steep thread how to create?

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

steep thread how to create?

Post by Norus » Wed Mar 25, 2020 10:16 am

a screw for medical issue has to be designed. The thread is not like a M...something.

Using the helix with sweep a thread is designed, but the angle of the shoulder has 13°, should be 22°.

Cannot find a parameter or workaround to create this thread.

Any ideas?

thank´s a lot

norus
Attachments
schraube_steigungswinkel.PNG
schraube_steigungswinkel.PNG (320.12 KiB) Viewed 247 times

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papyblaise
Posts: 1743
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Location: France

Re: steep thread how to create?

Post by papyblaise » Wed Mar 25, 2020 11:47 am

M ... is not only used for a "normal" thread but also in all cases where the principle is respected: nominal diameter of the "rod" of the screw and external thread at this diameter
If you must have a precise thread profile you must orient the "normal" profile to the helix
To find this angle: either you use your maths knowledge with sine and cosine,
either like me more laughable, you make a small right triangle one side = pi X D other side = pitch and measure the angle
Attachments
M10x1.7x22°.FCStd
(26.71 KiB) Downloaded 4 times
M10x1.7x22°.PNG
M10x1.7x22°.PNG (15.31 KiB) Viewed 228 times
Last edited by papyblaise on Wed Mar 25, 2020 11:50 am, edited 1 time in total.

kisolre
Posts: 2134
Joined: Wed Nov 21, 2018 1:13 pm

Re: steep thread how to create?

Post by kisolre » Wed Mar 25, 2020 11:49 am

Because it is a double start/lead thread: https://en.wikipedia.org/wiki/Screw_thr ... and_starts
Create a single thread with pitch = distance between 1 and 3 thread teeth and then polar patter that with 2 occurrences.

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

Re: steep thread how to create?

Post by Norus » Wed Mar 25, 2020 1:47 pm

thank you for the tips.

I have to be more exact what the target to achieve.

its not a double thread. One is Freecad, the other is a picture.

Using the helix parameters pitch 1,7 height 19 and radius 1,75 the angle becomes 13°.

question is how to reach another angle, for example 23° with the same pitch of 1,7 mm

May be what I want is wrong? but it is existing.
Attachments
Schraube_entwurf_2.PNG
Schraube_entwurf_2.PNG (603.29 KiB) Viewed 210 times
Schraube_entwurf_1.PNG
Schraube_entwurf_1.PNG (190.68 KiB) Viewed 210 times

chrisb
Posts: 24392
Joined: Tue Mar 17, 2015 9:14 am

Re: steep thread how to create?

Post by chrisb » Wed Mar 25, 2020 2:24 pm

You may calculate such values as papyblaise suggested or you use Sketcher to perform the calculations. You have it already in your screenshots. Add appropriate construction lines and measure them with a so called driven dimension (they come in blue).

kisolre
Posts: 2134
Joined: Wed Nov 21, 2018 1:13 pm

Re: steep thread how to create?

Post by kisolre » Wed Mar 25, 2020 2:31 pm

I did not say DOUBLE THREAD. I sad DOUBLE START THREAD. Dont take this as shouting. Had you read the Wikipedia article I linked in the previous post?

Here is an example. Note the red surface and how this looks as two independent threads?
.
DoubleStartThread.JPG
DoubleStartThread.JPG (90.81 KiB) Viewed 188 times
Attachments
DoubleStartThread.FCStd
(338.22 KiB) Downloaded 5 times

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Willem
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Re: steep thread how to create?

Post by Willem » Wed Mar 25, 2020 2:35 pm

Hi, the angle of 13 degrees is in my design defined in sketch001
Attachments
Med_thread.FCStd
(999.96 KiB) Downloaded 12 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 3:28 pm

Hello again,

thanks a lot for all these tips.

kisolre: this is a very interesting solution, two starts and double lead. I am not sure to use it in bones because the self-friction is smaller as in single threads.

Willem: yes, the 13° are not needed in the geometrie of the thread. The helix shoud be stronger. It has 13° and should have 23° or something else.

chrisb: I understood papyblaise, but I am not able to reach 23° in the helix like the screenshot,

maybe I am now in a tunnel and its time to have a break.

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

Re: steep thread how to create?

Post by Norus » Wed Mar 25, 2020 3:35 pm

self-retention not self-friction, sorry

kisolre
Posts: 2134
Joined: Wed Nov 21, 2018 1:13 pm

Re: steep thread how to create?

Post by kisolre » Wed Mar 25, 2020 3:49 pm

We dont know what you want to achieve in the end. I assumed you want to recreate the thread in the background image and what I proposed is one way to do so. If this is not the case please rephrase the question and give some extra info.

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