steep thread how to create?

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chrisb
Posts: 24369
Joined: Tue Mar 17, 2015 9:14 am

Re: steep thread how to create?

Post by chrisb » Wed Mar 25, 2020 5:09 pm

Steps for xx degree helixes:
- Sketch an equilateral triangle with a horizontal line in the middle,
- use symmetry to place the origin in the middle of the horizontal line, and the right end in the middle of the vertical line
- set the angle to xxx
- set the height to your specified 1.7, this is how it looks like:
Snip macro screenshot-dbbca2.png
Snip macro screenshot-dbbca2.png (5.93 KiB) Viewed 134 times
- switch to dimension referencing mode with Image
- select the right point and add a horizontal distance constraint, this is how it looks like. What you see in blue is the radius:
Snip macro screenshot-1ba435.png
Snip macro screenshot-1ba435.png (8.02 KiB) Viewed 134 times

Norus
Posts: 91
Joined: Tue Oct 13, 2015 9:33 am

Re: steep thread how to create?

Post by Norus » Wed Mar 25, 2020 6:19 pm

Ok, I think I understood, but the next step is to create the helix.

sorry I am blind, have no idea

Norus
Posts: 91
Joined: Tue Oct 13, 2015 9:33 am

Re: steep thread how to create?

Post by Norus » Wed Mar 25, 2020 7:03 pm

thats what I want, its very strange, indeed
Attachments
Schraube_entwurf_4.PNG
Schraube_entwurf_4.PNG (8.61 KiB) Viewed 118 times
Schraube_entwurf_3.PNG
Schraube_entwurf_3.PNG (529.47 KiB) Viewed 118 times

kisolre
Posts: 2131
Joined: Wed Nov 21, 2018 1:13 pm

Re: steep thread how to create?

Post by kisolre » Wed Mar 25, 2020 9:20 pm

Norus wrote:
Wed Mar 25, 2020 7:03 pm
thats what I want, its very strange, indeed
I repeat my question again - do you want to recreate the thread in your screenshot? If YES you should understand that this are two distinct thread profiles and model them as such. If NO please describe some more of what you want to achieve.

Norus
Posts: 91
Joined: Tue Oct 13, 2015 9:33 am

Re: steep thread how to create?

Post by Norus » Thu Mar 26, 2020 9:30 am

Thank you kisolre for your patience.

Yes I want to achieve the thread of the picture. pitch 1,5 - 1,7 is ok. I am wondering that the angle is 23° in the picture and 13° in freecad. If the pitch is fixed the angle should be too. It´s crazy.

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papyblaise
Posts: 1738
Joined: Thu Jun 13, 2019 4:28 pm
Location: France

Re: steep thread how to create?

Post by papyblaise » Thu Mar 26, 2020 9:47 am

Obviously you know nothing about mechanics, this angle is only an apparent angle, which does not correspond to reality
if I take an example:
you want to know the slope of a mountain road, you measure the angle between the foot and the summit on a photo, without taking into account the zig-zag of the road
you do not take into account either that it is a screw with 2 threads

kisolre
Posts: 2131
Joined: Wed Nov 21, 2018 1:13 pm

Re: steep thread how to create?

Post by kisolre » Thu Mar 26, 2020 9:49 am

And as I already explained this is not a single start thread but a double start one. So there should be two threads with pitch around 3.4 (2x1.7) turned 180deg from one another - the polar pattern in the file I attached. Please read that wikipedia article about the threads to see what a multiple start thread is. Here is a Tripple Start Thread with the same file - see how the thread is every third tooth:
.
Attachments
TrippleStartThread.JPG
TrippleStartThread.JPG (62.03 KiB) Viewed 92 times

alberich
Posts: 54
Joined: Thu Aug 17, 2017 2:09 pm
Location: Texas

Re: steep thread how to create?

Post by alberich » Thu Mar 26, 2020 10:31 am

Perhaps a better way to see that your photo has a double-start thread. Here's your image again with the green lines added. They show the completion of the thread's turn behind the screw.



Notice that in the photo image to the right the green line skips over a thread to complete the helix. That's the second thread of the double start.
Attachments
bone-screw_2.PNG
bone-screw_2.PNG (320.56 KiB) Viewed 85 times

Norus
Posts: 91
Joined: Tue Oct 13, 2015 9:33 am

Re: steep thread how to create?

Post by Norus » Fri Mar 27, 2020 8:55 am

Hello alberich,
thanks a lot, you brought the light into my tunnel, I was totaly blocked.
Kisolre showed me the right way, but I didn´t check the math behind, only handling the pitch of 1.7.

Kisolre: sorry for that and thank you a lot.

Great guys, great forum, keep well

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