Default stock models in madCAM

[Toolrunner]

Say in the 3-axis or 4-axis version of madCAM I wanted to cut holes into the web of a pre-manufactured gear wheel, or I wanted to machine a casting. The stock model is a default primitive that I can't define except as a general envelope for the work, right? So then I have a set of connected questions:

- Will the problems be collisions, abrupt entry and excessive air cutting?
- Would use of region curves avoid these?
- Is this application of region curves valid?
- What would be the disadvantages of this approach?
- Instead, what other strategy would you use?
- Looking at it another way, what is the advantage of custom stock models?

[JOM]

-It will be no collisions and necessarily not any cutting air if just making holes.

-Yes regions will reduce this and you can also use clipping planes for reducing the height and depth of the toolpath.

-Yes you can use region curves in the entry level and in the four axis version of madCAM.

- It depends on how complex the model is.

-If cutting a casting, it is possible to use the “stock to leave” and cut in two or more steps.

-It saves time and creates a toolpath that doesn’t cut in the air because the user defined stock model is a 3-dimmensional region. On simple parts when just cutting some holes, it won’t make much of an advantage.

Joakim

[Toolrunner]

Thanks Joakim. You have mentioned a feature I couldn't find in the madCAM 'help' file:

You say "-If cutting a casting, it is possible to use the “stock to leave” and cut in two or more steps."

Can you explain this just a little more?

[JOM]

Hello Toolrunner,

It is not a feature, but you can change the stock to leave and recalculate the toolpath for making “step downs” in 3D. For example: Set the stock to leave to 1mm and calculate the first toolpath. Then change it to 0 mm and recalculate for having the final toolpath.
The “stock to leave” works for every 3D toolpath strategy in madCAM.

Joakim

[Toolrunner]

Joakim, thanks. I can't visualise it in my mind - it is possibly a matter of imagining the kind of casting that you are thinking of. But, I am now alert to the idea, and perhaps it will all become clear in the coming madCAM tutorials mentioned a couple of days ago.

[Dan B]

Hi Toolrunner,

I can picture what you are talking about, and I believe madCAM will perform like a champ for you.

Dan

[Toolrunner]

Ok Bob, if you can see my concern about not being able to closely define a tight-fitting stock envelope in the 4-axis version to fit around, for instance, a prototype casting to be machined, and if you reckon it will handle this situation well anyway, then that's good.

I'm watching the currency exchange rates ready to pounce when our AUD is up a bit.

[svenakela]

Toolrunner, could you send me a PM and describe what you need to get described and I'll add it to the tutorials todo list.

If it's the Stock To Leave you're thinking about it's actually pretty easy. Lets say you have a sphere that has a diameter of 50 mm. If you set Stock To Leave to 1 mm, the toolpath will leave a sphere that is 52 mm. The tool will stay away from the object with 1 mm in every direction. Then you can create a new toolpath with Stock To Leave set to zero and that will make you a sphere with exactly 50 mm in diameter. With this strategy the last toolpath will only run in 1 mm of material and will make a very smooth surface.

It also work with negative values which is very important when for example making die sinking graphite tools, as they're smaller than the hole they're going to create. But it's very useful for other stuff as well.
Lets say you have a model, like a simple cube you want to wrap in kangaroo skin. You work a lot with your little box to get the perfect size. Now, when you come to the CAM preparation, you realize that the skin will add another millimeter to the cube. So, instead of you being forced to make a copy of your cube that is smaller to compensate for the skin thickness, you can let MadCAM do that for you by setting the Stock To Leave to a negative value equal to the skin thickness.
I use it all the time, I make a lot of foam cores that I laminate with carbon fibre on top. I know how thick my laminate will be and I set that value in Stock To Leave (like -4 mm). Then I'll get a core that is smaller than the modelled one but with my laminate added it's spot on.

[svenakela]

I made two images, it may explain it a litte bit better.

With a positive value the work piece will contain more material than the model.
With a negative value the work piece will contain less material than the model.

[Toolrunner]

Svenakela, those last two posts clarify things a lot. In fact I think I had the wrong idea until now. What you have just explained is that Stock to Leave will in many, most (or all?) cases be used as an offset (similar to OffsetSrf).

This was the statement that made me understand: "Lets say you have a sphere that has a diameter of 50 mm. If you set Stock To Leave to 1 mm, the toolpath will leave a sphere that is 52 mm. The tool will stay away from the object with 1 mm in every direction. Then you can create a new toolpath with Stock To Leave set to zero and that will make you a sphere with exactly 50 mm in diameter. With this strategy the last toolpath will only run in 1 mm of material and will make a very smooth surface."

Normally I am quick to learn, so I wonder what got in my way. Anyhow, for the tutorials the above might be a key statement around which you can build further explanation. I think the word 'offset' helps too.

[svenakela]

Originally Posted by Toolrunner Svenakela, those last two posts clarify things a lot. In fact I think I had the wrong idea until now. What you have just explained is that Stock to Leave will in many, most (or all?) cases be used as an offset (similar to OffsetSrf). ...

Now you got it.
Great that it helped, I'll add some more about it in the tutorials.