topic Re: Thread mills technically violate bottom heights in Fusion Manufacture Forum

Thread mills technically violate bottom heights

programming2C78B — Mon, 10 Feb 2025 12:41:40 GMT

I noticed this because its in a blind hole with an undercut.

Re: Thread mills technically violate bottom heights

seth.madore — Mon, 10 Feb 2025 13:10:36 GMT

How odd, send me the file please?

Re: Thread mills technically violate bottom heights

programming2C78B — Mon, 10 Feb 2025 15:15:40 GMT

I can, but it's happened on at least 3 different ones this week.

emailing now.

Re: Thread mills technically violate bottom heights

seth.madore — Wed, 12 Feb 2025 19:24:05 GMT

Oh, this is being caused by Helical Leads. I don't believe it's a bug, more like "intended behavior".

Re: Thread mills technically violate bottom heights

leo.castellon — Wed, 12 Feb 2025 21:15:00 GMT

IMO, that shouldn't be allowed. If the user sets a bottom height, then there should never be an occasion when it goes deeper than the user selected bottom height. Most people are using thread mills in harder material, so if the tool bottoms out in the hole, the user is out an expensive thread mill and possibly an expensive part.

LeoC

Re: Thread mills technically violate bottom heights

seth.madore — Wed, 12 Feb 2025 21:35:12 GMT

I agree, which is why I've opened up CAM-60529 to investigate the issue. I suspect it's always been like this but never really picked up on.

Re: Thread mills technically violate bottom heights

programming2C78B — Thu, 13 Feb 2025 12:03:42 GMT

Helical Lead:

Regular:

Where does .00285 even come from? 11.5 tpi tool, 0.75" od

Im wondering now if Helical leads are even necessary - not much info on what they do online except for this post where they have the same issue (it also sounds like OP isn't aware of how to properly set his bottom heights)

https://forums.autodesk.com/t5/fusion-manufacture/feature-request-thread-milling-distance/m-p/11428598/highlight/true#M127676

Re: Thread mills technically violate bottom heights

seth.madore — Thu, 13 Feb 2025 12:15:04 GMT

Yes, I would recommend using helical leads, as you will likely have a false cut on the lead in/out move if you don't do helical. Minor issue for single profile threadmills, more of a concern for full-form. You could also just do a zero radius lead out move so it goes from a G1 link to a G3 cutting move, but it's possible Wear/Control comp might complain to you (at the control).

The .00285 is the calculated distance required for the tool to lead in/out on the pitch of the thread for the sweep angle needed

I chatted with a developer yesterday afternoon, and while this behavior is undesired, it's likely intentional (that's not to say we can't improve it). All toolpaths (3d toolpaths for example) are understood to have retracts and lead/links that go outside the boundaries of Top/Bottom height. It's the actual cutting that is constrained within those limits, not the links.

Re: Thread mills technically violate bottom heights

leo.castellon — Thu, 13 Feb 2025 17:30:30 GMT

I can understand that the 3D tool paths would violate the Bottom height as those are model aware and those are "generally" external of the model tool paths. But a thread milling operation is generally performed in a blind hole where there is no room to move around in. I could see if Fusion wants to add a helical move in a vertical direction for a lead in, but make that in Z+, not Z-. It would be preferrable to have a quarter or even half a turn less thread engagement then having the tool hit the bottom of the hole and break the tool. We make quite a few parts in 17-4 and 15-5 in the higher hardness specs and it would totally suck to break a $100-250 thread mill. My employer would not be a happy camper if I kept breaking thread mills.

LeoC

Re: Thread mills technically violate bottom heights

marcus.toepke — Fri, 14 Feb 2025 12:02:10 GMT

I am of the opinion that this is also the case with the Heidenhain control if you use the machine cycle. This is normal due to the Helix approach.

Re: Thread mills technically violate bottom heights

jeffescott — Sat, 15 Feb 2025 22:39:25 GMT

It occurs to me that the thread must always end higher, than the bottom of the tool, since thread mill form is an equilateral triangle.

I made a generous allowance for this by cutting the boss deeper than the thread.