Fits

[mklotz]

Fits of shafts and holes are frequently referred to by a term, e.g, press, shrink, etc., rather than an explicit numerical size difference. Professionals memorized all this in their apprenticeship but It can be very frustrating for the amateur machinist.

Machinery's Handbook devotes nearly fifty pages to the subject of various fits of a shaft to a hole. Tubal Cain's Model Engineers Handbook devotes less than half a page to the subject. I extracted the latter material and converted it into a program (FITS) that can be downloaded from my page. However, for the benefit of folks who don't wish to download the program, here is the information it contains in numerical form. The necessary math is trivial so the program, while convenient, isn't really necessary to obtain an answer.

Entries in the table below are: fit name, constant, allowance
constant is measured in thousandths of an inch
allowance is measured in thousandths of an inch per inch of shaft diameter

Examples:

For a push fit on a nominal 1" shaft, machine the hole to exactly 1.0000",
and machine the shaft to -0.35*(1.0) - 0.15 = -0.5 thou less than the nominal size (0.9995").

For a shrink fit on a nominal 1" shaft
1.5*(1.0) + 0.5 = 2.0, i.e. shaft size = 1.002"

Shrink,0.5,1.5
Force,0.5,0.75
Drive,0.3,0.45
Push,-0.15,-0.35
Slide,-0.3,-0.45
Precision Running,-0.5,-0.65
Close Running,-0.6,-0.8
Normal Running,-1.0,-1.5
Easy Running,-1.5,-2.25
Small Clearance,-2.0,-3.0
Large Clearance,-3.0,-5.0

[cdakers]

Any chance you will make a 64 bit version, lol. Everything I have now days is 64 bit Windows. FITS refuses to run.

[petertha]

Yup, I made a spreadsheet out of what looks to be the same info, select fit type from a drop-down menu. Just used it the other day in fact!

[cdakers]

Where can I find that, petertha?

[petertha]

From my hard drive - Haha

Hmmm.. I only see upload pictures & videos, do you know how I can upload .xls file?

[cdakers]

No, I'm a newbie here. Email me a copy if you don't mind? cdakers at fastrans dot com.

[jensor4]

Yup, I made a spreadsheet out of what looks to be the same info, select fit type from a drop-down menu. Just used it the other day in fact!

Could you email me copy of your spreadsheet.
jensor4 at Verizon dot net

[petertha]

done & done

[thehomeengineer]

Hi Marv
While working for a pump company years ago they had a bookcase housing some of the British Standards. From shaft fits, bore sizes, key ways, and splines to the correct size of tool handles. I loved thumbing throw them when I was an apprentice (I am a sad case I know). The bookcase must have been six foot by three foot. Then these were replaced with another BS: ISO2000 (I think) so these were no longer current, if I remember correctly they said each new BS book was going to be about £500 each. I did ask if I could have the old book, on limits and fits for shafts and bores. I was lucky enough to receive it. The book itself is about 12” by 8” 3” thick. Have used it many times to look up fits that I do not know.
The Home Engineer

[mklotz]

Any chance you will make a 64 bit version, lol. Everything I have now days is 64 bit Windows. FITS refuses to run.

Lots of folks have requested my permission to port the programs on my page to other systems. I've always given my permission freely; after all, the programs are already in the public domain. To date, no one who has requested permission has ever reported converting a single program.

With that sort of interest level, I'm understandably not interested in making any conversions. I detest spreadsheets so that isn't an option either although others are welcome to follow that path.

In my opinion the option outlined in the Introduction on my webpage is the best solution that involves the least work if one needs to use several of the programs. Download DosBox and install it. This will provide the facility to run any legacy DOS program, mine included. There are a lot of useful legacy programs out there; not just mine. While the code for mine is made available, that usually isn't true for other people's work. Using DosBox allows you to run these programs without having the code available or needing to recode it.