Talk:Screw axis

A merger

There is a lot of repitition between this page and helical axis. Does anbody think we should merge some of this? Davwillev (talk) 15:11, 13 May 2008 (UTC)

I support the idea of merging helical axis into screw axis. User A1 (talk) 00:57, 14 May 2008 (UTC)

I have merged the two and redirected helical axis to screw axis. Please discuss if anybody has issues with this.Davwillev (talk) 21:44, 17 June 2008 (UTC)

Revisions to this article

If it is ok, I would like to make some revisions to this article to organize the presentation. You can see some of my work on other articles at machine (mechanical), linkage (mechanical) and Burmester's theory. Thank you, Prof McCarthy (talk) 15:47, 16 June 2011 (UTC)

Rating

I think this article deserves higher ratings. Prof McCarthy (talk) 01:56, 27 November 2011 (UTC)

This article is a train wreck!

The mathematics in this article seems correct.

But the explanation of it displays a complete lack of understanding of how to communicate this mathematics, starting with the first sentence:

"The screw axis (helical axis or twist axis) of an object is a line that is simultaneously the axis of rotation and the line along which a translation occurs. "

What rotation? What translation? We are talking about a rigid motion of the object here, but no mention is made of the rigid motion or of any other kind of motion. An object does not have any special "line", so the phrase "the screw axis of a an object" makes no sense whatsoever.

Many more such examples are found throughout this article.

It badly needs to be rewritten.Daqu (talk) 00:30, 11 September 2014 (UTC)

I agree it is in need of attention. So far there have been only 129 edits and 29 contributors. Proceed with WP:BOLD, revert, discuss cycle and see if any editors are watching (less than 30 have it on their watchlist). The jumble effect comes from the variety of contributions; preserving them may require separate sections and introductory text. Use existing links as a guide to smoothing text.Rgdboer (talk) 02:31, 11 September 2014 (UTC)

I'm watching, but not prepared to edit. My observation is that 2D glide reflection is related to the 3D screw axis, that is to say a 180 degree screw,2₁, is identical to a glide reflection in a hyperplane. So my little effort would just link that in see also! Tom Ruen (talk) 11:21, 11 September 2014 (UTC)

OK, I've now added a "Geometric argument" subsection to the article. If someone more qualified than I would like to make the printing look nicer, then please by all means go ahead and do so.Daqu (talk) 03:14, 17 September 2014 (UTC)

Someone improved the appearance of the Geometric argument — thanks!.

I've now tinkered slightly with that subsection to make it a bit clearer. One frustrating thing is that the geometric argument seems so simple in my mind, yet seems to require a much longer argument than I would like, if it is to be conveyed clearly. Alas, this may just be the nature of math.Daqu (talk) 18:34, 17 September 2014 (UTC)

Finding the screw axis

Given a Euclidean motion combining a rotation and a translation, one has the challenge of finding the appropriate axis to express the motion as a screw displacement. Meeting that challenge involves viewing the Euclidean group E(3) as displaced rotations. Quaternion analysis#Homographies provides an approach. Some text, now obscured, should be restored.Rgdboer (talk) 22:45, 12 September 2014 (UTC)

I am happy to introduce quaternions, or more specifically dual quaternions, as a representation of spatial displacements in terms of the screw axis, but this is not what was previously written. What was written was an odd hybrid notation combining quaternion operations with vector addition to define a displacement with no reference to the topic of the article which is a screw axis. Prof McCarthy (talk) 06:03, 13 September 2014 (UTC)

In my opinion there is no need to introduce quaternions for this purpose. I happen to love quaternions. But I believe that since the axis of the screw displacement can be found using simple geometric reasoning, introducing quaternions for this purpose would serve only to confused people unnecessarily.

(On the other hand, after a simple geometric argument, if someone would like to add a quick proof for those familiar with quaternions, that would not hurt a bit, as long as it's not presented as the main argument.)Daqu (talk) 05:13, 16 September 2014 (UTC)

Enantimorphous?

   and the enantiomorphous 32, 43, 64, and 65.

I'm pretty confident this is referring to reflected analogs of the previous items, but this term is only used once in the page.

https://en.wikipedia.org/wiki/Enantiomorph redirects to https://en.wikipedia.org/wiki/Chirality_(mathematics), so this is a simple fix. I thought I would double check before making the change myself.

Sobeita (talk) 12:21, 26 November 2017 (UTC)

I added that link. - Patrick (talk) 12:27, 9 August 2020 (UTC)

GIF

Hi all,

Because biomechanics requires motion, I believe this article would benefit by including a GIF of a screw moving.

Brom20110101 (talk) 02:42, 18 October 2022 (UTC)

This article should be moved to Screw displacement or similar

The primary topic should be the Screw displacement, a kind of geometric transformation, not about its axis. I similarly recently merged "glide plane" into glide reflection. Does anyone object? –jacobolus (t) 20:19, 17 January 2024 (UTC)

The main article is Screw theory. Note some parts of this article are not screw theory. Since kinematics/mechanics writers have developed the topic, there are a number of related articles. — Rgdboer (talk) 02:27, 21 January 2024 (UTC)

Screw theory is a field of study, whereas "screw motion", "screw displacement", or "screw transformation" (or others?) is the geometric transformation, and "screw symmetry" or similar is the (continuous or discrete) symmetry of a figure invariant under a screw motion. The relation of the articles screw theory and screw motion should be the same as the relation between group theory and group or knot theory and knot, etc.

The "screw axis" is a particular line fixed by a 3-dimensional screw motion. This particular line is not really the subject of this article, which describes the transformation in general, and should therefore be retitled to screw motion or similar.

some parts of this article are not screw theory – can you be more explicit? –jacobolus (t) 02:40, 21 January 2024 (UTC)