Dimensioning bores 2

[Grindy]

I'm currently designing a parts catcher for a machine. Doing detailed design work is something relatively new to me so I'm unsure about drawing standards and dimensioning.

I have a shaft that is 45mm in diameter. A 'sleeve' will slide over the shaft. I require a clearance fit (H11). According to my Zues book a H11 fit for a hole in the region of 45mm dia would result in a bore size of 45.160mm.

My question is this:

In the drawing do I label the bore to be machined to 45mm with a H11 fit or do I label the bore to be machined to 45.160mm.

Also, could anyone recomomend a good drawing standards and geometric tolerancing book (SI)?

How do I then go about giving the machinists a tolerance?

Would the 45.160mm be my maximum bore size or would I have a tolerance +/- either side of 45.160?

 

[KENAT]

Are you in the UK? If so you're probably best off working to BS8888, which is essentially a compendium of ISO standards

http://www.roymech.co.uk/Useful_Tables/Drawing/Drawing.html

has some usefull information.

Having worked in the UK, the old H11 etc fits seemed a bit of a hit and miss on if they'd be understood by machinists/vendors so I always used to give the actual dimensions on the print. Exception was on screw threads where I did just give the fit class info.

The tolerance on the bore is given in the fit tables. The fit tables give a range. So in your case I believe it's 45 to 45.16 HOWEVER for this to work properly the shaft will have to be toleranced similarly based on the same shaft/hole fit standard. Not sure what class your shaft as you don't give it.

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[KENAT]

Oh and on a lighter note, you came to the right place for 'Dimensioning Bores' - there are several that frequent this forum;-).

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[fcsuper]

::yawn::

dang, KENAT, you beat me to the joke!

Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion

 

[axym]

KENAT,

I was just going to go there, and you beat me to it.

Something like "Oh, so you've attended a Y14.5 meeting, have you?"

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[fsincox]

KENAT,
I resemble that remark.
Gringy,
What is zues? I have heard that someplaces (ISO people)do not specify tolerance limits just like you referenced, are you ISO?
KENAT is right, the American standard is to explicitly specify tolerances (do the calculation for them).

 

[KENAT]

Zues is typically a pocket guide for machinists. I have one here on my shelf though I haven't used it in anger since I came to the States.

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[fsincox]

KENAT,
Thanks, Now you just had to rub it in , I am jealous.

 

[fsincox]

Wow, I can't even get that on the internet it converts it to zeus??

 

[KENAT]

Ok, I'm a dullard and didn't pick up on the spelling, it is ZEUS I just grapped mine off the shelf.

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[Grindy]

Thanks for the info, jokes and link.

I am UK based.

The shaft is 45mm to 44.96mm dia. An H11 fit is stated to be 0 to +0.160mm. Therefore if on the drawing I state the tolerance to be 45.00 to 45.16 and the machinist cuts the bore at the lower end of the tolerance then I will end up with very little clearance. So should I bring the minimum closer to the maximum tolerance? 45.10 to 45.16?

Can any of you recommend a good book for drawing standards and geometric tolerancing (ISO)?

 

[dgallup]

If you change the tolerance it won't be H11 anymore, your looking more like an E9 or a D10. Which class you choose depends on how you want it to function.

 

[KENAT]

Your question on fit really depends on your function.

The shaft fit tables only really work when you pick both parts based on them. I don't see the fit you state for your shaft in my zeus book. Certainly it doesn't seem to be a c11 witch is the suggested match for an H11 to give a loose clearance fit. The clearance fit comes from both parts not just one.

Now if you want to emulate the minimum clearance from an H11/c11 fit you can achieve that by setting your min sleeve dia as 45.14 if I'm reading my chart right. However, since your shaft doesn't even match the tolerance range of a c11 you don't emulate the fit across the full tolerance range.

So, if your shaft dia is fixed then I'd use the chart for guidance, check with manufacturing what tolerance they can hold on the sleeve, check against your real functional requirements and go from there.

As to books, I used to just read over the standards but they aren't the most user friendly.

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[Grindy]

I hadn't taken the C11 into account when designing the part. I simply picked 45mm dia as that was the round bar size available and I don't have the ability to turn the shaft to the required size. (I'll now remember to match tolerances in future)

I'll have to make do with making the sleeve dia min at 45.14mm. For the function required of the shaft this should be fine.

Thanks again for the help and advice.

 

[fsincox]

Grindy,
I are you new to the profession? Are you ISO schooled (non-US background)? Company standards inch or metric based normally?

 

[Grindy]

Hello fsincox,

I've been in the profession 11 years, in a maintenance engineering role. So I haven't really had too much to do with the creation of 'correct' technical drawings and the standards associated with them. I'm starting/trying to drift away from maintenace and take a greater role in the (mechanical) design of various parts for different machinery. (Although at the moment I appear to be making the odd mistake)

I am ISO schooled and my company is metric based.

 

[KENAT]

Are you using stock bar rather than machined shaft? In that case you may have another issue, the straightnes of the bar, that you'll need to look into, as well as the bar dia tolerance. In fact, while I'm rusty on some of the implications, ISO generally treats size and form control separately so you'd need to think about it even if it's a precision shaft plus maybe how round it is.

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[Grindy]

I'm using stock bar (cost reasons, i'm on a very tight budget). I have measured the bar at various points along its length and have found the bar to be between 44.96 and 45.00.

For the application a stock bar is acceptable although I understand that there are potential issues relating to varrying dimensions and accuracy.

 

[juergenwt]

Grindy - If your shaft is 45.000 - 44.960 you have a 45h8 shaft. If you want a 45H11 hole you will not have a clearance fit. You will have anything from a fine to a wide sliding fit. H on h is the best you can have without interference.If you want a clearance fit you need to go to lower on the shaft. More like a 45e8.
You give the dim on the print as: Shaft 45e8 and on the hole 45H11. On the bottom of your print in a special box you list all ISO Tolerances that are on your print for the machinists use. I.e. 45e8 = 45 -50/-89
45H11 = 45 0/+160
The reason for this will be clear to you once you get deeper into ISO tolerances and I do not want to get into this at this time.
As for a good book order the reference guide book "Tolerance Table for Nominal Dim.s 1 to 500mm as per ISO/DIN 286 from "Beuth" in English. ISBN 3-410-12677-5. Specify "English". It is a small and handy booklet for everyday use. Order some for the shop.
Go here for good info:

http://www.roymech.co.uk/Useful_Tables/ISO_Tolerances/ISO_LIMITS.htm

And here:

http://www.beuth.de/cn/J-7CFB1F358C...bGV2ZWw9dHBsLWhvbWUmbGFuZ3VhZ2VpZD1lbg**.html

 

[fsincox]

Jergenwrt,
do you know ISO?
Jergenwrt & Grindy,
I have a thread on ISO 2768 and general tolerancing mehtods it in the ISO standards, I would like to know how you feel about working in that envioronment. Can you still use position on surfaces?