Setting max depth on roughing pass

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Setting max depth on roughing pass

Postby allistar » Sun Jun 30, 2019 12:05 pm

Hi there,
I'm carving a 3D model and am using an 8mm endmill for the main roughing pass. The issue is that there is some 28mm deep detail that the 8mm endmill won't fit into, so the roughing pass doesn't touch any of this at all. I would like to run a 2nd roughing pass with a 3mm endmill. This can only cut 15mm deep, so I would like to set a limit on how deep it goes. This should remove enough material for the 0.5mm tapered ballnose to do the finishing pass. I have found out how to add a plane and "bake" it to the model so the second roughing pass doesn't go deeper than 15mm. I would like to set a start depth as much of the material has already been removed in the first roughing pass. At the moment about half the programme on the second roughing pass is cutting air.

Is there a way to do what I'm after? This is in VCarve Pro 9.517.

Thanks,
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Re: Setting max depth on roughing pass

Postby Adrian » Sun Jun 30, 2019 12:21 pm

The roughing toolpath will cut to the depth needed to leave the amount of material specified in the Machining Allowance so I suppose one way would be to specify a large allowance.
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Re: Setting max depth on roughing pass

Postby TReischl » Sun Jun 30, 2019 1:26 pm

Yup, deeper cutting gets tricky. Not sure I have sorted it out either. Seems like every one I have done has some special considerations.

How about defining two modeling planes and doing a bake to control the depths as you go? And if there is a lot of air cutting do a bit of defining boundaries to control where it will be roughing?

On some of the ones I have done I only do 3d cutting around the model itself, the background gets done separately.

At any rate, IMHO, deeper models look really good!
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Re: Setting max depth on roughing pass

Postby IslaWW » Sun Jun 30, 2019 2:14 pm

You can specify a second roughing pass with a smaller endmill and have its cutting area (or areas) defined by a vector boundary that you define.
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Re: Setting max depth on roughing pass

Postby nicksilva » Sun Jun 30, 2019 3:12 pm

IslaWW wrote:You can specify a second roughing pass with a smaller endmill and have its cutting area (or areas) defined by a vector boundary that you define.


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Re: Setting max depth on roughing pass

Postby Adrian » Sun Jun 30, 2019 3:35 pm

That won't constrain the Z depth though just the X and Y unless there is something about vector constraints that I don't understand. I don't do a lot of 3D.
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Re: Setting max depth on roughing pass

Postby Inchlaggan » Sun Jun 30, 2019 4:33 pm

I do some deep 3D cutting up to 25mm.
Your maximum depth is always going to be limited to the length of bit that extends from the spindle and the rigidity of same. In your question, having 28mm of a 2mm end mill extending from the collet will deflect easily.
It is easy enough to set up a series of roughing cuts for end mills of reducing diameters. 8, 6, 4, 2mm for example. Produce finishing paths for each, but simply discard them, except for the last, leaving a reasonable machining allowance.
Run the roughing paths in diminishing order of diameter. You will be cutting a lot of fresh air most of the time, and your machining times will be very long indeed.
If you are using mills with a shank of a greater diameter then the working end, you will need to ensure that the shank does not foul on the workpiece.
By which I mean that your cuts cannot be made with movement in the Z axis alone. They must also move in either X or Y or the shank will foul and the end deflect.
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Re: Setting max depth on roughing pass

Postby TReischl » Sun Jun 30, 2019 8:35 pm

Inchlaggan wrote:......
Your maximum depth is always going to be limited to the length of bit that extends from the spindle and the rigidity of same..


Sorry, disagree. I have cut with the collet well below the top surface of the material as have many others. It depends on what you are cutting and how the model was designed. Things like draft angle on the model can allow the cut to be deeper than the length of the tool protruding from the spindle.

My max depth of cut has been 3.5 inches, roughly 88mm. IIRC the longest length of tool was 2 inches. The model height was 3.5 and had drafted sides. It is a flag with an eagle that I posted a month or so ago.
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Re: Setting max depth on roughing pass

Postby Inchlaggan » Sun Jun 30, 2019 10:11 pm

Indeed, but if, and only if, the design allows.
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Re: Setting max depth on roughing pass

Postby allistar » Sun Jun 30, 2019 11:42 pm

Thanks for your replies. I have used a rectangle to limit the X/Y of the second finishing pass and a zero plane to limit the depth. The way I prevent cutting too much air is to find the part of the gcode that is at a useable depth (say, 7mm down) and start the programme from there. LinuxCNC makes this easy.

It would be very handy if you could "stack" toolpaths in VCarve and have it know what was cut by the previous toolpath to avoid cutting a lot of air.
Also, setting a max depth of a bit in the tool database would also be helpful (but to have this apply to the actual depth of cut, not based on Z=0).
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Re: Setting max depth on roughing pass

Postby TReischl » Mon Jul 01, 2019 1:00 am

Deep cutting is not easy, that is for sure.

Sometimes what I do rather than bake a zero plane is add a component that I can then easily adjust the height of, same sort of thing as the plane but for some reason I think that is easier.

Tell the tool it can cut to china in the database.
Set the height of the limiting component to control the depth.
Cut
Reduce height of limiting component
Cut

wash, rinse, repeat.

Quite often I start with a big honking tool, then as I start to get down to the nitty gritty reduce the tool size. I am not sure if a really good solution is possible at this price point in software?
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