Creating an external core - extrude to a complex surface?

[douglas.angle2]

I'm a first time user with a relatively complex drawing.  I've posted a couple of times, learned a lot and thankful for the advice so far. 

The current issue is conceptually simple:  I have a completed* drawing and I'm making the cores.  

No problem with the internal ones - red and orange in the picture. 

I now want the orange core to extend to the arm at the back.  Conceptually, it means starting at the parting plane and extruding back until hitting something in the grey.  The complication is that it:

- should have a draft angle much higher than the pattern itself,

- give the variable distance to the part, that draft angle needs to vary,

so I can't just extrude the sketch that made the arm in the first place. 

I've managed to come close by various loft, extrude and taper commands.  There's just a few tiny voids left that I can't seem to manage. 

I did think about extruding the sketch then adding draft, but draft only goes from a planar surface.  What I need is essentially that the draft starts at the arm and goes forward. 

There has to be a simpler way of doing this, but any advice would be welcome.

* still two corners I can't fillet at the base of the ribs.  Weird considering the other 6 went fine.  As a last resort I have some old wax fillets I can use on the printed part.

[wmhazzard]

You are over thinking the problem. You can simply extrude a body and with a few cuts you can extend the core to the bracket. 

[davebYYPCU]

Does this help,   

Using your geometry, and Surface Extend, you can boundary fill inside the casting,

Some Combine ops and I think I have what you wanted.  Double check for draft interference, I didn't build the gray bits.

Might help....

[douglas.angle2]

Thank you both for your replies.  I have what I need, and more importantly, I think I understand both approaches and what I needed to do differently.

WMHAZZARD - Perhaps you used a file from a previous posting of mine?  I had tried the approach you showed, and I can see it worked with the file you used, but I needed it with fillets and draft included.  Especially problematic were the fillets at the outer edges, as the core should extend to the base of the fillet, not the face of the ribs. 

I do concede that I'm overthinking the problem and that, with some adjustments your method will work equally well with fillets in place - I would just need to move the cut planes to the corresponding locations.

I also noticed that you adjusted the draft angles where the core overlaps the hub.  Good catch; I hadn't considered that. 

davebYYPCU - This was exactly what I was looking for.  I had briefly looked at boundary/fill but didn't learn enough about it to make it work.  Thanks for fixing it. 

You mentioned that you didn't check draft angles and, given WMHAZZARD's approach including his adjustment to the draft angles, I'm now concerned that I missed a spot.  The area beneath the hub and between the ribs may have a negative draft.  I'll have to check. It seems complicated at first, but with what you've both shown me, I think I could sort that out now.

Many thanks!

[TrippyLighting]

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@douglas.angle2 wrote:

... I'm now concerned that I missed a spot...

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This might have been covered in a precious thread, post, but there is an inspection tool to allows checking for draft.

[wmhazzard]

Show us the completed pattern and core box and the casting when finished. 

[davebYYPCU]

There is a massive interference, cutting the horizontal grey bar, out of the base area of my boundary fill, leaves a hooking groove in the new piece.  (Found it after my last post.)

Might help....

[douglas.angle2]

> Show us the completed pattern and core box and the casting when finished.

I have 3 of the 4 pieces I need printed and made trial cores and molds.  Casting may not happen for a while yet.  I still need one more print, then everything gets copied mirror image as there's two of these, one for each side of the locomotive.

The front core looks good:

This was the second attempt.  In the first one, there was a little tearout around the hub.  In the drawing, Fusion moved the parting line when I added the fillet.  To me that's a bug as the parting line should remain a defined location, especially as there is only a fillet in part of the circle. Hence, there's a tiny negative draft in this area.  In this case, it's a small error, and I could get away with it with careful molding.

There's a small issue with the front pattern.  There is a little tearout in the sand, which I traced to a printing defect.  There was a slight overhang on the corner, easily fixed with a file (the steel kind, not the digital kind).  I was worried when I saw the tight corner (circled in the last photo).  Ideally the core print would be tapered 50 deg or so away from the part.  I got away with it this time, but the sand I'll actually use for cores isn't as strong so it may still be an issue.   Where the part and the core print meet is curved, so I can't use the draft function here.  Is this a case for loft?  Other suggestions?

The rear core has some defects in the ribs, but the fact that there was no sand left in the core box means it just wasn't packed enough.  It was an error in molding technique, not a design error.

Finally, the core in place in the front part of the mold.  It's a tight fit.  I should have reduced the size of the core box a little so that there is a little space between the core and the core prints.  In fusion terms, I modelled the core and used it two ways: 

1)  to combine with the pattern to produce core prints (both bodies are combined and printed as one)

2) as a cutting tool to make the core box.

Therefore, within Fusion the core and core print are exactly the same size.  In practice that's too close - it should be a loose fit.  The second picture shows the tight fit and the cavity that will produce the actual part.  Again, I can probably get away with it with some finesse during molding.

If you've been keeping score, there's still the back pattern to print.  There's trouble there, but I'll make that the subject of a separate post.

Thanks to all that helped me get this far.  I hope this has been educational, or at least entertaining.

[douglas.angle2]

The last step in my design is to join the rear pattern with the rear core to give a single unit for printing.  When I try, I get an error.

I've played with the section analysis tool, but I didn't find anything unusual.  Further, the core was (mostly) made by using the part as a cutting tool, so they should be a match.  Any ideas?

[wmhazzard]

Looking good so far. 

I offset the faces of the core prints by .01" all the way around to give clearance for the core pieces. 

I am not sure why the pattern and core won't combine but don't worry about it, just save both in the same STL file and slice both at the same time, they will print as one. 

It is also a good idea to over build your core prints like I had in my example, it will avoid problems like the sharp edges of the fillets on your core.