Last Pass Allowance

[piccyman2]

I have a slight problem with the Last Pass Allowance option.

I selected a .2 allowance for cutting a guitar neck where the depth of cut is 62.5mm, and sure enough the last pass was .2, but it was only cut at the bottom of the 62.5 mm not on the whole depth.

i guess option this can only be used if your cutters cutting length is longer that the depth of cut?

Is this correct?

[Adrian]

Yes, the idea of it is the last pass of the cutter will be the allowance amount over from the rest of the cut.

You can adjust the last pass depth in the Passes section of the toolpath so that the last pass depth is a greater part of the whole cut depth.

[piccyman2]

why would the last pass on a profile cut not be the whole depth by default and not just the last, i guess it wouldn't be to good for the cutter either

[glenninvb]

Yes, on the cutters flute length

I haven't had the need to use the last pass option in VCP8 yet but fairly sure I understand the process. It would seem the least amount of material left for the last pass and included allowance would yield the best results because of less tool deflection etc... (especially with 2d tabs)..... Regardless flute length must be equal to or greater than material thickness (if its thru cut) or tool shank will rub or worse as the shank is now trying to cut the uncut allowance.

I recommend a cutter w/flute length at least material thickness, if for nothing else chip evacuation, but you could always use the "regular" profile allowance offset for a multi-pass clean up using your cutter. However wood movement caused by stresses in material that thick may defeat the purpose.

[piccyman2]

I think the answer is to not use this feature as its not really well thought out, i will continue to use the 2 separate cuts a rough cut and a finish cut.

This means i can continue using my cutters and not have to find cutters with a minimum flute length of 62.5mm, if they exist

I still can't understand why you wouldn't do a final pass cut for the whole depth, just ask what your flute length is and that will give you the amount of passes required to recut the whole depth.

[Adrian]

If the last pass isn't done as a single pass then a lot of the benefit of doing it in the first place is lost. It's there to give an accurate, clean finish pass for cabinet type work.

Doing it as two separate toolpaths with the merge by part option will give you what you're looking for.

[glenninvb]

The "last pass option" is not what you should be using with your cutter, as its intended for a full depth last pass.
Use "regular" profile allowance, set allowance on first toolpath and zero on second toolpath. You may then adjust pass depths as you wish
You can merge if desired

1/2" diameter end mills w/ 3" flute length are readily available, they are generally 6" TL

[Art Mann]

I think the answer is to not use this feature as its not really well thought out, i will continue to use the 2 separate cuts a rough cut and a finish cut.

The feature works exactly like I want it too. I could already cut a profile using multiple passes and then cut the same profile again removing a little more material using multiple passes. That doesn't improve the quality of the finished cut as much as the new feature does. Of course, you have to buy a bit with flutes that cut from top to bottom. That is the price you pay for using this feature. It is certainly worth it to me.