Having trouble cutting up to an avoidance surface

[Sigurd]

I hope the thread title conveys what I'm trying to do. File is attached.

I want to leave grinding stock on the three gray surfaces and finish all the green surfaces:  (Roughing toolpath left out for file size reasons. Please ignore the undercut.)

 

In my program, I have set these surfaces up to be an additional machining region with .002 stock to leave. This is what I get. There's a cusp on that top edge.

This is what I want. No cusp. I set 0 stock to leave for this screenshot. 

 

 

I've run into this before, where I can't get Mastercam to violate the side of an avoidance surface. What I am missing? 

cav pin.mcam

[Leon82]

Steep shallow. Out the min depth above the very top

[Rstewart]

What kind of tool is that???

[Leon82]

3 minutes ago, Rstewart said:

What kind of tool is that???

That's probably a ball and though in the graphics card is creating a polygon

[Bob W.]

I generally create offset drive surfaces when I want to leave extra material.  Offset them by .002" or whatever extra stock you want and program it with zero stock to leave.  The reason you are getting the results you are getting is it wants to leave extra material on the face and all edges of the material, not just the faces.

 

[crazy^millman]

2 hours ago, Sigurd said:

I hope the thread title conveys what I'm trying to do. File is attached.

I want to leave grinding stock on the three gray surfaces and finish all the green surfaces:  (Roughing toolpath left out for file size reasons. Please ignore the undercut.)

 

In my program, I have set these surfaces up to be an additional machining region with .002 stock to leave. This is what I get. There's a cusp on that top edge.

This is what I want. No cusp. I set 0 stock to leave for this screenshot. 

 

 

I've run into this before, where I can't get Mastercam to violate the side of an avoidance surface. What I am missing? 

cav pin.mcam

Model prep them .002 higher and then drive them to zero and call it a day.

[Colin Gilchrist]

3 hours ago, Sigurd said:

I hope the thread title conveys what I'm trying to do. File is attached.

I want to leave grinding stock on the three gray surfaces and finish all the green surfaces:  (Roughing toolpath left out for file size reasons. Please ignore the undercut.)

 

In my program, I have set these surfaces up to be an additional machining region with .002 stock to leave. This is what I get. There's a cusp on that top edge.

This is what I want. No cusp. I set 0 stock to leave for this screenshot. 

 

 

I've run into this before, where I can't get Mastercam to violate the side of an avoidance surface. What I am missing? 

cav pin.mcam

The problem is you are telling the system to leave 0.002 stock "everywhere" on that surface. So the offset isn't just "in the face direction", it is leaving that extra amount around the outside edge of the surface too.

I'm in agreement with Ron > use Model Prep (on a copied and 'history removed' model), to build a model of the final part shape, with the extra stock modeled on those surfaces.

Many of the 3D High-speed Finishing paths will now let you use multiple 'drive geometry groups', each with separate wall and floor surfaces. So maybe use one of those paths, and set +.002 Floor, with +0.000 on walls. Then a 2nd geometry group, with the 0.000 for both floors and walls. Instead of 'Avoidance', which keeps your tool from touching that Avoidance geometry in the first place.

[Sigurd]

12 hours ago, Rstewart said:

What kind of tool is that???

I was trying to come up with something snarky like it was something I ground in the Deckel, but it's a .020" ballnose.

 

13 hours ago, Leon82 said:

Steep shallow. Out the min depth above the very top

You mean like "Min Depth +.001" or similar, assuming that Z0 is the top of the part? I'm only using Max Depth right now.

 

11 hours ago, crazy^millman said:

Model prep them .002 higher and then drive them to zero and call it a day.

Model Prep! You've suggested that to me before and I keep forgetting about it!

 

9 hours ago, Colin Gilchrist said:

The problem is you are telling the system to leave 0.002 stock "everywhere" on that surface. So the offset isn't just "in the face direction", it is leaving that extra amount around the outside edge of the surface too.

I'm in agreement with Ron > use Model Prep (on a copied and 'history removed' model), to build a model of the final part shape, with the extra stock modeled on those surfaces.

Many of the 3D High-speed Finishing paths will now let you use multiple 'drive geometry groups', each with separate wall and floor surfaces. So maybe use one of those paths, and set +.002 Floor, with +0.000 on walls. Then a 2nd geometry group, with the 0.000 for both floors and walls. Instead of 'Avoidance', which keeps your tool from touching that Avoidance geometry in the first place.

Thanks, Colin. That's exactly what I tried - a second drive group with stock on it. If I chained it as Avoidance, then the tool wouldn't get anywhere near it, like you said. I'll try adjusting the stock values, but I think I'm going to try Model Prep first; move the faces and then cut to zero.

[mayday]

"I generally create offset drive surfaces when I want to leave extra material"

Bob wins the internet

[crazy^millman]

14 hours ago, Bob W. said:

I generally create offset drive surfaces when I want to leave extra material.  Offset them by .002" or whatever extra stock you want and program it with zero stock to leave.  The reason you are getting the results you are getting is it wants to leave extra material on the face and all edges of the material, not just the faces.

 

Good suggestion and what we had before Model Prep. Problem on a surface like this is the gap between them when looking down from the top. This is a small area and the .02 endmill will only dig into the gap very little creating a .0002 small undercut. Where as with Model prep to move the faces .002 higher brings all the adjacent surfaces along with it not giving anywhere possible for the tool to create a possible undercut. 

[Bob W.]

3 minutes ago, crazy^millman said:

Good suggestion and what we had before Model Prep. Problem on a surface like this is the gap between them when looking down from the top. This is a small area and the .02 endmill will only dig into the gap very little creating a .0002 small undercut. Where as with Model prep to move the faces .002 higher brings all the adjacent surfaces along with it not giving anywhere possible for the tool to create a possible undercut. 

I'll have to keep that in mind in the future.  I usually leave the original solid intact and put the surfaces on another level but I guess I could copy the solid to another level and rename as a modified version.  Good to know, thanks for the tip.

 

[crazy^millman]

2 hours ago, Bob W. said:

I'll have to keep that in mind in the future.  I usually leave the original solid intact and put the surfaces on another level but I guess I could copy the solid to another level and rename as a modified version.  Good to know, thanks for the tip.

 

Bob look at the CAMInstructor series Mike put together Ron Week. I do this all the time. I dumb down solids  for HST toolpath calculations. Last thing want to fight is longer times making toolpaths because Mastercam is looking at many features not needed. I can see as much as a 30% reduction in calculation times on complex parts using this method. Helps in finishing areas of the part where cross holes come into and other things. Working on a Indy Billet Engine Block on a Integrex right now and it having a dumbed down model is helping tremendously, but I couldn't get everything done with Model Prep. I talked the Design Engineer and he was able to dumb one down in a few minutes from the CAD side and send it and saved me hours of time doing so. Either way Model Prep has tons of useful things related to what we do and good to see Mastercam expanded and improving these functions.

[Sigurd]

I appreciate all the replies.

[Colin Gilchrist]

Depending on the complexity of the solid, I've also had great luck with creating surfaces on the solid faces, and then going back to the solid, and using Model Prep to "remove" a feature. I can then offset the surfaces, and either create "extrude geometry" for making a cut, or I can "trim the solid to a surface".

Many different ways to get the final result, now that we've got Model Prep Tools available.