Introduction to the ThreadProfile WB

[DanielLeeWenger]

A 3d printed project needed a 3/8" -16 rod to tie together several pieces. I decided to try to print the rod using the ThreadProfile WB. This WB can be downloaded via the Tools/Addon manager in FreeCAD. Here I am using a version of 0.19 of FreeCAD.

The WB allows for the generation of external and internal threads. I chose to use only the external mode and to create any internal thread by subtracting an external thread from the object that needed the internal thread.

NOTE: The author of the ThreadProfile WB, TheMarkster, in a post below, discusses the differences in the profiles of external and internal threads when using together the external and internal modes of the WB. In this post I do not use the internal mode. The 3d printed results that I obtain have yet to be compared to those using the combined external and internal modes.

The ThreadProfile WB allows generation of a threaded part in either a Part Design WB Body or a Part WB Part. The steps in each case are given below. NOTE: These steps need to be expanded if internal treads are to be created directly.

In the Part Design WB create a Body or in the Part WB create a Part.

Switch to the ThreadProfile WB.

Select Create V profile thread from the ThreadProfile menu (another type profile is also offered).

In the Property window select Presets and select the desired thread type. There are many metric styles to choose from and at the end of the long menu there are the non-metric styles.

Specify the number of threads via the Thread Count field. Here, unless you know the number of threads, you need to calculate the number by knowing the length of the rod desired and the Pitch of the thread that you have chosen. Number = Length/Pitch.

Select the ThreadProfile from the Model View and then select Make Helix from the ThreadProfile menu. A Helix and a ShapeBinder is produced in the case of a Body. A Helix is produced in the case of a Part.

In the case of a Body, select the ThreadProfile and then the ShapeBinder from the Model View, in that order, using the Command key (on the Mac). Then select Do Sweep from the ThreadProfile menu.

In the case of a Part, select the ThreadProfile and then the Helix from the Model View, in that order, using the Command key (on the Mac). Then select Do Sweep from the ThreadProfile menu.

Enjoy the result.


Internal threads

After creating a 3/8” rod using the above steps I wanted to explore internal threads. ThreadProfile WB does have a mode for internal threads but I chose to simply create the external thread and then to subtract it from an object to achieve the internal thread.

The issue is how much clearance to use between the internal and external threads.

Beginning with a Minor Diameter for the 3/8” rod of 7.57682mm as suggested by the ThreadProfile WB and after a number of trial samples, arrived with a range of Minor Diameters for the internal thread rod.

The photo below shows the range of values, from 8.9mm for a very sloppy fit to 8.1mm for a snug fit on a test 3/8” SS rod. For a snug fit on the printed rod I found 8.0mm Minor Diameter was best.

This suggests about a 6.9% increase in Minor Diameter for an internal thread over the external thread

Summary

The above menu commands may be initiated via icons instead of via the menus.

A tutorial video exists made by the author of the WB, Mark Gunder, @TheMarkster. See

https://www.youtube.com/watch?v=k9iD-rkfap0

The author’s information page is at

https://github.com/mwganson/ThreadProfile


Hope this helps newcomers to come to appreciate this wonderful addition to FreeCAD.


I used Version 1.63 of ThreadProfile WB. There are updates to this version.

OS: macOS Mojave (10.14)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.22316 (Git)
Build type: Release
Branch: master
Hash: 9beeb53a98a5f350ff185bfe0e339f38faa70512
Python version: 3.8.5
Qt version: 5.12.5
Coin version: 4.0.0
OCC version: 7.4.0
Locale: C/Default (C)

[chrisb]

Good docs, thanks;
What diamter have the threads in the image? What printer did you use?

[DanielLeeWenger]

The threads in the photo above are 3/8" diameter, 16 threads per inch. ThreadProfile WB for this standard size gives a Minor Diameter of 7.57682 mm, Pitch 1.58750 mm in the preset menu. The nuts in the photo have Minor Diameters ranging from 8.9-8.1 mm Minor Diameters. Same pitch. This corresponds to about a 6.9% difference in Minor Diameter between Internal and external threads.

The FreeCAD objects were exported as stl files, sliced with PrusaSlicer and printed on the Prusa MK3 S printer.

The prints were made at .1mm layer, 20% fill with PETG filament and with 4 perimeter walls.

[chrisb]

Thanks for the info. The threads look pretty good!

[Kunda1]

pinged by pinger macro

[chrisb]

pinged by pinger macro

Any questions going with the ping?

[TheMarkster]

Thanks for the tutorial.

When making an external thread, such as the threaded rod, there is no need for the initial sketch. Only for making an internal thread, such as a hexagon nut, would you need to first have some sort of extruded hexagon from which to cut the threaded rod created for making the internal threads.

There are some differences between the external and internal threads. In particular, 1) the form is slightly different, and 2) the diameter is slightly smaller for external threads. The specification calls for the major diameter of the internal thread to be the nominal diameter. For example, a 1/2" nut should have a major diameter of 1/2". The external thread major diameter will be slightly smaller to allow for clearance. One can adjust the fit by increasing or decreasing the minor diameter property. In retrospect I should probably have included an offset property for this purpose. The presets are from Machinery's handbook, but they are mostly just starting points. Taking a cross section using Part workbench tool for that purpose can be useful for examining the fit onscreen prior to printing, but a small test print is probably the way to go to check the fit through trial and error. See the bottom image for an example of a cross section for this purpose. In that image I made a temporary compound of the 2 sweeps and created the cross section from the compound.

Snip macro screenshot-877feb.png (170.56 KiB) Viewed 4885 times

In the above image the thread on the left is the external thread while the one on the right is the internal. Notice how the crests are rounded on one while the troughs are rounded on the other. Note also how in the image below (with the 2 objects now in the same placement) the external thread (gold/yellow highlight color) has a slightly smaller diameter to provide for clearance.

Snip macro screenshot-4e8ed7.png (101.09 KiB) Viewed 4885 times

Notice that both internal and external thread objects get swept into threaded rods. Making an internal thread requires the additional step of cutting the rod from the nut.

But in Part Design a subtractive sweep is used when making the internal threads, so the additional cut is not necessary.

Snip macro screenshot-d1a11e.png (117.56 KiB) Viewed 4885 times

[DanielLeeWenger]

Thank you TheMarkster for your comment that allowed me to simplify my original tutorial. I hope at some point to compare the results of using the internal mode and of using only the external mode as I do in the tutorial.

Addendum: After execution of the instructions given in the first post of this series, but also selecting the Internal Mode in the Properties Menu of the ThreadProfile, I printed several nuts. I found that the nuts behaved the same as the first batch of nuts if the Minor Diameter was increased by 0.1mm. Conclusion is that for the purposes of 3d printing with filaments that there is no observable difference in using an External Mode rod and an Internal Mode rod while making an internal threaded nut.

[Petrus]

Hi

Thank you for the info. i got most working. The one tread that I struggle with is a 10/32. not sure if it is to small for printing.

If you can help it will be appreciated.

Thanks

[chrisb]

10/32 should be possible. We have seen here threads down to 5mm. The question remains if it is sensible to print threads instead of using proper inserts.