Limiting unnecessary 'air' milling?

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grant-m
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Limiting unnecessary 'air' milling?

Post by grant-m »

Hi All,

We are a boat-building company looking to purchase a large CNC router and software to go with it. The bulk of our work which will be 2D profile cutting from sheet material, either MDF or foam and composites, and from time to time we also need to shape 3D foam parts. VCarvePro looks like it'll do very nicely indeed for most of our workflow, but I'm hoping there are ways around the problem of limiting unnecessary machining time on large projects. It seems VCarve has some features which come some of the way to doing what we need, but not all the way.

The issue is that it assumes we start with a rectangular block of material, when in reality we don't - the parts we make are large and the foam we use comes in (expensive) sheets, so to minimize waste we would always laminate a stack of sheet cutouts to form a stepped approximation of the finished shape. If we then create a 'Roughing Cut' toolpath it'll waste many hours of machine time milling the air around our built-up stock.

The Machining Limit Boundary helps, but only in plan view/Z-axis. For example if the finished shape was to be a pyramid and the material was built up from progressively smaller square layers, the Machining Limit Boundary wouldn't save any machining time at all, you'd still be machining a whole cube of air above the square pyramid base. It would be great if you could also set similar boundaries in Y and X axes, or if a 3D model surface could be used as the 3D limit boundary.

The 'Finishing Cut' toolpath almost does what we want because it ignores the block and bases its path on the finished shape, but it only allows a final cut down to the finished surface. If it allowed you to set a machining tolerance/offset you would be able to create a few progressive roughing passes with it, this would be very useful.

The 'Slice' function is nice too, it's almost what we are doing with our built-up material, as each slice has its own limit boundary, but we want to machine all the slices (or a number of them) in position in the stack in one shot, rather than treating each as a separate job and assembling them afterwards. If this were possible it would be perfect for us.

A workaround I could probably use would be to raise the tool off the work without telling VCarve that I've done so, and use a smaller bit than what VCarve uses to calculate the 'Finishing Cut' toolpath, this would effectively give me a roughing cut with some allowance. Then I could create a second 'Finishing Cut' toolpath the usual way, with smaller stepover etc. Unfortunately this makes the toolpath preview pretty meaningless.

I could also offset the surface of my model outwards in Rhino and import that into VCarve. Creating a 'Finishing Cut' toolpath with a large stepover on that dummy surface would give me a rough cut with allowance on my real surface.

I can't be the first person to ever come up against this, so are there any better solutions or workarounds out there?

Any advice appreciated.

Grant

Mingra
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Re: Limiting unnecessary 'air' milling?

Post by Mingra »

Have you considered trying a finishing cut path but on a different geometry? For example you have a detailed ship hull. Create a second 3d "cage" model that encapsulates the detailed model but leaves a 1/2 cushion all around. So essentially you are running 2 different jobs but on the same stock.

tomgardiner
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Re: Limiting unnecessary 'air' milling?

Post by tomgardiner »

Depending upon how accurately you can be in you glue up of blanks, I would think that you could cut a sliced up model with an offset done in Rhino then glue up and run a finish pass to the complete block. In foam you can take a large depth of cut so your finish pass could clean up some part mismatch.
If you are clamping the foam then you can draw in some clamp flats in the rough sliced model.

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IslaWW
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Re: Limiting unnecessary 'air' milling?

Post by IslaWW »

Grant...
There are a few workarounds that can be used in conjunction with some manual toolpath editing to achieve your desired goal of efficient machining. That said, if you have production runs of multiples of a given piece or pieces this will work great. If you continuously do one offs and want to generate the most efficient toolpaths for an ever-changing quantity of 3D forms, one of the CAM engines that includes these machining options would be your best bet.

I do not expect to make an apples to apples comparison of 2 products where one costs 5 to times the other. VCPro at around $700 far outperforms its pay grade in this area, but in certain areas, and yours is one of them, there are products that include your desired features, albeit at a substantially higher cost.

If you would like to start a conversation about specifics regarding this, my email is in my signature

Gary
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eph210
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Re: Limiting unnecessary 'air' milling?

Post by eph210 »

The 3D roughing toolpath has an optional stategy called 3D raster. If you select this and edit your tool data to declare a large pass depth it will give you what you are looking for. If you edit the tool data in that toolpath it does not affect other uses, alternatively you could create a special roughing tool in your tool database.
Euan

grant-m
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Re: Limiting unnecessary 'air' milling?

