Parameter setting for CNC

[dcolley_ptfnola]

We run a lot of plywood through our CNC & design it all with Fusion.  I set up a parameter called PLY to which I input the measured plywood thickness.  Many other dimensions in my drawing are driven from this PLY parameter, including dado and rabbet depths (PLY/2).   The problem is that the CNC machine cuts those depths too deep.  Any input on this?

[HughesTooling]

Can you create a demo file with some toolpaths and share here? Export as an f3d. 

[Cave_Master]

If the extra depth cut is consistent across different plywood thicknesses then you could add a stock to leave to that toolpath setting.

[jmackniak]

How deep is too deep?  Where are you setting your Z zero?  is it acurate?

[dcolley_ptfnola]

yes,   zeroing out Z axis   As far as "how deep" goes.  it is prob. a 1/6+ deeper than ply/2

[Cave_Master]

What kind of machine and how are you holding the workpiece?  1/6" off is a lot of error.  Even if you have 1/16" off that is quite a lot for CNC.

Assuming everything is correct with the parameter settings, that you have solid workholding, and that your Z zero is set to where you want it then you could try leaving .1167 in of axial stock that will tell the program to leave .1167 (1/6) above the bottom of your pocket.

[HughesTooling]

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@dcolley_ptfnola wrote:

yes,   zeroing out Z axis   As far as "how deep" goes.  it is prob. a 1/6+ deeper than ply/2

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Is the zero the same in Fusion and on your machine? You don't have extra stock on the top of the part in the Fusion setup model or something like that, that's why I asked to se a sample file. Fusion is very accurate so if you're seeing 1/6 inch error you have something very wrong somewhere.

Mark

[dcolley_ptfnola]

That is a good workaround.

I am using the Felder Format 4 Profit HO8 which has a vacuum table.  Most sheets I put down are full 48 x 96.

[dcolley_ptfnola]

Here is one of the files I ran into trouble with.

[HughesTooling]

@dcolley_ptfnola  The models look correct. The material thickness is 0.719 and the cuts are at the mid plane 0.379, this matches the G code.

You have your origin set to the back face of the material, is this the same on the machine?

With the cutter you used did this still zero when you'd finished the job, any chance the tool pulled down?

Mark

[dcolley_ptfnola]

The bit was zeroed when it was installed and the owner of the company worked the %^&* out of it (prob too much).  But re-zeroing it is on my list of things to do.  - may have to re-zero before each job.

[Cave_Master]

At our shop we check the zero point each time we load a new tool or touch off a limit switch.   You can cut a small pocket, measure thickness and adjust your zero point from there.

[dcolley_ptfnola]

I think it is a good idea for me to make a habit of something like this - just write a short tool path to check the depth on each project before I begin - at least for now.  (I still think this is wonky and shouldn't be happening.)

[HughesTooling]

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@dcolley_ptfnola wrote:

  (I still think this is wonky and shouldn't be happening.)

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I make mould tools and have no problem holding 0.01mm so if you're seeing big errors it's either a setup problem or a machine problem. You might have found a bug I guess but you'll need to supply a design that's posting the wrong sizes, the design you attached above produces the correct Z depths with the postprocessors I tried.

You can download the back plotter I used above here to double check the code.

Mark

[dcolley_ptfnola]

@HughesTooling - definitely going to download that tool.  As noted by several people the code from Fusion seems to be correct so I'm thinking it is at the machine.   Thanks.