Milling 16mm hole when it should be 18mm

[tangi]

Hi

I have searched around for similar topics, have found some, but they haven't been able to help solve my problem. Besides that I hope it is to right forum to ask in, if not I apologize.

My setup is a DIY CNC, designing and making g-code with Fusion 360 and control the CNC with Mach3. I am a newbie with all this stuff, but have so far learned a lot, and have really enjoyed the journey in this cnc hobby world, though it is a bit frustrated at times, when things doesn't work out as they should. But it is a learning process.

I try to mill a hole in wood with a diameter of 18mm, it is milled at app. 16mm. It is like the machine leaves a bit of stock, but I have checked that mark off in Fusion 360. I have tried to mill with a 6mm end mill and a 8mm end mill, it doesn't work with none of them. I use the 2d Pocket cam function in Fusion 360 with multiple depths. Found something about compensation, and something about a possibility to change tool in Mach3, but as I have understood and tried from this info, it doesn't work too.

Hope someone can help me out here, thank you a lot!

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[zachlancy]

Yes, it sounds like fusion is posting your code expecting the control to compensate for the radius of your tool. If your controller supports cutter compensation, put 3mm in for the radius of your tool in the offsets page. Or look into turning cutter compensation off in fusion, which will post an arc move that is the 18mm but 6mm smaller.

[tangi]

Yes, it sounds like fusion is posting your code expecting the control to compensate for the radius of your tool. If your controller supports cutter compensation, put 3mm in for the radius of your tool in the offsets page. Or look into turning cutter compensation off in fusion, which will post an arc move that is the 18mm but 6mm smaller.

Thanks for reply Zachlancy. I have tried different things now, and it doesn't help. In the meantime I also found a post on another forum from a guy who have had similar problems, mostly caused by the post processor, something about turning use radius off. He used the same post processor as I do, so next I am near my machine I will try to use a different post processor in Fusion. Have anybody else have had this problem? What post processor do people use for a diy cnc with mach3 as controller software?

Lastly do anybody know of a software which is able to simulate the post processed g-code? It could be nice to have such software, and with a measure feature built in, so you could measure the milled part in simulation. I know about the simulation in Fusion but as I know it simulates before the g-code i processed, so it can be different from the g-code.
I

[dazp1976]

What size tool are you using?
Have a look at the last lines on the finishing pass and see if the numbers add up.
If they do then it's not the post processor, if they don't then it is that at fault.

If I try one in mine with my 0.0 in the centre of the circle I get this:
Last lines are:
6mm =
X-5. R5.
X5. R5.
So the X- & X+ cancel each other out and add to 0. So the 2 radius added together =10mm then add cutter and it adds to 16mm

8mm =
X-4. R4.
X4. R4.
Again X is 0. The 2 R4 add to 8mm. Add 8mm cutter and total is 16mm.

10mm =
X-3. R3.
X3. R3.
3+3= 6mm. + the 10mm cutter = 16mm.

So I know my post processor is right and any problems I have are either with Mach or are mechanical.
If this makes any sense at all!

[peteeng]

Look up CAMotics - its free -Peter

[tangi]

Hi thanks for the replies. The code is fine, so it must have something to do with my machine or mach3. If I set the hole to be 18,4mm, using mach3 as post processor in Fusion 360 and running a finishing pass (it seems it removes a bit more stock) then I am really close to a hole with a diameter of 18mm