slicing threads

[jameshs 42]

I have an odd one.

I am printing some threadded items

they are fairly big - 30-32mm diameter and cura won't slice the bolt.

Strangely yesterday it happily sliced the bolt when it had a bigger thread pitch, but today it puts a cylinder inside and then the thread is a cobwebby mixture.

the nut printed fine!

The threads yesterday had a bigger pitch - 3.5, and the ones today 2.0. Have I hit a limit of slicability? - I sliced as low as 0.1 but same thing, though I am using a .65 nozzle for rough work.

The wall thickness inside the thread is good and these are coming from Inventor - should I try and netfabb them?

Thanks

James

 

[IRobertI 520]

"The wall thickness inside the thread is good"

What IS the actual wall thickness? I'm guessing it's simply that the wall is so thin that cura has trouble fitting your 0.65mm nozzle in there.

 

[gr5 2,172]

You should make sure your wall thickness is thick enough for two passes - so 1.3mm would be the minimum although with the threads being at an angle from vertical the cad software might be off by .01mm or so. So I would consider maybe 2mm as a minimum wall thickness for the threads.

 

[gr5 2,172]

Did you slide the layer slider up and down a few times to make sure it all looked perfect before you printed? I assume your problems are the slicer as this sounds very likely.

Also did you play with the "fix horrible" settings in the expert tab? You might want to uncheck "A".

 

[jameshs 42]

 

So the odd thing is that the only difference between the two is the thread pitch.

 

Once that slices successfully has a smaller wall thickness, but larger pitch of thread.

 

Both seem to be large enough, being 2+mm (and the 2.1mm printed well, but the 2.5 is not.

 

Could it be that there is too much - I think cura is being confused by the threads or that the higher frequency of thread somewhere has too small a part so cura sees it as an outside part?

 

Has anyone printed a thread with a pitch of 2mm.

 

I went to 2mm pitch from 3.5 as I am making a pole mount and the outer ring squeezes the inner ring to grip (like a telescopic paint handle) so the OD of the inner piece is 30. When I printed the threads as 30od and the nut at 30 id as an experiment they did not fit. The next ISo defined thread in inventor is 33 @ 3.5 which printed well, but was slightly too loose for my liking (workable and printed, but I am trying to push the tolerance)

 

So as there is no defined thread at 32 3.5 pitch I changed the 30 od to 2mm pitch and the nut to 32 2mm pitch, which I have defined - and that is when the 'bolt' wont slice but the nut sliced and printed fine.

 

So I think it is the pitch of the thread.

 

I don't know enough about thread definitions to 'make' a 32 3.5 which is what i want and none of the auto table generators seem to match the definitions in the inventor thread xls tables.

 

Anything I can d to fool cura (I don't have ANY fixes ticked and when I tried them they just sealed every hole available!)

 

I will try pushing it through a few mesh fixers and see if they can find any holes, but inventor seems quite good at clean meshes.

 

Thanks for the suggestions - I enjoy hacking away at these items and am continually impressed at the usable details that I can print into functioning things.

 

Autodesk inventor has really opened up the opportunities but hence increased the challenges

 

James

 

[jameshs 42]

hmm - so I did aclean version of a 30mm cylinder and then applied a thread with a

3.5mm pitch

3.0mm pitch

2.5 mm pitch

2.0 mm pitch

and then popped them on the board to slice.

The 2.5 and 2.0 fail, but the 3mm + slice fine.

These are solid cylinders so something happens when the threads hit less than 3mm.

Something in the thread is too small for cura and makes it think it is hollow.

Any clever fixes I am missing or do I have to go back to trying ti figure out ISO thread tables to make a 32 3.5 thread definition ?

TIA

 

[IRobertI 520]

Would you mind sharing the files? That might make it easier to figure out since it's not obvious, to me at least, why it would fail.

 

[jameshs 42]

Happy to but I can't work out how to attach a file - do I upload it as an image?

grrr

 

[illuminarti 18]

If you click the 'More reply options' button in the bottom right corner of this page, does that then take you to a page where you can add attachments? I can, but it may be a moderator-only thing at this point.

 

[jameshs 42]

https://www.dropbox.com/s/1pxnx0tslt81cfn/test%202.0.stl'>https://www.dropbox.com/s/1pxnx0tslt81cfn/test%202.0.stl

https://www.dropbox.com/s/1pxnx0tslt81cfn/test%202.0.stl

does this work? - a link to dropbox rather than an attachment?

 

[jameshs 42]

https://www.dropbox.com/s/le5aqf9dmk9slir/test%203.0.stl

this is the one that works

In the more reply I don't have an attach button and can't add to my gallery so hope the dropbox ink works

Thanks

James

 

[takei-naodar 0]

The problem lies in how the model is built.... try fix horrible A in the expert Settings

 

[jameshs 42]

That certainly works on the solid 'bolt' but when I then introduce a hollow central section it just fills in the whole thread making it solid :(

is it something leaky in the stl - strange that they are all made the same way and that they behave differently depending on pitch.

 

[IRobertI 520]

Yeah it looks like it's the actual model. KISSlicer pukes on it pretty hard as well.

 

[jameshs 42]

 

Just ran it through netfabb and it was not a god model!

 

The fixed version slices perfectly in Cura.

 

So a mystery as to why inventor can output a watertight model in one thread type and not in another ..... but I have a workflow now so thank you for all your help.

 

James