Tolerance...

Best response I've seen yet!

Maybe this link will help:

http://www.mitcalc.com/

or go directly to:

http://www.mitcalc.com/doc/tolerances/help/en/tolerancestxt.htm

The correct way to specify this by calling out the fit that you want weather it be a transition fit, clearance fit, or press fit. But the best and most accurate way is by calling out the sketch or drawing with a tolerance, in 3 places.

ie.. hole dia=.500" +.001/-.000 shaft dia= .499" +.000/-.001 this way there is no confusion by the machinest of what you are looking for. The best place to find more information on this is in the "Machinery's Handbook"

In general you would specify the nominal size then designate the type of fit that you require. See other replies for references to ANSI standards for fits.

The fit that you describe will require a clearance between the shaft and the hole of .0002 to .0005 (inch). The shaft will be free to slide or rotate in the hole without any noticeable lateral play. Close tolerance ground shaft stock with a nominal diameter of 1/2" is readily available with a tolerance of +0/-.0002. So the machinist will have to bore the hole to a diameter of .5003/.5001 to give the fit that you want.

If you're not an engineer or even a mechanic for that matter, I suggest you cut to the chase (rather than try to decipher slip-fit tolerances or bother with charts and tables) and just go speak with the machinest one-on-one. I started out as a machinest, toolmaker, engineer, etc. - and beleive me - machinests are used to requests from farmers, barbers, boaters - folks from all walks of life that need things made. Just draw up a sketch with dimensions you are sure of, explain what it is used for and if it's not his first day on the job, there's a pretty good chance you'll get exactly what you want. Too many folks are unable to think outside of the box, and tend to overcomplicate things. Besides - if you just want it to work, any extra precision added to your thing-a-ma-jig is just going to drive the cost up.

Phrogengr hit the nail on the head this time, not much really needed to be said after that...good luck and God bless ya

Well Said.

There are 2 sets of standards; std HOLE, & std SHAFT.

For std hole, you'ld spec a 0.5000 hole, w/ a, say, 0.4995 shaft to give a tight slip-fit.

For std shaft, you'ld spec a 0.5005 hole to be similar fit w/ .5000 shaft.

My personal preference is to call for standard shaft; less specialisation for suppliers; i usually generate the hole.

Actually all this chatter is for not. Simply access any copy of Machineists Handbook and all your questions will be answered.

Absolutely true!

However, if one does not know what one is looking @, things become a muddle.

Yes ,although no more muddled than this thread has become. Simply look under tolerances for fits. No hyper bely just the proper answer.

If you want a close fit and want the shaft to still be able to move the shaft by hand, Specify that you want to have the hole to be .002" to .004" larger than the hole "close fit."

If you want to have the shaft to be able to be driven in with a "light drive fit," so that once the shaft is in place it won't move, Specify that you want the hole to be .002" to .004" smaller than the shaft

Do you think Vermin will ever come back to tell us if we've answered his question or is he curled up in a corner holding his head & screaming for us to stop?

The latter, probably!

The fit depends upon the application.

Allowing for expansion, UK heritage railway practice is to drill 28mm Ø holes in a 60' bullhead rail for 15/16" BSW fishbolts to pass through. Anything tighter will cause a loss of sliding action at a fishplate joint and the track will just buckle.

What are "fishbolts"? Is that a UK term?

The fishbolts hold the fishplates in place creating a fixed joint for railway use...

But not totally fixed as he said its to provide a sliding fit () so that the rails can expand and contract!

John.

Is there something particular in the design of a fishbolt, where you could look at one and identify it as a fishbolt? Or is it just a railroad term given to a common bolt when it is used to hold a fishplate?

http://en.wikipedia.org/wiki/Rail_tracks

fishplates in there.

Assume, that you want a machinist to create a block of steel with a 1/2" hole in it, and you also want him to create a shaft that will fit snugly into the 1/2" hole - not too snug, but with no wiggle room.

Whew! When I finally caught up with all the responses since yesterday one thing became very clear. This is a perfect example of what can happen if you set subjective requirements without a clearly defined application.

I agree 100% with those who said "check the Machinery's Handbook". I also agree 100% with those who said a good experienced machinist can deliver what you want on a "one-off" basis at a minimal cost, but only if he truly understands what it will be used for and chooses his clearance/interference based on the application and the materials being used.

