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Any idiots guides to modelling threads?

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Posted · Any idiots guides to modelling threads?

Instead of my previous reply, now to really answer your question. :)

I think you are facing two problems:

1) First you need to design your thread within the tolerances according to the ISO-standards. On this site, you can find a "metric thread size and tolerance calculator":

http://www.amesweb.info/Screws/IsoMetricScrewThread.aspx

Here you can select the desired thread (e.g. M4), and the site calculates all tolerances such as min and max diameters, etc.

Or Google for: tolerances in metric thread design

This subject seems to be quite complex, way too complex for me anyway. :) And to further complicate things, there appear to be several tolerance classes: loose fit, standard fit, tight fit,...

2) And then you need to 3D-print it, so that it falls within these standards. This is going to be even more difficult, I guess, since accuracy will vary with your printer model and state, nozzle size, printing speed, printing temp, bed temp, cooling, material flow, the type and brand of filament, and whatever else...

Also, since the filament is going to "cut corners" when extruded around bends, both inner and outer threads will be too small. (Even a plain 3mm hole often ends up as a 2mm hole in my prints.) So this is going to affect fit also. Maybe this might be the biggest problem.

So I think it is going to be "trial and error". But if you change any of the printing parameters afterwards, or you let it print by someone else, it is not going to fit anymore. Small metric threads will probably require rework with thread cutting tools anyway. So if you need standard metric threads, I would recommend using the calculations above and design it accordingly to these standards. Print it and then finish it with a thread cutting tool. Otherwise you have to change your design for every possible printing circumstance.

Maybe big and really forgiving custom threads with plenty of play, such as those on big plastic bottles, might work.

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Posted · Any idiots guides to modelling threads?

This is a great thread but keep in mind that the original question was posted about a year ago.

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Posted · Any idiots guides to modelling threads?

This is a great thread but keep in mind that the original question was posted about a year ago.

 

HA! You are right! I totally did not even notice that. :) Jan 2016, then nothing, then Dec 2016.

(The sad part is I was wondering why Robert had not responded to all the messages we've been posting.) :D

D'oh!

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Posted · Any idiots guides to modelling threads?

HA!  You are right!  I totally did not even notice that.  :)  Jan 2016, then nothing, then Dec 2016.

(The sad part is I was wondering why Robert had not responded to all the messages we've been posting.) :D

D'oh!

 

I actually read through it today thinking "wait, didn't I post this a looong time ago?" :p

I barely even remember why I started the thread in the first place. I believe I was working on a different nozzle-holder and wanted to make threads that actually matched properly. I had made threads that worked, but I wanted to do it correctly by actually following the standards for how a thread should be cut. That's when I fell down the rabbit hole of standards...

Like I mentioned in the first post I've made "fake" threads before where you just sweep a profile around a helix. Sometimes a simple 45 degree one, sometimes ones with flats etc (my spool holder uses a "fake" thread where only the screw part is modelled, the nut part is formed by just indenting the thread into it. But when I posted my rant I wanted to learn how to make threads that followed the proper standard just to make things the right way, and because I wanted to learn.

But hey, keep the thread going in whatever direction you guys feel, as long as it stays useful I'm happy :)

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Posted · Any idiots guides to modelling threads?

This is a great thread but keep in mind that the original question was posted about a year ago.

 

I hadn't noticed the date either, haha. It appears in addition to being completely banner-blind, I am now getting "date-blind" too. :)

I guess this revival of old threads is a side effect of entering forums via Google.

Anyway, it may benefit others. Or even myself in a year or so, after I have long forgotten all my own good design rules... :)

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Posted · Any idiots guides to modelling threads?

But hey, keep the thread going in whatever direction you guys feel, as long as it stays useful I'm happy :)

 

Surely a thread about threads cannot go in so many directions? Sorry, now I'm screwed and you all think I am nuts. Yeah, I read through this thread hoping for some puns! ;)

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Posted · Any idiots guides to modelling threads?

One thing that was really helpful for me when learning about how to make threads, was downloading the solidworks files of different bolts from McMaster Carr. Their website has almost every part cadded up in solidworks and you can look at the steps they take to make each part.

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Posted · Any idiots guides to modelling threads?

One thing that was really helpful for me when learning about how to make threads, was downloading the solidworks files of different bolts from McMaster Carr. Their website has almost every part cadded up in solidworks and you can look at the steps they take to make each part.

 

great tip! thanks

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Posted · Any idiots guides to modelling threads?

I've worked as an CNC operator for 13 years, and when you do threads for a living I know for many types of threads you need to buy the books (afaik).

The metric and imperial ones you can find many pdf's online to get the tolerances correct (for metal threads) and they are difficult to read and understand.

Basic principle for threads are to subtract/add the given tolerance off the thread dimention.

So an M3 thread the bolt is allowed to be between 2,980 - 2,874mm

The bottom of the thread is allowed to be between 2,367 - 2,256mm

To get the thread approved according to the standard you need to measure the flank

with a ISO calibrated gauge. The flank is measured between the top of the thread to the bottom of the thread, an M3 bolt is allowed to be between 2,655 - 2,580mm on the flank.  

Then you have the M3 nut, with its own values to get tolerances correct.

There are Coarse and Fine variants of the same thread, UN threads have 2A,3A

spesific tolerances of the same thread, then you have TPI and pitch.

The Nut needs to have a chamfered edge around the same height as the pitch to easy entry for the bolt,  bolt needs a chamfered edge too, some or most do 45° chamfer because its faster do, but it should be same angle as the thread profile (60° for metric,55° for BSP)

Threads is a mess and pain in the ass to do :)

I ended up with writing my own plugins for work. I listed all the thread tolerances in a excel sheet and the plugin got the thread data from there, so in my CAM program (Gibbscam) the plugin generated the 3D model and toolpath data.

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Posted · Any idiots guides to modelling threads?

 

One thing that was really helpful for me when learning about how to make threads, was downloading the solidworks files of different bolts from McMaster Carr. Their website has almost every part cadded up in solidworks and you can look at the steps they take to make each part.

 

great tip! thanks

 

These components are also integrated in Fusion 360 which has quite a good tool for modelling threads

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Posted (edited) · Any idiots guides to modelling threads?

A way that i have used many times to get accurate threads on printed parts is tap and die tools. Instead of modeling a thread you model a simple cylinder or circular hole. You just need to use the recommended outter diameter for each metric. Then chose at least 4 to 6 perimeter layers or print parts with at least 80 percent infill. Once you have the part printed, It takes a couple of minutes to carve perfect threads using these tools. I recommend to use some oil drops when using the tools, to prevent plastic burning and breaking.

Edited by Guest

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Posted · Any idiots guides to modelling threads?

SolidWorks 2016 and later has a Thread Feature built in.  You'll find it in Insert>Features>Thread.

Very simple and straight forward.

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Posted · Any idiots guides to modelling threads?

One thing that was really helpful for me when learning about how to make threads, was downloading the solidworks files of different bolts from McMaster Carr. Their website has almost every part cadded up in solidworks and you can look at the steps they take to make each part.

 

Thanks for that, the Soldiworks part files are a godsend! Mine is 2015 so no inbuilt threads function.

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Posted (edited) · Any idiots guides to modelling threads?

Solidworks has a library of just about every thread there is but you have to pay for it; maybe if you have the top level of software it might come free?

http://www.3dprintmanual.com/best-3d-modeling-software/

Not sure how you create yours but e.g. for a threaded bolt we create a helix of appropriate dimensions, which is a pathway and then extrude a triangle along that pathway...

Edited by SandervG

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