FreeCAD threads: Five Ways to Fail, With Workarounds
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- เผยแพร่เมื่อ 15 มิ.ย. 2024
- In this video I show five ways I've failed while making threads in FreeCAD 0.19, and how I've worked around those problems. TL;DR - you can watch the under-7-minute version that just tells you what do: • How to Make Threads in... "How to Make Threads in FreeCAD 0.19 (the quick version)"
I've learned the hard way how to make threads in FreeCAD, from various projects I've designed and 3D printed. Some techniques in this video apply to any CAD application, but others are workarounds for FreeCAD's specific quirks and bugs.
I started from the FreeCAD tutorial text, wiki.freecadweb.org/Thread_fo.... Its "Method 3. Sweeping a vertical profile" is a good start, but I found it wasn't obvious how to avoid some of the issues it describes.
Index of this video:
00:00 Introduction: I'm using FreeCAD 0.19 pre from February 14, 2021.
00:39 Starting to make a thread.
07:09 Problem: the Helix isn't part of the Body I want to edit. Solution: Use a Shape Binder.
08:37 Problem: Sweep failed. Solution: Make the thread profile overlap with the cylinder wall.
10:23 Problem: Sweep failed. Solution: Make the thread profile shorter than the pitch, to avoid making a self-intersecting thread.
12:21 Problem: Sweep fails after Refine Shape. Solution: rotate the thread profile and helix to avoid the cylinder's seam.
15:38 Problem: Sweep still fails after Refine Shape. Solution: Reduce Helix height to cross the cylinder's seam only once.
18:21 Problem: Multiple turn threads fail. Solution: Make a one-turn thread and use a Linear Pattern Feature to duplicate it.
20:57 Problem: The Linear pattern fails after Refine Shape. Solution: Make a slightly-less than one turn thread to avoid a self-intersecting linear pattern.
23:42 Problem: A large-scale thread could fail to print. Solution: Make the thread's angles 45° or less from vertical.
25:49 Problem: I don't like the sharp edge of the thread. Solution: Make the thread profile a trapezoid.
28:25 The 3D printed result. Yay! - แนวปฏิบัติและการใช้ชีวิต
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It's the kind of content that FreeCAD users need. I run into wonky stuff like that all the time, but it's not always that I can figure out on my own.
Thanks a lot!
Thank you a ton. The "move the profile away from the cylinder seam" saved me. Wanted to do a quick model on the weekend for fun and was super frustrated, you saved my Sunday!
Thanks for an excellent tutorial! As a newcomer to FreeCAD, I get frustrated when I run into problems like this, because I think I'm doing something wrong.
It's a relief to realize that even experienced users have to work around weird issues.
Thank yoy so much for this! The information that you presented was the most complete that I found anywhere. It got me past the issues that i was having doing an subtractive helix to make a thread. I was making a lot of the mistakes that you pointed out. Too few others do that. They have success and assume that you will to. This would be true if they told you EVERYTHING that they did but most leave out details which are not as trivial as they suppose them to be. My mantra is "nobody can be assumed to know what 'everybody knows'". Beginners will not.
Great information! Being new to 3D drawing with FreeCAD, when issues arise I don't know what to do. I got the strange situation when hovering over the cylinder and the one where it didn't draw the entire thing correctly. Big help. Took notes on this in case it comes up and I won't be wondering where I saw this.
Sorry for the late comment as I just found your channel. What I think you ended up with is an “acme” thread which is very strong yet forgiving as to close tolerances. In the oil field this was also referred to as “hammer lock” thread. A once common coupling that utilized this type of thread could be tightened by hand , then “hammered” tight using ears that protruded on the sides of the coupling.
Great videos. Thanks for sharing.
thank you!
The Fasteners Workbench makes good threads. I have used it to make nuts and bolts and have created an internal thread in a block.
Good catch, pieter cloete, on the accessibility issue with the small mouse cursor size. I'll be sure to make the cursor much larger on my future videos - thanks!
Thank you
Running version 19, Release date 2021/12/04, and it appears this bug is fixed. After the initial ShapeBinder creation, FreeCAD was able to refine the shape without issues. Appreciate the tutorial!
Sadly, at least on my Dell laptop running FreeCAD 0.19.4 Release Date 2022/02/28, when I walked through the video, step by step, all the errors still happened. The one difference I saw was that at 21:23 the Refined Shape looks deceptively ok, but when I ran a Check Geometry on that refined part, FreeCAD showed several errors. Thanks for taking the time and trouble to test a newer FreeCAD than I used in the video, and I'm glad it seems to behave for you. Thanks again.
@@BradfordNeedham Thanks for the video. Do these bugs still happen in the newly released 0.20 version?
@@lxc3909 Good question. I'll. try it out when I get a chance.