It also became abundantly clear that the description given by Vermin, does NOT make clear what the application is, nor even whether or not this so-called "snug fit", "not too snug, but with no wiggle room" is even an interference (press) fit, or a clearance (slip/loose) fit. Several different, and presumably knowledgeable, CR4 denizens have interpreted his requirements in opposite directions, one (who shall remain nameless ) even switching his interpretation from one way to the other! Not his fault, of course, since the description is totally ambiguous!

A very close slip fit could be seen as "not too snug, but with no wiggle room", yet allow motion along its axis. On the other hand, a slight interference fit might be thought of as "not too snug" since it could be easily assembled with a very light press, yet allow NO motion along its axis. Even a "perfect fit" with zero clearance/interference might or might not allow axial motion, depending on surface finish, straightness, roundness, cylindricity, etc. You could even get a fit that slips at some points and sticks at others as it goes in. That could certainly be called "snug", but would it be performing the way Vermin wants it too? No way to tell, since he never gave any clue!

I think that if you look at Vermin's question he does not have any particular application in mind. he was asking how, in general, one decides what tolerance is appropriate for any given situation.

It's very clear to me that Vermin just wants, as he said "a rule of thumb". Although that phrase in itself is very ambiguous, it is also a request for something specific. A Rule of Thumb by its very nature covers a broad range and is not meant to be specific. It is, for lack of a better way to put it, a "specific un-specificness".

He does not have a particular application. He stated that clearly. So all of you that are chastising him for not providing enough information ... well, that comment is not relevant. He wants to learn the general theory of shaft size vs. hole size. And he gave the 1/2" as an example ... a "for instance".

The answer to his specific question is as I've stated, and consists of two items:

1. .002" to .004" actual size difference between shaft and hole will, as a "Rule of Thumb", give approximately the results he is using as an example, i.e. the broad term of "not too snug ... with no wiggle"
2. Further and more specific information can easily and clearly be found in The Machinery's Handbook

Does anyone disagree with my assessment of this entire thread and my interpretation of Vermin's actual intent when he asked the question? I do believe he was simply trying to get a feel for what kinds of measurements are involved, so that he can extrapolate from there.

a "specific un-specificness".

Oh, come ON! That is like saying, a "dry rain", or a "warm snow", impossible!

A "rule of thumb" is generally used to describe a response or a solution that could be effective as an approximation in a given situation or set of circumstances, within limits. You can't have a "rule of thumb" that covers ALL cases and applications. I am sorry, but his description was just asking too much for one answer, except that one that says, "go look it up in the handbook".

Your interpretation may be that he wants an answer for slip fit, but there were just as many people who interpreted his request in the opposite way! That is because of the ambiguous nature of his request.

I could say, "give me a Rule of Thumb for selecting a material to use in designing widgets", but the answers would be many and varying and depend on what the widgets would be used for and what other parameters might apply.

Now if I had said, "give me a Rule of Thumb for selecting a material to use in designing widgets for underwater basket-weaving" that might have narrowed the scope down a bit and allowed some valid suggestions, such as "use a non-hygroscopic grade polymer for most applications or a Stainless Steel alloy for high strength or high temperature applications" and that could be a valid answer.

However, Vermin requested "how do you calculate the difference in diameter of the block and shaft so that they fit together snuggly?!" without defining what he meant by "snuggly" other than "not too tight, but with no wiggle room".

I could be facetious and answer it with "Subtract the hole diameter from the shaft diameter to calculate the difference and determine the amount of 'snugness' you will have. Positive snugness will be an interference fit and prevent relative axial motion as well as eliminate 'wiggle'. Negative 'snugness' will allow relative axial motion. Minimizing negative 'snuggle' will also minimize 'wiggle'."

Is that enough "specific un-specificness" for you?

The number of exclamation points (!) in your reaction to my benign comments suggest to me it may be past time for your medication, STL.

You wrote "You can't have a "rule of thumb" that covers ALL cases and applications."

I agree 100%. In several of my comments, I said exactly that. And I didn't say that my answer covers ALL applications. A rule of thumb is a general guide ... a starting point. And my answer gave him exactly that, just as he asked for.

