5 axis Bottom Fillet on an Undercut

[Anonymous]

I'm trying to generate the last toolpath to finish the 1" dia fillet using a 1/2" ballnose. I've tried steep and shallow, scallop, but I believe a multi axis contour should be the way to go, the thing is I can't get a smooth finish, the tool path always leaves a ledge. 

[DarthBane55]

I've done very similar before with steep and shallow, but I don't have the extensions enabled right now.  There is a setting where you control the tool axis vector, you then would select "from curve" or "away from curve", something like that, and select a curve similar to what I show below.  The tool axis will always go though this curve, so it makes a really smooth path.

However, Fusion does not currently support undercutting, even in multi-axis.  There is a way to make a very small undercut, which you will have to cheat to enable, but in your case it might not work...  I explain:

1st, you need to define your ballmill as a lollipop cutter, with a very tiny shank.  In your case, you need to say 1/2" lollipop with say 0.001" shank diameter.  I would then do undercuts...  but I believe only to what the tool would be able to reach as viewed from the tool orientation in your operation.  It means you would be able to do a 0.2495 undercut maximum (with the 0.001" shank).  And in your case, it is not enough unfortunately.

To prove this, make the top of the pocket bigger, so that as viewed from the top, you'd be able to see some of the bottom radius you want to cut.  That would enable some undercutting, providing you define the tool as I said.

Then you have to imagine that this is a ballmill with a 1/2" shank, and decide if the shank would hit anywhere or not (in real life).  In your case I think it would be fairly easy to determine that if there is a tilt bigger than the inner wall, it would be safe to go with the ballmill in real life.

But again, you will have to make the top of the pocket bigger, which is probably not allowed for your part.  Play with that tho, it's really nice with steep and shallow.

Now to make this actual part with Fusion, I'm afraid you will have to resort to indexing a few times and do a 3-axis path. 

[mattdlr89]

Interesting problem. I just had a play and seemed to get it to work with the flow toolpath. It isn't perfect but perhaps with a bit more tweaking it can be better. Take a look at the attached file. 

Edit: might have misunderstood your problem. You mentioned an edge you can't get rid of which I'm not sure I've solved. Anyway worth a look...

[DarthBane55 · Accepted solution]

Good to see this semi-working with flow!  But the path is really kind of all over the place, it retracts a lot (and gouges doing so), I'd rather just index a few times and 3-axis it than this path, it basically is what it's doing anyways except it adds a few 5-axis moves in the corners, but the way the path is generated is really weird.  I had tried with flow too but gave up on it, I just wonder why flow cannot connect the faces together and keep going around and around.  It's cool that it almost works, but really it doesn't work which is disappointing.  I even created 1 stitched surface for that blend radius all around, hoping that flow would then connect them properly, but it did not.  Of well, it's still nice to see it sort of handle it.  It's not missing much...  hopefully soon...  😀

The back and forth and not connecting together is probably due to the undercuts not being supported.  I tried "blend", but I'm not familiar enough with that path to see what would be needed to make it work, I failed miserably with it.  Maybe you can try that if you know how the path works, never know...

[DarthBane55 · Accepted solution]

@mattdlr89 

I was intrigued by what you could do with flow, considering I thought it cannot do undercuts, but you did it.

I played with your path and got it to go around and around in 1 shot, see attached file below.  Well at the very end, it does a retract and comes back for a final pass, and that pass really is bad, a lot of wiggles on the tool.  There must be a way to eliminate that last pass, probably leaving a few thou allowance on the bottom or something like that, but I ran out of time.  Anyways, 95% of the path is nice.  I'd prefer to be able to start fanning earlier than when it hits the corners to avoid sharp C-axis moves, but not sure it can be done, not too too bad in this part cause the part is pretty big, so the corners are big.

1 thing I did, which I don't know if that is what made it work or not, because I changed a bunch of stuff in 1 shot (bad idea when you wanna know what triggers what...), but I deleted that radius and added it back.  Sometimes imported models have tiny issues with geometry and creates problems.  I don't know if it helped or not, but I think so because now flow connects all the faces in 1 go.

Attached file.

[mattdlr89]

@DarthBane55 

yeah I’ve used flow a lot but it can be a pain sometimes when you’re selecting lots of surfaces and the tool path decides to retract a lot rather than join them together. 

blend is a lot better but it fails too many times. I guess that’s why it is still a preview feature. I did try to do the fillets with blend but it was failing straight off. 

[Anonymous]

Fantastic! Thank you guys, I must have spent countless hours on this.