Bare or Full

I'd think that 10% is too much, I'd go for "just detectable with a good ruler", or about 0.010" which agrees generally with your latter figure. But it also depends on the nominal dimension so perhaps a bit less on a dimension as small as 3/16".

This may not be the right answer … but it works for me

Consider ‘spot-on’ as the mid-point between ‘bare’ and ‘full’

If you are making a shaft and a hole:

• If both items are spot-on they won’t slide together

The bare and full options give the choice of :

• no chance of getting that in there
• a nice bearing-fit
• rattling loose

The relevant numbers, of course, depend upon the sizes involved and your own sensitivities.

MichaelG.

I'd ignore it; it's a hang over from the days when most people didn't have access to micrometers but relied on plain calipers and rules. Just make it to size, or maybe a thou or two smaller if the part needs to fit in a hole.

Andrew

In 40 years of working in a mechanical design, I have never heard of the term Bare and Full.

The only reference I found was a post in ME in 2016 which said :"the terms "Bare" and "Full' are used meaning minus a bit and plus a bit, leaving the fit to the builder.". A very poor way of specifying a dimension on a drawing. A much better way is to specify the allowable tolerance from the required size.

Edited By Paul Lousick on 14/10/2022 12:03:44

Thank you for the answers. I am not refering to a bore size rather the length of a shaft which requires the fitting bearing to freely rotate IE: if a rod need to be held on by a nut yet is able to freely rotate which means the measurement is classed on the plans as full, however if the component needs to be a tight fit then it refers to this as being a bare fit.

Clive the 10% was just a figure I plucked out of thin air and only used as an example.

I must say that a tolerance would have been a better way to have put this on the plans or an over sized measurement to suit the application

Edited By Derek Lane on 14/10/2022 12:13:56

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Exactly the same principle applies, Derek … I just used diameter as a way of demonstrating the concept.

MichaelG.

Yes really you just want the length to be enough so that when the nut is done up you just want enough clearance so the part on the shaft is not pinched so 1% or 1-2 thou would be about right. You do need to take the two mating parts into account to give the "fit" some context be it a shoulder as you have now mentioned or a shaft in a hole as you would want the shaft full for a press fit or the hole bare.

Although not mentioned in recent mechanical design any old ME article, books or plans are likely to have it and as Andrew hinted it goes back to a time when most hobby workshops would have had a steel rule, home made scribing block and a pair of firm leg callipers so little point is specifying 0.1885" when there was no way to measure that exactly.

As Jason says. The difference is basically the smallest change that you can see / feel. With good, well practiced feel changes of the order of 1 thou (or even less) can be detected using reasonably small calipers. The big ones 12" or so are so heavy that the weight destroys feel.

It is said that highly skilled craftsmen can reliably maintain bore to rod clearances of the order of a thou using an inside / outside pair of calipers. The scatter in actual dimensions will generally be rather larger so you don't get true, close tolerance interchangeability.

I don't have any great trouble feeling a thou or so difference with ordinary calipers. But forget doing anything with it without bringing a micrometer into play.

Clive

The terms are well known in carpentry and joinery, the difference from nominal normally being taken as 1/64".

Edited By ega on 14/10/2022 14:00:39

When I first started work in a mechanical design department the section leader, who had worked in the office since the early 1920's, quite often referred to "full or bare" dimensions when discussing a design. It was then left up to you to decide what that tolerance would be. As has been said, it harks back to the early days of manufacturing when precision measuring instruments were not always available.

For me it depends on what you are working on. In woodwork I would take it to be either one side or the other of the pencil line, depending on how blunt your pencil was. In metal work I would be be thinking more along the thickness of the engraved line on a good rule, certainly less than 1/64".

I have only really seen it used for linear dimensions, I don't think I have ever seen it used for diameters, which are usually described as "machine to a good fit", what ever that might be?

If you find it on a drawing, it is a case of looking to see how the relevant parts interact with each other and then deciding on your course of action. Model design drawings are not "tablets of stone". Unlike industrial design drawings, which require good reason and lots of paperwork to modify or change, our model designs can be modified to suit your particular requirements or machining limitations, provided that you understand how the design actually works.

I find that the use of some of these old-fashioned terms can be quite enlightening and sometimes amusing in these days of following a design rigidly to the letter. I like seeing them on old drawings, but that's just me.

Neil

I learned all my woodworking skills from my father and we used to say "line in" or "line out" to trim to the inside or the outside of the pencil line.

William.

A somewhat similar question raised four pages of replies: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=122024&p=1

Some of which might be of interest.

MichaelG.

I've never come across them either. The terms don't seem to me much use, as the actual value of the dimension would depend on the corresponding dimension of the mating part, which would complicate detailing considerably if there are multiple instances on a GA and it isn't instantly obvious which is supposed to be fitting what.

The Tool Design office I used to work in was in process of transition from Imperial to Metric standards - as indeed was the product - and in the Imperial case I *tended* to use the spectrum of fits from 'Loose Running' to 'Heavy Drive' with the mating Detail No. specified; whilst in Metric it would *usually* be ISO Hole Basis fits.

*My memory might be imperfect and I can't swear to've been totally consistent

It could get quite complicated sometimes when the component to be produced had Geometric Tolerances specified in Baroque detail. And I have to admit that I don't think I've seen any such since.

I've never heard of it in my 40 years of mechanical design office work either, but we once saw a drawing from an outside firm that described the fit of a pin in a hole as a 'cheesy fit' which caused a bit of amusement.

I have just been a-googling for a couple of minutes, and found this

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The reference on Page 427 is particularly interesting [Mr Greenly, no less]

… does anyone have that 1904 issue to hand ?

MichaelG.

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Edit: __ the image quality is Google’ problem, not mine !

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Edited By Michael Gilligan on 14/10/2022 15:50:31

I think that well-known ME workshop character "Inspector Meticulous" would fully understand these terms.

Inspector Meticulous would probably have something of the barrister as well as engineer in him when examining that paragraph.

My view is best avoid these terms.

Examine what the parts actually do, and work as closely as you can to achieve that. If a matter of fits in holes, where critical, we would not go far wrong by applying trade practice as outlined in, say, the Zeus Book.

We are after all, making either workshop tooling that has to be right to give correct results; or replicating old industrial products. So although most of us probably don't have Rolls-Royce Aerospace machine-tools and metrology standards in our sheds, I regard the arbiter as, "What would the trade do, and how closely can I match that?"

Hi MichaelG, as it happens, I have a few issues of vol. 11 1904 and amongst those few I have found page 427, a scan of which is below, but some of the blue from the covers have bleed into the pages, undoubtable they were stored in a damp place at some time to me acquiring them, but it can be read without too much difficulty.

Regards Nick.

Excellent … Thank you, Nick

MichaelG.

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Edit: __ Now, of course, I’m desperate to know what Oakham Splice wrote

… and, presumably, what Mr Greenly wrote before that.

Edited By Michael Gilligan on 14/10/2022 18:31:22