@@lxc3909 Yes, I get the same errors in FreeCAD 0.20.1 on my Dell laptop running Windows 10.
thanks for great video - would be great if you could so a follow-up which specifically looked at how to read off BSP type threads from specs and draw them in freeCAD for bolts and nuts. Specifically BSPT (Tapered) and BSPP (Parallel), thought i'd ask as it would useful for many others as well I feel ;-)
Wow! That is so far beyond what I currently know. I only recently learned that the various thread standards exist, and when/where they came into use. Perhaps someone who reads this comment can pick up the ball from here.
Thanks for making this! Any tips for how to add a chamfer to the end of a threaded rod? I have so far been unsuccessful using a groove feature and using a Boolean cut of a revolution feature.
Good question - I haven't tried it myself.
I really like your video, although I have one small complaint. I don't like all the "how to fail" parts mixed in. I would rather like to see a simple straightforward "how to succeed" video, with the "how to fail" parts at the end or in a follow up video. In any case, thank you very much for your time and efforts.
To answer that very complaint I created "How to Make Threads in FreeCAD 0.19 (the quick version)": th-cam.com/video/wsfLP7pLsSg/w-d-xo.html It's under 7 minutes long and covers only the How To, without all the side-tracks.
Nobody learns anything from getting things right, you learn from mistakes. Being shown one right way means that's all you know. Figuring out FreeCAD is about learning what its quirks are and how to avoid them. (Most quirks are not FreeCAD's fault, it's the representation of 3D space it has to use.)
@@alucostrix Good observation: that knowing FreeCAD's quirks lets you avoid mistakes in other models. ...though I do wish its threads had fewer quirks :-)
@@BradfordNeedham As an engineer, it was very difficult to get my head around why it fails when (geometrically) you're not asking for anything unreasonable - such as when surfaces are just touching (as per your helix around the cylinder). I think this boils down to the inevitable limits on the precision of calculation: rounding errors only have to place the helix outside the cylinder by one least-significant-bit and so far as the modelling is concerned there is an unacceptable void. Your video has been very useful in "remodelling" my understanding of this!
Another example is fillets. When intersecting fillets have close to the same radius, the dividing line between the individual surfaces becomes more and more contorted due to (I believe) insufficient precision of calculation (or perhaps precision in the position of the control points), until the contortion becomes extreme and the model fails (when, geometrically, there shouldn't be a problem).
I do not believe there is a solution to these quirks, I believe they are a consequence of quantisation - ie the digital representation of continuous space. Solution would involve representing space in a non-quantised fashion in the first place, ie as equations and not numerically, but that would mean inputting your primitives as equations too!
fantastic tutorial, could you do one for inner threads as well? I'm having a lot of trouble when I go to use boolean subtract. I worked around it by adding the "thread inverse" to the inside instead, but I'm still curious to see you show to do it properly. too bad the wiki does have a page on inside threads like the "Thread for Screw Tutorial" page .... or maybe it is not possible because of the join algorithm helix problem?
Just like you, I have created inner threads by adding a "thread inverse" to the inside. I think of it as a thread on a cylinder and a matching thread on a round hole. That is, as two threads that match, rather than as a thread and a cutout that matches the thread.
@@BradfordNeedham ah glad I'm not the only one! kinda annoying that something this basic needs a work-around, but oh well
I see one chap uses the lowest selection on the Helix Primitive and selects Frenet and also selects multisection to create sweeps. Why multi section ?
OK I think I see why.
Refine Shape is irrelevant, the model can still be exported and printed regardless.
I've found sometimes if I don't do a Refine Shape the exported model is corrupted. It hasn't happened in a while, so it could have been a bug that's been fixed.
So basically no good and robust solution
It does look grim when I lay it out like this. I've put up a short video, "How to Make Threads in FreeCAD 0.19 (the quick version)", th-cam.com/video/wsfLP7pLsSg/w-d-xo.html, that makes it much more palatable.
The only two problems that get in my way are 1) a multi-turn thread will likely fail, and 2) a thread that starts on the cylinder's seam will likely fail.
Everything else is just good design practice: having the thread overlap with the cylinder's outside edge, avoiding a self-intersecting thread, and make angled surfaces less than 45 degrees off vertical so they 3D print properly. Because multi-turn threads worked in earlier versions of FreeCAD, I expect that problem is a bug that will be addressed once it gets enough attention / love.
I understand FreeCAD is not easy, ... and threads are a complex topic... but this video did NOT help me ONE BIT. All i heard was a seasoned, well-versed CAD guy going yaddy yaddy yaddah... nope... I'll say it... slow the F down if you wanna have FreeCAD teaching videos ESPECIALLY when it comes to 3D printing threads... I really do NOT want to use "TinkerCAD"... well.. for "reasons".. FreeCAD rocks... it is just HARD finding good "teachers" of this amazing piece of software.. this channel? Nope... not my preferred form of teacher vs. student when it comes to "Comprehension/retention"... and nope.. I'm not stupid...just not my style of teacher. That's all.
You might prefer the short version i did, explaining only how to successfully do threads. This video, in contrast, goes into probably too much yadda yadda on how threads can go wrong. Thanks for the feedback, and best of luck