Mechanical Drawing Notes 3

[turner91]

So I am trying to make mechanical drawings for a part that I need made but I don't know how to make the notes for the bearing to be press fit inside of it. How do I do this if I have a bearing with an outside diameter of 100mm?

 

[Eltron]

It depends upon the type of fit you need. Take a look at

http://www.skf.com,

and you should find everything you need to know.

Dan

http://www.eltronresearch.com

Dan's Blog

 

[KENAT]

What kind of bearing, what tolerance on the bearing dia, what are the material(s), do the bearing manufacturers (if an off the shelf bearing) not give this information?

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[turner91]

Thanks for the help!

Okay, so if I pick out one of their bearings that has an OD of 100 mm and I choose the housing fit that I want and it says use tolerance P7 what do I do?

 

[turner91]

I was originally using Mcmaster Carr for the bearing and they did not give this information at all. The housing material is 1018 carbon steel and I believe the material of the bearing is steel.

 

[Eltron]

You put the dimensions and tolerances on your drawing.

Dan

http://www.eltronresearch.com

Dan's Blog

 

[turner91]

So I literally write P7 on it?

 

[KENAT]

Do you know what the 'P7' is all about - standard limits & fits?

What drawing standards are you working to/where are you located?

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[turner91]

I honestly have no idea what P7 means at all. I have never worked with bearings before and have never had to use different fits before. I am a first year engineering intern and we haven't covered anything about it yet. I am working for a very small government contractor and am designing a machine for them.

 

[europipe]

http://www.nadro.nl/mark/iso-passingstelsel.html

Unfortunately I don,t know an English version, but maybe this explains a little

 

[rerig]

When you identify the bearing either by "Part Number" or "Find Number" add a "Flag Note #" and then over by the Header Block or Part Number Listing create a Flag Notes List and describe in text the spec or specific instructions to press fit the bearing.

Rerig

 

[Eltron]

Do a search for limits and fits charts. You will find your P7 fit in a chart with the standard tolerance to be added and/or subtracted from your nominal dimensions. Put the dimensions and tolerances on your drawing(s). If you want you can put a note at the bottom that calls out that P7.

Dan

http://www.eltronresearch.com

Dan's Blog

 

[SnTMan]

turner91, you may never "covered anything about it" in your classes. They only go so far.

A learned skill that will be valuable in your career is to identify who might know the things you need to know don't but, and ask them your questions. Nobody expects you to know everything.

As an example, the applications engineers at SKF. Most manufacturers of engineered equipment have them, and that's what they are there for.

Of course you did start here, so that's good

Regards,

Mike

 

[tygerdawg]

(sigh)

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

http://www.wisetool.com/fit.htm

http://www.engineersedge.com/general_tolerances.htm

http://www.lmgtfy.com/?q=fits+and+tolerances

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[Tmoose]

The loading direction, and what is rotating will determine if the fits with bearing OD and ID should be some level of interference, or could be a "slip fit." Often only one needs to be interference, which is good (maybe even a lifesaver) for assembly

P7 is a bore tolerance. (Bores use capital letters, shaft tolerances are lower case letters , p, k, n, r , etc). On a 100 mm bearing It would result in a theoretical interference fit with the bearing outer race of 14 to 54 microns ( ~ 0.0005 inch to roughly 0.002 inch ) . Those are diametral fits, not radial.

Beyond the size there are equally important tolerances for shoulder runout, bore and journal coaxiality (relative runout is sometimes recommended as easier to gage), roundness and cylindricity, etc.

The info is online and in most catalogs, but I'd talk to an application engineer until you are real comfortable with all the design steps. It takes a while.

These days machine more machine shops are familiar with the ISO fit designators. I think it is smart to include a copy of the appropriate hunk of the ISO fit table right on the drawing. It sure beats having a whiny pillow fight about mysterious or imaginary tables when parts are the wrong size.

 

[drawoh]

turner91,

Who is going to press fit the bearing, you, or the fabricator?

This affects how your drawing is presented.

A dig for SKF here. If you need info like the tolerances on the OD of your bearing, buy your bearings from people who publish this information. Better yet, buy your bearings from people who publish handbooks telling you how to analyze your bearings and design and tolerance the mounts. SKF might cost more, but if they support your engineering, you will get your job done right, the first time.

JHG

 

[hydtools]

Turner1, have you even looked at the SKF reference given by Eltron? It should answer all your questions.

Ted

 

[turner91]

Ok, thanks for all the help guys! I think I have it down now.