.138mm.

My real manufactured test is  measuring 18.80mm if I could this little hole and 18,20 if I measure somewhere else.

The post processor I use is this one: https://learn.ooznest.co.uk/Wiki/WorkBee_Firmware_Releases#Section_Fusion360

Regards,

Benjamin

[engineguy · Accepted solution]

@VGBenjamin 

Try using your "Sketch 2" for both the "Pocket Selection" and the "Stock Contours", this will give you a correct circle, modified file attached as an example, modify the Helix to suit you:) 🙂 🙂

Hope this helps

Stay Safe

Regards

Rob

[DarthBane55 · Accepted solution]

Yes, the toolpath is not a circle because of the break on the sidewall.  The tool is going in that gap as far as it can, as it should, because it doesn't know you only want to do the circle portion of it.

To avoid it do as @engineguy  said, or use "bore" operation, which only deals with circles, so it will turn this into a normal cylinder.

[VGBenjamin]

Hello,

I have been able to test it today and the shape is perfect thank you for both the solution and the additional explanation that was also usefull.

The only problem I have is the machine itself. I need to create the model biggert that what I really want like 22mm to have a diameter of 20mm and the same for the depth I need to set to 17mm to have a depth of 15mm.  But when I test with a theoritical depth of 5mm I have a reality of 5,35mm so it is really strange but machine related.

Thanks a lot guys!