You also wrote "I am sorry, but his description was just asking too much for one answer"

Sorry, I don't see that to be the case. He's asking very little. He's asking for generalities. I've seen questions in CR4 that ask for entire blueprints, complete formulas, answers to homework ... etc. That is asking too much. Vermin's question is hypothetical and is asking very little.

The colloquial language he used is very much like the language that many non-metal-working people might use if they went to see a mom & pop machinist to help them with a little project. And it seems to be the consensus here, that most experienced non-anal-retentive machinists could probably give him pretty close to what he needed. The language he used is similar to what you might hear standing around the pickle barrel in the General Store while chewing tobacco and discussing a gizmo you're thinking of making. I'd be willing to bet that the cotton gin was developed without Eli Whitney resorting to terms like "an H11 Locational Transitional Fit", and was probably made without ever mentioning a dimension like .0015"

I'll stand by my answer as being definitive and appropriate to the question.

To the Cotton Gin point you were making.

Ely Whitney came up with the idea and may even have produced a drawing, but I might have left the .0015" tolerance issues to those that were making the parts for him.

Are you suggesting that the original cotton gins were made to tolerances of .0015" ?

I don't know. I wouldn't think so. But I'm just making an educated guess.

But the evolution of tighter and tighter tolerances, and how and when they fit into history would be an interesting subject. Of course it's very closely tied to the evolution of instrumentation that can accurately measure increasingly tighter tolerances.

No I'm being hypothetical. They had to work with tolerances then to make the machine work properly. They had to to through several prototypes before actually producing a production copy.

After seeing what was working and not working and the cause for it not to be working, they had to set specifications for the replacement parts to be within a certain tolerance.

The cotton gin was still made up of gears and moving parts. They may have been to crude to be as concise as +/-0.0015" but there were plans drawn up and tolerances specified.

I'd be willing to bet that the cotton gin was developed without Eli Whitney resorting to terms like "an H11 Locational Transitional Fit", and was probably made without ever mentioning a dimension like .0015"

Of course, not. Practical measuring instruments were not so precise in his time. Machine tools were not capable of holding tight tolerances either. However, some manufacturers did develop sufficient capabilities to change manufacturing from a craft to a true industry.

Funny that you mention Eli Whitney. His other claim to fame was being the first manufacturer to develop interchangeable parts. He won a contract to supply the federal government with firearms and implemented a process to use interchangeable part in their assembly. Although he had not invented the idea, nor perfected it, he is known to be the first to put it to a practical test. This required designing parts with precise dimensions and very tight tolerances to achieve the desired fits (slip or press). Prior to this, gun-smithing was an art that required the same kind of one-off, make-it-fit craftsmanship that made interchangeability of parts almost impossible. Whitney pressed the idea of interchangeability in manufacturing and is generally credited with developing the modern American manufacturing industry, including innovations in cost accounting, use of power machinery, and division of labor.

Back to the main point, though....

Oh, never mind. I would just be repeating myself, and it is obvious you ignored, or hadn't thoroughly read, or just did not understand, what I wrote in the first place.

You said "I would just be repeating myself, and it is obvious you ignored, or hadn't thoroughly read, or just did not understand, what I wrote in the first place."

I feel the same way about your reaction to my comments. I can assure you I did not ignore what you wrote. And I did thoroughly read it. As far as not understanding ... perhaps that was the case.

there also needs to be mention of smoothness, as that is the real limitation in close fitting parts, and even they, at the limit. fail due to self bonding problems

there also needs to be mention of smoothness, as that is the real limitation in close fitting parts, and even they, at the limit. fail due to self bonding problems

I believe I discussed surface finish (measured as "roughness", not "smoothness") back in my post #58.

Does anyone disagree with my assessment of this entire thread and my interpretation of Vermin's actual intent when he asked the question?

I do. Put on your boxing gloves.

Actually, I think you are probably right that he was trying to get a feel for the kinds of measurements involved. (Or... on the other hand, maybe he was throwing us all in the jar, and shaking it up to see if we'd fight. Vermin has a sociopathic side.)

I agree with STL that there is a lot of room for interpretation. I initially read "no wiggle" to mean just that: "no" wiggle. That means the fit has to be a light press fit, because unless you have all day, there are no zero clearance fits.