Post by grant-m »

Mingra wrote:Have you considered trying a finishing cut path but on a different geometry?.
Thanks, yes I have, that's pretty much what I was describing in my 2nd last paragraph. It might be a pain to do in practice though, Rhino's offset doesn't always produce a good surface.
tomgardiner wrote:Depending upon how accurately you can be in you glue up of blanks, I would think that you could cut a sliced up model with an offset done in Rhino then glue up and run a finish pass to the complete block. In foam you can take a large depth of cut so your finish pass could clean up some part mismatch.
Thanks Tom, I think it might prove to be a bit fiddly to have to work on each slice before we glue them up, ideally we'd like to cut the parts from sheet in one operation, assemble our rough stack, then machine it as a single piece.
IslaWW wrote: If you continuously do one offs and want to generate the most efficient toolpaths for an ever-changing quantity of 3D forms, one of the CAM engines that includes these machining options would be your best bet.
Most of our work will indeed be one offs, so I think we'll need a solution that streamlines this aspect of the process, fiddly workarounds might prove to be an expensive time-sink in the long term. I was hoping to avoid looking at a more sophisticated software option, only because I think it would be underutilized. Our work is pretty simple and VCPro looks like it'll do what we need.
eph210 wrote:The 3D roughing toolpath has an optional stategy called 3D raster. If you select this and edit your tool data to declare a large pass depth it will give you what you are looking for.
Thank you Euan, that large depth pass is the key I had missed. I've just tried it in the Trial, setting depth pass = to the total material height and it looks like it'll do the trick nicely!

Thanks again everyone.

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Re: Limiting unnecessary 'air' milling?

Post by LittleGreyMan »

grant-m wrote:
eph210 wrote:The 3D roughing toolpath has an optional stategy called 3D raster. If you select this and edit your tool data to declare a large pass depth it will give you what you are looking for.
Thank you Euan, that large depth pass is the key I had missed. I've just tried it in the Trial, setting depth pass = to the total material height and it looks like it'll do the trick nicely!
It probably runs nicely on screen, but imagine what will physically happen: you'll need a very long tool with a very important cut depth and it will have to cut at full depth. Is it realistic?

For this kind of work, as Gary said, you need a CAM system which manages stock, ie which take into account the stock shape to compute the roughing toolpath.
Best regards

Didier

W7 - Aspire 8.517

grant-m
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Re: Limiting unnecessary 'air' milling?

Post by grant-m »

LittleGreyMan wrote: It probably runs nicely on screen, but imagine what will physically happen: you'll need a very long tool with a very important cut depth and it will have to cut at full depth. Is it realistic?

For this kind of work, as Gary said, you need a CAM system which manages stock, ie which take into account the stock shape to compute the roughing toolpath.
I think it should work, the glued-up stack of layered foam looks a lot like the result of a Z-level roughing pass, so this 3D raster roughing pass (or passes) only needs to cut away the steps formed by the foam layers. The trick is in knowing exactly where those are in space. The foam layers need to be worked out accurately so there's sufficient coverage of the work but not too much waste for the bit to run into. For safety one could set up a quick 'exploratory' pass, with a stepover of, say, 10 x tool dia, that skims over the piece just nicking the steps here and there to check that the surface of the foam is where you think it is.

Edit: Nope, looks like I'd need to lie about the tool diameter in order to set a really large stepover, it won't let me set a stepover larger than the bit.

LittleGreyMan
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Re: Limiting unnecessary 'air' milling?

Post by LittleGreyMan »

This is exactly our process. Unless you want to experience machines crashes or spend a lot of time searching for workarounds, choose a product able to manage stock material.

As these 3D CAM are not always very efficient for 2D work, considering Vcarve for 2D is a good choice.

For more information, feel free to PM me.
Best regards

Didier

W7 - Aspire 8.517

grant-m
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Re: Limiting unnecessary 'air' milling?

Post by grant-m »

LittleGreyMan wrote: For more information, feel free to PM me.
Thanks LGM, but it looks like I can't send messages yet.

LittleGreyMan
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Re: Limiting unnecessary 'air' milling?

Post by LittleGreyMan »

And I can't send you a PM as you're a new user.

You can mail me at addresstrashcan2009 at laposte dot net

Translate address into adresse (with one "d") and trash can into poubelle.
Best regards

Didier

W7 - Aspire 8.517

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