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Machining undercuts, NO really I need to, but can I

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Message 1 of 7
billbarschdorf
283 Views, 6 Replies

Machining undercuts, NO really I need to, but can I

Hey all,  I have a complex organic-shaped part that is the 3rd piece of a casting mold that will be machined in 6061. It's a pretty complex shape with undercuts from both sides.  SO I will need to machine it from top and bottom in 2 machining operations. About 90% of the surfaces are accessible from the tooling in the Z direction even though I will need to mill from boths side. 

 

 The bigger dilemma is that there is one area of the mold cavity that is undercut in the X & Y directions, in other words, no tooling access from the Z direction.  The depth is not terribly deep, so Im winding if Fusion is capable of creating tool path on surfaces such as this.  Im thinking if I use a 1/4 lollipop-style end mill the sides of the cutter should be able to get to the surfaces, question is will Fusion create the tool path.  I don't have a final mold PC done yet but can post it once si get there.  I just wanted to get some general input before I commit to this.  The other option is to resculpt that are of the mold in ZBrush and regenerate surfaces from the mesh sculpt.  But big problem with that option is it starts to effect the function of that are of the final cast part which Im trying to avoid.  

 

I am of course considering a 3rd set up in my milling giving it a bit of angle to get a standard ball end in there.  BUT Im honestly new to metal working CNC and would like to avoid a 3d machining operation if I can.  

6 REPLIES 6
Message 2 of 7

There are a few 3D toolpaths that are capable of undercuts; 3D Contour, Steep and Shallow as well as the new Blend.

If you could share an image of your part (or the part itself) we could toss those toolpaths against it and see what we can come up with 🙂


Seth Madore
Customer Advocacy Manager - Manufacturing
Message 3 of 7

Here is the mold pc part file in Fusion.  I figured I would set it up in cam if anyone would like to do some programming on it to show me. the options I have regarding getting access to those undercut surfaces.  

 

Im including a screen shot to show an area (highlighted in yellow) of the mold cavity that I need resculpt and generate new surfaces again, so you can just disregard this area in you thoughts. 

 

As you will see if you look at the modeling module there is an end cap for this mold cavity and ultimately this is actually a 4th mold pc. However I wanted to see if you guys have input on machining this entire cavity as a closed cavity.  IS this even an option OR do I absolutely need to machine this from both sides????

 

Regarding the ugly nature of the topology of the surfaces is there any downside to this when it comes to programming and machining this mold cavity? This part was originally scanned, and resculpted in ZBrush, from that mesh a sub-D was created then the surfaces were generated from that.  I did not do any guide curves to influence the topology I just got what I got. and I I’m not sure that would result in anything much better than what I have here.  So the question is dose it matter at the end of the day when it comes to machining this part? Other option is to work directly with the mold cavity as meshes which Im trying to avoid.

 

https://a360.co/40zeV6W

Message 4 of 7

Due to the size of this part (it's rather small) and my assumption that this will be done on a 3 axis machine, yes, most certainly, you are going to be doing this from both sides. 

Consider the amount of overhang you're seeing on either side of the part. I don't think you're going to find a tool that can get completely underneath any of the undercuts and allow for machining everything.

Here's a 3D Contour and a key cutter (as an example):

2023-03-27_18h15_25.png


Seth Madore
Customer Advocacy Manager - Manufacturing
Message 5 of 7

Yes im going to machine what I can from side one, then flip and machine the other side. That's the only way I see getting to the surfaces from Z direction.  There is only a small section of the model that is not accessible from Z that undercuts. 

 

 What are the dimensions of that tool so I can start looking into that type of tooling?  

 

Also what options does Fusion have to analyze undercut areas, I assume mold draft analysis will show me exactly where the undercut areas are.  It's really hard to see exactly where the undercuts are for sure. 

Message 6 of 7

That would be "accessibility analysis" under your cam setup > work coordinate system. 

Message 7 of 7

What would you do with this part? Would you machine it at an angle? Face off both sides, clear out most of the material then do all finish passes at an angle.  If yes what angle would you rotate the part to AND would you rotate in a single axis OR angular like from diagonal corner to corner?  and what do you think is the best repeatable way to fixture this?  I planning on buying a SMW fixture plate and mod vises Im on a Tormach 1100M.  BUT Im i better off on the Kurt vise for this set up? 

 

I may have access to a 4th axis I can borrow from work, I dont have one yet myself. Is this the better option? 

 

Also as a general rule, how much draft angle should I have on a vertical wall for cutter accessible with a  1/8 ball end mill? Specifically the shelf area with the vertical wall on the part, Im going to add a draft to that wall. 

 

I am analyzing what I can do to reduce some of the really tricky areas and reduce them a bit more by resculpting those areas.  

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