Adjustable parallels - a quick question.

[RJSakowski]

The parallels are not measuring an average width but they are not measuring the narrowest width either. Consider a circular slot. The outer parallel would touch at its ends while the inner parallel would touch at the middle. The distance between the parallels would not be a measure of the width of the slot. In fact, they are not even measuring the maximum width for a key unless the key is shorter than the parallels or the parallels are longer than the slot.


On another note, I watched the video on You Tube. No one had made a comment about measuring the slot width with adjustable parallels in the first 100 or so comments. This is the danger of You Tube How To's. Many people are using them as their textbook and don't know enough to batch an error on the part of the presenter.

 

[Dabbler]

I can't see how they can measure any larger than the smallest width.

Consider a circular slot.

This is (another) case of using inexact language. She doesn't mention all the assumptions about using adjustable parallels, and the circular issue is one of many... But for many low-accuracy applications, such as a sliding block for a steam locomotive, which must necessarily have .001 - .003 clearance, *usually* the adjustable parallels way works just fine.

Most youtubers make assumptions that they are talking to novices, and so capturing all the factors in making a high-accuracy measurement aren't even considered.

On a side note, there are enough examples of this in industry also. A professional fabrication place making a simple square frame in square tubing, to 1/16 tolerance for square, and .003 for flatness, not even coming close. A professional machinist making a lapped bore , and claiming it is 'to a tenth' but actually being oversized by .001 and the part being scrapped. Some people cannot measure to the accuracy they claim to machine to. And even more don't know how to derive their measurement from an accurate source, such as gauge blocks. [end of rant]

 

[whitmore]

Thanks for replying, I was referring to one measurement over the length of the slot with both opposing faces inside the entire length. I can't see a use for an average width.

Good point; you want something to fit snugly in the slot, but still slide/come free, so average of the size would be the target
for making a slot-riding element that gets stuck half the time... you can work an adjustable parallel for the sliding feel you want.

 

[Parlo]

The parallels are not measuring an average width but they are not measuring the narrowest width either. Consider a circular slot. The outer parallel would touch at its ends while the inner parallel would touch at the middle. The distance between the parallels would not be a measure of the width of the slot. In fact, they are not even measuring the maximum width for a key unless the key is shorter than the parallels or the parallels are longer than the slot.
View attachment 458916


Thanks for replying, the circular slot is an odd possibility & probably other shapes are too. Although if the example showed the parallels extending past both ends, the measurement would be the maximum width of a parallel bar that could fit in the slot, ie. the minimum slot width.

I assumed that in general an average would be referring to "wavy" sides to the slot. This is where one side of the adjustable parallel would sit on the two highest crests and the other side touch on the highest crest on the opposite side. This is how I saw the maximum possible opening of the adjustable parallels showing the minimum width of the slot.

On another note, I watched the video on You Tube. No one had made a comment about measuring the slot width with adjustable parallels in the first 100 or so comments. This is the danger of You Tube How To's. Many people are using them as their textbook and don't know enough to batch an error on the part of the presenter.

You won't find comments that challenge the content, they are quickly removed instead of challenged. I pointed this out in the first hour along with some tips relating to thin parallels, it was deleted within an hour. So perhaps there were many others. It is a shame to deny the facts to the viewers and subscribers by deleting comments that clarify misleading information. Unfortunately there is nothing that can be done to call out errors in the comments if they are continually deleted. This happens on loads of machining channels & exposes their real motive for uploading content.

 

[Dabbler]

You won't find comments that challenge the content, they are quickly removed instead of challenged.

It is now how the youtube business works. Quinn likely doesn't have time to moderate her own youtube comments. (being full time employed, operating her own company in addition, and making videos) She probably has it farmed out to someone on the basis of a flat -fee-per-video. The going rate is about 100US$. These people are hypersensitive to negative tone and weeding out trolls and spammers advertising mail order drugs, and many other classes. To get a comment to 'stick', especially with a criticism, it has to be worded with positive imagery and phrased as a supportive comment. The youtuber that hires this out only sees the edited list of comments. So Quinn likely never saw your comment.

Joe Piecyzinski moderates his own youtube comments, as does Tom Lipton, but many channels with over 100K subscribers hire out the moderation.

 

[RJSakowski]

You won't find comments that challenge the content, they are quickly removed instead of challenged. I pointed this out in the first hour along with some tips relating to thin parallels, it was deleted within an hour. So perhaps there were many others. It is a shame to deny the facts to the viewers and subscribers by deleting comments that clarify misleading information. Unfortunately there is nothing that can be done to call out errors in the comments if they are continually deleted. This happens on loads of machining channels & exposes their real motive for uploading content.

That explains a lot. I recently commented on a You Tube site and when I refreshed the page, my comment was gone. If true, that is a dangerous situation. Comments are a way of peer review, a proven process that is used by the scientific community for "sifting and winnowing".

When I see some misinformation on a You Tube video about something that I happen to know about, I have to assume that there is potential misinformation about subject that I have no experience with and therefore, I can't trust that presenter. This includes some of the popular presenters on subjects pertaining to machining.

 

[higgite]

So, there is no way to tell who is being called out for misinformation and who isn’t. Not very reassuring. I think I’ll stick with the known pros like Joe Pie and Oxtool for Youtube machining tips and practices. ymmv

Tom

 

[jbaccell]

I have picked up quite a few useful tips from this guy, he seems to know his stuff:

https://www.youtube.com/@deedeeindustrialsuperprecision

 

[RJSakowski]

The old mantra "trust but verify" applies. I have made correcting comments of both Tom Lipton's and Joe Pieczynski's sites and have received acknowledging replies. I would include in the pro list, Kieth Fenner. Some call him out for safety concerns or his sometimes unorthodox methods but generally his info is good and he always "gets 'er done". OTOH, I have seen too many bits of misinformation from some of the more popular presenters to trust them explicitly.

 

[Parlo]

That explains a lot. I recently commented on a You Tube site and when I refreshed the page, my comment was gone. If true, that is a dangerous situation. Comments are a way of peer review, a proven process that is used by the scientific community for "sifting and winnowing".

When I see some misinformation on a You Tube video about something that I happen to know about, I have to assume that there is potential misinformation about subject that I have no experience with and therefore, I can't trust that presenter. This includes some of the popular presenters on subjects pertaining to machining.

I called out & debunked loads off stuff from a big name machinist, often quoted on here. Comments relating to improvements of his often very protracted methods or misinformation are aways deleted.