On the other hand, if he wants a sliding fit, then I would give him .0008 to .0012 clearance, and I'd go over both the shaft and hole with 600 emery cloth before measuring. For something as small as 1/2 inch, .002 to .004 is between a loose and free (class 1 or 2) fit... definitely not a snug (class 4) fit.

Of course, then there are a slew of other issues and possible interpretations. Might Vermin want to be able to replace the shaft with another? Then you have to think more like a production job. I nicely fitted .5002 shaft in a .5010 hole won't do him much good if the replacement shaft is .5015.

And perhaps he was asking so he would know more generally about tolerancing, which gets into statistical process process control and many other areas, and companies can diverge pretty widely on what they consider standard tolerances, etc., etc.

So I can appreciate both STLs points and yours. When we have a deadbeat poster who blows though and never comes back, how can one know exactly what he had in mind?

But at least it is all entertaining, and keeps us thinking and attempting to communicate.

There was a thread about calculating efficiency of a steam turbine not long ago. It had two responses, one with a fairly lengthy formula, and the other with a more general description. Both responses were pretty good. It's a substantially more complex subject than this one -- but we have almost 150 answers to this one so far!

Non-engineering types would have to be completely blown away: "Hey Jim, get a load of this! These guys are arguing about how to drill a 1/2 inch hole!! Ya just drill the dam hole, and either drop the shaft in or hammer it in. If it's too tight, just oil it up good... it'll wear in."

I can't disagree with what you wrote. 95% of the comments in this whole thread contain accurate information.

But the bottom line, despite all that I previously wrote, is one thing. "Vermin's actual intent when he wrote the question".

My answer does answer what I believe was his actual intent in asking the question.

Perhaps I didn't decipher it properly. Perhaps I did. I think I did. And that's all I've got to say about that.

My prediction though ... if Vermin ever puts his two cents in, regarding our responses ... it's likely he will simply say "Thanks for all the excellent information". And we won't know any more than we do now, regarding the issues we're debating here. And that's all I've got to sat about that.

"For those that are questioning that practice, it's either a case of them trying come off as being perfect, or they really don't have much experience at it."

I am well aware of "wallowing out" a hole with a hand drill. I have even done it myself at home with a hand drill for simple repairs or installations with a limited drill set, when mating parts either need clearance or will be filled up with glue anyway. I just don't believe that practice is pertinent to a discussion of "Tolerance..." in an Engineering forum, particularly when the example given was of mating a shaft with a hole in a block of steel.

"There is no reason to do that for a hole that is made on a drill press, lathe or mill. They just have to change out the bit for a larger size."

Absolutely right!

Such "wallowing" will produce a No Tolerance hole; folk who rely on this technique regularly, classify as: 'wankers'; not just is it dangerous (take a peek @ my stubby digits as a reinforcement lesson on post drill safety!) but it will ruin the guiding land on the diameter of the drill. TWIST DRILLS ARE END CUTTING ONLY! If you need more clearance, get a larger tool.

I'd find it seriously hard to believe that there was a single person in this forum that has not at one time or other in their lives, resorted to wallowing out a hole to some extent, under some kind of circumstance. Whether it be in woodworking, where you want that bolt to slip in without a hammer, or in repairing your car thru some sheet metal, or whatever. It's already been established that the person who first mentioned it here wasn't referring to a drill press ... which means he didn't interpret Vermin's question the same as most of us ... he was thinking of a scenario where a hand drill was appropriate, and his wiggle room interpretation was much broader. If you're on the farm in the barn repairing your cast tow bar on the tractor by putting in a new hole for a bolt ... you hardly need to go change drill bits if the bolt sticks a little. You move your drill around a little. That's common sense. That hardly classifies one as a wanker, or stupid.

That isn't the scenario that Vermin was asking about, but still ... there is a time and a place for "wallowing". I'm not going to do it on a precision part that I'm manufacturing for the Department of Defense. But there are plenty of times when it's perfectly fine with a hand drill. Not everyone has a full set of 60 drill bits in .015" increments. Lots of folks have 9 assorted bits somewhere in their greasy toolbox, that have seen better days. And they seem to get the job done. That's called flexibility and ingenuity. That's also real life. And okay, it's not "by the book". But sooner or later "the book" doesn't cover some real life situation. That's when the wallower gets the job done, and the book man sits and tries to explain why the job didn't get done. Some of these comments are a bit pretentious, in my opinion.

