Tables For Non-Preferred Fits / Choosing a Press Fit Tolerance Zone 1

[RMG143]

I apologize in adavance if this is a silly question but I am just starting to understand the ISO 286 standard and would really appeciate some help with a question I am trying to answer.

I am creating an assembly which uses an off the shelf linear actuator with a 4H7 hole for locating. The 4mmx10mm SS dowel pin my company currently uses from McMaster has a tolerance of +0.004mm to +0.012mm so therefore a tolerance zone of m6. I would like to create a hole in which to press fit the dowel pin.

So two questions:

1. Obviously the 4H7 hole in the actuator will provide a clearnace fit with the 4m6 pin but is there a tabel similar to the preferred fit tables in ANSI B4.2 or similar which states this verbally "Clearance"

2. What would be the best method of choosing a tolerance zone for the hole in which to press the 4m6 pin into? Is there a table similar to the preferred fit tables in ANSI B4.2 where I could look to and see a "Clearance" tolerance zone for the provided 4m6?



Thanks in advance all.

 

[KENAT]

If you're looking for a deliberate press fit then you might want to do the calcs & estimate the insertion force etc.

I believe there is a FAQ on one of the forums for that.

Posting guidelines faq731-376

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

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

 

[gearguru]

If you can not order pins with different tolerances, then you have to use different hole tolerance. You might need the custom made tools to machine the holes.
Per my calculations (I have an old ISO 286-2 1988 standard, but I do not think that the charts changed)

The 4H7/m6 creates the fit with possible 0.008mm clearance to 0.012mm interference
4J7/m6 creates the fit with possible 0.002mm clearance to 0.018mm interference
4K7/m6 creates the fit with possible 0.001mm interference to 0.021mm interference
4M7/m6 creates the fit with possible 0.004mm interference to 0.024mm interference

The ISO fit charts/recomendations work nicely for larger parts. For the small diameters, like 4mm, it is often not possible to simply pick something from the standard. Your fit selection/tolerances also depend on the material of both parts etc.
Actually the 4H7/m6 statistically can create the intereference fit too.

 

[RMG143]

@gearguru

Thanks for the response. So you are saying that even with the full standard on hand (unfortunately I do not have it) the designer is still responsible for using the tolerance zone charts to determine what he/she would consider a proper fit and there is no simple solution such as presented in the preferred shaft and hole basis fit charts in ANSI B4.2 which present the designer with an H or h value and then visually outline some clearance, transition and interference fit solutions.

It seems that in a perfect world, I would be able to get my hands on a 4h6 dowel which would fit into both preferred clearance (G7/h6, H7/h6) and interference fits (P7/h6, S7/h6, U7/h6) according to ANSI B4.2.

Regarding your calculations I did a quick check and everything looks to be spot on so it seems that the charts have not changed (at least from the ANSI B4.2 excerpts I got off the net).

 

[gearguru]

RMG143,
these ISO charts exist for decades as do the drawings/parts using those tolerances, therefore they do not change them. The only improvement I recall was adding the JS and js data to the charts.
You are right - if you could get the 4h6 pin than you could "play" with the holes. (it would be the "preferred shaft" way of tolerancing).
And definitely the designer is responsible for picking the best fit. If he can select it from the chart, then there is a good chance to get the standard tools to machine the parts.
Just FYI: The combinations of those letters (capitals for holes, small letters for shafts) give you an idea what kind of fit you can expect: H combined with anything alphabetically before "h" creates a clearance; "H" combined with anything alphabetically after "h" creates an interference - the more the closer to the end of the alphabet it is.
So : H/f = clearance; H/d =larger clearance; H/m = interference; H/r = a lot of interference...
And obviously you can say exactly the same for F/h, D/h, M/h, R/h.
We discussed years ago the ISO fits system here, try to search within these forums.

 

[juergenwt]

RMG143 you may want to look at this page with many calculators.

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

A table in DIN 7157 / ISO 1829 can give you a lot of help for practical application of different fits. I believe they are now included in ISO 286.
Under DIN 7157 there is a great table of "Play and Interference)based on practical experience. I could not find anything like it on the Internet but it should be available
from:

http://www.beuth.de/en