Sleeve transition fit --> effect on ID tolerance 1

[WvPetegem]

Hello,

I am having difficulties selecting the correct tolerances for a sleeve (stationary bush) which will be fitted (with a H7/m6 transition fit).
Attached the situation sketch.

Some fixed figures:
Hub outer diameter: 700 mm
Hub inner diameter: 356 H7
Sleeve outer diameter: 356 m6
Bush outer diameter: 340 s6

(Hub material: S690QL, sleeve material: S420NL, bush material: unknown).

After the transition fit (H7m6) the inner diameter of the sleeve will be smaller.
This means that the inner-diameter of the sleeve should be slightly larger than desired.
The desired ID (thus after installation) of the sleeve should be 340 H7.

Question:
What should be the machining diameter and tolerance of the inner-diameter of the sleeve before installation; in order to get a 340H7 ID after the installation with the transition-fit?

Thanks a lot for your help!

Regards, Wim

 

[drawoh]

WvPetegem,

If you are using ISO H7 and m6 tolerances, you should be able to read them straight off the chart, which is in the Machinery's Handbook, among other things. Those dimensions are as-fabricated. What happens after assembly is not relevant to whoever is fabricating and inspecting the part.

The bush diameters on your drawing are 280 and 296. Where is 340mm coming from?

--
JHG

 

[JNieman]

If you are concerned about the form or size of internal components after assembly, as interference-fit parts, then it's likely you would need to look into a post-assembly honing/grinding process.

 

[WvPetegem]

Hello JNieman,
Post-assembly machining (line-boring) is what I like to avoid.
We first like to line-bore the hub inner diameter 356H7 and then insert the sleeves with H7m6.
This may make the inner diameter of the sleeve to shrink. I thought it shrinks the same as the interference of the H7m6.
I thought that by making the original inner diameter of the sleeve slightly over-sized than H7; this will Ben finally 340H7 after installation of the sleeve.
How reliable do you think this will be ?

 

[JNieman]

Those sizes are a bit beyond my intimate experience. I don't have much hands-on experience with hose features of those size react with different severity of transition or interference.

However, I do know that when trying to avoid collapsing at all, I've typically had to accept more of a transition fit. This is for small sizes from 5mm up to around 150mm. However, if your sketch is generally proportional to your 356mm situation, you're not going to have a very good time. That's a very thin-walled bushing for its diameter. The thinner the wall, in relation to the diameter, the more likely it is to deform under the stresses of tight fitment.

How much interference do you absolutely need? For your design, can you accept a much lighter fit, possibly with a chemical retaining compound? Common example: Loctite 620 "green".

 

[WvPetegem]

Hello,

Locking the sleeve with Loctite is a good idea. In that case I can choose a lighter transition fit (H7/k6).
With 356H7/k6 there is a max. interference of 0.040mm and max. clearance of 0.053.
In order have the sleeve's ID 340 within H7-tolerance (+0.057/0.000) after installation, I think I can choose 340 (+0.057 / +0.040) before installation.

In case of max. interference (0.040), the min. ID would be 340.040-0.00.40 = 340.000 (within H7, thus OK).
In case of max. clearance (0.053), the max. ID would be 340.057-0.000 = 340.057 (within H7, thus OK).


The fit H7/k6 is meant for accuracy, not for locking.
The locking is done by the weld and the loctite.

 

[pmarc]

Wim,

In general I agree with JNieman's suggestion to do final sizing of sleeve ID after assembly.

But also, I have two other comments:
1. With the assumed transition fit between hub ID and sleeve OD (H7/m6 or H7/k6), you may end up with a loose between these two items and then I am afraid your entire plan of making the sleeve ID "slightly over-sized" to 340 +0.057/+0.040 will not get you to what you need.
2. Assuming that you still don't want to do a post-assembly sizing of sleeve ID, and your plan worked, that is you were lucky to always have an interference between sleeve OD and hub ID of exactly 0.040 (which is so unlikely to happen, by the way), notice how much more accurate the over-sized sleeve ID will have to be comparing to the initial idea of having this ID controlled with H7 tolerance. The +0.057/+0.040 means there is only 0.017 of total tolerance available, which more or less corresponds to IT4 tolerance grade for diameter of 340. IT4 vs. IT7 (in case of H7 tolerance) means that you will need much more accurate (read more expensive) process to achieve your goal. Did you take it into account?