This has little to do with the original question. And my own career has been built around precision. But the "wallower" seems like he needed a friend here. You folks are rough! Nothing is so absolute.

Some of these comments are a bit pretentious, in my opinion.

You folks are rough! Nothing is so absolute.

I think Sidevalveguru's post is anything but pretentious or rough. He wrote: "Such "wallowing" will produce a No Tolerance hole; folk who rely on this technique regularly, classify as: 'wankers'; (underlining mine). Of course we have all, at one time or another, wallowed out a hole, knowing that it is not the method of choice: it's bad for the drill bit, it's unsafe, and it makes a sloppy hole. Doing so regularly is very bad practice.

I would hope that not one of us has attempted to make a hole through a block of steel so that a 1/2" shaft would fit snugly "without wiggle" by wallowing out the hole with a drill bit. Clearly, Vermin asked, "What do professional machinests do?" Professional machinists do not size a hole by wiggling the drill bit around.

But the "wallower" seems like he needed a friend here.

Why? Should we also be offering support to those who begin repair work on a machine without locking it out? Should we support those who hold things on the drill press table by hand, rather than with a vice, or those who grind without a face shield or weld without welding mask?

At least Sidevalveguru did not laugh at the drill bit wiggler's post, as you did:

"wiggle the bit..."

hehehe

That is inadvisable ... on sooo many levels ...

Rough? Pretentious? Perhaps you should evaluate your own posts before evaluating those of others.

Was your post #55 (DANG IT! I should have thought to suggest that! It's so obvious! ) intended to be sarcastic?

Ken, I don't come here to solve the worlds problems. I come here for enjoyment. All my comments on these various subjects are my own opinions, just adding my own experience to the pool of knowledge. And many of my comments are light hearted or sarcastic.

The only time I feel strongly about an issue is under two circumstances. When someone pretends to know so much that they speak in absolutes. Nothing is absolute. And the other time is when someone is made fun of ... but in a hurtful way, not in a fun way.

I'd wager to say that the average intelligence here might be somewhat higher than on a forum devoted to .. say, knitting. And along with higher intelligence, usually comes a proportionate amount of arrogance. That's normal, in my opinion. So for my own peace of mind, I try to temper that atmosphere of "know-it-all-ness" so that those people that are NOT The Regulars here, don't get turned off by the negative aspects of that.

Forums can easily evolve into a personal territory of a select few. I've heard all of you gurus. Tens of thousands of posts by a dozen people. I love all the knowledge that you bring to this place. But I also know for a fact that I have personal friends that have tried entering conversations here and been turned off by the put-downs and general rude and arrogant tone of some of the Regulars. Personally I've stuck it out cuz I gain alot of interesting trivia here. So I apologize if sometimes I stand up to the clique of gurus and try to encourage a bit of manners toward those that don't visit that much. Or those that don't know so much. Or those that don't feel like getting pummeled. I'd like them to come back. It's supposed to be enjoyable. I'm curious how many register here and leave forever after a dozen posts, because of this propensity here.

So when i see people speak in absolutes, or ridicule without light-heartedness ... I speak up.

So that's where I'm coming from.

And yes, my post #55 WAS sarcastic. I suggested the Machinery's Handbook in my first post, which was #21. Surprisingly, no one had mentioned it in the first 20 posts. So yes, I was being sarcastic to the fact that the poster obviously hadn't read the previous posts when he suggested the same book. Because by then it had been mentioned by probably a dozen people. I found that humorous. I intended to make the previous poster feel silly, and laugh at himself. That's different than making them feel stupid.

"I found that humorous. I intended to make the previous poster feel silly, and laugh at himself. That's different than making them feel stupid."

How is making someone feel "silly" that different from making them feel "stupid"?

If you look up the word "foolish" in a thesaurus you find:

Text: 1 showing or marked by a lack of good sense or judgment <foolish people who thought that the world would end in the year 2000> <a foolish scheme that was supposed to make us all rich> Synonyms..., silly, ... stupid, ...

What a hypocrite! And I mean that in the nicest way. (Yes, I am being sarcastic here!)

At least I am an honest curmudgeon!

