Sperate Last Pass... Not working

[edawson@ru-wood.com]

Hi,

Does anyone have a trick or tip on using the Sperate Last Pass feature when writing the tool path?
I click "Sperate Last Pass" but it doesn't do anything. When I post process my g-code is the exact same with and without the "Sperate Last Pass".
Thanks!
Erich

[Rcnewcomb]

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[edawson@ru-wood.com]

Sure,
Here it is,
Erich

[adze_cnc]

As I expected before looking at your file. Your bit’s pass depth is greater than the total depth of cut. Therefore the tollpath is being cut with one pass. Separate last pass is for >1 passes.

Given that your Allowance (A) for the separate last pass is 1 inch the question to ask is: just what are you hoping to achieve? Usually that value is something small like 0.010 inches so that the material is shaved off to prevent “waterlines” or “witness marks”.

[edawson@ru-wood.com]

Hi,

Oh yea, I forgot that was still set at 1" Allowance in the crv file.
I did that as another test. It didn't work with 0" Allowance. I first changed to 0.01" Allowance, then changed to 1".
Didn't matter all three tests failed to post process a final pass.

Are you saying since my first and only pass goes to the table (0"), therefore it doesn't recognize a second pass even if I want it to go again at the table height 0", or even slightly lower, say -0.01"? If this is correct you have pointed me in the right direction.

Thanks,
Erich

[adze_cnc]

I think you need go back to basics or read the help file.

If you are cutting two inches deep and want the tool to cut using multiple passes you set the pass depth within the tool (e.g. if you want 8 passes you set the tool’s pass depth to 0.25”). Open the toolpath for editing and click on the edit button next to the tool,

[edawson@ru-wood.com]

Huh, this is confusing...

I'm asking why the "Sperate Last Pass" doesn't work, and you are directing me to the passes area.
You said.. ."and want the tool to cut using multiple passes you set the pass depth within the tool "

I don't want that. I want one pass or one cut, then I want a "Sperate Last Pass".

If the Sperate Last Pass area (in image uploaded) doesn't work and I need to manage this in the pass area that is fine.

Erich

[Adrian]

You can't have a separate last pass if you set the toolpath to cut one pass. You have to have two passes at a minimum.

If you are cutting 0.5" deep and the pass depth of the tool is 0.5" or greater then you will only get one pass so no separate pass. If the pass depth of the tool is 0.25" then you will get two passes and the separate lass pass will work.

You can override the automatic pass calculation by using the Edit Passes button in the toolpath.

[SteveNelson46]

This is from the help file:

Do Separate Last Pass

A separate allowance can be specified for the last pass. If this allowance is given then all but the last pass will be undercut by the specified allowance with the final pass being the only pass which cuts to size.

Note

This is intended to be just a thin skin of material to be cut away as the tool will have to cut through this allowance at the full depth of the cut where all the previous passes undercut. There will be a warning displayed if the last pass allowance is greater than 1/3rd of the tool diameter but the last pass allowance should ideally be kept a lot smaller than this. Keeping this as small as possible reduces the chances the final pass will fit in areas where the previous passes will not and reduces the amount of material the last pass is having to cut through. If using a last pass allowance for the toolpath you should check that you are happy with the amount of material left for the last pass to cut through. The toolpath will fail to calculate if the last pass is cutting a significant distance into material which has not been cleared by the previous passes.

[edawson@ru-wood.com]

Thank you Adrian,
That is very helpful,
Much appreciated,
Erich