Stock to Leave when Milling from Boundary Curve

[SkyG]

Hello -

I'm trying to generate some toolpaths using the Boundary Curve milling feature. I want to leave some stock, but what I've found is that it doesn't matter what I enter in the "Stock to Leave" box - the toolpaths are always the same - they take off all the material.

Does the Stock to Leave in Boundary Curve milling work, or am I doing something wrong?

On a related note - it would be really nice if you could do roughing from a boundary curve. This is essentially what I'm trying to do here. I'm being lazy and trying to not "build a box" around my surface, but instead just go straight to toolpath generation. If 3D roughing and Boundary Curve milling could be combined, that would be ideal!

I just bought MadCAM last week, and I have to say that even with this issue, it's extremely easy to use (I was making parts in about two hours) and I really like it!

-Sky

[SkyG]

I now realize that I can do what I was asking - roughing with a boundary curve - by utilizing the Select Region Curves function. Still not sure why changing the Stock to Leave in Boundary Curve Milling has no effect for me.

-Sky

[svenakela]

I'll see if I can try it out later today. I'll forward the question as well, so hang on there and you'll have an answer.

[svenakela]

I heard you already did talk to Joakim at Madcam, so you got the explanation (very helpful guy). When it comes to your region it seems you got it all right now? You use that, namely the function "region" to keep the milling inside a boundary. What is important to now is that the center of the tool will go to the region curve, so either make a curve with offset from your planned region, or extrude the curve into a surface straight down in the model. That will stop the tool already at the tool edge.
There are tutorials coming up soon, they may help you a bit. In the mean time the simulation tool is really handy to test and to get an idea of how the functions work.

I tried to set the Stock To Leave-value in the roughing dialog and I think I got the same behaviour in version 4.1. But it seems it only happens in the roughing dialog, if you set the STL value directly in the tool settings or if you run a planar finishing it goes like it should. Version 4.2 is to be released any day now and it doesn't have the behaviour.

Regards,
Sven

[SkyG]

Hello Sven -

Actually I didn't get any word from Jaokim, so maybe we got our wires crossed so to speak. He should have my email address since I'm a registered user, I'd be interested in what he has to say about the issue.

Yes, I do have the region function well figured out now. For the stuff that I'm currently working on, it's ok that half the cutter goes outside the boundary, but I'm sure in the future I'll need to use that trick.

Looking forward to version 4.2!

-Sky

[svenakela]

Originally Posted by SkyG Hello Sven - Actually I didn't get any word from Jaokim, so maybe we got our wires crossed so to speak. He should have my email address since I'm a registered user, I'd be interested in what he has to say about the issue. Yes, I do have the region function well figured out now. For the stuff that I'm currently working on, it's ok that half the cutter goes outside the boundary, but I'm sure in the future I'll need to use that trick. Looking forward to version 4.2! -Sky

You can use the 4.2 right away, as a registered user you can download a beta and install it. It's stable, and a lot faster.

[Dan B]

You use that, namely the function "region" to keep the milling inside a boundary. What is important to now is that the center of the tool will go to the region curve, so either make a curve with offset from your planned region, or extrude the curve into a surface straight down in the model. That will stop the tool already at the tool edge.

Can you explain this? There are scenarios where I would like the region curve to define the edge of the cutter, so the extrude idea sounds interesting. Unfortunately it didn't work when I tried it so I must be doing something wrong.

Maybe sometime down the road we could get an option on how madCAM deals with regions. WorkNC allows you to select whether the cutter stops on the curve or when it touches the curve (edge).

Thanks,

Dan

[svenakela]

Originally Posted by Dan B Can you explain this? There are scenarios where I would like the region curve to define the edge of the cutter, so the extrude idea sounds interesting. Unfortunately it didn't work when I tried it so I must be doing something wrong. Maybe sometime down the road we could get an option on how madCAM deals with regions. WorkNC allows you to select whether the cutter stops on the curve or when it touches the curve (edge). Thanks, Dan

Here's a short explanation of what I mean. I assume you know how Rhino and Madcam works in general. Step 1-6 shows how it will be if you go with a standard region, the rest shows the surface trick (next post).
So, here's an explanation how to stop the tool at the edge of the region curve instead of going to the center of the cutter.

1. I made a simple model, a box and a sphere. The circle polyline will be our region.
2. Select the model and make the stock box, i.e. the surfaces etc for the toolpath calculation. Choose a cutter, I selected a 5 mm ball end.
3. Select the region curve and click the menu option Regions-Select Region Curves.
4. Now the calculation box is the same size as the region, our circle that is.
5. To show the region effect, I generated a planar finishing. It's already visible in this perspective that the toolpath is all the way out to the region curve.
6. Here, you can see clearly that the tool path is all the way out.

I can only make 6 attachments in each post, the trick will be just after this one.

[svenakela]

Now, let's go for the trick!

7. Select the region curve and extrude it as a surface straight into the model. You can do that with the command ExtrudeCrv and just drag the length and direction.
Select all surfaces including the new region curve surface. Make the toolpath calculation box.
8. Select the region curve and go for the Select Region Curve command.
9. Now, when the toolpath is generated the tool will stop by the tool edge when it reaches the region curve surface. The toolpath generator will still try to reach the middle of the tool, but the surface is in the way.
10. In this picture it's visible (from the side) that the tool edge goes to the surface. I used a 5 mm ball end and now there's 2.5 mm left in the toolpath to the region curve. In this example the tool will lift up to get the tool center to the curve. But the tool will be inside the region when cutting the model.

I hope this helps.

EDIT: The advantage with it this way instead of making an offset curve inside the region curve, is that the cutter size doesn't matter. If a region is made with an offset curve, in this case 2.5 mm inside, the toolpath will go outside the expected region if a bigger cutter is selected. But with extruded-surface-way the same region can be used for any cutter size, one big can be used for roughing and a really small one for the finishing without any changes to the region.

[Dan B]

Hi Svenakela,

Thanks for taking the time to prepare this response. It turns out that I was doing it correctly, but I was expecting the tool to stop when it hit the extrusion, not climb on top of it. No harm done that way, it's just that I thought I would see it stop there, and I didn't so I thought I was doing something wrong.

Thanks again,

Dan