As has been pointed out to me in the past, intent is not nearly as important as effect. How do you know that your sarcasm made the poster "laugh at himself"? Maybe it just made him mad at you! The point is, you made yourself the judge, jury, and executioner on that one, so what business do you have criticizing others for doing the same thing?

You want to be nice, not "rude and arrogant" when it suits your purposes, cutting down others for NOT being nice, yet you reserve the right to be sarcastic when YOU feel like it! Is there really a NICE way to be sarcastic?

Yes, I got sick of hearing the same answer over and over again, but at least I didn't make fun at the expense of those people. Hey, maybe I should have!

To me it just sounds like more of the same PC ("Can't we all just get along?"), with you being one of the Thought Police in training. Now, THAT is harsh, dude!

BTW, you were NOT the first to suggest using the Handbook, although you did identify it correctly. Bwire suggested using "The Machinist's Handbook" in his post #13, making your later suggestion just as lame as the others! I do give you credit for correcting the error by giving the correct title, though.

Did I make you mad? OH MY! I was only trying to "ridicule" with "lightheartedness"!

I want to be sure to make fun of you in in a "fun way", not a "hurtful way"!

What's up with you STL? I'm butting heads with you yet again.

Okay, you win. I guess I'll leave this place to the guru clique.

When the enjoyment ends, that defeats the purpose. If encouraging civility is the Thought Police .. well I have no response to that.

Freakin shame. It's always the few that ruin it for the others. You've ruined it for me.

By the way ... what I said was true. I've encouraged several of my peers to come here. They all tried. They all left. How often do you think that is happening daily? This is a world wide forum, yet out of millions of engineers .. how many care to spend time here? The dozen or so of you, have somehow taken over and made it what you want it to be for yourselves. Civility out the window except among yourselves. You tease each other in fun, but yet you talk down to many of those not of the chosen.

This could be sooo much better. The concept was good. You should police yourselves with a little integrity. Not a good old boy mentality. You could be truly world wide. And attractive to hundreds of thousands of the best minds on the planet.

enjoy.

Also ... wallowing can't be done on a drill press; unless you move the part. And that's not what was suggested. So it can only be a hand drill. And again ... there are times when it's appropriate with a hand drill.

Yes, I know .. off the original topic. But it is relevant to the many comments of those who doth protest too much ... the technique of moving a drill bit around. In fact .. unless you are The Terminator or some other robot (or cyborg), you will never get a "toleranced and proper" hole with a hand drill. Not thru anything thick enough to support an inserted shaft.

I recall a car repair guy who wanted to 'wallow' out a hole in the frame under a car, so there he was with a 3/4" electric drill, lying on a creeper cart, with his hands extended and the drill speed control set fairly low, and so he starts it, pushes the button (to save him the effort of keeping the trigger pulled) and starts to wallow this hole with alittle sideways. Well, the drill bit and he was suddenly rotating while the drill was stuck, and the button was pressed and he lost his grip and the drill faithfully kept turning until it had torn the twist lock plug out by the roots. He was lucky, he got some shaved knuckles, but he lived to fight another day, and to work at another shop

Once again you guys are making this waaaaay too hard on yourselves. Speaking as a former professional machinist, first off I would never ever turn down a larger diameter piece of stock to 1/2" dia. I would simply just order 1/2" dia rod stock, cut it to length and finish the ends. Turning down a larger piece is costly and wasteful.

As for the block, obviously if you use a half inch drill bit, the hole is going to be slightly larger then 1/2", otherwise the bit would not move through the material. This could be all the "tolerence" you need. If, however you required more snug of a fit, I would drill the hole slightly under 1/2" and use reamers to enlarge the hole untill I achived the desired fit. A precision reamer would give a tolerence of +/- 0.0008. How snug is snug? 90% of this job would just be trial and error on the part of the machinist if this was a one off part.

Avery Montembeault

The company I work for manufactures machinery that use a lot of different sized shafts.

Sometime we have to turn down a 1-7/16" Precision shaft to 1/2" to fit a small sprocket on the end of it that has a 1/2" bore. We do that ourselves. I just wanted to point out that there are applications where there is a need.

"Once again you guys are making this waaaaay too hard on yourselves"

WHAT??!! We NEVER do that!

This in responce as to whether Whitney had the ability to measure to .0015. He did and you should all visit the American precision Museum housed in the factory where he built his first rifles in Windsor VT.

Whitney died about 1825 when Whitworth was but a lad of about 22. Most of Whitney's accomplishments were completed either before Whitworth was born or when he was very young.

"OOOPS" So I pasted the wrong paragraph. Try this one.

Maudslay also recognized the importance of true plane surfaces, developing a method of using a marking compound and scraper and checking three plates simultaneously. Both of these developments allowed him to produce a micrometer in 1805 which became known as the "Lord Chancellor".

"It consisted of a gun-metal bed carrying two saddles fitted with end-measuring faces, one of them extending downwards through a slot in the bed to terminate in a split nut. The saddles have bevel edged windows through which the graduations on the bed may be read.

The screw which engages the split nut has a pitch of 100 threads to the inch and carries an index wheel marked with 100 divisions on its periphery. Each division thus represents 0.0001 of an inch of movement between the measuring faces. Tested by the National Physical Laboratory in 1918 its accuracy was found to be quite extraordinary for its age." (Rolt 1965;96)

Nice! I KNEW this would be interesting!

Finally!

Both of these developments allowed him to produce a micrometer in 1805 which became known as the "Lord Chancellor".

Gee, I really hate to be the party pooper, but if this is your evidence that Eli Whitney had access to gaging that allowed him to check a tolerance of .0015 inch in 1793 (when he invented the Cotton Gin) or in 1798 when he won a contract to deliver muskets to the US Army in 1800, it is doubtful that he could have used a micrometer invented in 1805. Now considering that new technology rarely becomes commonplace or even available immediately after it is invented we have to allow some time lag for copies of the gage to be reproduced, sold on the open market, and obtained by Whitney for use in his manufacturing business. Perhaps that is one of the reasons why he did not deliver on his contract to produce weapons with interchangeable parts until 1809, nine years later!

In general we use wringing fit in such cases where the hole size is 10 to 20 micron higher than the shaft. However, it is fair to not to use cylindricity in case the engagement length is around 2 times the diameter. But if the engagement length is higher, you should apply cylindricity also to the hole and shaft accordingly and that is a different story all together.

In case you want general tolerance to take care of such situations you can use H-h tolerance ie. Hole H7 and shaft h5/h6.

anjula1008@rediffmail.com

As a professional Machinist two .500 measurements will not fit together. However if you want to fit a .500 dia. rod into a hole, it needs to typically be two tenths small (.0002), but you haven't explained any usage here, and we haven't accounted for heat, bearing surfaces, what type of finish the holes should have, talk to your machine shop about what you want and they can help you.

Machinist here!

What do you mean by fit snugly but not too snugly. The Application is important

If it is for a Hydraulic shaft, it must be ground to -1/10,000 of an inch (.0001) less then the hole. Since the oil molecules are ~.00005 inch and the tolerance must consider both sides, there must be minimum .0001 inch total clearance to ensure a film of oil.

If it is for a one time fit, as in installing a ball bearing, it can be turned on a lathe to -1/1,000th of an inch (.001). Most lathes and micrometers are in 1/1000 of an inch.

A shrink fit, the shaft is actually larger than the hole about 2/1000th of an inch.

It all depends on the usage. Will the shaft be exposed to heat?. There is standard formulas to calculate how much the shaft will expand due to the operating temperature. Extra tolerance must be added in for this.

If the the shaft must slide easily, will it be lubricated? and with what. The required bearings will depend on the force and how often will it slide (nylon, oilite, ball). also Friction coefficients will affect the heat and wear. An oilite bearing will normally have a tolerance of 2/1000th of an inch. An Nylon bearing normally has a tolerance of up to 5/1000th of an inch. A teflon bearing 3 to 4/1000th of an inch. Without a bearing, you will have larger tolerances. Remember 5/1000 of an inch is about the thickness of a strand of hair.

A store bought rod will not be as accurate as a turned shaft. (for both roundness or straightness)

A drilled hole is not as accurate as a bored hole.

dear,

in any fitment,straightness,cylindericity,surfacefinish are the most dominating factors

Once you know this, you start paying more attention towards the processes by which

holes & shafts are made.

we can have good slide fit with 15 microns clearance in hardened ground hole & shaft of about 1/2 " size.

but such sliding fittment wth 15 microns clearance is not possible in turned finish.